-,~
~OREAMBLE
- VIINSTRUMENTS
OPERA TOR’S
MANUAL
1820/1822
DIFFERENTIAL AMPLIFIER
Revision D
August 1999
Table of Contents
Section 1
Specifications
Introduction
.............................................................................
1- 1
1820/1822
Specifications
........................................................
1-2
Nominal
Characteristics
..........................................................
1-3
Warranted
andTypicalCharacteristics
....................................
1-4
Environmental
andPhysicalCharacteristics............................
1-5
Section 2
OperatingInstructions, Controls and Indicators
Front
Panel
..............................................................................
2-1
RearPanel
...............................................................................
2-4
Oscilloscope
Settings
...............................................................
2-5
Model
1820Operation
.............................................................
2-6
Section 3
General Operating Information
Getting
Started
.........................................................................
3-1
1822FrontPanelOperation
.....................................................
3-1
Comparison
Voltage
Operation
...............................................
3-2
Differential
OffsetOperation
..................................................
3-3
UserTrapstoAvoid
................................................................
3-4
Section 4
Performance Verification
Introduction
.............................................................................
4-1
TestEquipment
Required
........................................................
4-2
Preliminary
Procedure
.............................................................
4-3
Procedure
.................................................................................
4-3
1820/1822
TestRecord
..........................................................
4-11
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182011822
Operator’s
Manual
Section 1
Specifications
Introduction
The 1820 and 1822 are stand-alone high performance
100 MHzdifferential amplifiers. They are intended to act
as signal conditioning preamplifiers for oscilloscopes,
digitizers and spectrum analyzers, providing differential
measurement capability to instruments having only a
single-ended input.
(PVG)that can be set to any voltage between+15.5 volts
(+10 volts in Differential Offset) with 5 1/2 digit
resolution. Eachdigit of the voltage generator output can
be individually incremented or decremented. Positive or
negative polarity can be selected. The PVGoutput can
be selected as an input to the inverting (-) input of the
amplifier for operation as a differential comparator or
applied internally as a true differential offset voltage.
The PVGvoltage is also available to be used externally
through a rear panel connector. In the 1820, this
connector becomesan input through which the user can
apply an external voltage to achieve the samedifferential
offset and comparatorfunctions.
The high gain of the 1820/1822can extend the sensitivity
of an oscilloscope with 1 mV/divto 1 laV/div. A built-in
input attenuator maybe separately set to attenuate signals
by a factor of 10, allowing gains of 1000, 100, 10, 1, or
0.1 and commonmodedynamic range of +15.5 V (+1)
+155 V (+10). Optional probes further increase the
maximum input signal and commonmode ranges in
proportion to their attenuation ratio, but not exceedingthe
probe maximum
input voltage rating. Effective gain of
the 1822, including probe attenuation, amplifier gain and
attenuator settings, is automaticallydisplayed.
The 1820/1822 operates
without line switching.
from 100 to 250 VACline
A wide range of high performancedifferential probes are
available from Preamble Instruments for use with the
1820/1822. These include the +1 XC200low capacitance
probe, XCI00selectable (+10/+100) attenuation probe,
and the XC350+100 high impedance (92 M~/ 2.6 pF)
probe. Differential probes with higher voltage ratings are
also available from PreambleInstruments.
The 1820/1822 has a bandwidth of DCto 10 MHz,but
the operator can select from a full complementof high
and low frequency -3dB points. In critical measurements,
the signal-to-noise ratio can be greatly improved by
restricting the 1820/1822’s bandwidth to the frequency
rangeof interest.
The 1822 features a built-in Precision Voltage Generator
1-1
1820/1822
Operator’s
Manual
1820/1822 Specifications
Except where otherwise noted, the following specifications
Differential Amplifiers.
apply to model 1820, 1822, 1820-PR2 and 1822-PR2
The specifications are valid for instruments whenthe following conditions have been met:
¯
The instrument is being operated from a powersource which meets the line voltage and frequency specifications.
The instrument has been operating for at least 30 minutes in an environment which is within the operating
environmentalspecifications.
The instrument has been calibrated within the last 12 months. Calibration was performedin a controlled environment
of 25 +5°C.
NominalCharacteristics
Nominalcharacteristics
associated tolerances.
describe parameters and attributes
which have are guaranteed by design, but do not have
General
Input Configuration:
Offset Capability
+ Input CouplingSelections
- Input CouplingSelections
Input Connectors
MaximumNon-Destruct Input Voltage
Output Configuration
Output Impedance
Intended Output Load
Output Connector
Amplifier Gain
Input Attenuation
BandwidthLimit Filters (Upper Limit)
BandwidthLimit Filters (LowerLimit)
BandwidthLimit Filter Characteristics
Autobalance
Effective Gain Indicator
(1822 and 1822-PR2models only)
TrueDifferential, + and - Inputs.
Precision Voltage Generator (1822 and 1822-PR2
models), or external offset reference source (1820
and 1820-PR2models) can be selected as - input
source in VCOMP
mode.
The Precision Voltage Generator (1822 and 1822PR2models), or external offset reference source
(1820 and 1820-PR2models) can be used
providetrue differential offset.
AC, Off (Precharge),
AC, Off (Precharge), DC, VcouP
BNC.+ Input incorporates Probe Attenuation
Codingsensing connector (1822 Only).
Withstands up to +250 V.
Automaticinput disconnect with manualreset
Single Ended, Groundreferenced.
50
50f)
BNC
X1, X10, XI00, or X1000
+1 or +10
100 Hz, 300 Hz, 1 KHz, 3 KHz, 10 KHz,
30 KHz, 100 KHz, 300 KHz, 1 MHz,3 MHz
0.1 Hz, 1 Hz, 10 Hz, 100 Hz, 1 KHz, 10 KHz
Single pole, 6 dB/octave
Amplifier initiates an automatic balance cycle
wheneither gain button is depressed.
LEDsindicate the effective gain by factoring
Probe Attenuation, Attenuator and Gain settings.
(Probes must have coding connectors.
+ 1, + 10, + 100, and + 1000probes are
recognized.)
1-2
182011822
Operator’s
Manual
NominalCharacteristics (continued)
Dynamic Ranges
Maximum
Differential Linear Input:
~
X 1000 Gain, + 1 Attenuator
+5 mV
j+50 mV
X100Gain, +1 Attenuator
1+0.5 V
X 10 Gain, - 1 Attenuator
I
XI Gain, +l Attenuator
+5 V
I_+50 mV
XI000 Gain, +10 Attenuator
l
X 100Gain, + I 0 Attenuator
¯ +0.5V
~
X 10 Gain, + ! 0 Attenuator
+5 V
t+50 V
XI Gain, +10 Attenuator
Maximum CommonMode Input
1+15.5 V
+ 1 Attenuator
l¯ +155V
+ 10 Attenuator
Differential Offset Range(VD~FV
Mode)
(referred to input)
X 10, X 100, X 1000Gain, + 1 Attenuator I¯ +! V
1¯ +!0V
X 1 Gain, + ! Attenuator
Xi0, X100, XI000 Gain, +10 Attenuator l±10 V
I±100 V
X ! Gain, +l 0 Attenuator
Comparison Offset Range (VcoMPMode)
(referred to input)
I_+15.5V
+ 1 Attenuator
I¯ +i55V
+ 10 Attenuator
Output Range
Limitedto _+5 V into 50 ~ load
t Voltagesare referred amplifier input connector. Multiplyby probe attenuation factor to obtain value refer to probe
1 becomes+0.5Vat the probe tip whenusing a +10 probe.)
input. (e.g. _+50mV
Precision Voltage Generator (1822 and 1822-PR2models only)
Output Range
Resolution
Control
Reference Type
Output Routing
Autozero
±15.5 V
1 O0p.V
Individual increment and decrementbuttons for
each digit. Digit carries over to next decade.
Ovenstabilized buried Zener
Canbe applied to - input and available at rear
panel BNCconnector.
Removesoutput offset when0.0000 volts is
selected and periodically thereafter.
Power Requirements
Line Voltage Range
Line Frequency Range
100 - 250 VAC
48 - 66 Hz
1-3
1820/1822
Operator’s
Manual
WarrantedCharacteristics
Warranted characteristics describe parameters which have guaranteed performance. Unless otherwise noted, tests are
provided in the PerformanceVerification Procedure for all warrantedspecifications.
Gain Accuracy
Bandwidth(- 3dB)
X1 or XI0 Gain
X 100 Gain
X 1000 Gain
Rise Time (XI or X10 Gain)
CommonMode Rejection Ratio
(X 1 or X 10 Gain)
70 Hz
100 KHz
1 MHz
Precision Voltage Generator Accuracy
+1%+ Uncertainty of termination resistance
>10 MHz
>2.5 MHz
>1 MHz
<35 ns (Calculated from Bandwidth)
>100,000:1 (100 dB)
>100,000:1 (100 dB)
>1,000:1 (60 dB)
0.05%of reading + 500 ~tV (15° to 45° C.)
Typical Characteristics
Typical characteristics describe parameters which do not have guaranteed performance. Tests for typical characteristics
are not provided in the PerformanceVerification Procedure.
Input Resistance
+1 Attenuator
+ 10 Attenuator
Input Capacitance
ACInput Coupling Capacitance
+ 10 Attenuator Accuracy
DCDrift (X10Gain, referred to input)
Input Leakage Current
(X 1 or X 10 Gain, + 1 Attenuator)
Differential Offset Accuracy
X i 0, X100, X 1000Gain, + 1 Attenuator
XI Gain, +1 Attenuator
X 10, X 100, X 1000Gain, + 10 Attenuator
XI Gain, +10 Attenuator
Precision Voltage Generator Temperature
Coefficient (1822 and 1822-PR2models)
Power Consumption
1 MF2or 100 Mr2
1 Mr2only with attenuating probe
1 Mr2
20 pF
0.1 ~tF
0.05%
50 ~tVPC
<10 pA(0° - 45° C.)
O. 1%+ 250 laV
20.1%+ 500 ~tV
2O. 15%+ 500 ~tV
2O. 15%+ 5 mV
<5 mVPC
of full scale
26 W, ~ 36 VA(1820 and 1822)
52 W, ~ 72 VA(1820-PR2 and 1822-PR2)
2 Voltages are referred amplifier input connector. Multiply by probeattenuation factor to obtain value refer to probe
input. (e.g. 0.1%+ 50 ~tV2 becomes0.1%+ 500 laV at the probe tip whenusing a +10 probe.)
1820/1822
Operator’s
Manual
EnvironmentalCharacteristics
The Environmental Characteristics are tested to specification MIL-T28800D
Class 5.
performanceverification of environmentalcharacteristics is required.
Temperature Range, operating
Temperature Range, non-operating
Refer to this specification if
0° - 50° C.
-40° - 75° C.
Physical Characteristics
Height
Width
Depth
Weight
Shipping Weight
7.29 cm (2.87") (1820 and 1822 models)
8.75 cm (3.4") (1820-PR2and 1822-PR2models)
21.2 cm(8.36") (1820 and 1822 models)
43.9 cm (17.3") (1820-PR2and 1822-PR2models
without rack mountingears installed)
23.2 cm(9.12") (1820 and 1822 models)
42.5 cm (16.7")(1820-PR2 and 1822-PR2 models)
2.15 kg (4 Ibs. 12 oz.) (1820 and 1822models)
9.5 kg (21 lbs.) (1820-PR2and 1822-PR2models)
3.12 kg (6 lbs. 14 oz.) (1820 and 1822models)
11.3 kg (25 lbs.) (I 820-PR2and 1822-PR2models)
Compliances
ECDeclaration of Conformity
Designed to complywith EN61010-1: 1993
Installation Categoryl, 42.2V,pollution degree 1.
Conformsto LowVoltage Directive 73.72 EECfor
product safety.
1-5
1820/1822
Operator’s
Manual
Section 2
Operating Instructions, Controls, and Indicators
previous mode. Autobalance usually takes less than one
second. This handy feature allows the operator to DC
balance the 1820/1822 simply by pushing the GAIN
button which is already illuminated. Whenchanging
gains, the Autobalancefeature is automatically invoked,
freshly adjusting the amplifier’s DCbalance.
Front Panel
Attenuator
Signals connected to the +INPUTand the -INPUTare
connected either directly to the 1820/1822’s amplifier
inputs or to the input attenuators. The input attenuators
are passive networkswhichdivide each signal by ten.
+Input Coupling
In ÷1 modethe front panel input connectors are directly
connectedto the 1820/1822amplifier’s differential inputs.
INPUTCOUPLING
CAPACITOR
0.I~
+ INPUT
l
[
(AC-OFF-DC)
.......
r---
CONNECTOR
[----11-- 7 AC~11
In ÷10 mode each front panel input connector is
connected to a passive 1 Mr2attenuator. The attenuator
output is connected to the 1820/1822 amplifier’s
correspondingdifferential input. The signal at each input
is attenuatedby a factor of ten.
10
900 K~
, ¯
I+1[i
+10
ATTENUATOR
11111
Gain
The 1820/1822amplifier gain (amplification) is selectable
XI, XI0, XI00 and XI000. The amplified signal appears
at the rear panel AMPLIFIER
OUTPUT
connector.
In OFFmode, the input connector is disconnected from
the amplifier input, and the amplifier input is connectedto
ground. The ACcoupling capacitor is connected between
the +INPUTand ground through 1 M~(either the input
attenuator or the input resistor), independent of the
INPUT RESISTANCE
selected.
In this mode, the AC
coupling capacitor is quickly charged to the average DC
input voltage. OFFmodeis also referred to as precharge
mode.Precharge is particularly useful whenplanning to
ACcouple and measure voltages in excess of 19 volts.
The 1820/1822 input coupling is set to OFF and
connected to the circuit under test. Whenthe +INPUT
is
changed from OFFto ACmode, the coupling capacitor is
already charged, and the trace properly centered on the
oscilloscope screen. Additionally, the risk of tripping the
input overload detector and automatically disconnecting
the input is eliminated.
A signal connected to the +INPUTwill maintain its
polarity at the output connector. A signal connected to
the -INPUTwill be inverted in polarity.
Proper gain is obtained whenthe 1820/1822drives a 50
load such as an oscilloscope with input impedanceset to
50 fL An oscilloscope with only 1 Mr2 input impedance
available should have a 50 f2 coaxial termination placed
on its input connector. The ! 820/1822is then connected
to the oscilloscope throughthe coaxial termination.
The amplifier gain and the input attenuator
are
individually selectable to provide versatility.
For
example, the comparison voltage range is changed from
+15.5000 to ±155.000 volts by changing the
ATTENUATOR
from +1 to ÷10. The overall gain can
still be set to 100, 10, 1 or 0.1 by selecting the GAIN
mode,XI000, X100, XI0 or XI, as desired.
Autobalanceis a feature invoked whenany gain button is
pushed, even if a different gain is not selected.
Autobalance momentarily sets the INPUTCOUPLING
to OFFand determines the offset necessary to set the
output at 0 volts within about 25~tV. During this process
the front panel input coupling controls are unresponsive.
Whenfinished, the INPUTCOUPLING
returns to its
2-1
In the ACmode, the +INPUTis connected through an
ACcoupling capacitor to the amplifier input or the input
attenuator. The coupling capacitor retains its charge
when the input is switched to DC, makingit possible to
return to the samecircuit without the precharge time. But
this also makes it possible to discharge the coupling
capacitor into another circuit undertest if its DCvoltage
differs by more than approximately 19 volts from the
voltage on the coupling capacitor.
Although the
discharge current is limited to about 70mA,this could
damagesomecircuits. It is therefore recommendedthat
182011822
Operator’s
Manual
inverting input. The 1820/1822output is therefore zero
wheneverthese two voltages are equal. For this reason,
the voltage applied to the inverting input is called a
comparison voltage, VcoMP.
the +INPUT COUPLINGfirst
be changed to OFF
(precharge) when measuring a new circuit point. This
will safely recharge the ACcoupling capacitor in less
than 0.3 seconds. The value of the ACcoupling capacitor
is 0.1laF.
is often used to make precise measurements of
large signals by comparing the accurately knownVcome
with the unknownsignal. It is also used to measure the
actual voltage at any point ofa waveform.
VcoMP
DC and low frequencies are attenuated by the AC
coupling capacitor and the input resistance. With the
ATTENUATOR
set to +10, or set to +1 with the INPUT
RESISTANCE
set to 1 Mr2, the low frequency cut off
(-3dB point) is approximately 1.6Hz, lower than most
oscilloscopes by a factor of 5. Whenthe input attenuator
is set to +1, the INPUTRESISTANCE
may be set to
100 M~,and the -3dB point is 0.016Hz. This extremely
low frequency cut off is often handy in observing low
frequency noise riding on large (up to 400 volts)
voltages.
PVGoutput range is +15.500 volts. The PVGis never
attenuated by the input attenuator. Attenuation of the
+INPUT
signal by the -10 input attenuator will cause the
PVGto null out an input voltage up to ±155.00 volts
which is ten times larger than the actual PVGvoltage.
Whenthe 1822 is used with attenuating probes that
feature readout, the PVGdisplay is changed to indicate
the voltage at the +INPUT
probe tip which will bring the
amplifier output to zero.
In the DCmode, the +INPUTconnector is connected to
the amplifier either directly or through the input
attenuator, and the ACand DCattenuation are the same.
-Input
Coupling
The -INPUT connector is not useable when Vcomeis
selected.
(differential offset voltage) is an instrument mode
rather than a type of input coupling. The VBIFFmode
allows the PVG(or an external source in the 1820)
inject an offset signal into the 1820/1822while still using
both inputs for full differential operation. This modecan
be used as a position control to movethe trace on the
oscilloscope
screen in preference to using the
oscilloscope’s position or offset control.
The
oscilloscope’s position and offset controls should always
be set to zero so that the 1820/1822’s dynamicrange is
properly centered. Operation of the 1820/1822using the
VD|FF function is the same as VCOMP except for the
following:
VDIFF
(AC-OFF-DC-VcoMP)
FROM
PRECISION
VOLTAGE
)-
100II
Vcoup
v A_
~
REFERENCE
/ (’O--I
INPUTCOUPLING
CAPACITOR
- INPUT
~
CONNECTOR
("~
I
I.~
1 I
/-"
/7/
~ -+lOT
I
.........
l r Ac
HI
I1~
900
KI]
/
/
I
]
I
M
OF L
~______.~..~’~O
~*10-
INPUT
I
ATTENUATOR
111.1KI2
ION-
).
AMPLIFIER
-INPUT
~1 Mr1
INPUT
RESISTANCE
100Mfl
fl
¯
The -INPUTremains active, allowing full use of the
1820/1822as a differential amplifier.
The maximum range of the PVG (1822) or the
external source (1820) is ±10.000 volts in XI Gain
and ±1.0000 volts in X10 to 1000Xgain settings.
The effects of the +10 input attenuator and probe
attenuation are the same as when using VCOMP,
i.e.
any input attenuation multiplies the effective offset.
The -input has the same coupling modes as the +input
plus one additional option, VcoMv
(comparisonvoltage).
The 1822 generates a voltage controlled by the push
buttons above and below the front panel numerical
display. This voltage is called the Precision Voltage
Generator (PVG).
In VCOMP
mode, the 1822’s PVGis connected to the
amplifier’s inverting input through an internal filter
designed to eliminate radio and television signal
interference. The 1820 does not have the PVG,but uses
an externally supplied voltage. See Page 2-6 for VcoMv
operation with the 1820.
The1820/i 822’s amplifier subtracts the voltage applied to
its inverting input from the voltage applied to its non2-2
The 1822’s PVGdisplay is changedto indicate the voltage
that, if applied between the +INPUTand -INPUT,would
bring the amplifier output to zero. Whenthe 1822 is used
with attenuating probes that feature readout, the PVG
display is scaled to include the effect of probeattenuation.
1820/1822
Operator’s
Manual
frequency -3 dB points are 3MHz, I MHz, 300kHz,
100kHz, 30kHz, 10kHz, 3kHz, IkHz, 300Hz and 100Hz.
Selections for the lower -3 dB points are 0.1Hz, IHz,
10Hz, 100Hz, lkHz and 10kHz. These filters make it
possible to improvethe signal-to-noise ratio whenmaking
measurementson microvolt magnitude signals.
Input Resistance
When the input ATTENUATOR
is set to -1 and no
attenuating probe is connected, the input resistance can be
increased from 1 Mr2 to 100 Mr2 by pressing the
100M/IMbutton. This is advantageous when measuring
high impedance circuits or when ACcoupling is needed
with a very low frequency cut off. Whenthe input
ATTENUATOR
is set to -10 or an attenuating probe
with readout capability is attached, 1 Mr2(IM) input
resistance is automaticallyselected.
Precision
Voltage Generator (1822 Only)
The PVGgenerates the voltage which is used in the
VCOMP
and VDWF
modes and appears at the rear panel
PRECISION
VOLTAGE GENERATOR OUTPUT
connector.
Unbalanced source impedances can have an adverse
effect on commonmode rejection.
For example, a
differential source with impedancesof 1000 and 2000 [2,
each loaded with 1 M£2 will have a common mode
rejection ratio (CMRR)of 1000 to 1. The commonmode
rejection ration can be improvedto 100,000to 1 by using
100 M~input resistance.
Aboveeach digit is a push button which increments the
corresponding digit by one whenpushed. Whenheld, the
digit continues to increment, eventually incrementingthe
next higher digit.
This limitation is also apparent when trying to make
accurate measurements using VCOMP.A 10.000 volt
reference with a 1000 f2 output impedance will be
reduced to 9.9900 volts by the 1820/1822 1 M~input
resistance, introducing a 10 mVerror in the measurement.
Increasing the input resistance to 100 M~decreases this
error to 100~tV.
Similarly, below each digit is a push button which
decrementsthe correspondingdigit.
Oscilloscope inputs have a small input current which can
cause an offset whenmeasuring high impedancecircuits.
The offset can be observed by opening and shorting the
input to ground. The 1820/1822 has a temperaturecompensatedinput current pull away(cancellation) which
works in both the 1 M~ and 100 Mr2 INPUT
RESISTANCEmodes. Its input offset current is
considerablyless than that of most oscilloscopes.
Autozero resets the PVGoutput to zero to eliminate any
drift which may have occurred in the PVGdue to low
frequency noise, or long term drift. Autozero is invoked
each time the ZERObutton is pressed and re-invoked
approximately every minute thereafter. This is useful
whenthe instrument has been unplugged and a cold start
is required.
The 4- button above the left-most digit changes the PVG
output polarity. The ZERObutton below the left-most
digit sets the output to zero and invokes the Autozero
function.
Overdrive (yellow)
Effective
Gain (1822 Only)
Whena signal is applied to either input of the 1820/1822
that exceeds its ±15.5 volt input range the yellow
OVERDRIVE
indicator is lighted. The light remains on
as long as the input remains larger than the linear range.
The linear range is multiplied by the ATTENUATOR
factor and by the use of an attenuating probe.
Sevenlights (LEDs)across the top of the 1822front panel
indicate the total gain from the instrumentinput to output.
Whenthe X1light is lighted, the overall amplifier voltage
gain (amplification) is unity. Similarly, XI0 indicates
overall amplification of ten times. +10 indicates the
voltage amplificationis 0.1, and so forth.
The yellow OVERDRIVE
light is intended to warn the
user of potentially distorted waveforms.
WhenPreamble Instruments or other encoded probes are
properly used, the effective gain includes the probe’s
attenuation factor.
Overload (red)
Whena signal which could damageto the 1820/1822 has
been applied to either input connector, the 1820/1822
protects itself by disconnecting the signal. The input
Upper and Lower -3 dB Points
The 1820/22allows the user to select both the upper and
lower frequency -3 dB points. Selections for the high
2-3
182011822
Operator’s
Manual
The decimal in the display will be in the correct location
to indicate the voltage at the PVGoutput whenno probes
are attached and ÷1 attenuator and X1gain are selected.
The PRECISION
VOLTAGE GENERATOR OUT
BNCalso presents the same voltage used internally for
differential offset whenVDIFFis selected. Because the
PVGis applied to the amplifier to create a true differential
offset, the relationship betweenVDIFrand the voltage at
the PVGoutput BNCchanges with the amplifier gain
selection accordingto the followingtable:
coupling
mode changes to OFF, and the red
OVERLOAD
light is turned on.
The 1820/1822 is reset and the OVERLOAD
light goes
out whenany of the input coupling modesis selected.
Whenthe ATTENUATOR
is set to -1, a signal of
approximately ±19 volts will cause the input to draw
current
and the OVERLOADlight
to come on.
Transients too rapid to he disconnected by the input
coupling relay will draw up to about 70mAof input
current. Inputs in excess of 250 volts may cause
permanentdamageto the i 820/1822.
The input is not disconnected when the ATTENUATOR
is set to +10.
Rear Panel
Power
Normal instrument operation
position.
The instrument
performance in 30 minutes.
Maximum
PVGOutput
FrontPanelSettings
is obtained in the ON
reaches its specified
Gain
Atten
X1
+1
+IOV
+IOV
Xl
+10
+I00V
+10v
XI0,X100,
XI000
+1
+IV
+10v
Xl0,Xi00,
Xl000
+10
+lOV
±lOV
VDIFF
The maximum VDIFF is multiplied
by any probe
attenuation factor. Whenusing readout encoded probes
which the 1822 senses, the PVGreadout calculates the
effective differential offset at the probe tip. Of course,
both probes must have the sameattenuation factor.
PRECISION
VOLTAGE GENERATOR
OUTPUT (1822 Only)
The
rear
panel
PRECISION
VOLTAGE
GENERATOR
OUTPUTBNC connector is a monitor
of the Precision Voltage Generator (PVG).It is the same
voltage that is applied to the -INPUTwhen the -INPUT
coupling is VCOMe
or internally to the 1822 whenVDIFF
is selected.
The PRECISION
VOLTAGE
GENERATOR
OUTPUTcan be used either to monitor
the PVGwith a DVM
(digital voltmeter) or as an input
one or more Preamble 1820s or 1822s. There is a
1.59kHz single-pole low pass filter between the PVG
output and the -INPUTwhich removes radio frequency
interference (RFI). This filter does not attenuate the PVG
signal.
Amplifier
Output
The amplifier’s output BNCis intended to be used with an
oscilloscope, spectrumanalyzer or digitizer having a 50 if2
input resistance. The 1820/1822 output impedance is
50 f2. Withoutthe 50 ~ load, the amplifier gain is twice
the amountindicated on the front panel. Additionally, the
signal presented to an oscilloscope (spectrum analyzer or
digitizer) is as large as ± 10volts.
Probe Coding Input (1822 Only)
The PVGoutput is not attenuated by the input attenuator
or probes, whereas the input signal is. Therefore the
effective range of V¢OMP
is increased by a factor of 10
whenthe +10 attenuator is selected or a +10 attenuating
probe is used to attenuate the input signal. The PVG
numericaldisplay reflects the attenuator setting and probe
attenuation when the probe is readout encoded. As an
example, if there are no probes attached, the +10
attenuator is selected and the display is set to read
+155.000,the PVGoutput will actually be _+15.5volts.
This jack is to be used with PreambleInstruments probes
and other probes that have multiple selectable attenuation
factors. Other manufacturer’s probes with standard probe
coding capability will be properly decoded through the
1822’s front panel +INPUTBNCconnector.
2-4
182011822
Operator’s
Manual
Oscilloscope
Set the oscilloscope vertical sensitivity to no less than
500mV/div.The most useful range for the oscilloscope
deflection
factors will be between ! mV/div and
500mV/div. Using a deflection factor of 2V/Div will
bring the nonlinear portion of the 1820/1822’soutput on
screen.
Digitizers should not expect accurate
measurements for high frequency signals from the
1820/1822 exceeding +2.5V into a 50 ~ load. This is
equivalent to +5 divisions of deflection at 500mV/divin
an oscilloscope.
Settings
The Preamble Instruments 1820/1822 output is intended
to connect directly to the input of an oscilloscope,
spectrum analyzer or digitizer, but it is important to
observe some rules so that the 1820/1822 delivers its
specified performance.
Oscilloscope
Input Impedance
The 1820/1822 output impedance is 50 f~ and the
intended load impedance is also 50 ~. Nominal gain
(amplification) is obtained only whenthe oscilloscope (or
digitizer)
input impedance is set to 50fL
The
EFFECTIVEGAINdisplay is correct only when the
1822is properly terminatedinto 50 f~.
More sensitive settings (e.g. 100~tV/div) available on
someoscilloscopes are perfectly acceptable, but their
usefulness maybe limited by noise, particularly with the
full bandwidth limit selection and without averaging.
With the oscilloscope set to lmV/div and the 1820/1822
in the XI000gain mode,the over all deflection factor will
be 1 laV/div.
A factor of two additional gain is achieved by setting the
oscilloscope input impedance to 1 MfL However, the
operator needs to be aware that all the 1820/1822 gain
indicators will be off by a factor of two.
In its Xl0 gain mode, the 1820/1822is somewhatquieter
than most oscilloscopes, so it is preferable to use the
1820/1822 X10 gain mode and a lower oscilloscope
deflection factor rather than the other way around. For
example, to obtain the best noise performance at
lmV/div, set the 1820/1822 to XI0 mode and the
oscilloscope to 10mV/divrather than the use XI mode
and lmV/div. Other oscilloscopes give up bits of
resolution to obtain ImVor 2 mV/div sensitivity. The
1820/1822is very quiet in its XI0 or greater gain mode,
but no better than most oscilloscopes in the X1mode.
Sensitivity,
Position, and Offset
Oscilloscopes are designed to maintain their accuracy for
that portion of a signal that is displayed on-screen. When
the signal is large enoughto drive the display off-screen,
the oscilloscope’s amplifier must limit the signal in a nonlinear mode.Oscilloscopes are designed so that no matter
howthe sensitivity, position and offset controls are set,
the operator cannot view this distorted portion of the
signal.
The maximum
1820/! 822 output is carefully controlled so
it will not exceed +5V when the output is properly
terminated into a 50 ~ load.
The oscilloscope’s gain and position controls should be
properly set to avoid displaying the non-linear portion of
the 1820/1822’s output signal whenit is in overdrive.
This can be accomplished by observing the two following
rules:
Turn the oscilloscope input coupling to "OFF"or
"GND",
set the oscilloscope position control to center
screen, and do not changeit! If the oscilloscope has an
offset control, it too should be set to zero. Return the
oscilloscope’s input coupling to "DC". Subsequently
adjust the trace position on the oscilloscope screen using
the 1822 PVG(an external source for the 1820) and
VDIFFmode or VCOMP
input. This assures that the
oscilloscope is looking at the center of the 1820/1822’s
dynamicrange.
2-5
Anyoscilloscope bandwidthlimit setting maybe used so
long as the unlimited signal does not exceed full screen
before invoking bandwidthlimit. This is a good rule to
follow in using oscilloscopes with or without the
1820/1822.
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1820/1822
Operator’s
Manual
Model 1820 Operation
Notethat the effective voltage is alwaysincreased by the
attenuator. It therefore follows that any probe will
increase the effective voltage of both VCOMP
and VDIFF
by its attenuation factor. In other words, a probewith a
+100attenuation factor will increase the effective full
scale range by 100.
The performance and operation of the 1820 Differential
Amplifier is identical to that of the 1822 except as
follows:
The 1822 EFFECTIVE GAIN indicator
is not
included in the 1820. The 1820operator will need to
keep track of the various attenuator and gain settings
to accurately account for the proper deflection factor
on the oscilloscope.
.
Front Panel
Settings
The VcoMeand WHIFF functions operate the same as
in the 1822. The 1820does not contain the Precision
Voltage Generator, but the voltages required for the
operation of VCOMP
and VDIFFcan be provided
from an external source. This voltage source is
applied
to the 1820 through the OFFSET
VOLTAGE
connector on the rear panel. By using a
stable voltage source and monitoring the level with a
DVM,operation and accuracy similar to that of the
1822 can be achieved. The maximuminput voltage
that can be applied depends on whether the 1820 is
operated in VCOMPor VDIFF.
Whenoperating the 1820 with an external voltage source,
the applied voltage should not exceed 15.5 volts in
Comparisonmode and 10.0 volts in Differential Offset
mode.
Whenthese maximumexternal voltages are applied, the
effective voltage as seen by the amplifier is as follows:
GAIN
ATTEN
EffectiveFull Scale Range
VCOMP
VDIFF
XI
+10
+155V
+lOOV
XI0, xl00,
xl000
+1o
+155v
+lOV
XI
+1
+15.5V
+lOV
Xi0, xl00,
xl000
+!
+15.5V
+lV
GAIN
ATTEN
X1
+10
+15.5kV
+lOkV
XI0
+!0
±15.5kV
41000V
X!
+!
+ 1550V
+ ! 000V
Xl0
+1
+1550V
+iOOV
VCOMP
VDIFF
Althoughthe full scale range maybe 10kVor 15.5kV,
most probes have a much lower maximuminput voltage
rating which must not be exceeded.
The following charts will help the operator stay within the
maximuminput voltage limits and understand the
relationship between the actual voltage applied and the
effective voltage. Effective voltage is alwaysreferred to
the input of the 1820or the probe tip if a probe is used.
Whenusing probes, the maximum
effective voltage range
may be limited by the maximumvoltage rating of the
probe.
FrontPanelSettings
Effective Full Scale Range
with +100 Probe
2-6
1820/1822
Operator’s
Manual
Section 3
General Operating Information
Getting
Started
This section will help the first time user becomefamiliar
with the operation of the 1822and howit interfaces with
an oscilloscope. Operation of the 1820is very similar
except an external voltage source is neededfor operation
of the comparisonand differential offset modes.
To carry out the following exercises, the operator will
need an oscilloscope and a general purpose function
generator.
Power Connection
Check to make sure the POWER
switch located on the
rear panel is in the OFFposition. Connect the power
cord to an appropriate power source. The 1822 will
operate on a 50 or 60 Hz AC power source with a
nominalvoltage range from 100 volts to 250 volts.
Connection to and Setting up the Oscilloscope
Connect a 50 f2 coaxial cable between the AMPLIFIER
OUTPUTBNC on the 1822 rear panel and the
oscilloscope’s input connector. If the oscilloscope has
1 Mtq and 50 if2 input capability, select 50 f2. If the
oscilloscope has only a I Mf2 input, terminate the
coaxial cable at the oscilloscope’s input with a 50
feed-throughterminator. It is importantthat the 1822be
terminated into 50 fL
Set the oscilloscope scale factor to 50mV/div.Set the
oscilloscope’s input coupling to GNDor OFF and
position the trace to center screen. Do not movethe
oscilloscope position setting after this initial set-up.
Changethe oscilloscope input coupling to DC.
1822 Front Panel Operation
lighted as well as all segments in the Precision Voltage
Generator display. After approximately 3 seconds, the 1822
will be set to its power-up
reset state. This state is as follows:
OFF
+ INPUT
OFF
- INPUT
Nolights on(full BW)
HF-3dB POINT
No lights on (DC)
LF-3dB POINT
Xl
GAIN
ATTENUATOR
+10
1M
INPUT RESISTANCE
+ 00.000
PRECISION VOLTAGE GENERATOR
COMPARISONor DIFFERENTIAL
COMPARISON
EFFECTIVE GAIN
-10
Attenuator and Gain Operation
Connect the function generator output to the +INPUTBNC
connector and apply a sinewave of 50 kHz and 0.5V peak
amplitude. Push the DCbutton on the 1822’s +INPUT.The
signal on the oscilloscope should be 2 divisions peak to peak
amplitude. Adjust the oscilloscope’s time/division and trigger
to display at least two completecycles of the waveform.
Press the +1 ATTENUATOR
button. The waveform’s
magnitudeon the oscilloscope’s display will increase by a
factor of 10 and extend off the top and bottomof the screen.
The XI light will be lighted in the EFFECTIVEGAIN
display. Reducethe function generator’s output until the
oscilloscope’s display is again 2 divisions peak to peak. The
overall sensitivity of the 1822 and the oscilloscope is now
50mV/div.
Nowpress the Xl0 GAINbutton. Observe the following
changes: The +INPUT
DClight will momentarily go out and
its OFFlight will be lighted before returning to their previous
states. This momentarychange is the result of the 1822
automatically adjusting its DCBalance. The XI0 light will be
lighted in the EFFECTIVE
GAINdisplay and the display on
the oscilloscope will again extend off screen. The overall
sensitivity of the 1822and the oscilloscope is now5mV/div.
Change the POWER
switch located on the 1822’s rear
panel to ON and observe the 1822’s front panel
indicators. Initially, there will be abouta 2 seconddelay
and then each function, other than the upperand lower 3dBpoints, will haveone indicator light lighted. The red
OVERLOAD
and yellow OVERDRIVE
lights will be
3-1
182011822
Operator’s
Manual
Comparison Voltage
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Operation
(VcoMP)
Leavethe 1822set up as in the previous exercise or set
as follows:
+ INPUT
DC
- INPUT
OFF
HF-3dB POINT
Nolights on(full BVV)
LF-3dB POINT
Nolights on (DC)
GAIN
Xl0
ATTENUATOR
+1
INPUT RESISTANCE
t M
PRECISION VOLTAGE GENERATOR+ 0.0000
COMPARISONor DIFFERENTIAL COMPARISON
EFFECTIVE GAIN
Xl0
¯ Function Generator output: 50 kHz 50 mVpksine
wave. connected to the 1822’s +INPUT.
¯ Oscilloscope: Set at 50mV/div(equivalent to 5 mV/div
with 1822 at X10GAIN)and time/division adjusted for
2 to 3 cycles.
Underthese conditions, the display on the oscilloscope
will extend off the top and bottomof the screen.
Change the oscilloscope’s sensitivity from 50 mV/div to
10mV/div.Overall sensitivity, including the 1822, is now
lmV/div. Temporarily change the oscilloscope’s input
coupling from DCto GND(or OFF)and re-center the trace
center screen using the oscilloscope’s position control. Return
its input coupling to DC. Nowpress the XI0 button on the
1822 to invoke its Autobalancefunction. (Note that pressing
the gain button that is already selected causes the 1822 to
adjust its DCbalance, but does not changeits gain.)
Changethe Precision Voltage Generator’s reading to again
place the negative peak of the waveformat the oscilloscope’s
center screen. Note that the Precision Voltage Generator’s
display represents the negative peak voltage of the waveform
with greater resolution.
Return the oscilloscope’s sensitivity to 50mV/div
and press the
1822’s -INPUTOFF (or ACor DC) button. The Precision
VoltageGeneratorwill retain its setting and the display on the
oscilloscope will be centered about the center line. Press the
-INPUTVCOMP
button again and observe that the Precision
Voltage Generator’s output is again connected to the minus
input of the 1822’s -INPUT.
Following are a few observations on using the 1822
comparison voltage mode (VCOMP):
Press the -INPUT VCOMP
button. This internally
applies the Precision Voltage Generator’s output to the
1822’s -INPUT and the OFF light goes out (the
-INPUTconnector is disabled).
The negative input and its AC, OFFand DCcoupling are
disabled. Instead of being a differential amplifier, the
1822becomesa differential comparator. It comparesthe
voltage present at the +INPUTwith the output of the
Precision Voltage Generator and whenthey are equal, the
output of the 1822is zero volts.
The positive and negative peaks of the waveform
displayed on the oscilloscope are (respectively)
divisions above and belowthe display center line. Push
the button abovethe digit that is twoplaces right of the
decimal (10 mV)in the Precision Voltage Generator
(PVG)until the positive peak of the waveformappears
the oscilloscope’s display. Continue incrementing and
decrementingPrecision Voltage Generator’s digits until
the peak of the waveformis at the centerline of the
oscilloscope’s display. The numberin the Precision
Voltage Generator display is the waveform’spositive
peak voltage.
The value displayed by the Precision Voltage Generator
indicates a waveform’svoltage, with respect to ground,as
it passes throughthe oscilloscope display’s centerline. It
is very important that the oscilloscope’s trace be
positioned to center screen if an accurate measurement
is
to be madeusing this method.
By using the 1822 in the comparison voltage modeand
the oscilloscope in a high sensitivity setting, highly
accurate voltage measurementscan be made.
Press the + button in the Precision Voltage Generator.
Observethat the negative peakof the signal is nowat or
near the oscilloscope’s display centerline.
By
incrementing and decrementingthe digits, the negative
peak can be positioned to the oscilloscope’s display
center line. Nowthe numberin the Precision Voltage
Generator’s display is the waveform’snegative peak
voltage.
The Precision VoltageGeneratorcan be used as a position
control whichallows the 1820/1822to operate in its linear
region.
3-2
182011822
Operator’s
Manual
Differential
Offset Operation
Leavethe 1822set up as in the previous exercise or set
it up as follows:
DC
+ INPUT
VCOMP
- INPUT
Nolights on (full BW)
HF-3dB POINT
Nolights on (DC)
LF-3dB POINT
Xl0
GAIN
ATTENUATOR
)1
INPUT RESISTANCE
1M
PRECISION VOLTAGEGENERATOR- 0.0500*
COMPARISONor DIFFERENTIAL COMPARISON
EFFECTIVEGAIN
XI0
*approximate
¯ Function Generator output: 50kHz 50mVpksine
wave. connected to the +INPUTof the 1822.
¯ Oscilloscope: set at 50mV/div(equivalent to 5mV/div
with 1822 at X10GAIN)and sweepadjusted for 2 to
cycles.
¯ Externally trigger the oscilloscope on the function
generator’s output (samesignal as is applied to the 1822’s
+INPUT)
Underthese conditions, the negative peak of the display
on the oscilloscope should be very near center screen.
Adjust the value in the Precision Voltage Generatoruntil
the negative peakis at center screen.
Press the Vaw
F button. This internally applies the output
of the Precision VoltageGeneratorto a point within the
1822’samplifierthat facilitates a true differential offset.
Also note that the Precision Voltage Generator display
was reset to zero (+ .00000) and the -INPUTcoupling
changed. The VcoMP
light went out and the OFFlight
was lighted. In the line under the Precision Voltage
Generator
display
(COMPARISON or
DIFFERENTIALOFFSET), the COMPARISON
light
went out and the DIFFERENTIAL
light was lighted.
This indicates that the Precision Voltage Generatorwill
nowbe applied as a differential offset rather than as a
comparisonvoltage as in the previous exercise. Boththe
+INPUTand the -INPUTinputs are now enabled.
oscilloscope’s display.
Continue incrementing and
decrementing the digits in the Precision Voltage Generator
until the peak of the waveformis at the center line of the
oscilloscope’s display. The numberin the Precision Voltage
Generatordisplay is the value of the waveform’spositive peak
voltage.
Press the + button in the Precision Voltage Generator.
Observethat the negative peak of the signal is nowat or near
the oscilloscope display’s center line. By incrementing and
decrementingthe digits, the negative peak can be positioned to
the oscilloscope display’s center line. Nowthe numberin the
Precision Voltage Generator’s display is the value of the
waveform’snegative peak voltage.
Change the oscilloscope’s sensitivity from 50mV/div to
10mV/div.Overall sensitivity, including the 1822, is now
ImV/div. Temporarily change the oscilloscope’s input
coupling from DCto GND(or OFF)and re-center the trace
center screen using the oscilloscope’s position control. Return
its input coupling to DC. Nowpress the XI0 button on the
1822 to invoke its Autobalancefunction. (Note that pressing
the gain button that is already selected causes the 1822to
adjust its DCBalance, but does not changeits gain.)
Changethe Precision Voltage Generator’s reading to again
place the negative peak of the waveformat the oscilloscope’s
center line. Note that the Precision Voltage Generator’s
display more accurately represents the negative peak voltage
of the waveform.
Return the oscilloscope’s sensitivity to 50 mV/divand again
press the 1822’s VDwv
button. The VmFF
light will go out and
the display on the oscilloscope will be centered about the
center line. Notice that the PVGretains its setting, but the
output of the PVGis not applied to the amplifier. Press the
VD=FF
button again and observe that the Precision Voltage
Generator’s output is reapplied internally to the 1822
amplifier.
Following are a few observations on using the differential
offset mode(VDw~)of the 1820/1822:
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Both the positive and negative inputs (AC, OFFand DC)
are enabled and the 1820/1822remainsa true differential
amplifier.
The value displayed by the Precision Voltage Generator
indicates a waveform’sdifferential voltage, with respect
to the -INPUT,as it passes through the oscilloscope
display’s center line. It is very important that the
oscilloscope’s trace be positioned to center screen if an
accurate measurementis to be madeusing this method.
The voltage applied to the 1820’s EXTERNAL
The positive and negative peaks of the waveform
displayed on the oscilloscope are 10 divisions aboveand
below(respectively) the center line of the display. Push
the button abovethe digit that is twoplaces right of the
decimal (10mV)in the Precision Voltage Generator until
the positive peak of the waveform appears in the
3-3
i
182011822
Operator’s
Manual
User Traps to Avoid
VOLTAGE
INPUTalso indicates the waveform’s
differential voltage with respect to its -INPUT.
By using the 1822in the differential offset modeand
the oscilloscope in a high sensitivity setting, high
resolution voltage measurementscan be made. The
-INPUTis the reference for these measurements.
The Precision Voltage Generator can be used as a
position control whichallows the 1822to operate in
its mostlinear region.
Which Offset
Mode Should be Used?
The operation of the Comparison (VcoMv) and
Differential Offset modes(VwvF)are quite similar. The
Comparisonmodeis easier to understand and has a wider
range, 15.5 volts versus 10.0 volts. The Differential
Offset modeprovides offset operation while allowing the
1822to function as a true differential amplifier.
For most applications, the Differential Offset (VDIFF)
mode has advantages over the Comparison (VcoMv)
mode. Whenusing the Comparisonmode, the Precision
Voltage Generator’s output is subtracted from the
+INPUT.Except for the PVG’soffset, operation is the
same as a standard single-ended oscilloscope - only one
1820/1822input is available. In the Differential Offset
mode,the 1820/1822functions as a differential amplifier
- both +INPUTand -INPUTfunction. This allows the
operator to choose a measurementreference point other
than ground. Even in ground referenced measurements,
signal degradation can be reduced by using the -INPUT
probe to select a groundreference point with the least
noise. This methodis especially useful in eliminating
humand noise from ground loops.
There is one instance in which the Differential Offset
(VmFv)modemight result in more noise. Magneticpickup is proportional to the area betweenthe probes. If
twisting the probe leads together is not sufficient to
reduce magnetic pick-up, the ComparisonOffset (Vco~)
modemaybe preferable.
Because the ComparisonOffset modeuses the CMRR
of
the 1822 while the Differential Offset modeuses an
internal amplifier, the Comparison Offset modeis
slightly moreaccurate.
The Differential Offset (VDIFF) modeis usually the mode
of choice if the wider range or higher accuracy of the
Comparison(VcoMP)modeis not needed.
There are a few situations the user of either the 1820or 1822
should be awareof to avoid somepotential measurementtraps.
Exceeding
the Common Mode Range
The 1820 and 1822 Differential Amplifiers have the largest
commonmoderange available for this type of amplifier and
are very good at measuring small differences between two
large signals. However,care still mustbe taken not to allow a
large commonmodesignal to exceed the available common
mode range.
The maximumcommonmode range is +15.5 volts when a
signal is applied directly (+1 ATTENUATOR
and no probes)
to the 1820/1822’s + and - inputs. The yellow OVERDRIVE
light illuminates to warn the user of possible waveform
distortion caused by exceeding+15.5 volts.
Attenuating the input signal extends the commonmoderange
by the same factor as the attenuation. Pressing the +10
ATTENUATOR
button increases the commonmode range to
+155 volts, and using a probe with a +10 attenuation factor
will too. The effect of the internal +10 ATTENUATOR
and
the attenuation factor of probesis multipliedjust as the signal
is attenuated. As an example, using the amplifier’s +10
ATTENUATOR
with a probe having a +100 attenuation
factor (total attenuation of+1000)results in a common
mode
range of 15,500 volts. In this case, the probe’s maximum
voltage rating probably limits the maximumcommonmode
input voltage.
The gain setting of the amplifier has no effect on common
moderange; it is the same in XI000, XI00, XI0 or XI gains.
Whenmaking measurements on circuits that are line
referenced, be sure to use enoughtotal attenuation to keepthe
peak voltage at the amplifier input below15.5 volts. The US
line can exceed170 peakvolts andtherefore at least a total
attenuation of +100 should be used. Line voltages in some
other countries are larger but their peakvoltages do not exceed
the 1550 volt commonmode range that a +100 attenuation
factor provides.
Movingthe oscilloscope
center screen
position setting
away from
Whenoperating the 1820/1822with an oscilloscope, it is very
importantto set the oscilloscopeposition and/or offset control
to center screen. Thereare a couple of reasons for this:
3-4
182011822
Operator’s
Manual
First, the linear portion of the 1820/1822’s+5Voutput
range is around zero volts. As the 1820/1822
approachesits limits, the output signal will be distorted.
Moving the oscilloscope position control way from
center screen can allow these distortions to appear on the
oscilloscope’s screen where they maybe mistaken for
part of the displayedsignal.
Second,proper operation of the 1822’s Precision Voltage
Generator (PVG)depends on the operator knowingthe
location of zero volts on the display. Thereadout in the
PVGis designedto display the voltage of the signal as it
crosses the center line of the oscilloscope screen. If the
oscilloscope position or offset control has been moved,
incorrect readingscould result.
Failure to Terminate the Amplifier into 50 f2
"All the signals displayed on myoscilloscope seemto be twice
as large as they should be." This commentresults from not
havingthe output of the 1820/1822properly terminated into 50
if2. The 1820/1822 output impedance is 50 f). The cable
connecting the 1820/1822 to the oscilloscope or spectrum
analyzer should be 50 f2 and be terminated with a 50 ~ load.
If the termination at the end of the connectingcoaxial cable
is missing, the amplifier will not be properly terminated.
The gain of the amplifier will be twice that indicated by the
front panel settings and the 1822’s EFFECTIVEGAIN
indicator will be offby a factor of two.
In somemeasurements,the operator can take advantageof this
increased gain if the problemscaused by not terminating the
output are fully understoodand taken into account.
Using Oscilloscope
500 mV/Div
V/Div Settings
Greater than
"I knowthe input to the 1820/1822is a sinewave,but I
am seeing a square wave on the oscilloscope." This
commentis the result of the operator setting the
oscilloscope sensitivity to somethingless than 1V/div. If
the oscilloscope sensitivity is set to 2V/div, the
1820/1822will limit at 2-1/2 divisions aboveand below
center screen (zero volt point if the oscilloscope’s
position control is properly set). Thus, a sinewavelarge
enough to overdrive the 1820/1822 will appear as a
square waveon the oscilloscope.
The 1820/1822is designed to cleanly limit the output
signal to +5V. Keepingthe oscilloscope’s position at
center screen and using oscilloscope sensitivities between
500mV/divand I mV/div (or the oscilloscope’s most
sensitive setting) will insure goodsignal integrity. When
the displayed signal contains mostly low frequency
components, the operator can use the oscilloscope’s
1V/div setting to allow large signals to be completely
shownon screen.
3-5
1820/1822
Operator’s
Manual
Section 4
Performance Verification
Adjustment should only be performed by qualified
personnel. Removingthe covers from the instrument
mayalter critical compensationadjustments, requiring
the instrumentto be re-calibrated. Re-establishing these
adjustments requires the use of special calibration
fixtures. Therefore, the covers should never be removed
by the user. The Adjustment Procedure is part of this
service manual.
Introduction
This procedure can be used to verify the warranted
characteristics of the 1820 and 1822 series of
Differential Amplifiers.
NOTE
Unless otherwise noted the 1820refers to the 1820, and
1820-PR2.1822 refers to the 1822, and 1822-PR2.
Test Equipment Required
The-PR2models contain two complete single channel
amplifiers within a single housing. To verify the
performance of the -PR2 models, complete the entire
procedure on one channel, then repeat the procedure
with the remaining channel.
Table 4-1 on the following page lists the test
equipment and accessories, or their equivalents,
which are required for performance verification of
the 1820/1822.
The recommendedcalibration interval for the model
1820 and 1822Differential Amplifiers is one year. The
complete performance verification procedure should be
performedas the first step of annual calibration. Test
results can be recorded on a photocopy of the Test
Recordprovided at the end of this section.
This procedure has been developed to minimize
the number calibrated test instruments required.
Only the parameters listed in boldface in the
Minimum Requirements
column
must be
calibrated to the accuracy indicated.
Performance verification can be completed without
removingthe instrument covers or exposing the user to
hazardous voltages. Adjustment should only be
attempted if a parameter measured in the Performance
Verification Procedure is outside of the specification
limits.
Because the input and output connector types may
vary on different
brands and models of test
instruments, additional adapters or cables may be
required.
4-1
182011822
Operator’s
Manual
TABLE4-1
List of required Equipment
Description
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Q
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
MinimumRequirements
Test Equipment Examples
Wide Band Oscilloscope
100 MHzbandwidth
2 mV-200mVscale factors
1 ns-10 [as time/division
2%vertical accuracy
50 ~ termination
LeCroy LT342 or
LeCroy LC584AM
Oscilloscope Preamplifier
200laV-10mYscale factors
10 MHzbandwidth
Wideband oscilloscope plus Preamble
1822.
Digital Multimeter
DC: 0.2% accuracy
AC:0.2% accuracy to measure
200 mVand 2 Vrms @ 1 kHz
6%digit resolution
HP 34401A, or
Fluke 8842A-09, or
Keithley 2001
Oscillator/Function Generator
Sinewave output
5 Vp-p
50 Hz - 1 MHzfrequency range
Stanford Research Model DS340, or
Hewlett Packard 33120A,or
Leader LAG-120B
Leveled Sine WaveGenerator
Relative output level accurate to
3%flatness from 1 - 100 MHz
and 50 kHz.
Output adjustable to 2 Vp-p
TegamSG503with TMseries mainframe
with 012-0482-00 precision BNCcable.
A semiautomatic software leveled signal
source calibrated with a powermeter may
be substituted.
Terminator, in-line, BNC
50 f2 + 1%coaxial termination
ITT Pomona4119-50, or
AIM 27-9008
Terminator, precision, BNC
50 ~ + 0.05%
Tektronix 011-0129-00
Attenuator, BNC,(2 ca)
50 f~ + 2%, +10 (20 dB),
ITT Pomona4108-20dB, or
BNCcoaxial cable, (2 ca)
Male-male BNC(approx. 1 meter)
ITT Pomona 5697-36
BNCcoaxial cable, (2 ca)
Male-male BNC4"-6" length
Pasternack Enterprises PE3067-5
BNC’Y’ connector
Male to dual female, BNC
AIM 27-9294
BNCTee connector
Male to dual female, BNC
ITT Pomona3285, or
AIM 27-8140
BNCadapter
Female to female
AIM25-7430, or
ITT Pomona 3283
BananaPlug adapter
BNCfemale to banana plug.
ITT Pomona 1269
Note: Boldface indicates parameters required to be calibrated. Other parameters are compensatedfor in the procedure
and can be approximate.
4-2
1820/1822
Operator’s
Manual
Preliminary
1.
Procedure
Procedure
1. CheckXl Gain Accuracy
Connect the Differential Amplifier to an ACpower
source within the range listed in the Nominal
Characteristicsin the Specificationsection.
1.
Allow at least 20 minutes warm-uptime for the
1820/1822and test equipmentbefore performing the
VerificationProcedure.
2.
Turnon the other test equipmentand allow it to warm
up for the time recommended
by the manufacturer.
a.
Set the 1820/1822 +INPUTto DC.
b. Connect the High Amplitude Sine Wave
generator via a 50 f2 BNCcoaxial cable, a
standard 50 f2 termination to a female BNC
to bananaplug adapter.
The warranted characteristics of the 1820/1822series
Differential Amplifiers are valid at any temperature
within the Environmental Characteristics listed in
Section 1. However, some of the other test equipment
used to verify the performance mayhave environmental
limitations required to meet the accuracy requirements
needed for the procedure. Be sure that the ambient
conditions meet the requirements of all the test
instruments used in the procedure.
c.
Set the DMM
to measure ACvolts.
d.
Connectthe banana plug adapter to the
DMM.
e.
Set the sine wavegenerator to 70 Hz and the
output amplitude to read 2 Vrms+ 50 mVon
the DMM.
f. Record the DMM
reading to 100 laV
resolution as ’Sine WaveGenerator Output
Voltage’ in the Test Report.
g. Disconnect the sine wave generator output
cable with the 50 f2 termination from the
BNCto banana plug adapter on the DMM.
Leavethe bananaplug adapter installed on
the DMM
for the remainder of the
procedure.
NOTE
When the oscilloscope input is connected to the
1820/1822 AMPLIFIEROUTPUT,the oscilloscope
input impedanceshould be set to 50 .(-2 unless otherwise
stated Use a 50 .(2 inline termination when using an
oscilloscope without an internal 50 .(2 termination.
h. Connect the sine wavegenerator via the
coaxial cable with the standard 50 f2
termination to the +INPUT
of the
1820/1822.
Position the oscilloscope display to center screen.
Unless otherwise noted, the oscilloscope position and
offset must remain at zero for the duration of the
adjustment procedure.
i. Connect the 1820/1822 AMPLIFIER
OUTPUT
connector via another coaxial
cable and the precision 50 ~ termination to
the banana plug adapter on the DMM.
Set the 1820/! 822front panel controls as follows:
j. Press the XI GAINbutton to remove any
residual DCoffset from the input. (A DC
componentmay interfere with the RMS
computation in some DMMs.)
HF -3 dB POINT
All LEDsOff
(Maximumbandwidth)
LF-3dB POINT
All LED’sOff
(DC)
GAIN
Xl
ATTENUATOR
.-1
k. After the DMM
has stabilized, record the
reading to 1 mVresolution as ’Amplifier
Output Voltage’ in the Test Record.
INPUT RESISTANCE
1 MQ
1.
+INPUT
OFF
-INPUT
OFF
VCOMP
OFF
VDIFF
OFF
Divide the measuredoutput voltage from
step 1-k by the sine wavegenerator output
voltage (amplifier input voltage) in step i-f.
Subtract 1.0 from the ratio and multiply the
result by 100%to get the error in percent.
I
Measured Output Voltage _ 11 x
Error = Amplifier
Input Voltage
100%
PRECISION VOLTAGE 00.000 V
GENERATOR
4-3
I
1820/1822
Operator’s
Manual
3,
m. Recordthe result to two decimal places
(±0.xx%)as ’Xl Gain Error’ in the Test
Record.
n.
NOTE
CHECK
-- That the XI GAINerror is less
than ± 1%.
Because most DMMsdo not provide the required
accuracy on lower ACvoltage ranges, the check for
XIO, XIO0 and XIO00 Gain Accuracy uses a ratio
technique with an external +10attenuator. The actual
attenuation of the attenuator is determinedusing higher
amplitude signals.
2. Check +10 Attenuator Accuracy.
NOTE
The accuracy of the internal +10 attenuator is not a
warranted specification. However, the attenuator will
be used in the XIO00 gain test where it’s absolute
accuracywill be included in the calculations.
a.
i. Disconnect the amplifier output cable and the
precision 50 f2 termination from the BNCto
banana plug adapter on the DMM.
j. Disconnect the sine wavegenerator output
cable from the +INPUTand removethe 50 f2
termination from the coaxial cable.
Verify that the measuredoutput voltage is still
the samevalue as recorded in step l-k.
b.
Set the 1820/1822 ATTENUATOR
to +10.
c.
After the DMM
has stabilized, record the
reading as ’Amplifier OutputVoltage’ in the
Test Recordto 10 laV resolution.
Dividethe attenuation calculated in step 2-d
by 10.0. Subtract the 1.0 from the result and
multiply this numberby 100%to get the
attenuation error in percentage.
Error=(Actual
f.
Attenuation(StePlo
k.
Connect one female end of the BNCTee to
the sine wavegenerator cable.
1.
Connecta 50 f2 + 10 attenuator to the male
end of the BNCTee followed by a standard
50 f~ termination.
m. Connect another coaxial cable from the
banana plug on the DMM
to the other female
end of the BNCTee.
d. Divide the output voltage recorded in step 1-k
by the attenuated output voltage recorded in
step 2-c. Recordthe result to four digit
resolution in the Test Record. This is the
’Actual Attenuation’.
e.
Check the Xl0, Xl00 and Xl000 Gain
Accuracy.
n.
Set the sine wavegenerator output amplitude
to read 2.00 Vrms ± 50 mVon the DMM.
o.
Recordthe reading to 1 mVresolution as
’Sine WaveGenerator Output Voltage’ in the
Test Record.
p.
Removethe DMM
cable from the BNCTee.
q.
Connectthe 50 if2 termination end of the
termination/attenuator/BNC Tee combination
of the sine wavegenerator cable to the DMM
banana plug adapter.
r.
Record the DMM
reading to 100 laV
resolution in the Test Recordas ’ Actual
Amplifier Input Voltage’.
(Note: This reading should be approximately
200mV.If it is not, verify that the in-line
attenuator and terminationare installed in the
correct order. The 50 if2 termination should
be closest to the DMM).
xl00%
2-d)-13
Recordthis value as ’+10 Attenuator Error’ in
the Test Record.
g. Addthe attenuation error recorded in step 2-f
to the X 1 gain error recordedin step l-k. Be
sure to include the signs of the two terms
whenperforming this addition. Recordthe
result to two decimal places (±0.xx%)as ’XI
Gain + +10 Attenuation Error’ in the Test
Record.
s. Divide the DMM
reading in step 3-j into the
output amplitude measuredin step 3-g. This
is the exact attenuation of the attenuatortermination combination.
h.
t.
CHECK-- That the combined X1 Gain +10
Attenuationerror is less than ± 1%.
4-4
Recordthe result to four digit resolution as ’
Exact Attenuation’ in the Test Record.
182011822
Operator’s
Manual
u.
Disconnect the termination/attenuator/BNC
Tee combination from the DMM.
v.
Connectthe terminated end of the
termination/attenuator/BNC Tee combination
to the 1820/1822 +INPUT.
jj.
Recordthe calculated error to two decimal
places (+0.xx%)in the Test Recordas ’X
Gain Error’.
kk. CHECK
-- That the calculated error is less
than + 1%.
11. Press the XI00 GAINbutton on the
1820/I 822.
to the free female end of
w. Connect the DMM
the BNCTee connector.
Adjust the sine wavegenerator output
amplitude to read 200 mVrms+ 50 mVon the
DMM.
mm.Multiply the actual input voltage of the
1820/1822which was recorded in step 3-w by
100.0.
y. Record the DMM
reading to 100 p.V in the
Test Record as ’Sine WaveGenerator Output
Voltage’.
nn. Recordthe result to four digit resolution in the
Test Record as ’Expected Amplifier Output
Voltage’.
z.
oo. After the DMM
has stabilized, record the
measuredoutput voltage to 1 mVresolution
as ’MeasuredAmplifier Output Voltage’ in
the Test Record.
x.
Disconnect the DMM
cable from the BNC
Tee.
aa. Connect the DMM
cable to the 1820/1822
AMPLIFIER OUTPUTconnector.
pp. Calculate the error by dividing the measured
output voltage recorded in step 3-gg by the
expected output voltage recordedin step 3-ff.
Subtract !.0 fromthis ratio and multiply by
100%to get the error in percent.
bb. Insert the precision 50 f) termination between
this cable end the bananaplug adapter on the
DMM.
cc. Set the 1820/1822 GAINto XI0.
dd. Divide the sine wavegenerator amplitude
recordedin step 3-q by the actual attenuation
calculated in step 3-1. This represents the
actual voltage on the input of the amplifier.
Error
I
Measured Output Voltage
= Expected Output Voltage
1") x 100%
)
ee. Recordthe result as ’Actual Amplifier Input
Voltage’ in the Test Record.
ff. Multiply the actual input voltage as recorded
in step 3-wby 10.0 to obtain the expected
output voltage.
qq. Recordthe calculated error to two decimal
places (+0.xx%)in the Test Recordas X i00
Gain Error.
gg. Recordthe result to four digit resolution as
’Expected Amplifier Output Voltage’ in the
Test Record.
rr. CHECK
-- That the calculated error is less
than + 1%.
ss. Press the +10 ATTENUATOR
and then the
X1000GAINbutton on the 1820/1822.
hh. After the DMM
reading has stabilized, record
the measuredvoltage to 100 !aV resolution as
’MeasuredAmplifier Output Voltage’ in the
Test Record.
tt.
ii. Calculate the error by dividing the measured
output voltage recorded in step 3-z by the
expected output voltage recorded in step 3-y.
Subtract 1.0 fromthis ratio and multiply by
100%to get the error in percent.
Divide the actual input voltage recorded in
step 3-w by the internal +10 attenuation
factor, recordedin step 2-d. This represents
the effective amplifier input voltage.
Multiply this numberby 1000to get the
expected output voltage.
uu. Recordthis reading as ’Expected Amplifier
OutputVoltage’ in the Test Record.
Error= ~,(.Measured
Expected Output
Output Voltage
Voltage _ 11 x 100%
)
4-5
vv. After the DMM
has stabilized, record the
measuredoutput voltage to I mVresolution
in the Test Recordas ’MeasuredAmplifier
Output Voltage’.
182011822
Operator’s
Manual
ww.Calculate the error by dividing the measured
output voltage recorded in step 3-00 by the
expected output voltage recorded in step 3.
Subtract 1.0 from this ratio and multiply by
100%to get the error in percent.
Error =
Measured Output Voltage
Expected Output Voltage
f. Set the sine wave generator output frequency
to 50 kHz, and the amplitude to
approximately 3 Vp-p.
g. Set the oscilloscope V/div to 50 mV/divand
the time/div to 20 p.sec/div. Adjust the trigger
level for a stable display.
1) x 100%
h. Adjust the sine wavegenerator output for an
amplitude of exactly 6 divisions (300 mV)
the oscilloscope.
i.
xx. Recordthe calculated error to two decimal
places (±0.xx%)as ’X1000Gain Error’ in the
Test Record.
NOTE
yy. CHECK
-- That the calculated error is less
than ± 1%.
°
The displayed waveformwill be compressed in time to
form a solid rectangle. It is not necessary to alter the
time/div setting as long as the peak amplitude can be
measured.
Check X1 and XI0 Bandwidth and Calculate
Rise Time.
a.
Connect the AMPLIFIEROUTPUTto
channel 1 of the oscilloscope.
b.
Set the channel input coupling to 50 fL
j.
If the oscilloscope does not have an internal 50 [2 input
termination, inset the standard inline 50 [2 termination
betweenthe cable and the oscilloscope input.
Use the standard wide bandwidth 50 [2 termination.
The precision termination is not accurate at frequencies
higher than 100 kHz.
Set the 1820/1822 GAINto XI and the
ATTENUATOR
to +10.
d.
Connecta BNCcable to the output of the
leveled sine wavegenerator.
Slowly increase the output frequency of the
sine wavegenerator until the displayed
amplitudedecreases to exactly 4.2 divisions.
This is a 3 dB reduction in amplitude.
, k. Record the frequency where the X1 Gain -3
dB amplitude is obtained in the Test Record
as ’Measured-3 dB Frequency at X I Gain’.
NOTE
c.
Set the sine wavegenerator output frequency
to 500 kHz. Be careful not to alter the output
amplitude.
1.
CHECK--That the frequency is > 10 MHz.
m. Divide the 0.35 by the -3 dB frequency
recordedin step 4-k. The result is the
’Calculated Rise Timeat X 1 Gain’. Record
the result in the Test Record.
n. Set the sine wave generator output frequency
to 50 kHz. and the amplitude to
approximately 300 mVp-p
o.
Set the 1820/1822 GAINto XI0.
p.
Set the oscilloscope sensitivity to 5 mV/div.
q. Adjust the sine wavegenerator output for an
amplitude of exactly 6 divisions (300 mV)
the oscilloscope.
NOTE
Many leveled sine wave generators, including the
SG503,are calibrated only whena special BNCcable is
used on its output. Be sure to use a cable which is
specified for the generator.
r. Set the sine wavegenerator output frequency
to 500 kHz. Becareful not to alter the output
amplitude.
s.
Insert a standard 50 ~ termination on the free
cable end and connect the termination to the
+INPUTof the 1820/1822.
4-6
Slowly increase the output frequencyof the
sine wavegenerator until the displayed
amplitudedecreases to exactly 4.2 divisions.
This is a 3 dB reduction in amplitude.
182011822
Operator’s
Manual
t.
Recordthe frequency where the X l0 Gain -3
dB amplitude is obtained in the Test Record
as ’measured-3 dB Frequencyat X l 0 Gain’.
u.
CHECK
-- That the frequency is > l0 MHz.
v.
Divide the 0.35 by the-3 dB frequency
recordedin step 4-t. Theresult is the
’Calculated Rise Timeat Xl 0 Gain’. Record
the result in the Test Record.
n.
Slowly increase the output frequencyof the
sine wavegenerator until the displayed
amplitudedecreases to exactly 4.2 divisions.
This is a 3 dB reduction in amplitude.
o. Record the frequency where the -3 dB
amplitudeis obtained in the Test Recordas
’Measured-3 dB Frequency at XI000 Gain’.
p.
CHECK
-- That the frequency is > 1 MHz.
5. Check XI00 and X1000 Bandwidth.
a.
6. Check High Frequency CMRR.
Continuewith the sameset up as in step 4.
b. Set the sine wavegenerator frequency to 50
kHz and an amplitude of approximately 30
mVp-p.
c.
NOTE
CommonMode Rejection Ratio (CMRR)is defined
the Differential
ModeGain divided by the Common
Mode Gain (normalized inverse of the CommonMode
Feedthrough). At higher frequencies where the
bandwidth of the amplifier begins to attenuate the
differential modesignal, both the differential modegain
and the commonmode feedthrough must be measured to
derive the CMRR.
Set the 1820/1822 GAINto XI00.
d. Adjust the amplitude of the sine wave
generator for a waveformamplitude of
exactly 6 divisions on the oscilloscope.
e. Set the sine wavegenerator output frequency
to 500kHz. Be careful not to alter the output
amplitude.
a.
NOTE
f. Slowly increase the output frequency of the
sine wavegenerator until the displayed
amplitudedecreases to exactly 4.2 divisions.
This is a 3 dB reduction in amplitude.
CHECK
-- That the frequency is > 2.5 MHz.
i.
Insert a + 10 attenuator betweenthe sine wave
generator cable and the 50 f~ termination.
j.
Set the sine wavegenerator frequencyto 50
kHz.
k.
Set the ! 820/1822 GAINto XIO00.
1.
Adjust the amplitude of the sine wave
generator for a waveformamplitude of
exactly 6 divisions on the oscilloscope.
e
e
e
e
e
e
c. Set the 1820/1822 GAINto xl,
ATTENUATIONto +1, INPUT
RESISTANCEto 1 Mr), BANDWIDTH
to
FULL, +INPUTto DC, -INPUT to OFF.
g. Record the frequency where the -3 dB
amplitudeis obtained in the Test Recordas
’Measured-3 dB Frequency at X100Gain’.
h.
Makethe set-up the same as used for the
bandwidthtests (Steps 4-a through e).
b. Connect a BNCcable from the Frequency
Reference Signal Output of the high
amplitude sine wavegenerator to the External
Trigger Input connector of the oscilloscope.
(If the sine wavegenerator does not have
FrequencyReference Signal Output, insert a
BNCTee adapter into the Output connector
and attach the external Trigger BNCcable to
the BNCTee adapter.
The displayed waveformwill be compressedin time to
form a solid rectangle. It is not necessary to alter the
time/div setting as long as the peak amplitude can be
measured
/)
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
d.
Set the leveled sine wavegenerator output
frequencyto 50 kHz. If necessary, adjust the
output amplitudefor a display of exactly 6
divisions (300 mVp-p).
e.
Withoutchanging the output amplitude set the
output frequency to 1 MHz.
f. Measure the peak to peak output amplitude of
the 1820/1822. Record the answer as
’Amplifier Output Amplitudeat 1 MHz’to
two digit resolution (xx0 mV)in the Test
Record.
g.
m. Set the sine wavegenerator output frequency
to 500 kHz. Becareful not to alter the output
amplitude.
Divide the measuredoutput amplitude by 300
mV. Recordthe answer to two digit
resolution (0.xx) as ’Differential ModeGain
4-7
!
1820/1822
Operator’s
Manual
mV)by 5,000 mV. Record the result to two
significant places as ’Common
ModeGain at
1 MHz’in the Test Record. (Keepall of the
leading zeros or use scientific notation.)
at I MHz’in the Test Record. This is the
Differential ModeGain at 1 MHz.
h.
Removethe leveled sine wavegenerator from
the input of the 1820/1822.
i. Connect a BNCcable from the output of the
high amplitude sine wavegenerator to the
Channel2 input of the oscilloscope. Do not
terminatethe cable into 50 f2, and verify that
channel 2 coupling is set to DCand 1 Mr2.
j. Set the oscilloscope to display channel 2,
vertical scale to 1 V/div, horizontal scale to
500 ns/div, and trigger source to external +10.
If necessary,adjust the trigger level for a
stable display.
k.
I.
Set the sine wavegenerator frequency to
i MHz,and the output amplitude to exactly 5
Vp-p(5 divisions on the oscilloscope).
Calculate the Common
ModeRejection Ratio
(CMRR)at 1 MHzby dividing the
Differential ModeGain at 1MHz(recorded in
step 6-0 by the Common
ModeGain recorded
in step 6-u. Recordthe result as ’Common
ModeRejection ratio at 1 MHz’to two
significant places in the Test Record. (Keep
all of the trailing zeros.)
t.
CHECK
-- That the CMRRat 1 MHzis
greater than 1,000:1 (60 dB).
u.
Leavethe test setup for the next tests.
7. Check Low Frequency CMRR.
NOTE
Removethe sine wave generator output cable
from the oscilloscope. Onthe free end of the
BNCcable, install the female to female BNC
adapter, BNC’Y’ adapter and two 6" BNC
cables.
The attenuation of the 1820/1822at 70 Hz and 100 kHz
is so insignificant that the Differential ModeGaincan
be assumedto be unity (1.0). However, the high value
of the CMRR
specification requires a preamplifier to
boost the level of the commonmode feedthrough to an
amplitude where it can be measured.
m. Set both the 1820/1822 +INPUTandINPUT to DC.
n.
s.
Connectthe two free ends of the 6" cables to
the 1820/1822 +INPUTand -INPUT.
a.
o. Set the oscilloscope to display channel 1
(1820/I 822 output signal). Increase the
vertical sensitivity to maximum.
Verify that
the oscilloscopeis still triggered on the
FrequencyReference Signal Output of the
sine wavegenerator.
Disconnectthe output cable of the 1820/1822
under test from channel 1 of the oscilloscope.
Install a 50 f2 inline BNCtermination the free
end of the cable.
b.
Connectthe terminated input to the + input of
the oscilloscope preamplifier. Usinganother
BNCcable connect the output of the
oscilloscope preamplifier to the channel 1
input of the oscilloscope.
c.
Set the input coupling termination of the
oscilloscope channel 1 to what is required by
the oscilloscope preamplifier (50 f~ ifa 1822
is being used.)
p.
The displayed signal is the Common
Mode
Feedthrough. Measure the peak to peak
amplitude. (Use the oscilloscope ZOOM
function if neededto increase the size of the
displayed waveform.
d. Disconnect the output cable of the sine wave
generator from the female to female BNC
adapter. Reconnectthe free end of the cable
to the channel2 input of the oscilloscope.
NOTE
The amplitude of the CommonMode Feedthrough
should be very small lf the output waveformappears to
be a 10 V square wave, check that both of the
1820/1822inputs are set to DC.
e. Set the oscilloscope to display channel 2,
vertical scale to 5 V/divand horizontal scale
to 10 ms/div.
f.
q. Record the ’CommonModeFeedthrough at 1
MHz’amplitudeto two digit resolution in the
Test Record.
r.
Calculate the Common
ModeGain by
dividing the Common
ModeFeedthrough (in
4-8
Set the sine wavegenerator frequency to 70
Hz and the output amplitude to exactly 30 Vpp (6 divisions). Adjust the oscilloscope
trigger level for a stable display if necessary.
1820/1822
Operator’s
Manual
g.
Verify that both the +INPUTand-INPUTof
the 1820/1822are set to DC.
h.
Removethe output cable of the sine wave
generator from the oscilloscope input and
reconnect the cable to the female to female
input of the BNCadapter and cables attached
to the inputs of the 1820/1822.
i.
j.
u. Set the oscilloscope to display channel 2, the
vertical scale to 5 mV/divand the horizontal
to 5 laV/div. If necessary, adjust the trigger
level for a stable display.
v.
w. Adjust the output amplitude of the sine wave
generator to 30 Vp-p(6 divisions). Readjust
the oscilloscopetrigger level if necessaryto
maintaina stable display.
Set the + Input Couplingof the oscilloscope
preamplifier to AC, GAINto X100, Offset
Off, any bandwidthlimiting controls to Off or
Full Bandwidth.
x.
Set the oscilloscope to display channel 1 and
the vertical as necessaryto measurethe
amplitude of the displayed waveform.
Autozerothe oscilloscope preamplifier if
necessary to keep the displayed trace on
screen.
z. The displayed signal is the Common
Mode
Feedthroughmultiplied by 100 by the
preamplifier.
Record the displayed CommonMode
Feedthroughamplitude to two digit resolution
in the Test Record as ’CommonMode
Feedthrough X100at 70 Hz’.
aa. Record the displayed CommonMode
Feedthroughamplitude to two digit resolution
in the Test Record as ’CommonMode
feedthrough X 100 at 100 kHz’.
m. Divide the result recorded in step 7-1 by 100
to determine the Common
Modefeedthrough
at the output of the 1820/1822undertest.
n. Record this as ’CommonModeFeedthrough
at 70 Hz’to twodigit resolution in the Test
record. Keepall leading zeros or use
scientific notation.
o.
p.
bb. Divide the result recorded in step 7-aa by 100
to determine the Common
ModeFeedthrough
at the output of the 1820/1822under test.
cc. Record the CommonMode Feedthrough
amplitude to two digit resolution as ’Common
ModeFeedthrough at 100 kHz’ in the Test
Record. Keepall leading zeros or use
scientific notation.
Calculate the Common
ModeGain by
dividing the Common
ModeFeedthrough (in
laV) by 30,000,000~V. Recordthe result to
two significant places in the Test record as
’CommonModeGain at 70 Hz’. (Keep all of
the leading zeros or use scientific notation.)
dd. Calculate the Common
ModeGain by
dividing the Common
ModeFeedthrough (in
laV) by 30,000,000InV. Recordthe result to
two significant places as ’Common
Mode
Gain at 100 kHz’ in the Test Record. (Keep
all leadingzeros or use scientific notation.)
Calculate the Common
Moderejection Ratio
(CMRR)
at 70 Hz by dividing the Differential
ModeGain at 70 Hz (I .0) by the Common
ModeGain recorded in step 7-0.
ee. Calculate the Common
ModeRejection Ratio
(CMRR)
at 100 kHz by dividing the
Differential ModeGain at 70 Hz (1.0) by the
Common
ModeGain recorded in step 7-dd.
q. Record the result as ’Common
Moderejection
ratio at 70 Hz’to twosignificant places in the
Test Record.(Keepall of the leading zeros.)
r.
Removethe sine wavegenerator output cable
and reconnect it to the female to female BNC
adapter and cables attached to the 1820/1822.\
inputs.
y. Set the oscilloscope to display channel 1 (the
output of the 100Xpreamplifier driven by the
1820/1822output signal), and the vertical
scale as necessary to measurethe amplitude
of the displayed signal. Autozerothe
oscilloscope preamplifier if necessary to keep
the displayed signal on screen.
k. The displayed signal is the Common
Mode
Feedthrough multiplied by 100 by the
preamplifier.
I.
Set the sine wavegenerator to 100 kHz.
CHECK
-- That the CMRR
at 70 Hz is
greater than 100,000:1(I 00 dB).
s.
Removethe sine wavegenerator output cable
from the female to female BNCadapter
ff. Record the result as ’Common
Moderejection
ratio at 100 kHz’to twosignificant places in
the Test Record.Keepall of the trailing
zeros.)
t.
Reconnectthe cable to the channel 2 input of
the oscilloscope.
gg. CHECK
-- That the CMRR
at 100 kHz is
greater than 100,000:1(100 dB).
4-9
1820/1822Operator’sManual
hh. Removeall cables and connections from the
i 820/1822.
O
e
O
O
O
e
O
O
O
e
e
O
O
O
e
O
e
e
O
e
O
O
O
e
e
e
o
o
e
e
o
o
o
e
o
e
o
o
o
.
Checkthe Precision Voltage Generator
Accuracy(1822 Only).
a. Connect a BNCcable from the OFFSET
VOLTAGE
output connector on the rear
panel to a DMM
without a 50 f2 termination.
b.
Push the PVGZERObutton.
c. Set the DMM
to DCVolts on the most
sensitive range. After the display has
stabilized record the reading as ’PVGZero
Output Voltage’ in the Test Record.
d.
CHECK
-- That the measured 0.0000 V
output is within + 0.5 mVof zero.
e.
Set the DMM
range to read 15.5 V.
f. Press and hold MSBincrement button (button
to right of+ button) until the display reads
+15.000V. If necessary, press the + button
onceto invert the polarity.
g. After the DMM
display has stabilized record
the reading as ’PVGOutput Voltage at + 15.5
V’ in the Test Recordwith 100 p.V resolution
h.
CHECK--That the measured output is
within15.4917 to 15.5082 V.
i.
Press the + button to changethe output
voltage to -15.5000 V.
j. After the DMM
display has stabilized record
the reading as ’PVGOutput Voltage at -15.5
V’ in the Test Recordto 100 ~tVresolution.
k.
CHECK--That the measured output is
within -15.4917 to -15.5082 V.
!.
Disconnect DMM
and all cables from
amplifier.
This completes the PerformanceVerification Procedure.
File the test results as required to supportyour internal
calibration procedures.
4-I0
182011822 TEST RECORD
This record can be used to record the results of measurementsmadeduring the performanceverification of the 1820/1822
series of instruments.
Photocopythis page and record the results on the copy. File the completed record as required by applicable internal
quality procedures.
The section in the test record corresponds to the parameters tested in the performance verification procedure. The
numberspreceding the individual data records correspond with the steps in the procedure which require data recording.
Steps printed in Boldface type are the actual specification limit check. Other steps are for recording intermediate data
usedin the limit calculations.
Permissionis granted to reproducethis pagefor the purposeof recording test results.
Model:
Serial Number:
(PR-2 models only)
Right or Left Channel:
Date:
Technician:
EQUIPMENT USED:
Model
Oscilloscope
Preamplifier
Digital Multimeter
Oscillator/Function Generator
Leveled Sine WaveGenerator
Power Meter
(If used to level Sine WaveGenerator)
Notes:
Serial Number
Calibration Due Date
Step
0
0
0
0
0
0
0
0
e
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
9
0
0
0
0
Q
0
0
0
0
0
Description
Intermediate Data
Test Result
XI Gain Accuracy
l-f Sine WaveGenerator Output Voltage
V
I-k Amplifier Output Voltage
V
%
1-m XI Gain Error (Test Limit: < + 1%)
+10 Attenuator Accuracy
2-c
Amplifier Output Voltage
2-d
Actual Attenuation
2-f
+ 10 Attenuator Error
2-h
XI Gain ++10 Attenuator Error (Test limit < + 1%)
V
%
%
XI0, XI00 and X1000 Gain Accuracy
XIO Gain Accuracy
3-g
Sine WaveGenerator Output Voltage
V
3-j
Actual Amplifier Input Voltage
V
3-1
Exact Attenuation
3-q
Sine WaveGenerator Output Voltage
V
3-w
Actual Amplifier Input Voltage
V
3-y
Expected Amplifier Output Voltage
V
3-z
Measured Amplifier Output Voltage
V
3-bb XI0 Gain Error (Test Limit: < + 1%)
%
XI00 Gain Accuracy
3-ff
Expected Amplifier Output Voltage
V
3 -gg Measured Amplifier Output Voltage
V
3-ii
%
XI00 Gain Error (Test Limit: < + 1%)
XI000 Gain Accuracy
3-mmExpected Amplifier Output Voltage
V
3-nn Measured Amplifier Output Voltage
V
3-pp XI000 gain Error (Test Limit: < + 1%)
%
XI and XIOBandwidthand Calculated Rise Time
4-k
Measured -3 dB Frequency at XI Gain (Test Limit: > 10 MHz)
MHz
4-m
Calculated Rise Timeat XI Gain
nsec
4-t
Measured -3 dB Frequency at X10 Gain (Test Limit: > 10 MHz)
MHz
4-v
Calculated Rise Timeat X10Gain
nsec
XI00 and XI000 Bandwidth
5-g
Measured-3 dB Frequency at XI00 Gain (Test Limit: >2.5 MHz)
MHz
5-o
Measured-3 dB Frequency at XI000 Gain (Test Limit: >1 MHz)
MHz
High Frequency
CMRR
6-f
Amplifier Output Amplitude at 1 MHz
6-g
Differential ModeGain at 1 MHz
6-q
CommonMode Feedthrough at l MHz.
6-r
CommonMode Gain at 1 MHz
6-s
Common
ModeRejection Ratio at I MHz(Test Limit: > 1,000:l)
Low Frequency
V
V
CMRR
7-1
CommonModeFeedthrough xl00 at 70 Hz
V
7-n
Common
ModeFeedthrough at 70 Hz at Amplifier Output
V
7-o
CommonMode Gain at 70 Hz
7-q
Common
ModeRejection Ratio at 70 Hz (Test Limit: > 100,000:l)
:l
7-aa CommonModeFeedthrough at 100 kHz
V
7-cc CommonModeFeedthrough xlO0 at i O0 kHz
V
7-dd CommonMode Gain at 100 kHz
7-ff
Common
ModeRejection Ratio at 100 kHz (Test Limit: > 100,000:l)
:l
Precision Voltage Generator Accuracy
8-c
PVGZero Output Voltage (Test Limit: <+ 500 ~V)
V
8-g
PVGOutput Voltage at +15.5 V (Test Limit: 15.4917 to 15.5082 V)
V
8-j
PVGOutput Voltage at -15.5 V (Test Limit: -15.4917 to -15.5082 V)
V
0
0
0
0
0
0
0
Copyright@
1999,Preamble
Instruments,Inc. All rights reserved.
Printedin U. S. A.
Preamble
Instruments,Inc. productsare coveredby U. S. andforeign patents, issuedor pending.
Specificationchanges
reserved.Informationcontainedin this publication supersedes
all previously
publishedmaterial.
Preamble
Instruments,Inc. and -,A
,~OR~C.MBLE
are registered trademarks.
- V IINS’rRUMENI~
WARRANTY
Preamble
Instrumentswarrantsthe productsit manufactures
andsells to be free of defectsin materials
andworkmanship
for a period of three years, (one year for passiveprobesandprobeaccessories).
Preamble
Instrumentswill repair or replace,at its option, anyproductwhichprovesdefectivewithin the
warrantyperiod.
To obtain warrantyservice, the customermustcontact Preamble
Instrumentswithin the warrantyperiod
to obtain a ReturnMaterial Authorization.Thecustomershall be responsiblefor the properpackaging,
insuranceandshippingchargesfor the return of the productto Preamble
Instruments.Preamble
Instrumentswill paythe shippingchargesfor the return of the productto the customer.
This warrantydoesnot apply to damage
resulting from the improperuse or abuseof the product. The
warrantyalso excludesanydamage
resulting from repair or modificationsof the productwhichwerenot
performed
by Preamble
Instrumentsor its authorizedservicefacility.
This warranty is exclusive and no other warranty shall be madeby PreambleInstruments or its
representatives, express or implied. PreambleInstruments disclaims any implied warranty of
fitness for use. PreambleInstruments’ sole responsibility underthe foregoingconditions of this
warranty is the repair or replacementof products. PreambleInstruments and its representatives
will not be liable for anyspecial, indirect, incidental, or consequentialdamages
resulting from the
useof this product.
PREAMBLE
INSTRUMENTS,
Inc.
P.O. Box 6118
Beaverton, OR97007-0118
U.S.A.
(503) 646-2410
FAX:(503) 646-1604
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