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E-HELP: Can multiple 4-20mA signals be placed on one 4-20mA signal as HART dynamic variables?

E-HELP: Can multiple 4-20mA signals be placed on one 4-20mA signal as HART dynamic variables?

Q: You have a product called HART Interface Module (HIM) that will pull the 2nd, 3rd and 4th HART variables from a transmitter signal and create one 4-20mA signal for each. Do you have or know of an instrument that will take multiple 4-20mA signals and output them on one 4-20mA signal as HART dynamic variables? I would like to read three transmitters on one 4-20mA signal by reading the variables on my DCS system.

A: We have two products that take multiple inputs and output a HART signal that can be read by a HART host. Those two products are the TCM and the THZ3/TDZ3.

The TCM is a 16 channel input module that accepts multiple temperature, resistance and millivolt signals and offers a HART output or a MODBUS RTU output. For 4-20mA inputs the TCM accepts them across a resistor or shunt input as a mV input. Those signals can then be read by a HART host using a custom HART command. For a MODBUS RTU output a separate HART to MODBUS converter, called the HMC, is used. For more information on the TCM and HMC (which together comprise the TCS) download the TCS data sheet

The THZ3/TDZ3 Smart HART Temperature Transmitter can accept two (not three) 4-20mA
signals and write them to two of the HART dynamic variables riding on the analog 4-20mA
output.

A wiring diagram showing how to wire the THZ3 to accept two 4-20mA input signals is available in the Installation Manual which you can download here. For more information, download the THZ3 data sheet.

For more information on the HIM, download the data sheet.

Published: April 19, 2016
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