Overview 5
Overview
Congratulations on your purchase of the WattNode
®
Modbus
®
watt/watt-hour transducer (meter).
The WattNode meter offers precision energy and power measurements in a compact pack-
age. It enables you to make power and energy measurements within existing electric service
panels avoiding the costly installation of subpanels and associated wiring. It is designed for use
in demand side management (DSM), sub-metering, and energy monitoring applications. The
WattNode meter communicates on an EIA RS-485 two-wire bus using the Modbus protocol.
Models are available for single-phase, three-phase wye, and three-phase delta configurations for
voltages from 120 VAC to 600 VAC at 50 and 60 Hz.
Measurements
The WattNode Modbus meter measures the following:
●
True RMS Power - Watts (Phase A, Phase B, Phase C, Sum)
●
Reactive Power - VARs (Phase A, Phase B, Phase C, Sum)
●
Power Factor (Phase A, Phase B, Phase C, Average)
●
True RMS Energy - Watthours (Phase A, Phase B, Phase C, Sum)
●
Reactive Energy - VAR-hours (Sum)
●
AC Frequency
●
RMS Voltage (Phase A, Phase B, Phase C)
●
RMS Current (Phase A, Phase B, Phase C)
●
Demand and Peak Demand
One WattNode Modbus meter can measure up to three different “single-phase two-wire with
neutral” branch circuits from the same service by separately monitoring the phase A, B, and C
values. If necessary, you can use different CTs on the different circuits.
Communication
The WattNode meter uses a half-duplex EIA RS-485 interface for communication. The standard
baud rates are 9,600 and 19,200 baud, and rates from 1,200 to 38,400 baud can be configured.
The meter uses the industry standard Modbus RTU (binary) communication protocol, allowing
up to 127 devices per RS-485 subnet. The WattNode meter can auto-detect RS-485 polarity on
properly biased networks, simplifying installation.
There are numerous low-cost RS-485 interfaces to PCs, using both USB and serial ports. There
are many PC programs and standalone devices for collecting and recording Modbus data.
Diagnostic LEDs
The meter includes three power diagnostic LEDs—one per phase. During normal operation,
these LEDs flash on and off, with the speed of flashing roughly proportional to the power on each
phase. The LEDs flash green for positive power and red for negative power. Other conditions are
signaled with different LED patterns. See
Installation LED Diagnostics (p. 23)
for details.
The Modbus WattNode meter includes a communication LED that lights green, yellow, or red to
diagnose the RS-485 network. See
Modbus Communication Diagnostics (p. 28)
for details.
Options
The WattNode Modbus meter can be ordered with several options. For more details and docu-
mentation, see article
WattNode Modbus - Options
on our website.
General Options
●
Option CT=xxx
- Pre-assign xxx as the global
CtAmps
value.
