Schneider Electric PM870, PM820, PM810, PM850 manual How Date and Time are Stored in Registers

PowerLogicTM Series 800 Power Meter	63230-500-225A2
Appendix B—Register List	3/2011

How Date and Time are Stored in Registers

The date and time are stored in a three-register compressed format. Each of the three registers, such as registers 1810 to 1812, contain a high and low byte value to represent the date and time in hexadecimal. Table B–1lists the register and the portion of the date or time it represents.

Table B–1: Date and Time Format

Register	Hi Byte	Lo Byte
Register 0	Month (1-12)	Day (1-31)
Register 1	Year (0-199)	Hour (0-23)
Register 2	Minute (0-59)	Second (0-59)

Table B–2provides an example of the date and time. If the date was 01/25/00 at 11:06:59, the Hex value would be 0119, 640B, 063B. Breaking it down into bytes we have the following:

Table B–2: Date and Time Byte Example

Hexadecimal Value		Hi Byte	Lo Byte
0119	01	= month	19 = day
640B	64	= year	0B = hour
063B	06	= minute	3B = seconds

NOTE: Date format is a 3 (6-byte) register compressed format. (Year 2001 is represented as 101 in the year byte.)

How Signed Power Factor is Stored in the Register

Each power factor value occupies one register. Power factor values are stored using signed magnitude notation (see Figure B–2). 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 power meter 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 B–2: Power Factor Register Format

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

0

0

0

0

0

Sign Bit	Unused Bits	Power Factor
0=Leading	Set to 0	in the range 100-1000 (thousandths)
1=Lagging

When the power factor is lagging, the power meter 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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