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E-HELP: Replacing Temperature Transmitters With Changing Power Sources

E-HELP: Replacing Temperature Transmitters With Changing Power Sources

Q: I want to replace a THZ Temperature Transmitter (Model THZ/PRG/4-20MA/12-42DC [DIN]) with a CPT PC-Programmable Temperature Transmitter (Model CPT/TPRG/0-20MA/117AC/-C-RF [DIN]). The THZ unit we are replacing gets its power from the 4-20mA current loop while the CPT unit is going to be powered by 120Vac. Does the CPT need to be specified as "source" or "sink" to work as a drop-in replacement for the THZ unit?

A: The default version of the CPT provides voltage on its output (source). If you would like the output to be passive so it can be wired to an active (voltage supplied) input, specify the "-SINK" option. The CPT will still require 120Vac power on the power terminals.

Note that the newer two-wire output loop powered THZ3 Dual Input Smart HART Temperature Transmitter (Model THZ3/PRG/4-20MA/12-42DC [DIN]) is now available.

Q: My concern is that we will damage the unit or the equipment it is connected to it if we specify the wrong type of output. This unit will be connected to an Allen Bradley 4-20mA analog input module. The previous THZ device got its power from the analog input module so I believe the correct specification would be "sink" for the CPT. Is this correct? Also, can the "source" or "sink" option be changed in the field or does this have to be set at the factory?

A: You are correct that you will need to choose the "-SINK" option on the CPT. The choice of "source" or "sink" for the CPT must be specified in the model number and supplied from the factory that way. It cannot be field changed. Your complete model number for this application would be: CPT/TPRG/0-20MA/117AC/-C-RF-SINK [DIN].  Note that you have also selected an auxiliary alarm contact and enhanced RFI/EMI protection.

Published: October 30, 2015
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Categories: E-Help
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