GE EPM 9650/9800 manual Structure for a combination is

Channel identification is performed by referencing the internal data table of the EPM device, by specifying the Line Number and Point Number for a particular value. For example: to monitor 1 second VAN values, use Line 34, Point 0; 1 second VBN, use Line 34, Point 1; 1 second IA, use Line

36, Point 0; Thermal Average VAN, use Line 51, Point 0. To leave a Limit unassigned, use Line 65535, any point.

Comparison values are entered using percentages relative to the programmed full scales of the system. For VAN, the phase-to-neutral Voltage Full Scale would be referenced. If it is programmed

to 120.0 V secondary with a phase voltage PT of 120:1, then a comparison of 13.2 kV primary would be a limit of 108 V secondary or 90.00% of the Full Scale. A 90.00% comparison for IA with

a phase Current Full Scale of 5.0 A secondary and a phase current CT of 2000:5 would be a comparison of 4.5 A secondary or 1800 A primary. Negative percentages would be used where appropriate (Watts, VAR, etc.). Special cases like PF and KF would depend on fixed internal Full Scales. Human interfaces could represent this in terms of quadrature and angle, instead of the internal percentage representation.

Each comparison has a direction associated with it - Above or Below. A 90.00% comparison could be for above 90.00% or below 90.00%.

Finally, each limit object is able to produce a third output which is a combination of the two comparisons. This combination could be an AND, OR, NAND, NOR, XOR or Hysteresis. So, a user can produce a band of between 40.00% and 80.00% by combining above 40.00% AND below 80.00%; over 110.00%/under 90.00% alarms by combining above 110.00% OR below 90.00%, on after over 110.00%, off after below 90.00% by combining above 110.00% and below 90.00% with Hysteresis.

The structure for a combination is :

2 byte	Line Number
1 byte	Point Number
1 byte	Direction and Combination (SAB)
2 byte	Comparison 1 Percentage (Value 1)
2 byte	Comparison 2 Percentage (Value 2)

Total of 8 bytes per Limit Object, total of 256 bytes for 32 Limit Objects.

The structure for the Direction and Combination byte is:

Bits 7-5	Unused, set to 0
Bit 4	Negate combination (AND -> NAND, etc.)
Bits 3-2	00	= AND combination
	01	= OR combination
	10	= XOR combination
	11 = Hysteresis combination
Bit 1	0 = Comparison 2 is below
	1 = Comparison 2 is above
Bit 0	0 = Comparison 1 is below
	1 = Comparison 1 is above

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