How to Re-transmit and Isolate 4-20mA Signals from Remotely-Mounted 3-Wire Gas Detection Sensors Application Note
Defining the Problem:
Typically, signals from 3-wire remote sensors monitoring combustible and toxic gases are transmitted directly to the remote gas monitor or controller. However, there are cases when it’s desirable to send the signal to more than one destination. This can either be accomplished by re-transmitting the existing signal to additional locations or by completely isolating the signal and then sending it to multiple locations.
A 3-wire remotely-mounted gas detection sensor which transmits a 4-20mA signal. It is important to note that a 3-wire loop is where the sensor and receiver share a ground connection with power, and the sensor uses a third wire to connect to power outside the current loop. You can use either 2-wire (or 4-wire) isolators to re-transmit the loop to a 2-wire (or 4-wire) splitter for complete isolation of the output(s).
Implementing the Solution:
- Acromag’s signal isolators will take a 4-20mA field input and provide isolated 4-20mA output signals. Each channel (splitter units) operates independently and is isolated from the others to prevent interaction between channels.
- 600T Series isolators and splitters are field adjustable with zero and span trim pots located on the front of the units. TT Series isolators are factory calibrated for 4-20mA in-out. However, re-calibration can be preformed using either our windows software or the Acromag Agility™ mobile application for Android®.
- Follow the proper wiring practices as detailed in the user manual. Connect earth ground as indicated.
- 2-wire Acromag Isolators: 651T-0600, TT236-0600
- 4-wire Acromag Isolators: 631T-0500 (DC Power), 631T-0100 (AC Power), TT336-0700
- 2-wire Acromag Splitters: 653T-0600, SP236-0600
- 4-wire Acromag Splitters: 633T-0500 (DC Power), 633T-0100 (AC Power), SP336-0700
Gas detectors are usually installed in hazardous areas. These isolators and splitters are designed for UL/cUL Class 1 Division 2 safety rating for hazardous environments. These transmitter’s default configuration is for 4-20mA input and output making installation simple and with up to 1500V of isolation, the protection is excellent.
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