4 20 mA signal dropping


Thread Starter


HMM100 of Vaisala humidity transmitter (2 wire) connected to the 3504 of Eurotherm controller. it shows Humidity process value some time and some time it shows sensor break.

What could be the reason.

Bob Peterson

Is it possible you are getting an intermittent open circuit? That would be the straightforward explanation.
My watch doesn't work. What could be the problem?

How would you answer that question? Probably with twenty questions, right? Is it wind-up watch or a digital watch? Did you wind it recently, or how long since you put a new battery in it? When did it stop working? What have you done to try to resolve the problem?

<b>When did the problem with the HMM100 start?

What have you done to troubleshoot the problem?

What were the results of your troubleshooting?

Did you check the tightness of the screw terminations along the entire length of the wiring between the sensor and the controller?

Do you know it's not the controller that's the problem? Have you tried simulating an input to the controller at the controller and then from the sensor end to see if it's the controller or the wiring between the controller and the sensor?

Have you cleaned the sensor recently?</b>

If you want a concise response--instead of twenty questions--provide more information. Try to anticipate the questions you might be asked and provide the answers to the questions. Let us know you have used some initiative and done something to try to resolve the issue, and what the results were, instead of just saying, "It doesn't work. What should be done?" Do you find yourself saying as you read the above, "We've already tried that. It didn't work!" If so, then you should have told us we wouldn't waste your--or our--time asking.

Troubleshooting and resolving a problem is a methodical and logical process. It requires an understanding of the circuit and process--not something that is always intuitive or obvious and sometimes takes some research (more than asking, "Why doesn't it work?" on an World Wide Web forum).

So, tell us about the circuit, the wiring, sensor cleanliness, etc. Help us help you.