Tips about testing an multimeter ...  - Page 1
Forum section: electronics / general

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 03, 2010, 10:02:17 pm
content: After getting an reference voltage and Amperes tester, plus by making my own high accuracy resistors box, I started to test my meters .By my opinion , it looks that the possibility that something can go wrong, about the meter accuracy,goes by one percentage in relation with the measured unit .For example , it less possible an meter to have issues on the DC range.Or its more possible one meter to handle well Ohm resistors , and have issues at the MOhm range.The AC measurement ( Just mains ) , its also one measurement that true accuracy is questionable.My advice in general would be , that if you do own an " non-auto range" multimeter,to get at list few high quality resistors at 0.1% , and test its range .For example one meter with resistors range like:2 - 20 - 200 ohm 2K - 200K - 2MOhm 20MOhm 200 MOhmIt can be tested with eight resistors : 1 Ohm - 10 - 100 Ohm 1K 100K 1MOhm 10MOhm 100MOhmThe 95% of the multimeters out there will never see an calibration lab due cost mostly,so my suggestion its an cheap alternative and easy to do.Currently from my collection of accuracy verification tools ,is missing one AC source , that could produce AC with base frequency above the 60Hz ,so to be able to test accuracy over bandwidth = True RMS .If some one can point out, an easy to build design, please do so .

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 03, 2010, 11:27:34 pm
content: If you have access to a good meter, use it to calibrate yours.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 04, 2010, 12:20:42 am
content: About the AC voltage generator , I did some playing with my sound generator ,and funny enough at the square wave and at triangle, it does produce AC voltage on the output .The generator it goes up to 25KHz .And I can have an 0-8V peak output.I am out of my waters with signals, but is this generator an equivalent voltage generator with low output?

author: DJPhil
author_rank: Frequent Contributor
timestamp: September 04, 2010, 02:26:19 am
content: Quote from: Kiriakos-GR on September 04, 2010, 12:20:42 amYep, in sine mode an audio generator is probably going to have a lot less noise and a bit more distortion than mains AC. If you set your signal generator to mains frequency and amplified the heck out of it you'd be able to power something just as you would from the wall socket. Most DC to AC converters use a nasty looking square wave instead, as it's easier to generate and a bit more efficient if you're not generating power mechanically.I've got a few TDA2030A audio amp chips to play with and I was considering using one with a 60Hz stable wein bridge oscillator to make a transformer test rig for all the salvaged mains transformers I've got.

author: Unknown
author_rank: Unknown
timestamp: September 04, 2010, 08:32:03 am
content: Quote from: Kiriakos-GR on September 04, 2010, 12:20:42 amThat should work fine, as long as you don't expect great stability in either frequency or amplitude. That's usually not a design goal for an audio generator (no way your ears can distinguish 1% change in amplitude, and neither can most scopes). The high AC ranges are the hard part: a few hundred volts RMS, frequencies up to the kHz range, and <1% accuracy/stability/noise. Sines are used for basic accuracy, but sometimes square waves or triangle waves are used to verify the RMS unit. Should all be documented in the service (or calibration manual) of the meter, although it will recommend 'real' calibration equipment.Quote from: DJPhil on September 04, 2010, 02:26:19 amI doubt that the distortion would be higher as long as you don't overload it. A decent audio generator will probably be <1% distortion. Mains can be severely distorted by loads like fluorescent lights or switch mode power supplies.

author: DJPhil
author_rank: Frequent Contributor
timestamp: September 04, 2010, 10:06:13 am
content: Quote from: alm on September 04, 2010, 08:32:03 amVery true, I'd forgotten about that. I was thinking of something my electrician friend mentioned, but he works mostly with unloaded systems.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: September 04, 2010, 04:46:42 pm
content: Thanks for confirming my theory ...The generator specs are :Max distortion 0,5%Output voltage : 4V ( 10V peak to peak at triangle & sine )Output voltage : 10V ( 16V peak to peak for square )Output resistance : 600 Ohm.Ok , found an nice way to kill my afternoon,at my generator , I had only install an single output plug on the case , as I used it more for sound tests,now I will add and the rest two BNC plugs , so to have all three wave outputs.And then I will start testing the multimeters with it .At the latest 100$ DMM review , Dave used as base test frequency the 3KHz and 10KHz ..Any way , I have some work ahead so to get there ...Later the rest ...