I have an VOM BEST 9205M, I wonder that if I use the AC current measurement to measure a DC current, what will happen, will the VOM break. And in other hand, if I have an AC but use the DC current measurement to measure it, what will happen. Hope you guys can help me with this. Thank you so much

 

Welcome to AAC.

You will get inaccurate readings, but as long as you don’t exceed the current capacity of the range nothing else.

 

Depending on the frequency, if you measure an AC signal (that has no average, or DC, component) with a DC instrument, you will get a reading of zero. Going the other way is a bit harder to predict because it depends on whether there is a DC blocking capacitor in the path.

As long as the peak applied voltage is within the allowed limits of the meter, it shouldn't damage it, you just get useless readings.

 

Depending on the frequency, if you measure an AC signal (that has no average, or DC, component) with a DC instrument, you will get a reading of zero. Going the other way is a bit harder to predict because it depends on whether there is a DC blocking capacitor in the path.

As long as the peak applied voltage is within the allowed limits of the meter, it shouldn't damage it, you just get useless readings.

Thank you so much for your sharing. I'm really grateful

 

Welcome to AAC.

You will get inaccurate readings, but as long as you don’t exceed the current capacity of the range nothing else.

Thank you so much for your sharing. It helps a lot

 

It is difficult to measure amplifier output with any AC or DC test meter. Many test meters on AC range are intended for measuring 50Hz or 60Hz AC LINE signals only. If you want to measure amplifier output it is better to use an oscilloscope.

 

A current meter has a resistance (the shunt) in series with the load. Then the resistance reduces the actual current of the circuit which also reduces the voltage at the load (voltage divider).

 

As your meter has both AC & DC current ranges I assume the question is academic.

The logical reason to ask being to determine if the meter will be damaged by selecting the wrong position on the range switch and the answer should be no provided you do not exceed the rating of that range, so the 20A range should cope with 20A DC or 20A AC RMS, or a combined waveform (AC with a DC offset) providing its RMS value does not exceed 20A.

Although I do not have personal experience with this meter I might hesitate to maintain the full 20A for a sustained period as cheap meters are often designed with little margin to keep costs down.

Also having looked at the specification for your meter it does not appear to be true RMS, hence measuring any AC signal that is not a true sinewave will result in the wrong value being displayed, also beware that there may be errors at higher frequencies - you would have to check the meter's manual to see how its accuracy is affected by frequency.

To comment on a previous answer, some meters can give accurate results at high frequencies - I have a true RMS one that is accurate to 0.04% at up to 20kHz, 0.1% up to 50kHz and 0.55% up to 100kHz, it comes down to cost and a suitable oscilloscope would be much cheaper than that meter.