Strong magnet close to a multimeter - any potential issues ? - Page 1
Forum section: electronics / testgear

author: bdivi
author_rank: Regular Contributor
timestamp: April 16, 2014, 12:49:20 pm
content: Hello,I will appreciate opinions on the following:I want to use a strong magnet to keep the tilting stand of one of my multimeters - Fluke 187.I was thinking about that magnet somehow affecting the accuracy of the meter - any experiences ?

author: EEVblog
author_rank: Unknown
timestamp: April 16, 2014, 01:02:17 pm
content: No. You can get a magnetic strap hanger for the Fluke meters, so no problem.

author: strantor
author_rank: Contributor
timestamp: April 16, 2014, 02:42:56 pm
content: Fluke sells a magnetic strap hanger as mentioned (pretty damn strong magnet) and when not in use it rests against the back side of the meter, so no, at least as far as Fluke is concerned, not a problem. However, I keep my fluke 87 with the magnet magnet hanger accessory in the same tool bag with my Fluke 337 AC/DC clamp meter. I *assume* that since it measures DC, the 337 employs a hall sensor, and I further *assume* that this hall sensor would not appreciate the clamp being magnetized by an external permanent magnet, so I take extra care to keep the 87's magnet away from the 337 and away from my digital caliper. I might just be paranoid; the 337's clamp is probably ferrite or something else that can't be magnetized, but better safe than sorry.

author: bdivi
author_rank: Regular Contributor
timestamp: April 16, 2014, 03:27:13 pm
content: Thanks. I also thought so.After the magnet installation I tested it - no problems with the readings

author: Hugoneus
author_rank: Frequent Contributor
timestamp: April 16, 2014, 03:42:58 pm
content: Quote from: bdivi on April 16, 2014, 03:27:13 pmThe ultimate test would be to put it in an MRI machine.I am kidding of course. O0

author: theatrus
author_rank: Frequent Contributor
timestamp: April 16, 2014, 04:36:26 pm
content: Quote from: Hugoneus on April 16, 2014, 03:42:58 pmI'd be interested in see what happens! Do all the ferrous bits of metal turn into shrapnel? How much field strength would that take?

author: 128er
author_rank: Regular Contributor
timestamp: April 16, 2014, 05:20:54 pm
content: Short story (but without magnets, but rf fields) ...One of my work colleagues made ??a troubleshooting in a manufacturing plant. He did a rough current measurement on a 1,5kW 3 phase drive with his Fluke T5-1000. Then he got a call on his cellphone. During the call he was totaly perplexed at the moment when his meter shows 90-100 amps. Uhm? Later we tested several multimeter. his was the only meter which totaly freaked out when calling. But his was also the oldest. the new had the problem no longer.I think dave showed this in a video for the Fluke 87

author: Richard Head
author_rank: Frequent Contributor
timestamp: April 17, 2014, 08:06:17 am
content: When I worked in a switchmode lab all the multimeters we used were Flukes as the cheaper stuff got interfered with by the high EMI levels.I think it's simply that the more expensive multimeters have a foil screen on the inside of the plastic case.Dick

author: KedasProbe
author_rank: Frequent Contributor
timestamp: April 17, 2014, 10:03:35 am
content: A constant magnetic field, not likely. A strong changing magnetic field, maybe.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 17, 2014, 01:02:58 pm
content: I know for certain that using a meter around a high field magnet (MRI) will not hurt the meter. The trick is to keep any electronic devices from the bores of the magnet by walking the perimeter of the room. I also know that digital watches can reset in / around the bore but it has no permanent effect on the watch.Of course the newest 3T magnets are a different beast and I have no experience around them. I would have to check with someone who does.

author: SeanB
author_rank: Super Contributor
timestamp: April 17, 2014, 03:58:00 pm
content: he problem with MRI is not the magnetic field but the RF punping, which will induce a very high current in anything metallic. That is why you are asked if you have fillings, implants or any other implanted metal in you. Fillings get hot in a MRI when they have your head in it.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: April 17, 2014, 04:15:26 pm
content: You are correct on the RF creating the induced current flow. But, not many people know that it is not limited to metallic objects. Patients have been known to be burnt through simply having their legs touching during part of their scan. It is rare, but I found it interesting that skin to skin contact during an MRI can cause enough current flow to burn someone.

author: SeanB
author_rank: Super Contributor
timestamp: April 17, 2014, 07:38:33 pm
content: Try the old trick of cut grapes in a microwave.