Energy & Power Meters History &Measurement Principle

Ben Kemink

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History and Types of Energy & Power Meters

1960’s 70’s 80’s 90’s

Current Transformer Input

Torque Balanced Type

APR2

Time Division Multiplier

Type 2885 (50 - 400 Hz)

Digital Display Power Meters

2533 (DC, 10Hz - 20kHz)

Electro-dynamic Wattmeter

(50 - 60 Hz)Traditional

Stable Loads

Current Shunt Input 2532(DC,20Hz-400kHz))

WT1600 (DC,0.5Hz-1MHz))

WT230 (DC,0.5Hz-100kHz))

Digital Sampling Power Meters

WT3000 (DC, 0.1Hz-1MHz)

Traditional

Stable Loads

Single Shot Power MeterNew Generation

Un-Stable Loads

PZ4000 DC – 2MHz

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The heating-wire is very thin and easily burned out by an over-current.

This instrument can be used to measure both DC and AC.Frequency bandwidth Current: up to approx. 10 MHz Voltage: up to approx. 100 kHz

A moving coil instrument is used to indicate the result.

The thermocouple generates a DC-voltage proportionally to the temperature difference of the junction and the reference point.

Thermocouple WATT-meter

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This instrument can measure DC and AC.

Frequency bandwidth Current: up to approx. 1000 Hz Voltage: up to approx. 150 Hz

If fixed coils are representing the load-current and the moving coil the voltage-representative current, we are directly measuring electric power.

Electro-Dynamic WATT-meter

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Electro-Dynamic WATT-meter

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Thermal Watt Meter versus Electro-dynamic Meter

i

i

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T

0

).().(T

1 dttituAverage power

To A/D converter

Voltage input circuit

Current input circuit

RMS circuit

MEAN circuit

RMS circuit

u(t)

i(t)p(t)=u(t).i(t)

Low pass filter

Analogue multiplier

X

T

0T

1averageP p(t).dt

Analogue Measurement, Digital Readout

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Analogue calculation, Digital Readout

Yokogawa 2533E

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Time-division multiplication principle

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i(t)

u(t)

SampledInstantaneous current I(n)

SampledInstantaneous voltage value U(n)

DSP

Voltage input circuit

A/D

To next stage

Current input circuit

Digital Signal ProcessingI.U )n(

N

1n)n(N

1 Power Active

A/D

Today: WT-Family en PZ

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Digital Calculations and Display: WT-Family and PZ

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Example of true digital type

Yokogawa 2531A

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Measurement via DSP operation 32-bit floating point operation 80ns for WT2000

(250ms display update) 50ns for WT1000

(100ms display update)

Urms Irms W VA Var PF

Measurement via CPUcomputation

Range conversion Scaling

DSP versus CPU

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Energy & Power Measurement Trend

Requirement

1950s 1980s Present time Near future

Stability / Repeatability Accuracy / Bandwidth Real time / Analysis Efficiency / Control

Background Boom of house appliances Boom of Inverter Harmonics / Flicker Ecology / Energy

Object / Target Commercial frequency Static power Static power / Analysis Transient power

Sensing Coil CT, DC/CT Non inductive shunt High freq . probe/sensor

Method Moving coil Analog circuit or IC Digital circuit or IC Digital IC

Principle or

Acquisition

method

Electrodynamometer Feedback time divisionmultiplier system

Feedback pulse widthmodulation

Counting A/D C

DSP

Digital multiplier

Sampling A/D C

Real time FFT analysis

MEMORY

DSP

Sampling A/D C

Theme Accuracy Isolation / Software Probing/ CalibrationResponse

Fixedcoils

Movingcoil

Fixedcoil

Movingcoil Fixed

coil

Pointerof meter

V

A

A-D

LPF

CPU

V

A

A-D

A-D

CPUDSP

MEMORY

V

A

A-D

A-D

A-D

A-D

DSP

DSP

CPU CRT