Can measuring over limit with DC amp clamp wreck it? - Page 1
Forum section: electronics / beginners

author: Superkryptonite
author_rank: Contributor
timestamp: November 06, 2019, 12:52:17 am
content: Hi guysI bought a Uni-T UT210E AC/DC amp clamp (love this thing), which says it's rated to a maximum of 100A DC.If I put it around my cars battery terminal let's say during startup, it will definitely be drawing more than 100A...will that wreck the amp clamp/ruin it's accuracy in the future? Or it just won't read properly? Obviously I won't be making a habit of doing things like that but accidents happen.Thanks!

author: floobydust
author_rank: Super Contributor
timestamp: November 06, 2019, 03:05:00 am
content: Overloading a hall sensor will not wreck it, say if you hit it with 300A cranking.But I found with Agilent clamp-on meters, big DC currents the jaws get magnetized and then the meter cannot read low currents properly. It gets stuck reading an offset with hysteresis. Not sure how the Uni-T handles that. Like the meter gets stuck reading 30mA and putting in a wire with 10mA doesn't match both directions.I just demagnetize the jaws afterwards and all is OK. So you might notice that needs to be done afterwards.

author: Superkryptonite
author_rank: Contributor
timestamp: November 06, 2019, 03:24:48 am
content: Quote from: floobydust on November 06, 2019, 03:05:00 amThanks. How do you go about demagnetizing the jaws?

author: floobydust
author_rank: Super Contributor
timestamp: November 06, 2019, 03:50:30 am
content: It's the same way you demagnetize anything - An AC current through a solenoid coil with fade out. I use a cassette tape head demagnetizer but those are from the Jurassic era, on each open jaw end.You have to fade out the AC magnetic field to get the residual flux as low as possible. Slowly moving the solenoid further away.You could put a few wire loops in and measure AC current in a heater or something.It's only if you notice the jaws are magnetized (paper clip sticking lightly) and the readings seem low or sticky.Other people might have better methods.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 06, 2019, 03:53:30 pm
content: The clamp meter should not be so difficult to demagnetize. Just an AC current relatively close to the maximum (could be multiple turns to get more effective current) and may be a slightly smaller current should be sufficient. It has to handle smaller current with no problem, so no real need to fade down that much.

author: james_s
author_rank: Super Contributor
timestamp: November 06, 2019, 04:30:15 pm
content: Before I had a proper degaussing wand I used to use the back end of a Weller soldering gun. Pull the trigger, move it up close to the object, then back it away and release the trigger.

author: Superkryptonite
author_rank: Contributor
timestamp: November 11, 2019, 05:53:30 pm
content: Thanks guys. I've seen some videos of people doing it online. Just curious why they do it for only a split second at a time? Will doing it longer damage the unit?

author: Superkryptonite
author_rank: Contributor
timestamp: November 20, 2019, 11:08:47 am
content: Bump

author: Jwillis
author_rank: Super Contributor
timestamp: November 21, 2019, 06:45:51 pm
content: Quote from: Superkryptonite on November 11, 2019, 05:53:30 pmIdea is to reverse the magnetic polarity of the iron inside the clamp back to a non magnetic polarity. They do it for a split second as to not over shoot and defeat the purpose of deguassing the iron inside the clamp.It's like when you take a magnet and brush it a against a screw driver .It makes the screw driver magnetic. Reverse the polarity of the magnetic and brush the screw driver again and it demagnetizes the screw driver. to many time s and it magnetizes again but in the opposite polarity.And no it won't damage the clamp meter it held to long but you could over shoot and simply reverse the polarity to far and re magnetize the clamp. There by defeating the purpose of deguassing.

author: Superkryptonite
author_rank: Contributor
timestamp: November 22, 2019, 02:24:21 am
content: Quote from: Jwillis on November 21, 2019, 06:45:51 pmOh okay, that makes sense. Thanks.