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| Multimeters With Low Ohms Function |
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| David Hess:
Tektronix DMM916: Ohms 860 millivolts 0.41 milliamps Low Ohms 280 millivolts 0.03 milliamps Continuity Test 3.2 volts 0.41 milliamps Reads out ohms Diode Test 3.2 volts 0.41 milliamps Reads out volts Beckman RMS225: Ohms 650 millivolts 0.78 milliamps Continuity and Diode Test 3.2 volts 3.2 milliamps Reads out volts Tektronix DM501: Ohms 10.6 volts 1.0 milliamps 2k ohms range Tektronix DM502: Ohms 11.2 volts 1.0 milliamps 200 and 2k ohms ranges --- Quote from: Neomys Sapiens on January 17, 2022, 06:31:28 pm ---Another very good reason for a low test voltage and limited energy would be the presence of squibs/detonators. --- End quote --- Electrical squibs and detonators are deliberately designed to be as difficult to trigger as possible. They require high voltage at high current. |
| Neomys Sapiens:
The DM501 and DM502 don't have that switch. The 'A' models are completely different. -> TEKWiki |
| AVGresponding:
Well, that was as much work as doing the whole test before! The settling time is very long, due of course to the low currents involved. Two meters refused to settle, rising to a peak over a number of seconds, then falling continuously (but very slowly) beyond the point of my patience and in the case of the Metrix, beyond the limit of the auto power off. There is a broad pattern, but with exceptions, as you'd expect. |
| ermionesrl:
AVGresponding: Interesting: it seems that many multimeters use the same way as 34401A to measure >10Mohm, by inserting a parallel known 10Mohm resistor and do calculations. It's evident when the open circuit voltage is the result of the test current over 10Mohm, and when your previous measurement is the result of the test current over 5Mohm. About the fact that some didn't settle, I think that the voltage source is not very well stabilized and thus reflect the battery voltage, that fall continuously during the test. If they use a ratiometric method against a known resistor (like original Fluke 87), both the current and the voltage need not to be stable over a timespan longer than the 2 adc samples. |
| Neutrion:
--- Quote from: kripton2035 on January 16, 2022, 03:46:28 pm --- --- Quote from: Neutrion on January 16, 2022, 01:32:20 pm ---If the beeping function is as fast as on the Brymen, you can just start to probe around any circuit for shorts, to see wether you get any short false beeps where there are no shorts. But again, this only happens if the beeper function is fast enough. But if you did not design your circuit to avoid it, it would be a wonder if it would work. --- End quote --- the bip on the shorty has an audio tone proportionnal to the value of the short. so if there is a charging capacitor, the tone is changing, and you can hear it. --- End quote --- So there are no sudden beeps with your gear at all where there is no continuity, like with fast meters? Is it latched? --- Quote from: AVGresponding on January 17, 2022, 09:55:12 pm ---Well, that was as much work as doing the whole test before! The settling time is very long, due of course to the low currents involved. Two meters refused to settle, rising to a peak over a number of seconds, then falling continuously (but very slowly) beyond the point of my patience and in the case of the Metrix, beyond the limit of the auto power off. There is a broad pattern, but with exceptions, as you'd expect. --- End quote --- Nice spreadsheet, thanks for it! I also measured the BM789, but I don't have a high Z meter so I measured with the scope instead. Vcont (with 10MOhm meter) 2,38V p-p (with scope) 2,56V A in cont (with 10Ohm meter) 0,35mA V High Ohm (with 10MOhm meter) 0,221V p-p(with scope) 3,52V V in Low Ohm (with 10MOhm meter) 2,38V p-p(with scope) 2,56V A in low Ohm 0,35mA. Edited to make it more clear. It seems to differ from its specs as the open circuit volts in Ohms supposed to be less than 1,3V and less than 1,5 V for the 600 Ohms range. And there is no nifference in manual range. So only NTCs and PTCs are problematic? |
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