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PRELIMINARY

PM4301APDA

ANALOG INPUTS

The most important external circuitry required for the

SA4301A/SA9105G are the voltage sense input and current

sense input networks. These circuits translate the mains

voltages and load currents 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 currents and mains voltages and

convert them to signals that are appropriate for the

SA4301A/SA9105G,

n

to allow calibration of the meter,

n

to compensate for any phase shift present in the current

transformers 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 Networks

A typical three phase energy metering system has to use

current transformers (CTs) as current sensing elements in

order to provide the required isolation between the three line

voltages. The PM4301APDA has therefore been designed

to be used with current transformers as current sensing

elements. Three identical current input networks are

provided on the evaluation module, one for each phase of a

three phase system. All three current input networks should

be identical.

The PM4301APDA evaluation module has been set up for a

with a turns ratio of 1:2500. The current input networks can

transformer turns ratio by simply changing the current

transformer burden resistors (R1 and R2) as illustrated in

Table 1.

Figure 2 shows the circuit diagram of one current input

network as implemented on the PM4301APDA evaluation

module (Phase 1) with an external current transformer

connected. The circuit is repeated for the other two current

input networks.

network should be designed to supply an input current of

and IIP3/IIN3) of the SA4301A/SA9105G. The current sense

saturation occurs. Referring to Figure 2, the resistors R1

and R2 form the current transformers termination resistor.

The reference level is connected in the centre of the

termination resistor to achieve purely differential input

currents. The voltage drop across the current transformer

termination resistors at maximum rated mains current

transformers with a low phase shift and a turns ratio of

1:2500, the value of the termination resistors R1 and R2 is

therefore

B

MAX

CT

R

2

2

1

I

N

mV

100

R2

R1

=

W

»

´

´

=

=

the maximum rated mains current (60A).

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 values can be calculated as

follows:

C

B

CT

MAX

R

k

5

.

1

A

16

2

R

N

I

R6

R5

R4

R3

=

W

=

m

´

´

=

=

=

=

SA4301A

SA9105G

R5

R3

R1

IIN1

IIP1

GND

CT1

Current In

16μA

RMS

R6

R4

R2

Current Out

GND

GND

C1

C2

JS1 “P”

JS1 “N”

SA4301A

SA9105G

R5

R3

R1

IIN1

IIP1

GND

CT1

Current In

16μA

RMS

R6

R4

R2

Current Out

GND

GND

C1

C2

JS1 “P”

JS1 “N”

Figure 2: Current channel 1 input network on the PM4301APDA