Schneider Electric 4000 manual HOW Power Factor is Stored in the Register, 128

Appendix A—Abbreviated Register Listing	63230-300-212
How Power Factor is Stored in the Register	April 2001

For registers defined in bits, the rightmost bit is referred to as bit 00. Figure

A–1shows how bits are organized in a register.

			High Byte								Low Byte
0	0	0		0	0	0	1	0	0	0	1	0	0	1	0	0
15	14	13	12		11	10	09	08	07	06	05	04	03	02	01	00 Bit No.

Figure A–1: Bits in a register

HOW POWER FACTOR IS STORED IN THE 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–2below). 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.

15	14	13	12		11	10	9	8	7	6	5	4	3	2	1	0
	0	0		0	0	0
		Unused Bits									Power Factor
Sign Bit
0=Leading			Set to 0						in the range 100-1000 (thousandths)

1=Lagging

Figure A–2: Power factor register format

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

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