http://www.sames.co.za

3/14

PRELIMINARY

PM4301APDA

For best immunity to electromagnetic disturbances the

SA4301A/SA9105G requires low-pass filters on the current

sense inputs. Referring to Figure 2, these filters are realized

by means of the capacitors C1 and C2. The typical cut-off

frequency of these filters should be between 10kHz and

20kHz. The equivalent resistance associated with each

order of

C

C

CI

C

nF

22

k

5

.

1

kHz

10

1

R

f

1

C2

C1

=

»

W

´

´

p

=

p

=

=

filters of the current input networks.

different CT turns ratio typically only the current transformer

burden resistors need to be changed. This will then not

affect any other characteristics of the current input networks.

The new value for the burden resistors can be calculated

using

MAX

CT

C

I

N

R

A

16

2

R2

R1

´

´

m

´

=

=

The values of the burden resistors for some typical values of

Table 1, rounded to the nearest available resistor value.

Table 1: Current transformer burden resistors required for

Value of Burden Resistors (

W)

6

20

10

12

20

6.2

25

4.7

30

3.9

40

3

50

2.4

60

2

80

1.5

100

1.2

120

1

Voltage Sense Input Networks

The voltage input networks on the PM4301APDA have been

designed for operation at both 220V and 110V mains

voltage. The mains voltage is selected by means of jumpers

(J1, J2 and J3). The voltage input networks attenuate the

mains voltage signals to lower voltages by means of voltage

dividers. Trimpots are used to tap these voltage dividers at

different levels to effect calibration.

Figure 3 shows the voltage sense input network for channel

1 on the PM4301APDA. The circuit is identical for the other

two channels. The voltage sense input saturates at an input

voltage sense input should therefore be set between

allow for a mains voltage variation of up to +30% and –50%

without saturating the voltage sense input.

The input resistor R24 sets the current input into the device.

This resistor should not be too large else the capacitor for

the low-pass filter will be quite small. This could cause

inaccurate phase shift due to parasitic capacitances and

affect the performance of the module at low power factor.

Therefore R24 = 100k

W is chosen. For the purpose of the

evaluation module a very large tuning range on the trimpot

is selected, so let R23 and P1 be 1k

W each and the voltage

over the combination of R23 and P1 be 1.76V. This allows

the input currents on the voltage sense inputs of the device

The following equations can be used to obtain the remaining

resistor values:

W

+

+

+

+

W

=

k

2

22

R

21

R

20

R

19

R

k

2

V

220

V

76

.

1

and

W

+

+

W

=

k

2

20

R

19

R

k

2

V

110

V

76

.

1

This results in R19 + R20 = 123k

W and R21 + R22 = 125kW

and the values are chosen as R19 = 75k

W, R20 = 47kW,

R21 = R22 = 62k

W. The effect of R24 can be ignored in the

above equations, given the fact that R24 is significantly

larger than the combination of P1 and R23.