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1 GENERAL
This document specifies a subset of the Modbus serial communications protocol used to transfer data between a
master computer station and the PM172. The document provides the complete information necessary to develop
third-party communications software capable of communication with the Series PM172 Powermeters. Additional
information concerning communications operation, configuring the communications parameters, and
communications connections is found in "PM172 Series Powermeter, Installation and Operation Manual".
IMPORTANT
1. In 3-wire connection schemes, the unbalanced current and phase readings for power factor, active
power, and reactive power will be zeros, because they have no meaning. Only the total three-phase
power values can be used.
2. In 4LN3, 4LL3, 3LN3 and 3LL3 wiring modes, harmonic voltages will be line-to-neutral voltages; in other
modes, they will be line-to-line voltages. In a 3-wire direct connection, harmonic voltages will represent
line-to-neutral voltages as they appear on the instrument's input transformers. In 3OP2 and 3OP3 wiring
modes, voltage harmonics will be given only for phases L12 and L23.
3. Most of the advanced features are configured using multiple setup parameters that can be accessed in
some contiguous registers. When writing the setup registers, it is recommended to write all the registers
at once using a single request, or to clear (zero) the setup before writing into separate registers.