Data Formats; 16-Bit Scaled Integer Format - Satec EM720 Reference Manual

To map the EM720 register address to the range of the Modbus holding registers, add
a value of 40001 to the EM720 register address. When a register address exceeds
9999, use a 6-digit addressing scheme by adding 400001 to the EM720 register
address.

2.6 Data Formats

The EM720 uses three data formats to pass data between a master application and the
instrument: 16-bit short integer, 32-bit long integer and 32-bit modulo-10000 formats.
Binary values and counters are always transmitted in 32-bit registers, while analog
values can be read both in 32-bit and in 16-bit scaled registers.
Analog registers 256 through 308 and 6656 through 10935 contain scaled 16-bit
values.

2.6.1 16-bit Scaled Integer Format

16-bit scaled analog data is transmitted in a single 16-bit Modbus register being scaled
to the range of 0 to 9999. To get a true reading, a reverse conversion should be done
using the following formula:
X
=
Y
where:
Y
X
LO and HI
Refer to Section 4 "Data Scales and Units" for applicable data scales and measurement
units. The engineering scales are indicated for every scaled 16-bit register.
The default voltage scale in the device is 144V (120V+20%). It can be changed
through register 242 (see Section 3.1, Device Data Scales), or via the supplemental
PAS software. The recommended voltage scale is 120V+20% = 144V for using with
external PT's, and 480V+25% = 600V for a direct connection to power line.
CONVERSION EXAMPLES
1. Voltage readings
a) Assume device settings (direct wiring): PT ratio = 1; Voltage scale = 600V (480V + 25%).
Voltage engineering scales (see Section 4):
HI_ENG = Vmax = 600.0 × PT ratio = 600.0 × 1 = 600.0V
LO_ENG = 0V
If the raw data reading is 2000 then the voltage reading in engineering units will be as follows:
Volts reading = 2000 × (600.0 - 0)/(9999 - 0) + 0 = 120.0V
b) Assume device settings (wiring via PT): PT ratio = 14,400V : 120V = 120; Voltage scale =
144V.
Voltage engineering scales (see Section 4):
HI_ENG = Vmax = 144.0 × PT ratio = 144 × 120 = 17,280V
LO_ENG = 0V
If the raw data reading is 8314 then the voltage reading in engineering units will be as follows:
Volts reading = 8314 × (17,280 - 0)/9999 + 0 = 14,368V
2. Current readings
Assume device settings: CT primary current = 200A.
× −
( HI LO )
+
LO
9999
- True reading in engineering units
- Raw input data in the range of 0 to 9999
- Data low and high scales in engineering units
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