mA on fluke 87V - Page 1
Forum section: electronics / beginners

author: Al030787
author_rank: Newbie
timestamp: March 15, 2016, 04:10:46 am
content: I'm new to this, so I apologize in advance, I will get right to it. I have a fluke 87V and I've been troubleshooting my 4-20mA circuits and I'm not sure which way is correct. I turn my dial on my meter and put it to DC mA setting. I move the leads to the correct position on my meter for the mA. Now in my circuit we have 24v output on the white wire to the device and the device converts it to 4-20mA and sends it back to my plc on the black wire. If I'm trying to read that through my meter can I put my black lead on ground and the red lead on the wire sending 4-20mA back to my plc to get a proper reading or how would I put my leads to see what that device is sending out for a 4-20mA to my plc. If this is a basic question I apologize.

author: kendalll
author_rank: Contributor
timestamp: March 15, 2016, 05:51:12 am
content: Can you draw a diagram of your circuit and post it?I may have missed something in your question but it sounds like you might not have the amp meter *IN* your circuit. Also check to make sure you didn't blow the fuse in the meter by accidentally measuring between 24V and GND with the meter in the amps configuration. I did that to my DMM way back the first time I was playing with it.

author: retrolefty
author_rank: Super Contributor
timestamp: March 15, 2016, 05:51:37 am
content: Quote from: Al030787 on March 15, 2016, 04:10:46 amNo.Current measurements have to be measured only in series with either of the wires. So you can't measure the loop current without first having to disconnect one wire and measure in series. That of course means the the loop is put in 'manual' mode by the plant operator or else disconnecting the wire would 'bump' the process.

author: Simon
author_rank: Unknown
timestamp: March 15, 2016, 06:45:45 am
content: Put your meter in series. If you put it in parallel you are putting the meter with a fuse and tiny resistance across 24V. The idea is that you put the meter in series with the load. The resistance in the meter is tiny and the volt srop on it small so as to not disturb the load but the meter will measure the voltage drop on the resistance and from ohms law deduce the current.Don't wory, I watched a highly paid consultant at work use the 10A range to "measure" a 20A motor and put the meter in parallel. Having not learnt his lesson he went to try the 200mA range at which point i shouted at him.

author: blacksheeplogic
author_rank: Frequent Contributor
timestamp: March 15, 2016, 07:18:47 am
content: Quote from: Al030787 on March 15, 2016, 04:10:46 amif you need to take the measurement without breaking the loop you need a process clamp meter.

author: Al030787
author_rank: Newbie
timestamp: March 15, 2016, 11:15:56 am
content: Thank you very much that is extremely helpful. I appreciate the feedback everyone.

author: Aeternam
author_rank: Unknown
timestamp: March 15, 2016, 11:25:49 am
content: This might be helpful:http://www.allaboutcircuits.com/textbook/direct-current/chpt-3/safe-meter-usage/The part about current measurement starts at about halfway down.