MODBUS CURRENT AND VOLTAGE MONITOR

Data Sheet Extract	Caledon
INSTRUMENTS	MODBUS RTU TRUE RMS CURRENT AND VOLTAGE DATA ACQUISITION MODULE

FEATURES


	DIN rail mounted
	MODBUS RTU Slave
	True RMS readings
	Suitable for load monitoring with phase angle or burst fire control
	24V DC power supply
	Galvanically isolated comms port
	For use with either 1A or 5A Current transformer secondaries

Module Description

The module accepts 3 current inputs, 3 non-isolated single ended voltage inputs, and 3 (transformer) isolated voltage inputs. The module acts as a Modbus RTU slave, with a galvanically isolated communications port. The port may be connected either as RS422 with separate Tx and Rx pairs, or RS485 with a single pair for Tx and Rx

Two sets of values are transmitted for each voltage or current signal:-

This is simply the RMS value, continuously updated.
This reading is processed for monitoring of load voltage or current for use with burst fire control. The input signal is monitored over a timed period (either 15 seconds or 35 seconds, selectable by the digital input). At the end of the timed period the maximum RMS value recorded in the period is transferred to the register for access by the comms. This results in a steady reading of voltage or current when the thyristor stack is either on permanently, or burst firing with a period less than the timed period above, and a reading of near zero when the stack is permanently off, or off for longer than the timed period.

We should be pleased to consider custom variants of this module - please let us know your requirements

A version with DeviceNet communications is also available.

General Specification

Power Supply

The module requires a nominal 24V DC power supply, limits of range 20 to 28V. The supply should be fitted with a 250mA fuse. Current consumption is nominally 120mA

Enclosure

DIN rail mounted enclosure with clear polycarbonate cover, size 220mm long x 110mm high x 80mm deep when mounted on 35 x 8 mm symmetrical DIN rail.

Electrical connections are to screw terminals, with rising clamp connectors, suitable for cables up to 2.5mm^².