Products > Test Equipment
Multimeters With Low Ohms Function
AVGresponding:
--- Quote from: ermionesrl on January 18, 2022, 03:00:43 pm ---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.
--- End quote ---
Given the two meters that were the most difficult in this regard were the Metrix MX 57EX and the Agilent U1401B, I think this unlikely. The Agilent in particular is a process calibrator; its outputs are in my experience very stable. There must be another explanation, perhaps the meters are cutting the current back once the ohms over-range is detected for an extended period, in order to extend battery life a fraction?
Neutrion:
When you measure the volts with the BM869 in high Ohms range, is there any difference, if you measure the peak value with a scope?
--- Quote from: Per Hansson on January 16, 2022, 02:57:59 pm ---Should not the name of the thread (and any future video) include the word power or compliance voltage?
As I read it now it sounds like a meter that can show low resistances, like a 4-wire measurement or the dedicated low ohms mode of the Fluke 289?
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Good point. And the whole topic started because of the false beeps on continuity mode, which we forgot.
Hovewer it is also an interesting topic, and that is what can be annoying with many meters.
Kleinstein:
Ideally you want the choice:
High current is wanted to measure small resistors.
High voltage is needed to test higher voltage diodes, maybe even zeners and also high resistors work better this way.
A high voltage (e.g. >5 V) may however damage sensitive parts (e.g. LEDs, Transistors with BE in reveerse).
Not too high a current may be preferred for very small, temperature sensitve resistors.
A very limited voltage is needed for testing contacts in dry ohms, not braking through oxide films.
So no one setting is good for all. Only a few meters have different setting for the different jobs. For the usually limited resolution of hand held DMM the power from the test current is rarely a problem. It is more with some bench meters where the power could go over the top, like 10 mA with 12 V open circuit (and maybe 8 V with current ?) for the 3458 in the 10 Ohms range.
The beeps with a capacitor are a 2 sided thing: they can be confusing if you don't know about it. The can even help to detect capacitors. With a fast reacting beeper, there is no good way around it - waiting for a stable voltage would be a bit over the top and make the reaction slow.
AVGresponding:
--- Quote from: Neutrion on January 18, 2022, 07:28:07 pm ---When you measure the volts with the BM869 in high Ohms range, is there any difference, if you measure the peak value with a scope?
--- End quote ---
I'll give it a poke. I'd expect the relatively low impedance of a scope/probe to have a marked effect.
Neutrion:
--- Quote from: Kleinstein on January 18, 2022, 08:19:06 pm ---Ideally you want the choice:
High current is wanted to measure small resistors.
High voltage is needed to test higher voltage diodes, maybe even zeners and also high resistors work better this way.
A high voltage (e.g. >5 V) may however damage sensitive parts (e.g. LEDs, Transistors with BE in reveerse).
Not too high a current may be preferred for very small, temperature sensitve resistors.
A very limited voltage is needed for testing contacts in dry ohms, not braking through oxide films.
So no one setting is good for all. Only a few meters have different setting for the different jobs. For the usually limited resolution of hand held DMM the power from the test current is rarely a problem. It is more with some bench meters where the power could go over the top, like 10 mA with 12 V open circuit (and maybe 8 V with current ?) for the 3458 in the 10 Ohms range.
--- End quote ---
I hope if Dave does the video, he will cover also some practical and theoretical cases for damage.
But from the cited document above, with the 100uA "for less damage" so far we only got PTC and NTCs if I understand right. Or are there any other "temperature sensitive resistors" which we can encounter?
And I don't mean the 12V with 10mA, but the average handheld meters current and voltage.
--- Quote from: Kleinstein on January 18, 2022, 08:19:06 pm ---
The beeps with a capacitor are a 2 sided thing: they can be confusing if you don't know about it. The can even help to detect capacitors. With a fast reacting beeper, there is no good way around it - waiting for a stable voltage would be a bit over the top and make the reaction slow.
--- End quote ---
I was thinking about doing two really fast measurement. If the second shows less current, than there would be no beep because of capacitance. If they are equal, than comes the beep. Obviously it would need a dedicated circuit.
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