Common isolation application in wastewater plants using the 3186B Output loop-powered current isolator

Using a 4-wire level transmitter for monitoring the level in a storage tanks for clarified water is very common in wastewater plants. The challenge here is to connect the active output signal from the level transmitter to an active analog input card on a PLC.


As the level transmitter is a 4-wire transmitter with separate power supply, it creates an active 4…20 mA output. The PLC analog input card with a build-in voltage source (+ VSUPPLY) is also active. Connecting an active signal from the field directly to an active input card on a PLC is not an option.


This challenge can be solved by installing the PR 3186B, which is able to isolate two active mA signals from each other, as well as providing a passive loop-powered output for the active PLC. This means that it is now possible for the level transmitter’s active output to control the current flow through the PLC active analog input card. 


As the PR 3186B is loop powered, no additional power wiring is required.




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