Power measurement based on DSO
technology, really?
Michael Rietvelt
Technical Support Engineer
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Precision Making
Making
Precision
Development Stages
Oscilloscope
Architecture & Design
ScopeCorder
Verification & Prototyping
PowerMeter
Classification & Validation
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Precision Making
Types of power measurement instruments
Power Measurement
Streaming data
Traditional Average Type
Power meter
Norma (Danaher)
Hioki
Yokogawa
Digital Storage
DSO Type
Power meter
Tektronix (Danaher)
Newtons4th
ZesZimmer
Yokogawa
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Real DSO
Le Croy
Agilent
Tektronix
Yokogawa
25/06/2014
Data
Acquisition
Dewetron
NI
HBM
Yokogawa
Precision Making
Principle of operation
Streaming (Averaging type)
A/D conversion
DSP
Real Time Calculation
of measurement values
(integration / ΔT)
Calculation /
Data processing
for output
Storage in Acquisition
memory
DSP
Calculation of
measurement
values
Digital Storage
A/D conversion
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Calculation /
Data processing
for output
Precision Making
Traditional Averaging Type
Load needs to be stabilized to make it periodic
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Precision Making
Traditional Average type
P
average

1
Tperiod
T
Energy

[W]
Tperiod
 p(t ) dt [W]
0
1
Period time  Tperiod  [s]
f
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Precision Making
Digital Storage Type
Switching High Voltage Circuit Breaker
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Precision Making
Digital Storage Type
Olympic Arena China using HID Lamps
Inrush Current
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Precision Making
Digital Storage Type
Start-up sequence
u
i
p
Period time: T?
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Precision Making
Digital Storage Type
Duty Cycle, inductive cooking
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Precision Making
Digital Storage Type
User defined observation time & measurement between cursors
P
average

1
STOP

Tobservation START
p(t ) dt [ W]
Energy

[W]
Tobservation
P1: x.xxxxx W
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Start
Stop
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Precision Making
Characteristics of two types of Power Meters (1 of 2)
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Traditional Average Type
Digital Storage Type
Average of repetitive signals
Single shot
Fixed sample speed
Sample speed depends on
observation time
Sample speed 50 kS/s – 2 MS/s
Sample speed 2 – 100 MS/s
No raw data (data streamed)
Raw data (data stored)
A/D converter 16-bit
A/D converter 12-bit
1/3 of the A/D is used for range
2/3 used to measure distorted
waveforms and peaks
A/D converter 100% used for Normal
Mode Operation
Peak value range = full scale
CF multiplied by the range
(typical 300)
CF only within the selected range
(typical 20)
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Precision Making
Crest Factor
Definition
Peak Value
RMS Value
Peak value
Crest Factor 
RMS value
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Precision Making
Signal Crest Factor
Sine wave
1,5
1
Upeak 1V
Urms 0.707V
0,5
0
-0,5
-1
-1,5
Peak value
1
Crest Factor 

 1.414
RMS value 0.707
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Precision Making
Instrument Crest Factor
Example:
Selected range 100Vrms,
The allowable peak input voltage is 300Vpk
Yokogawa Guarantees measurement from 1% of
range.
300Vpk
100Vrms Range
Setting
Peak value 300
Crest Factor 

 300
RMS value
1
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Precision Making
LED
6 [W]
What is a realistic Crest Factor today
Inrush current: Crest Factor 180
PX8000: crest factor 200
Demo at table 10
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Precision Making
Characteristics of two types of Power Meters (2 of 2)
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Traditional Average Type
Digital Storage Type
Pavg = U x I x cosφ
Pavg = U x I
Specified Internal Phase shift
uncertainty ()
Unspecified Internal Phase shift
uncertainty
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Precision Making
Internal phase shift uncertainty of two channel instruments
δ
u(t)
Attenuator
A/D
DSP
i(t)
i(t) u(t)
SHUNT
Main part of the phase delay is
caused by this shunt due to its,
although very small, inductance.
Amplifier
A/D
The VOLTAGE input often needs a big attenuation
(e.g. 600V to 3V).
The small voltage drop across the
CURRENT-shunt on the other hand needs a very
high gain (e.g. μV to 3V).
OPAMPs show different amplitude gain
characteristics.
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Precision Making
Consequently there
will be an additional
internal
phase shift between the voltage and current input.
Effect of internal phase shift uncertainty
p(t) = u(t) x i(t)
p’(t) = u(t) x i(t)
5
4
3
2
Pavg
P’avg 1
u(t)
i(t)
0
p(t)
i'(t)
-1
p'(t)
-2
-3
cosⱷ
-4
ƍ
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Precision Making
Characteristics of two types of Power Meters (2 of 2)
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Traditional Average Type
Digital Storage Type
Pavg = U x I x cosφ
Pavg = U x I
Specified Internal Phase shift
uncertainty ()
Unspecified Internal Phase shift
uncertainty
BW specified in %
BW -3dB (Pavg-unc. + and - 50%)
RMS ranges
Peak ranges
Uncertainty based on RMS values
Uncertainty based on Peak values
High Precision HRM based on PLL
See Vermogens Elektronica 2012
Unspecified FFT with filters
Unlimited time integration
Limited time integration
Guaranteed data update rates
Selectable from 50ms to 20s
Unstable Update rate
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Precision Making
Guaranteed data update rate for Data Acquisition
Duration test 18 months
• 3 types of inverters
• Power measurement
• Solar intensity
• MW100 datalogger
• Temperatures
ECN SEAC
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Precision Making
Summary
Depending on the application a different type of power meter is required.
Streaming data, Traditional averaging type:
• For repetitive signals, the most accurate solution
• Production of specification sheets (Specified uncertainty)
• Efficiency specification
• Energy measurements (kWh)
• Data acquisition (Guaranteed data update rate)
Digital Storage:
• For single shot measurements
• Measurement of inrush currents
• Short circuit tests for generators and transformers
•
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Duty cycled signals (inductive cooking, microwave)
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Precision Making
Types of power measurement instruments
Power Measurement
Streaming data
Traditional Average Type
Power meter
Norma (Danaher)
Hioki
Yokogawa
Digital Storage
DSO Type
Power meter
Tektronix (Danaher)
Newtons4th
ZesZimmer
Yokogawa
23
Real DSO
Le Croy
Agilent
Tektronix
Yokogawa
25/06/2014
Data
Acquisition
Dewetron
NI
HBM
Yokogawa
Precision Making
Thank you for attending this presentation
Questions?
For more information visit us at table 10
Willem.van.leeuwen@nl.yokogawa.com
Roy.hali@nl.yokogawa.com
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