Help, how can I calibrate AC current - Page 1
Forum section: electronics / testgear

author: daisizhou
author_rank: Super Contributor
timestamp: June 10, 2023, 01:38:00 am
content: Hello everyone.I plan to calibrate a multimeter,I don't have a standard signal source for its AC current.Currently, I only have one digital oscilloscope and a 20M signal generator.Is there a good way to calibrate it? If you know, please let me know. Thank you

author: Fungus
author_rank: Super Contributor
timestamp: June 10, 2023, 01:40:55 am
content: What multimeter?

author: radiolistener
author_rank: Super Contributor
timestamp: June 10, 2023, 01:47:12 am
content: You can use oscilloscope to calibrate DMM RMS Voltage measurement. Just enable RMS measurement on the oscilloscope and setup proper calibration voltage on generator, then apply it to your DMM for calibration procedure.For RMS current - connect generator through DMM to a dummy load and use RMS measurement on oscilloscope to measure voltage drop on the dummy load and to setup proper calibration current by tuning generator amplitude, then calibrate DMM.When you know dummy load R and RMS voltage U, you can calculate RMS current with Ohms law: I = U / RBut note, that high frequency is sensitive to a wire configuration and can be affected with ringing due to wave reflections from impedance mismatch. So, use 50-1000 Hz for calibration.

author: Fungus
author_rank: Super Contributor
timestamp: June 10, 2023, 02:30:02 am
content: Quote from: radiolistener on June 10, 2023, 01:47:12 amAccuracy will be very limited.

author: daisizhou
author_rank: Super Contributor
timestamp: June 10, 2023, 04:10:01 am
content: I am referring to the AC current level

author: daisizhou
author_rank: Super Contributor
timestamp: June 10, 2023, 04:11:51 am
content: I understand, but different load resistors are required. Is there the simplest way?

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 10, 2023, 04:38:42 am
content: Not with those instruments.You could put another properly calibrated ammeter in series with the one to be calibrated. It's accuracy should be three or four times higher than what you're are trying to calibrate.The proper way is to use something like a Fluke 5080... But those are pretty expensive.

author: Fungus
author_rank: Super Contributor
timestamp: June 10, 2023, 04:58:10 am
content: Quote from: Kim Christensen on June 10, 2023, 04:38:42 amYep. This is really the only way.Even so, creating an AC current source isn't going to be easy. A signal generator won't do it past a few mA. Maybe you could do it with an audio amplifier.

author: daisizhou
author_rank: Super Contributor
timestamp: June 10, 2023, 05:13:15 am
content: I have successfully completed the DC voltage and DC current calibration。Unable to complete AC part calibration, including voltage and current,I also have an 8920a voltmeter, but I don't have an AC source, and an AC source that can change frequencyIs there an easy way, I mean make a PCB in my spare time to make it a standard source for AC calibration, used to calibrate AC voltage or current

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 10, 2023, 09:29:49 am
content: Again, as Fungus already asked, what meter are you calibrating?Most current meters measure the voltage over a shunt resistor of some known value, and you can do the same, except by using a higher value shunt resistor. For example, with a 10Vac test signal and a 100Ohm resistor (inclusive wiring and the shunt in your DMM to be calibrated) you get a 100mA test signal. Then measure the exact voltage over the 100 Ohm resistor to get the current, and adjust the DMM under test to display that same current.You write you don't have an AC source, so get some (half) decent function generator, and maybe combine that with some audio amplifier.

author: daisizhou
author_rank: Super Contributor
timestamp: June 10, 2023, 11:03:41 am
content: This instrument

author: radiolistener
author_rank: Super Contributor
timestamp: June 10, 2023, 03:10:09 pm
content: If you want to calibrate it with a good precision, you're needs another DMM with much better precision class which is already calibrated, so you can connect both DMM in a series between your signal generator and dummy load and calibrate one DMM by check value on second DMM which is already calibrated.Oscilloscope has precision about 5% which is probably much worse than your device, so if you calibrate it with your oscilloscope it will have very bad calibration and show you more than 5% error.

author: daisizhou
author_rank: Super Contributor
timestamp: June 10, 2023, 11:53:32 pm
content: Thanks.I understand what you mean.I completed the calibration plan for DC voltage and DC current using Fluke 8060a.But for the AC part, I don't have any AC power supply,AC power supply, I mean the type of AC power supply that can change frequency.So I am unable to complete the AC part of the test

author: radiolistener
author_rank: Super Contributor
timestamp: June 11, 2023, 12:01:30 am
content: Quote from: daisizhou on June 10, 2023, 11:53:32 pmYou can use your signal generator as AC current source. But if you connect it directly it provides too small current, about 100 mA max or even smaller. But you can attach high power audio amplifier to your signal generator and use output of power amplifier.For example, 100W output from power amplifier on 8Ω dummy load provide you about 3.535 Amps RMS current. But don't use speaker as a dummy load! Speaker is reactive load, it will give you wrong results. Use non inductive dummy load.But you're needs another DMM which has better accuracy and is already calibrated, so you can use it to check actual value.

author: J-R
author_rank: Super Contributor
timestamp: June 11, 2023, 12:03:39 am
content: Are you sure you're reading the calibration procedure correctly? I do not find that it uses anything other than a 190.0mA DC source for the mA calibration and 100mA over 1.9 seconds for the mAs calibration. Even the portion where you are in AC mode you are simply verifying the rectifier circuit by applying a negative DC current and checking that it shows a positive value instead. All other ranges and inputs are only used for verification of proper operation and cannot be adjusted.Appears to be sold by many companies: Fluke, Keithley, Inovision, CardinalHealthFluke manual:https://assets.fluke.com/manuals/35035___omeng0000.pdf

author: daisizhou
author_rank: Super Contributor
timestamp: June 11, 2023, 01:01:14 am
content: I have read this manual.As described in the manual, I have completed the calibration of the DC section,So I tried using a 19V small transformer with 220V AC input and 19V AC output.I use this 19V AC voltage and test it on a 19 ohm non-inductive resistor.I found that the current at this time is inconsistent with Fluke8060a,So I suspect that the communication part is malfunctioning.So I hope to test the AC current again