AC current measurement digital multimeter - Page 1
Forum section: electronics / testgear

author: arivel
author_rank: Regular Contributor
timestamp: October 14, 2023, 07:00:36 am
content: Hi everyone .I am not referring to a particular model but in general to all digital multimeters.When making an AC current measurement, which frequency range can I use? .I have never thoroughly investigated how multimeters measure alternating current, can you explain it to me? perhaps the measurement is related to the RMS voltage value?.

author: jonpaul
author_rank: Super Contributor
timestamp: October 14, 2023, 07:51:18 am
content: Chinese, consumer, cheap: $100< mains..1k Hz perhaps 2..5% accuracy avg respond.>$500 , HP, Keysight, Fluke 4.5..6.5 D TRMS mains...10k...200kHzj

author: Kleinstein
author_rank: Super Contributor
timestamp: October 14, 2023, 08:01:59 am
content: It depends on the models. Usually there are specs to show the frequency. Something like up to some 1 kHz maybe a bit more is common for cheap meters, but there are exceptions.With modern chip sets there are also relatively cheap (e.g. $25 range) RMS responding meters with a limited maximum frequency of some 1-3 kHz.Better handhelds may work up to some 50 or 100 kHz.Frequencies much below 40 Hz often don't work well, as there is a balance with the response speed.The precision of the current ranges is anyway often not that good. So here it is not just the AC part but also just the shunts, especially for larger currents with significant self heating or effect of the solder joints.

author: AVGresponding
author_rank: Super Contributor
timestamp: October 14, 2023, 08:38:02 am
content: The Fluke 8060A still stands out, for this type of measurement...https://assets.fluke.com/manuals/8060a_3vimeng0200.pdf

author: arivel
author_rank: Regular Contributor
timestamp: October 14, 2023, 11:17:03 am
content: Thank you

author: J-R
author_rank: Super Contributor
timestamp: October 14, 2023, 11:02:56 pm
content: If AC current measurements are important, then you absolutely need to dig deep into the DMM specifications because it's a relatively complex interaction between frequency, range and accuracy.Some DMMs may function outside the specifications charts, but the accuracy can be listed as undefined and it's not a calibration point (the 34401A and the 10mA AC range is a fun one).Fluke 8060a:Fluke 287/289:34401A:34461A:Brymen BM23x:Brymen BM78x:Brymen 86x:

author: Hexley
author_rank: Regular Contributor
timestamp: October 14, 2023, 11:16:13 pm
content: Quote from: arivel on October 14, 2023, 07:00:36 amYou might find this work by forum member HKJ interesting.https://lygte-info.dk/info/DMMFrequencyResponse%20UK.htmlThis is for voltage response, but is interesting none the less.

author: J-R
author_rank: Super Contributor
timestamp: October 14, 2023, 11:48:06 pm
content: Also, to measure frequencies beyond what a DMM can do, consider an oscilloscope current probe.

author: bdunham7
author_rank: Super Contributor
timestamp: October 14, 2023, 11:49:00 pm
content: Quote from: arivel on October 14, 2023, 07:00:36 amThe meter will run the current through a shunt resistor of a known value and then measure the voltage across that. So if it has a 1 ohm shunt and it measures 20mVAC across it, it will tell you that the current is 20mA. The frequency range that the meter can measure current are thus limited to the frequencies at which it can measure voltage accurately. Typically the current response is even less accurate at higher frequencies because there are additional sources of error in the current circuit.

author: BillyO
author_rank: Super Contributor
timestamp: October 14, 2023, 11:50:20 pm
content: Quote from: arivel on October 14, 2023, 07:00:36 amI feel no one has yet answered you question.What happens is the signal is passed through a resistor (called a shunt) then the voltage across the shunt is measured in the usual way as voltages and scaled to a current reading. As mentioned some really cheap DMM meters and older passive analog meters just give you an adjusted average, but most DMMs these days over about $50 will give you what is called a True RMS value. This means you'll get the RMS value even if what you are measuring is not a perfect sine wave.Edit: Looks like Mr. Dunham beat me to it by a few seconds...

author: J-R
author_rank: Super Contributor
timestamp: October 15, 2023, 05:16:07 am
content: If you check the AC voltage specifications of the previously mentioned DMMs, you will see the current measurement specifications have greatly reduced frequency limits. Shunts can become problematic at high frequencies due to inductance, capacitance and skin effects which must be accounted for. This feature is not going to be a high priority for a typical DMM design, since there are other products far better suited for this task.

author: jemarro12
author_rank: Contributor
timestamp: October 15, 2023, 10:25:35 am
content: UT181A: