metso automation maxPAC - Field Wiring for Redundant Modules with Common Transmitter

maxPAC Hardware Reference Guide
Metso Automation MAX Controls Inc. • 277596 •
2-8
Field Wiring for Redundant Modules with Common Transmitter
The following figure shows the recommended wiring for two redundant
IOP301 analog input modules that share a common two-wire or four-wire
transmitter.
Redundant inputs must be configured as voltage inputs with an external 100-
Ohm shunt resistor. The recommended maximum distance between the shunt
and the I/O module is 10 meters. The +24V connection should be
independently fused to each transmitter.
The connection to the (-) terminal of the 24v supply must be made at the (-)
side of the shunt resistor. The voltage that is developed across each 100-
Ohm shunt by the 4-20 mA signal from the transmitter is wired to the AI
module using twisted pair cables. A PTC thermistor is recommended
between the transmitter output and the 100-Ohm shunt. This protects the
100-Ohm shunt against over voltage and provides additional resistance to
increase the transmitter load to 250 Ohms. Kit IOP306 supplies 16 pairs of
100-Ohm shunts and thermistors to support two IOP301 analog input
modules.
thermistor
(-)
(+)
Primary
IOP301
AI Module
4 wire
Transmitter
(-)
(+)
Secondary
IOP301
AI Module
100
Twisted
pair
Four Wire Transmitter