10
2.6 Modbus Register Addresses
The PM130 Modbus registers are numbered in the range of 0 to 65535. From the Modbus
applications, the PM130 Modbus registers can be accessed by simulating holding registers of
the Modicon 584, 884 or 984 Programmable Controller, using a 5-digit “4XXXX” or 6-digit
“4XXXXX” addressing scheme.
To map the PM130 register address to the range of the Modbus holding registers, add a
value of 40001 to the PM130 register address. When a register address exceeds 9999, use
a 6-digit addressing scheme by adding 400001 to the PM130 register address.
2.7 Data Formats
The PM130 uses four data formats to pass data between a master application and the
instrument: 16-bit short integer, 32-bit long integer, 32-bit floating point 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.
32-bit analog and energy registers and counters can be read either in long integer or in
single precision floating point format. The register type can be selected in the meter
separately for analog registers, binary counters and energy registers via Modbus register
246 (see Section 3.1, Modbus Setup Registers). Refer to the "PM130 PLUS Powermeters,
Installation and Operation Manual, Device Options Setup" for information on how to setup
the type of 32-bit registers in your meter.
Analog registers 256 through 308 and 6656 through 10935 contain scaled 16-bit data.
2.7.1 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:
LO
9999
)
LO
HI
(
X
Y
+
−
×
=
where:
Y
- True reading in engineering units
X
- Raw input data in the range of 0 to 9999
LO and HI - Data low and high scales in engineering units
The engineering scales are indicated for every scaled 16-bit register. Refer to Section 4
“Data Scales and Units” for applicable data scales and measurement units.
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
690V+20% = 828V for a direct connection to power line.
CONVERSION EXAMPLES
1. Voltage readings
a) Assume device settings (direct wiring): PT ratio = 1; Voltage scale = 828V (690V + 20%).
Voltage engineering scales (see Section 4):
HI_ENG = Vmax = 828.0
×
PT ratio = 828.0
×
1 = 828.0V
LO_ENG = 0V
If the raw data reading is 1449 then the voltage reading in engineering units will be as follows:
Volts reading = 1449
×
(828.0 - 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
Provided
by
Northeast
Power
Systems,
Inc.
www.nepsi.com
