LM358 failed after 30 minutes and gets hot in 4-20mA pump circuit

[djzulu]

I did not find any IC 4-20mA to 4-20mA Isolation modules to add the the board.

[RogerThat]

You can build an isolator from two optocouplers, an op amp and some resistors. One optocoupler to adjust the current in the loop and one for feedback, the op amp as "controller". There is no need for a specific IC.

Edit: I normal 4-20mA circuits you define who is powering the current loop: sender or reciver. The one who is not powering the loop need to interact with the loop thru an isolator. The isolator prevents current flowing from sender to reciver. You migh have the case where the ground might be hundreds of volts different between the two...you can figure out what happens if that is the case and you don't have isolation.

[djzulu]

Here is a timeline of the failure,



The one channel failed relatively fast, it failed concurrently with a high voltage event.

It failed and then recovered before failing permanently.

We have now added TVS diodes to the inputs and the outputs of the board and will evaluate the board in January.