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PRELIMINARY

PM4104APDA

ANALOG INPUTS

The most important external circuitry required for the

SA4104A/B are the voltage sense input and current sense

input networks. These circuits translate the mains voltage

and load current into signals that can be sensed by the

energy metering device. These networks should be

constructed using good quality resistors and capacitors to

ensure adequate immunity to temperature and noise.

The functions of the current and voltage input networks are

the following:

n

to sense the load current and mains voltage and

convert them to signals that are appropriate for the

SA4104A/B,

n

to allow calibration of the meter,

n

to compensate for any phase shift present when a

current transformer is used for current sensing and

n

to filter all high frequency noise and other disturbances

in the current and voltage signals in order to maintain

adequate accuracy when electromagnetic disturbances

are applied to the energy meter.

Current Sense Input Network

A typical single phase energy metering system can use

either a shunt resistor or a current transformer (CT) as

current sensing element. The PM4104APDA has therefore

been designed to be used with either a shunt or a current

transformer.

The PM4104APDA evaluation module has been set up for a

resistance of 320μ

W. The current input network can easily

by simply changing the current input resistors (R3, R4, R5

and R6) as required. The evaluation module can also be

adapted to use a current transformer by adding the burden

resistors (R1 and R2) and changing the current input

resistors.

Using a Shunt Resistor

Figure 2 shows the circuit diagram of the current sense

input network when using a shunt resistor to sense the line

current as it is implemented on the PM4104APDA. The

shunt is connected externally.

The shunt resistor should be selected so that the voltage

maximum rated mains current the current input network

the current sense inputs (IIP and IIN) of the SA4104A/B.

The current sense inputs saturate at an input current of

headroom until saturation occurs. Referring to Figure 2, the

resistors R3 to R6 define the current flowing into the energy

metering device. The optimum input network is achieved by

setting the input resistors equal, i.e. setting R3 = R4 = R5 =

R6. Noting that the energy metering device creates a virtual

short circuit between the differential current sense inputs

(IIP and IIN) the value for the current input resistors can be

calculated as follows:

C

MAX

R

A

16

4

V

R6

R5

R4

R3

=

m

´

=

=

=

=

maximum rated mains current. Assuming a 320μ

W shunt

different shunt value the current input resistors should be

changed.

SA4104A

SA4104B

R3

R5

IIN

IIP

Current In

16μA

RMS

R4

R6

Current Out

GND

GND

C2

C1

JS1 “P”

JS1 “N”

JS1 “0”

GND

SHUNT

RESISTOR

SA4104A

SA4104B

R3

R5

IIN

IIP

Current In

16μA

RMS

R4

R6

Current Out

GND

GND

C2

C1

JS1 “P”

JS1 “N”

JS1 “0”

GND

SHUNT

RESISTOR

Figure 2: Current input network on the PM4104APDA when using a shunt resistor as current sensing element