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# Accuracy of multimeter?

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#### treez

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Hello, I wish to measure the voltage across a current sense resistor with this multimeter..............

.....it is 100mA to 1A flowing through 1 Ohm.

Will i be able to measure to the nearest 5mA?

Why do you want to measure the voltage across your current sensor?
You can measure the current across it by this multimeter.
I think all the multimeters can measure the currents in range from 100mA - 1A now.
However the range of current measured by multimeter exist in its datasheet.

good luck

treez

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Points: 2
Hello, I wish to measure the voltage across a current sense resistor with this multimeter..............

.....it is 100mA to 1A flowing through 1 Ohm.

Will i be able to measure to the nearest 5mA?

This is cheap class of instrument and probably have bad accuracy of measuring. I guess he have minimal range of 200mA. You can check specification for accurancy tolerance in %.

Do you want to measure current which flowing through shunt ? If yes you can use OpAmp such as LM358 to adjust metering range, for example 0-5V for 0-20A. By the way 1Ω is more resistor as load than current shunt. Current shunt should be in range of 10mΩ-100mΩ (0,01Ω-0,1Ω).

treez

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Points: 2
Thanks, but i think the 200mA range means 0-200mA, ...at least i hope so?

It is hard to assess from the datasheet/spec, just how accurate it will be with any given flowing value of current or value of voltage.

For example, how accurately will it measure 100mV?

How accurately will it measure 100mA?

Such instruments have tolerance 100mV +/- in 20V range. And each piece of thise cheap instrument are different. Take three instruments and each will show different measurement.

My opinion is that is better to use simple opamp to make more readable voltage range for this instrument.

If you want to measure current through shunt, you should meter voltage drop on shunt ends. For direct metering with unimer you should use mV range.

Or you can simply use unimer capability to measure current in circuit in serial connection. This cheap devices have very bad current shunt inside maded from Cecas material in 100mΩ range (drop of 100mV/A).

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treez

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Points: 2
Click on "specification" below the image and it will tell you !

Brian.

treez

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Points: 2
My understanding is:

1 You are right to be measuring voltage with this multimeter rather than current, as it has no 2A range.

2 Quoted accuracy is +/-0.5%, which is probably true when new, but there are no guarantees without calibration certificate.

3 You want +/-5 mV accuracy (which equates to +/-5mA) on 2 v range. This is the same as the quoted 0.5% basic accuracy quoted, but on top of that you need to consider that display granularity is 1mV. This means that theoretical accuracy is +/-5mV with granularity 1mv, so a 11mV (11mA) spread.

4 In real life, the multimeter probably has better accuracy than quoted and +/-5mA is a reasonable expectation.

5 If certainty is what you want, then a more accurate, calibrated and certified instrument is required.

Hope my ramblings help in some way

treez

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Points: 2
Thanks,

..and as far as the spec goes, it says 0.25% accuracy over the 0-200mV range..........................but that is fantastic accuracy.............surely it cant be true for such a cheap meter?........nobody would buy a more expensive one if these cheap ones were that good?

You can simply try with experiment. Use unimer in 200mV for start and try to measure voltage drop on shunt ends (You need mV not mA).

If you need to measure current in circuit better use two resistors of 0,1Ω in parallel to get 50mΩ (0,05Ω) shunt. That shunt will make 50mV/A voltage drop.

1Ω is too much for current sense, and will make lots of heat on higher values. In your exact case you should measure voltage drop in Volts.

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treez

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Points: 2
The DVMs available are more accurate then commonly available resistors, Any one quoting a price on a 1 ohms .1% 2 W resistor? Thats where the real problem is.
Frank

treez

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Points: 2
.....nobody would buy a more expensive one if these cheap ones were that good?
I have a cheap multimeter almost identical to the one you showed. It wasn't long before the probes broke off the ends of the leads.:sad: Presumably the more expensive ones offer better reliability and longevity, if not better accuracy.

treez

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Points: 2
In real life there is no need for any accuracy greater then 1% or so. The only area where extreme accuracy is required is where the analogue voltage relates to some thing that costs real money, i.e. the alcohol content of drink where tax is paid on the alcohol percentage. Or meter calibration instruments where .1% is enough
Frank

treez

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Points: 2