11
If the raw data reading is 250 then the current reading in engineering units will be as follows:
Amps reading = 250 × (400.00 - 0)/(9999 - 0) + 0 = 10.00A
3. Power readings
a) Assume device settings (direct wiring): Wiring 4LL3; PT = 1; CT primary current = 200A; Voltage
scale = 828V.
Active Power engineering scales (see Section 4):
HI_ENG = Pmax = Vmax × Imax × 2 = (828.0 × 1) × (200.00 × 2) × 2 = 662,400W = 662.400kW
LO_ENG = -Pmax = -662.400kW
If the raw data reading is 5500 then the power reading in engineering units will be as follows:
Watts reading = 5500 × (662.400 - (-662.400))/(9999 - 0) + (-662.400) = 66.313kW
If the raw data reading is 500 then the power reading in engineering units will be as follows:
Watts reading = 500 × (662.400 - (-662.400))/(9999 - 0) + (-662.400) = -596.153kW
b) Assume device settings (wiring via PT): Wiring 4LN3; PT = 120; CT primary current = 200A.
Active Power engineering scales (see Section 4):
HI_ENG = Pmax = Vmax × Imax × 3 = (828 × 120) × (200.00 × 2) × 3/1000 = 119,232kW
LO_ENG = -Pmax = -119,232kW
If the raw data reading is 5500 then the power reading in engineering units will be as follows:
Watts reading = 5500 × (119,232 - (-119,232))/(9999 - 0) + (-119,232) = 11,936kW
If the raw data reading is 500 then the power reading in engineering units will be as follows:
Watts reading = 500 × (119,232 - (-119,232))/(9999 - 0) + (-119,232) = -107,307kW
4. Power Factor readings
Power factor engineering scales (see Section 3.3):
HI_ENG = 1.000.
LO_ENG = -1.000.
If the raw data reading is 8900 then the power factor in engineering units will be as follows:
Power factor reading = 8900 × (1.000 - (-1.000))/(9999 - 0) + (-1.000) = 0.78
2.6.2 32-bit Long Integer Format
32-bit long integer data is transmitted in two adjacent 16-bit Modbus registers as unsigned
(UINT32) or signed (INT32) whole numbers.
The first register contains the low-order word (lower 16 bits) and the second register
contains the high order word (higher 16 bits). The low-order word always starts at an even
Modbus address. The value range for unsigned data is 0 to 4,294,967,295; for signed data
the range is -2,147,483,648 to 2,147,483,647.
If your Modbus driver does not support a 32-bit long integer format, you can read the two
16-bit registers separately, and then convert them into a 32-bit value as follows (using C
notation):
32-bit value = (signed short)high_order_register × 65536L + (unsigned short)low_order_register
EXAMPLES
1. Unsigned 32-bit Values
If you read unsigned Voltage V1 of 69,000V from registers 13952-13953, then the register readings will
be as follows:
(13952) = 3464
(13953) = 1
The 32-bit value is (1 x 65536 + 3464) = 69000V.
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