| Products > Test Equipment |
| Low R measurement on a DMM |
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| AVGresponding:
--- Quote from: 2N3055 on March 30, 2023, 12:00:06 pm --- --- Quote from: pope on March 30, 2023, 09:26:45 am ---The meter I'm using is a Brymen BM869s but as it has mentioned even a 4W meter isn't suitable for this job. Probably a hi-pot tester is the appropriate instrument for such measurements but unfortunately I can't afford one at the moment (they seem to go for over 1k) and secondly I don't feel very confident to use one as I've never done it before. AFAIK, you have to somehow discharge the DUT after the test and I have no idea how to do this. Also, although I appreciate the DIY recommendation I don't feel competent to to do it myself. So, I was wondering whether a PAT tester would be sufficient. For some reason it's almost impossible to buy one in EU. It seems to be a UK thing. Searching around I found this one (which will set me back a bit over 500 euro) but I don't know anything about its quality and whether it makes sense to buy one. For example in a youtube video there's the following comment: "I would love to know how this even qualifies as a PAT tester, it has a FAIL threshold of two Meg on a class one device according to the manual, yet the official threshold is one Meg. On a class two device it has a fail threshold of four Meg, when the the official threshold is two Meg, this all seems so very wrong when other testers are correctly calibrated, and this one seems to pass items other machines would fail." https://www.firststopsafety.co.uk/product-page/memorypat-tester-with-display-and-memory --- End quote --- Are you confusing earth continuity tester (that tests that grounding wiring is low enough resistance) with an insulation meter (HI Pot that tests that insulation is proper i.e. very high resistance)? That tester has both of these functions. It can test insulation leakage from live to ground with 500V applied, and separately with 150mA it can test that housing is connected to earthing on plug with low enough resistance.. As for insulation test, more is better .. few MΩ is already very low resistance... If instrument threshold is 4MΩ and standard is 2MΩ it means tester is more rigorous than standard, which means it errors on the safe side... Which means it will show failed on some marginal devices that would PASS on strictly calibrated devices. Problem is that even 4 MΩ is actually very bad insulation on most devices outside industrial environments.. 100W toroidal transformers i tested recently had resistance between primary/secondary in GΩ ranges. One that was outside in damp, salty, environment for 5+years was more than 50 MΩ still... --- End quote --- Heating elements in ovens/hobs etc can have quite low insulation resistances from cold, due to absorbed moisture. If it has a resistance of 100k or so it's a pass, and you're supposed to run it for a while before testing it again. I did fail one once and refused to turn it on; the measured insulation resistance was zero... don't think turning it on would have been a great idea. Was in a secondary school home ec lab... |
| pope:
--- Quote from: DX1 on March 30, 2023, 06:24:59 pm ---Please can you explain what you are trying to do? If low resistance PE to case and do not need to test to specification and have a power supply, Set current limit on power supply to 1A, connect the points you wish to test. Then measure the voltage drop with the Brymen. Thus use Ohms law to calculate resistance. Wire it 4 wire, which means that you connect to the measuring points, not to the power supply leads or clips. You can measure the power supply current as well to improve accuracy. --- End quote --- I build a fair amount of diy audio stuff with linear power supplies and I would like to be able to test for safety. Some of these devices are being used by other people too. |
| AVGresponding:
It's not often you see Class I audio gear, normally it's Class II..? At least in domestic settings, obviously pro grade stuff that goes on stage and tour will have a PE. It does sort of sound like a PAT/ISITEE machine is what you need, if you're making Class I devices. An installation tester will do an insulation resistance test, but it won't be able to test the PE with any significant current. If you're making Class II devices, any insulation tester would be fine, I should think. |
| pope:
--- Quote from: AVGresponding on March 31, 2023, 01:27:31 pm ---It's not often you see Class I audio gear, normally it's Class II..? At least in domestic settings, obviously pro grade stuff that goes on stage and tour will have a PE. It does sort of sound like a PAT/ISITEE machine is what you need, if you're making Class I devices. An installation tester will do an insulation resistance test, but it won't be able to test the PE with any significant current. If you're making Class II devices, any insulation tester would be fine, I should think. --- End quote --- As far as I'm concerned, almost all pro audio equipment has PE and in most cases it's class I. Definitely all the gear I make. Don't quote me on this one, but I believe some PAT testers can be plugged on the mains and provide a significant higher current than the battery powered ones (?). Tt least according to this video (3:40) but this specific model seems to be discontinued. |
| AVGresponding:
--- Quote from: pope on April 01, 2023, 10:40:52 am --- --- Quote from: AVGresponding on March 31, 2023, 01:27:31 pm ---It's not often you see Class I audio gear, normally it's Class II..? At least in domestic settings, obviously pro grade stuff that goes on stage and tour will have a PE. It does sort of sound like a PAT/ISITEE machine is what you need, if you're making Class I devices. An installation tester will do an insulation resistance test, but it won't be able to test the PE with any significant current. If you're making Class II devices, any insulation tester would be fine, I should think. --- End quote --- As far as I'm concerned, almost all pro audio equipment has PE and in most cases it's class I. Definitely all the gear I make. Don't quote me on this one, but I believe some PAT testers can be plugged on the mains and provide a significant higher current than the battery powered ones (?). Tt least according to this video (3:40) but this specific model seems to be discontinued. --- End quote --- Yes, the mains powered units can push up to 30A or so. Battery ones probably don't do any better than a couple of hundred mA, but I never use those so couldn't say for sure. Do you need a new unit? There's plenty on the used market, though I expect shipping on a mains one would be a bit dear; they're all quite heavy due to their big transformers. If you do have to buy new, Seaward, Kewtech, Martindale, Megger, are all quite expensive brands. Not sure if Robin are still around, but I believe Uni-T make these now, and there are probably other Chinese tier 2 brands at it. |
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