RM4301ASEA datasheet(8/19 Pages) SAMES

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PRELIMINARY

RM4301ASEA

equation(9):

fCI,-3dB ≈ 14.1kHz (acceptable)

equation(12):

RX = 200kW

equation(13):

choose RX0 = RX1 = 62k

W and obtain

RX2 ≈ 47k

equation(14):

RX3 = 30k

equation(15):

RX4 = 15k

W, RX5 = 7.5kW, RX6 = 3.9kW,

RX7 = 2k

W, RX8 = 1kW, RX9 = 470W, RX10

= 240

W, and RX11 = 120W. Some ratios are

not entirely accurate, but to ensure low cost

it is important to use only standard resistor

values.

equation(16):

using IVP = 11 obtain DF_LED ≈ 392

equation(17):

DF_MO = 8

Table 2:

FMS = '1', RB = 'Z', RA = '0'

MEASURING THE PHASE SHIFT OF

CURRENT TRANSFORMERS

The SA4301A derives the input current on the current sense

networks directly from the current transformers. For this

reason the actual phase shift added by the current

transformer is usually less than the manufacturers

specification. It is therefore advisable to measure the phase

shift in application on a small sample of CTs. The best

method to use is:

1. Design and implement the circuit using the procedure

described. Assume ½ the manufactures specification for

the phase shift of the CT when calculating the

component values.

2. When assembling the PCB do not place the capacitors

on the voltage sense networks.

3. Calibrate the meter at unity power factor using the

procedure described in the “Calibrating the Meter”

section. Ensure the error is as close to zero as possible.

4. Measure the error at power factor 0.5 lag and 0.5 lead

for each phase individually. Ensure that the error is

positive for 0.5 lag and negative for 0.5 lead. If this is not

the case the phase shift of the CTs is too large or the

cut-off frequency of the anti-alias filters on the current

input networks is too high.

5. Obtain the average of the absolute values of the errors

at 0.5 lag and 0.5 lead on all phases.

6. Using the result from step 5 calculate the overall phase

shift of the current sensing network. This value is the

phase shift of both the current transformer and the anti-

alias filter combined and is equal to the required phase

shift for the voltage sensing network:

÷÷

çç

æ -

100

Error

arccos

60o

(18)

7. Given the theoretical value of the current input network

phase shift from equation (6) the value of

fCT can be

calculated.

8. Recalculate RX12 and RX13 and modify the PCB. Also

add the voltage network compensation capacitors.

9. Recalibrate the meter and verify the performance at non-

unity power factor.

CALIBRATING THE METER

The RM4301ASEA is calibrated by means of a resistive

ladder on the voltage sensing networks. The nine resistors

can be chosen to represent any desired calibration range.

The calibration accuracy can be extended by adding

resistors to the ladder network. Soldering a jumper in

parallel with a resistor closed will remove that resistor from

the voltage divider network thereby providing a larger input

current to the SA4301A and so increasing the output

energy. The RM4301ASEA should be calibrated phase by

phase with all three mains voltages present at all times.

Each phase can be calibrated by first short circuiting resistor

RX3. If the error is now positive a larger resistance is

required so the jumper across RX3 is opened before

proceeding to the next resistor in the network (RX4). If the

error is negative then the process is simply continued with

the next resistor. These steps are repeated for all nine

resistors in the ladder network. The SA4301A is linear over

the

dynamic

range

required

the

IEC62053-21

specification, so calibration is only required at one current

value. Typically the basic current (Ib) is chosen as the

calibration point. The repeatability of error measurements at

Ib is typically better than 0.1% so the error of the meter can

typically be measured accurately by a single integration of a

very small number of pulses.

PCB CONNECTIONS

The three CTs for phases 1 to 3 are connected to JA11A /

JA11B, JB11A / JB11B and JC11A / JC11B respectively.

The current transformers should be connected such that a

positive current flows into JA11B, JB11B and JC11B when

forward energy is applied to the meter. The three mains

voltages should be connected to JA1, JB1 and JC1

respectively while the NEUTRAL line must be connected to

J1. The opto-isolator output should be connectd to J2 while

the stepper motor or impulse counter is connected to J3.

JUMPER OPTIONS

The RM4301ASEA meter is equipped with several

solderable selectors, which allow the meter to be set up

according to the required specifications. Table 3 describes

the functionality of the various jumpers. When working on

the meter care should be taken to avoid electric shock due

to the high voltages present.

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