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Appendix A—Abbreviated Register Listing 63230-300-212
How Power Factor is Stored in the Register April 2001
© 2001 Schneider Electric All Rights Reserved
128
For registers defined in bits, the rightmost bit is referred to as bit 00. Figure
A–1 shows how bits are organized in a register.
Figure A–1: Bits in a register
The circuit monitor registers can be used with
MODBUS or JBUS protocols.
Although the
MODBUS protocol uses a zero-based register addressing
convention and
JBUS protocol uses a one-based register addressing
convention, the circuit monitor automatically compensates for the
MODBUS
offset of one. Regard all registers as holding registers where a 30,000 or
40,000 offset can be used. For example, Current Phase A will reside in
register 31,000 or 41,000 instead of 1,000 as listed in Table A–3.
Each power factor value occupies one register. Power factor values are
stored using signed magnitude notation (see Figure A–2 below). Bit number
15, the sign bit, indicates leading/lagging. A positive value (bit 15=0) always
indicates leading. A negative value (bit 15=1) always indicates lagging. Bits
0–9 store a value in the range 0–1,000 decimal. For example the circuit
monitor would return a leading power factor of 0.5 as 500. Divide by 1,000 to
get a power factor in the range 0 to 1.000.
Figure A–2: Powerfactorregisterformat
When the power factor is lagging, the circuit monitor returns a high negative
value—for example, -31,794. This happens because bit 15=1 (for example,
the binary equivalent of -31,794 is 1000001111001110). To get a value in the
range 0 to 1,000, you need to mask bit 15. You do this by adding 32,768 to
the value. An example will help clarify.
Assume that you read a power factor value of -31,794. Convert this to a
power factor in the range 0 to 1.000, as follows:
-31,794 + 32,768 = 974
974/1,000 = .974 lagging power factor
010203040506070809101112131415
00 0000 01010100 00
Bit No.
00
High Byte Low Byte
HOW POWER FACTOR IS STORED
IN THE REGISTER
1023456789101112131415
00000
Sign Bit
0=Leading
1=Lagging
Unused Bits
Set to 0
Power Factor
in the range 100-1000 (thousandths)