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| Brymen BM079 – Strange voltage issue |
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| monkey_magic:
--- Quote from: _Wim_ on February 04, 2024, 07:14:19 am ---As you have other meters also, can you measure the input impedance of the brymen (so the resistance between the test leads when in voltage mode). This should be around 10MOhm. Input capacitance should be around 100pF according to the datasheet, but not sure if you can measure this as an LCR meter is needed probably. --- End quote --- I've checked with my Brymen 257S which shows the input impedance of the clamp meter to be 10.30MOhms in DCV and 10.51MOhms on ACV I don't have an LCR meter unfortunately so don't think I can measure the capacitance. |
| monkey_magic:
--- Quote from: AVGresponding on February 04, 2024, 10:43:26 am ---If you're prepared to take it apart, I'd recommend checking the pcb contacts for the rotary switch; it sounds like they might be a bit worn/dirty on the range you use the most. --- End quote --- I can certainly try this, although it has always been kept in a soft case and is spotless as I'm very fussy about keeping my tools and equipment clean but perhaps there is some oxidation somewhere. |
| monkey_magic:
--- Quote from: J-R on February 04, 2024, 10:11:39 am ---My AMP-330 is about 90pF and 10M on the input. I ran some more tests and the slow counting up only happens below about 1.62V. Above that it's instant, but if you let it start going down, say from 1.65V to 1.1V, then reconnect, it sits there for a while then slowly counts back up. Around 2V and above it's always snappy up and down. --- End quote --- I have just tried it on a 1.5V AA battery and timed it - to get from 0V to final reading of 1.5V took just over 13.5 seconds, or as near as I could react to stop the timer. I doubt I would have noticed a couple of seconds to register the voltage, but I am very certain it didn't perform like this previously. I simply would have noticed before now! I'm curious, I wonder if you could please time how long yours takes to count up to the same voltage. I have also replicated the situation from earlier using a 12V AC SELV lighting unit attached to a 35W halogen bulb to act as a load. The Brymen 257S on ACV shows 8.69V The Brymen 079 on ACV fluctuates between 0.1 and 0.9V |
| J-R:
I think I've figured out why you remember it being faster previously. Change the mode from DC only to DC+AC|VFD. |
| monkey_magic:
--- Quote from: J-R on February 05, 2024, 06:26:47 pm ---I think I've figured out why you remember it being faster previously. Change the mode from DC only to DC+AC|VFD. --- End quote --- I've just tried it on this mode and the time has reduced to ~ 7 seconds. This still seems quite a lot longer than I remember, although I'm not sure how this compares with yours? I'm pretty sure I would have previously measured only on the DC scale but I certainly could be mistaken. Any ideas on why it doesn't measure the AC voltage correctly? I’ve just tried it on all three voltage modes and it shows zero. The only thing I can think of is that being an electronic (dimmable) downlight driver it probably doesn't have a very clean AC waveform, but even so this seems strange it can’t see anything when other meters can. This is not the same driver I originally had the problem with, but a similar style of unit I have laying around to try and simulate the scenario. I always grabbed this meter in preference if I had to go out to do a quick job as it had all the functions I usually needed and I’ve never had cause to question it up to this point, but I've lost confidence in it somewhat. I know I shouldn’t rely on it for safe isolation, but even so… :-\ |
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