External current probe - Instruments et Systèmes

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ISW 8001
4 DIGIT (8000 COUNTS) PROGRAMMABLE
DIGITAL WATTMETER
with optional isolated output
User Manual
INSTRUMENTS ET SYSTEMES
ZI des Radars, 12 rue Diderot
91350 GRIGNY FRANCE
tel. : 33 (0)1 69 02 31 56
Fax. : 33 (0)1 69 02 08 93
www.instruments-systemes.fr
5/02
ISW 8001
Specifications
(+18°C to +28°C)
Voltage
True RMS measurement
Ranges:
50.00 V 150.0 V 500.0 V
Resolution:
10 mV, 100 mV, 100 mV
Accuracy:
20 Hz-1 kHz : ±(0.4% + 5 digits)
DC:
±(0.6% + 5 digits)
Input impedance: 1 M // 100 pF
Crest Factor:
max. 2 at full scale
Protection:
750 V peak
Current
True RMS measurement
Ranges:
160.0 mA 1.600 A 16.00 A
Resolution:
0.1 mA, 1 mA, 10 mA
Accuracy:
20 Hz-1 kHz : ±(0.4% + 5 digits)
DC :
±(0.6% + 5 digits)
Crest Factor:
4 max. at full scale
Protection:
16 A fuse
Power
Ranges:
Resolution:
Accuracy:
Reactive Power
Ranges:
Frequency:
Resolution:
Accuracy:
8.000W 24.00W 80.00W 240.0W 800.0W
2400W 8000W
1 mW, 10 mW, 100 mW, 1W
±(0.5%+ 10 digits) from 20 Hz to 1 kHz
± (0.5% + 10 digits) in DC
8.000VAr 24.00VAr 80.00VAr 240.0VAr
800.0VAr 2400VAr 8000VAr
20-400 Hz
1 mVAr, 10 mVAr, 100 mVAr, 1 VAr
± (2.5 %+ 10 digits)
Popwer Factor
Display of PF (0 to +1.00)
Resolution:
± 0.01
Accuracy (50-60 Hz):
± (2 %+2 digits) (U and I > 1/10 of range)
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ISW 8001
Isolated Analogue Output :
The output is floating with respect to the measuring circuits and digital
interface. The cold point is common with the cold point of the probe input. The
output shows the instantaneous power.
Connection:
Safety 4mm banana plugs
Output Level:
1Vrms corresponds to 8000 counts/full scale
Accuracy:
±2%
Polarity:
Same as instantaneous power
Output Impedance:
10 k
Bandwidth:
> 1kHz
Protection:
± 30V
Applied Common Mode Voltage: max. ±30V
Current probe input :
The input is isolated from the measurement circuits and from the >RS232
interface. The cold point is common with the cold point of the isolated output.
Sensitivity :
Frequency :
Protection :
Accuracy :
100mV/A
DC and 20Hz to 1kHz
± 30V
probe accuracy + 1%
Interface :
RS232 (3 wires). Xon-Xoff Protocol.
Transmission rates 1200 or 9600 Baud
Programmability of all functions and ranges.
Safety:
IEC 1010-1 Cat III 600 V
Power Supply:
Temperature
of Utilisation:
230 V ± 10% , 50-60 Hz, max. 7 W
Dimensions:
Weight:
240 x 240 x 75 mm (L x W x H)
about 1,3 kg
General:
4 Digits 25mm high LED Display plus sign
Rugged PVC Case with Handle
Buzzer indicates Overload
4
10-40 °C RH < 80 %
ISW 8001
Safety
INSTRUMENTS et SYSTEMES certifies that this instrument has left the
factory in perfect working order, both in operation and safety.
This instrument has been designed and manufactured with great care to bring
the user the best possible safety to the user. If the instrument no longer
functions properly or is damaged, it must be immediately disconnected from the
ac supply voltage, from the measured circuit voltages and returned for repair.
Opening, maintenance, repair and calibration must be carried out by qualified
and approved personnel.
Warranty
Provided it is used under the recommended conditions, this instrument is
guaranteed for a two year period against manufacturing defects and component
failure. This warranty applies to material and workmanship. The instrument
must be shipped back to an agreed repair centre. It will be repaired or replaced
without charge. Warranty repairs are made at the discretion of IES.
Maintenance
Your wattmeter does not need any specific maintenance. Whenever cleaning is
necessary, use a soft material. Avoid water or liquids that may penetrate inside.
Operation
Carefully unpack the instrument and make sure that it was not damaged during
transportation. Insert the power cord on the rear of the instrument and connect
to the ac supply. Switch power on by means of the power switch located on the
rear panel.
5
ISW 8001
6
ISW 8001
Symbols used
Indicates the possibility of a dangerous voltage
Refer to the user manual
Changing a fuse
Before you change a fuse, disconnect the instrument from
all possible dangerous voltages!
The defective fuse must be replaced using a fuse of the same type and value.
Two different types of fuses are used:
 100 mA time delay fuse on the ac power input circuit (T 100 mA)
 16 A semi time delay fuse in the ammeter circuit (16 A M)
Selectable Options
At start up, the instrument displays first the software version, the transmission
rate (- RS option only) of 1200 or 9600 Baud and finally selects the W function
(power measurement).
Buzzer
The buzzer indicates overrange conditions or manipulation errors. It can be
switched ON or OFF (toggle) in the following way:
Switch OFF the instrument. Hold the VAr key in and switch ON. Release the
VAr key when the W function is reached. The new state of the buzzer is kept in
memory until you decide to change it.
RS 232 Transmission Rate (1200/9600 Baud)
Proceed in the same way as for the buzzer but press the cos  key before start
up.
7
ISW 8001
About Electricity
RMS
VALUE
The RMS (Root Mean Square) value of a signal refers
directly to the power. The RMS value of a current which
circulates in a resistance equals the value of the DC current
which would produce the same heat in the resistance (same power). For this
reason, voltage and current measurements are carried out with RMS circuits.
The crest factor characterises the shape of a signal. It is the
ratio of the peak value to the RMS value (1.414 for a sine
wave). The electronic circuits that compute the RMS value
are generally sensitive to crest factor. The accuracy of measurements is
guaranteed only for moderate crest factors. The max. value of the crest factor is
given at full scale. Note that for smaller deviations, the crest factor may be
significantly higher.
CREST
FACTOR
In AC circuits, the power is not expressed as the product of
the voltage across the load by the current. If voltage and
current are sinusoidal, then the power is easily calculated
when the phase shift between them is known. Calculation of power parameters
becomes complex with non-sinusoidal waveshapes.
The ISW 8001 Wattmeter measures the average value of the instantaneous
power and remains accurate whatever the shape of the signal, provided it stays
inside the specification limits (frequency and crest factor).
POWER
When reactive elements are inserted in the generator/load circuit, the current
and voltage are phase shifted with respect to each other.
For :
- a sine wave voltage of RMS value V
- a sine wave current of RMS value I
- a phase shift  between voltage and current
8
ISW 8001
we can write the following relations:
Apparent Power (Volt Amperes)
Active Power (Watts)
Reactive Power (Volt Amperes Reactive)
VA = V x I
W = V x I cos 
VAr = V x I sin 
At some moments, voltage and current have the same polarity, at others the
signs are unlike. This indicates that some power is either expended in the load,
some is returned to the source. When the load is a pure reactance (perfect
inductor or capacitor) the power is only reactive and entirely returned to the
source.
The ISW 8001 Wattmeter measures all kinds of power and displays active or
reactive power. For sine waves it can also show the cosine of the phase angle.
POWER
FACTOR
The Power Factor is defined as the ratio :
PF = Pr / Pa ( True Power / Apparent Power )
When both current and voltage are sine waves PF = Cos 
9
A:
ISW 8001
Input Terminals
The ISW 8001 Wattmeter uses four input terminals on the front panel:
 a red plug and a blue plug ( SOURCE) which must be connected to the voltage
source.
 a red plug and a black plug (LOAD) which must be connected to the load.
Caution ! : the two red plugs are connected together inside the
instrument. The black plug is connected to the blue plug through
a low resistance path consisting of the resistive shunt and the
protective fuse.
No voltage should be applied between the two red plugs and
between the black and the blue plugs!
Two inputs terminals are mounted on the rear panel :


The red plug is the input of the external probe.
The black plug is the reference level of the external probe (ground).
Output Terminals
The isolated output uses a BNC connector (rear panel) to output the power
signal. The reference voltage (ground) is common with the current probe input.
Function selection
Press the appropriate key to select the measuring function. At start up the
default measurement function is W (power measurement).
The available functions are:
W:
VAr :
PF :
V:
effective power
reactive power
Power Factor measurement
True RMS voltage (DC + AC). If pure DC is applied, the DC
indicator is lit and the polarity displayed.
True RMS current (DC + AC). If pure DC is applied, the DC0 indicator is lit
and the polarity displayed.
10
ISW 8001
Measuring Ranges
Whatever the selected function, voltage and current default to autoranging –
e.g. the ranges are automatically switched.
There are three ranges for voltage and three ranges for current:
50.00 V, 150.0 V & 500.0 V for the voltage
160.0 mA, 1.6000 A & 16.00 A for the current
The selected ranges are indicated by LED’s on the right of the display.
To measure voltages
To measure voltages, select the V function. The voltage to be measured is
applied between the red plug and the black plug (LOAD). The range is
automatically selected.
If the voltage is pure DC, the DC indicator lights on and the indication of the
polarity is activated. A voltage is positive with respect to the black plug is a
positive voltage is present on the red plug. No sign is shown for a positive
voltage. A negative voltage is indicated by the - sign.
11
ISW 8001
To measure currents
The internal circuits are protected by a fuse. If the fuse is blown, it must be
replaced with the same type. The fuse is located on the front panel. Make sure
that no voltages are applied to the front panel inputs before removing the fuse.
The current to be measured is applied between the blue plug (SOURCE) and
the black plug (LOAD). The range is automatically selected.
If the current is pure DC, the DC indicator lights and the indication of the
polarity is activated. A current is positive if it flows from the black plug to the
blue plug (this is the polarity of a current delivered by a positive source
connected to the red source plug, to a load connected to the LOAD terminals).
No sign is shown for positive current. A negative current is indicated by the sign.
External current probe
12
ISW 8001
To perform current measurements, the switch located on the rear panel must
be in the EXT position (100mV/A).
The instrument measures the voltage which appears on the probe input to
determine the current flowing through the probe with a sensitivity of 100mV/A.
The current shunts remain connected to the black and blue plugs of the front
panel, and no voltage must be applied to these terminals.
The probe must have a sensitivity of 100mV/a for a direct reading of the
current. Probes with different sensitivities may be used, provided a correction is
applied to the current.
However, no voltage greater than 3Vrms (±4.25Vpeak) should be applied to
the input.
The input accepts DC or AC voltages. The probe must be connected with the
right polarity. A positive voltage applied to the red plug represents a positive
current. Reversing the probe changes the sign of the displayed current and
power.
The use of the external input is indicated by the EXT indicator on the front
panel.
To measure power
The ISW 8001 Wattmeter can measure true power (expressed in
W) or the reactive power (expressed in VAr).True power may be
measured in DC or AC (inside the bandwidth limits). But reactive
power makes sense only AC. It must be done only with sinusoidal
values at 50 Hz or 60 Hz.
13
ISW 8001
True power measurement is selected by means of the W key, reactive power by
means of the VAr key. The displays shows the power received (or delivered) by
the load. It may be slightly smaller (or greater) than the power dissipated by the
source because of the small power lost in the voltage divider and the current
shunt.
True power
The true power is generally positive if the generator delivers power to the load.
But some loads (batteries, motors) have a strong back e.m.f. and send power
back to the source. The wattmeter senses the circulation of the energy in the
circuit. If the source delivers energy to the load, the power is considered as
positive. If the load sends energy to the source, the value is negative.
Reactive power
Reactive power is considered as positive for inductive loads and negative for
capacitive loads, so, the sign of the displayed values indicates the nature of the
load.
TWO WATTMETER METHOD
14
ISW 8001
The power on 3 phase network without neutral wire is easily measured with the
2 wattmeter method. This method is also applicable on balanced 3phase
network with neutral connection. Generally, only one wattmeter is used with a
power switch. Two successive power measurements are necessary with the
switch in a different position. The total power is the sum of the two readings.
To measure the Power Factor
The source and the load are connected as for power measurements. If either
voltage or current is too low, the display shows moving signs " -- ".
With sine wave voltage and current, the power factor indicates the phase shift
between the voltage across the load and the current flowing through a load
(cos).
Isolated output
The isolated output allows the user to observe, with a high degree of safety, the
instantaneous power applied to the load with an oscilloscope. The output is
isolated from the load and from the RS232 interface.
To visualise the instantaneous power, select the WATT function.
The output level is calibrated: a level of 1 Vrms corresponds to a full scale
display of 2400 or 8000 digits according to the voltage or current range.
Note: in power measurement, an auto zero circuit corrects the zero drift. This
circuits nulls voltage and current at the input of the multiplier at regular
intervals. The result is a zero power during a small amount of time (100 ms).
This is visible on the oscilloscope especially at start up (cold circuits) every
three seconds. After one minute, the auto zero rate is approximately one auto
zero every two minutes.
15
ISW 8001
RS232 Interface (option)
To select the transmission rate
You have the choice between two transmission rates between the instrument
and the computer, 1200 or 9600 Baud. The Baud rate is displayed during a
short time at start up. To modify it, press the cos  key for a few seconds and
switch power on. The new selected rate is displayed and kept in memory until a
new change is done.
Connection
The dialogue between the computer and the wattmeter is accomplished by
means of a software protocol (Xon-Xoff). The connection needs only a simple
3 wires cable (Rxd, Txd and signal ground).
The connecting cable can be terminated at one end with a 9 pin connector and
at the other end with a 9 pin or 25 pin connector, this depends on the PC serial
port connector. The following connections should be followed:
25 pin
female connector (PC)
9 pin female
connector (PC)
9 pin male connector
(instrument)
2
3
7
3 (Tx)
2 (Rx)
5 (GND)
3
2
5
To check the communications
You can quickly and easily check the connection with the PC_WATT software
included with the instrument.
First install the software and then switch the instrument off and on to check the
transmission rate. If you want to change it see section "To select the
transmission rate".
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ISW 8001
Commands
The commands are sent as a string of ascii letters and digits. No special symbol
or space should be added. Once sent, the command is executed upon reception
of the carriage return character (CR = Hex 13). In terminal mode, this character
is transmitted by the ENTER key of the keyboard, along with the Line Feed
character which is ignored.
Note: the commands may be written either in UPPER or lower case.
Some commands will force the instrument to answer. It is the case for the
commands:




*IDN? : identification
VERSION? : software version
STATUS? : configuration of the instrument (see § STATUS string)
VAL? : measured value. If the command arrives during the measurement cycle,
the result will be sent only at the end of the cycle.
 MA1 : continuous output mode. Each result is sent to the computer. This mode
is cleared by the MA0 command.
The table of the last page lists all the available commands.
Measurement Result
The measurement result is transmitted :
-
- after a VAL?
after each measurement if the device is in the auto transmit mode
(MA1 command).
Ux = 150.1 E +0 Iy = 1.00 E +0 W = 150.1 E +0
^
^
^
|
|
| ___ W kW Var kVAr PF ACV
|
|
DCV ACI DCI
|
|
|
|______ I1 I2 I3 Ix1
|
|________ U1 U2 U3
17
ISW 8001
The result is transmitted only at the end of a measurement. If a result query
arrives during the measurement cycle, the data will be sent only after a small
amount of time (max. 250ms)
Automatic Measurements
Once the MA1 command has been sent, the measurement data is automatically
transmitted after each measurement. The output string includes the instrument
status and the value. In this way, the user is continuously informed of the
configuration of the instrument.
The automatic mode is reset by sending a MA0 command or switching off and
on the instrument.
Selection of voltage and current ranges
When the instrument is manually operated, switching between the different
ranges is performed automatically. The choice of the most convenient range is
decided by the microprocessor at the end of each measuring cycle.
The serial interface gives you the ability to override autoranging and allows the
user to select the current or voltage range.
At start up, the autorange is always activated. Manual range switching applies
to both voltage and current i.e. the selection of a current range will also cause
the voltage ranging to change to manual range mode.
Two different commands may be used:
- the commands MANUAL and AUTORANGE switch from automatic to
manual range selection. When switching from autorange to manual, the voltage
and current ranges remain unchanged.
- the commands of the type SET:Ux and SET:Ix select a voltage or current
range ( x = 1, 2 or 3).
To disable the front panel
The front panel may be disabled in remote operation by means of the command
FAV0. The instruments now only responds to the commands from the interface.
This mode is cancelled with the command FAV1 or when the instrument is
switched off and on again.
STATUS String
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ISW 8001
When the instrument receives a STATUS? command, it sends back a status
string which has the following structure:
WATT U1 I2
^ ^ ^
| | |________
| |___________
|______________
current range (I1 I2 I3 Ix1)
voltage range (U1 U2 U3)
function (WATT Var PF VOLT AMP)
The ranges are :
U1 : 50V range
U2 : 150V range
U3 : 500V range
I1: 160mA range
I2 : 1.6A range
I3 : 16A range
Ix1 : external probe (100mV/A)
Ix2 : external probe (10mV/A)
The characters contained in this string are separated with blanks and are easily
decoded to inform the user of the operating status.
19
ISW 8001
Table of commands
FUNCTION
RANGES
MODE
MISC.
WATT
VAR
VOLT
AMP
PWF
True Power
Reactive Power
Voltage
Current
Power Factor
SET:U1
SET:U2
SET:U3
SET:I1
SET:I2
SET:I3
MANUAL
AUTORANGE
Voltage Range : 50V
Voltage Range : 150V
Voltage Range : 500V
Current Range : 0,16A ***
Current Range : 1,6A ***
Current Range : 16A
***
Manual range switching (U & I)
Automatic range switching
MA1
MA0
Continuous output of data
To cancel MA1 mode
*IDN?
VERSION?
STATUS?
VAL ?
BEEP
BEEP1
BEEP0
FAV0
FAV1
Identification query
Version query
Status query
Measured value query
Beep once
Beeper ON
Beeper OFF
Disable Front Panel
Enable Front Panel
*** these commands have no effect if the switch on the rear panel is in
the EXT position.
20
ISW 8001
TO USE THE PC_WATT SOFTWARE
Installation and de-installation
Start Windows®. Insert the PC_WATT floppy disc and execute the file :
or
a:setup to install the software
a:desinst to de-install it
The directory ISW8001 will be created during installation. It includes the icon
used to start the software. If you want to keep the ability to de-install the
software, you must maintain the same structure.
21
ISW 8001
Operating modes
Two different operating modes are allowed, the "Terminal" mode and the
"Command" mode. In Terminal mode, the computer only monitors the front
panel of the wattmeter, which is driven with its own keys. In the Command
mode, the front panel is disabled and the instrument is operated with the mouse
or the keyboard of the computer. The software starts in Terminal mode. You
can modify this mode in the Configuration menu.
Starting
Connect the interface cable and double click onto the PC_WATT icon to start
the software. If the software finds the wattmeter, it directly enters the monitor
mode. Else, it opens a communication window where you can modify the
transmission speed or the PC serial port to use.
Display
The Display menu selects the different windows that appear on the screen:
- The function/range window which reproduces the front panel of the wattmeter
- The communication windows which displays the dialogue between the
instrument and the computer
Help
The help file is opened with the F1 key of the keyboard (dedicated help) or by
the ? menu (global help).
Measurements
The measurements may be accomplished and stored in a file at a desired rate.
22
ISW 8001
The Options menu opens a window where you can define the maximum number
of measurements, the time interval between measurements and the structure of
the object file. The measurement
cycle is initiated with the Start
button.
The cycle starts as soon as you
have typed the name and path of
the result file.
The result file is a text file with
different columns. Each column
represents a file selected in the
proposed list (function, value, unit,
time, date). Note that the value is
always selected.
The measurement cycle is halted or
started at any time with the Start
Measurement and Stop
Measurement options of the
Measure menu.
23
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