PM2002DP

3/10

http://www.sames.co.za

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.Th e resistors

usedinthemeteringsectionshouldbeofthesametypeso

temperatureeffectsareminimized.

ThevoltageinputoftheSA2002D(IVP)isdrivenwithacurrent

of14µAatnominalmainsvoltage.Thisvoltageinputsaturates

atapproximately17µA. Atanominalvoltagecurrentof14µA

allowsfor20%overdriving.Themainsvoltageisdividedwitha

voltagedividerto14Vthatisfedtothevoltageinputpinsviaa

1M resistor

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=4 7 , R11=22 k ,P1=10k

and

R12=1M

chosen.

Substitutingthevaluesresultin:

RB=26.29k

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

RA=386.84k

VoltageInputIVP

Ω

VoltageDivider

Ω

ΩΩ

Ω

Ω

Ω

are

Figure3:Mainsvoltagedivider

R1

R2

R3

R10

R11

R12

NEUTRAL

C7

R15

J16

P1

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StandardresistorvaluesofR1,R2,R3andR15arechosento

be47k ,150k ,47k

and150k .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.

The resistorsR6,R7definethecurrentlevelintothecurrent

senseinputsofthedevice.Thevoltagedropacrosstheshunt

shouldbeatleast20mVatratedconditions.Ashuntresistor

witha valueof50mV@80Awaschosenforth e application

moduleforitseaseofuse.Theresistorvaluesarecalculated

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

conditions.Fora80Ametertheresistorvaluesarecalculated

asfollows:

R6=R7=(I/16µA)x R /2

=80A/16µAx625u

/2

=1.5625k

I

Linecurrent

Astandardvalueof1.6k

ischosen.

Ω

Ω

ΩΩ

Ω

Ω

Ω

CURRENTSENSORINPUTRESISTORSFIGURE4(USING

ASHUNTRESISTOR)

L

SH

L=

Figure4:Current input configuration

R6

R7

R14

LIVEIN

LIVEOUT

L