Schneider Electric 4000 HOW POWER FACTOR IS STORED IN THE REGISTER

Appendix A—Abbreviated Regist er Listing 63230-300-212
HowPower Factor is Stored in the Register April 2001
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128
For registersdefined in bits, the rightmost bit is referred to as bit 00. Figure
A–1 shows how bitsare organized in a register.
Figure A–1: Bits in a register
The circuit monitorregisters can be used with MODBUS or JBUS protocols.
Although the MODBUS protocol uses a zero-based registeraddressing
conventionand JBUS protocol uses a one-based register addressing
convention,the circuit monitor automatically compensatesfor the MODB US
offset of one. Regardall registers as holding registers where a 30,000 or
40,000 offsetcan be used. For example, Current Phase A will reside in
register31,000 or 41,000 instead of 1,000 as listed in TableA–3.
Each powerfactor value occupies one register. Powerfactor values are
stored usingsigned magnitude notation (see FigureA–2 below). Bit number
15, the sign bit,i ndicatesleading/lagging. A positive value (bit 15=0) always
indicatesl eading.A negative value (bit 15=1) always indicateslagging. Bits
0–9 store a valuein the range 0–1,000 decimal. For example the circuit
monitorwould return a leading power factorof 0.5 as 500. Divide by 1,000 to
get a powerfactor in the range 0 to 1.000.
Figure A–2: Powerfactorregisterformat
When the powerfactor is lagging, the circuit monitor returns a high negative
value—for example, -31,794.This happens because bit 15=1 (for example,
thebinary equivalent of -31,794 is 1000001111001110).To get avalue 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 cla rify.
Assume that youread a power factor value of -31,794. Convert this to a
power factorin the range 0 to 1.000, as follows:
-31,794 + 32,768 = 974
974/1,000 = .974 laggingpower 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)