PM2002DP データシートの表示（PDF） - South African Micro Electronic Systems

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PM2002DP

Energy Meter Evaluation Module

South African Micro Electronic Systems 

PM2002DP

ANALOG SECTION

The analog (metering) interface described in thissectionis

designed formeasuring220V/80Awithprecisionbetter than

Class1.

The most important external components for the SA2002D

integratedcircuitarethecurrentsenseresistors,thevoltage

sense resistors and the bias setting resistor. T h e resistors

used i n t h e m e t e r i n g s e c t i o n s h o u l d b e o f t h e s a m e t y p e s o

temperatureeffectsareminimized.

VoltageInputIVP

ThevoltageinputoftheSA2002D(IVP)isdrivenwithacurrent

of14µAatnominalmainsvoltage.Thisvoltageinputsaturates

atapproximately17µA. Atanominalvoltagecurrentof14µA

allowsfor20%overdriving.Themainsvoltageisdividedwitha

voltagedividerto14Vthatisfedtothevoltageinputpinsviaa

1MΩ resistor

VoltageDivider

Thevoltagedivideris(Figure3)calculatedforavoltagedropof

14V.TreatC7asashortcircuitandignoreJ16.Equationsfor

thevoltagedividerinfigure3are:

RA=R1+R2+R3+R15+R10

RB=R12||(R11+P1/2)

Combiningthetwoequationsgives:

(RA+RB)/220V=RB/14V

Values forresistorsR10=47Ω, R11 = 2 2 kΩ,P1=10kΩ and

R12=1MΩ are chosen.

Substitutingthevaluesresultin:

RB=26.29kΩ

RA=RBx(220V/14V-1)

RA=386.84kΩ

StandardresistorvaluesofR1,R2,R3andR15arechosento

be47kΩ,150kΩ,47kΩ and150kΩ.TheresistorRAisdivided

so that the voltage drop across one resistor is within the

specified limits of the resistor type that is used, usually

200VDC.Theresistorvalueratiosarechosensothatshorting

J16themodulecouldbeusedona110VACmainssystem.

CURRENTSENSORINPUTRESISTORSFIGURE4(USING

ASHUNTRESISTOR)

The resistorsR6,R7definethecurrentlevelintothecurrent

senseinputsofthedevice.Thevoltagedropacrosstheshunt

shouldbeatleast20mVatratedconditions.Ashuntresistor

with a value o f 5 0 m V @ 8 0 A w a s c h o s e n f o r t h e application

m o d u l e f o r i t s ea s e o f u s e . T h e r e s i s t o r v a l u e s a r e c a l c u l a t e d

for an input current of 16µA on the current inputs at rated

conditions.Fora80Ametertheresistorvaluesarecalculated

asfollows:

R 6 = R 7 = ( IL/ 1 6 µ A ) x RSH / 2

=80A/16µAx625uΩ / 2

=1.5625kΩ

IL = Linecurrent

Astandardvalueof1.6kΩ ischosen.

LIVEIN

R14 L

R6

R7

LIVEOUT

Figure4:Current input configuration

R10

NEUTRAL

LIVEIN

http://www.sames.co.za

J16

R1

R2

R3

R15

C7

R12

R11

P1

Figure3:Mainsvoltagedivider

3/10

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