Voltage not matching - Page 1
Forum section: electronics / general

author: Jan Audio
author_rank: Frequent Contributor
timestamp: January 31, 2021, 05:46:09 pm
content: Hi, i have a new GW-instek GP4323 PSU.If i set the output to 5 volt, my aneng 8008 measures 4,9 volt.I have the feeling the aneng is correct, and my new PSU not good calibrated.What can i do to verify, the PSU has a nice calibration certificate, only with nothing connected it still measures some milliampere on channels 2 3 and 4.I need to have everything exactly calibrated, so it matches the final product and its tollerances, i need it to have the lowest value presicion trimmers in my design.

author: TiN
author_rank: Super Contributor
timestamp: January 31, 2021, 06:15:09 pm
content: Why you need everything exactly matching?Your total error is a combined uncertainty of both your DMM and PSU. If you get better DMM (e.g. calibrated 34401A) then you can use your PSU with much better accuracy by discipline output with 34401 readings. So evaluate your product accuracy requirements and use suitable equipment to verify it. Usually 10x improvement in accuracy means 50-100x increase in cost.

author: MK
author_rank: Regular Contributor
timestamp: January 31, 2021, 06:34:19 pm
content: Hi, it is a £10 multimeter, can you believe the cal cert that came with it? the PSU did not come up on google, so not sure what limits they state for the displays.If you are making something to sell then you need to trust that your measurements are safe. That means working out the accuracy level that matters for your product, then buying something that lets you get that. I fully agree with TiN about this. It might be that you only need 10% accuracy if the design is forgiving enough, but it is down to you to work out if either of those units is up to the task you require of them.

author: wraper
author_rank: Unknown
timestamp: January 31, 2021, 06:39:29 pm
content: Multimeter shows 4.9V or something like 4.980? I don't like such rounding. Also AN8008 is not something you should trust without confirmation by other meter.

author: dietert1
author_rank: Super Contributor
timestamp: January 31, 2021, 06:55:44 pm
content: The product is GPP-4323.If you search the technical description for "accuracy" it says current readback +/- 10 mA, voltage readback +/- 10 mV. Plus tolerances for voltage setting. If your supply violates the specs, you should return it.Regards, Dieter

author: WattsThat
author_rank: Frequent Contributor
timestamp: January 31, 2021, 08:15:23 pm
content: From the device datasheets:The ANG8008 is +/-0.5% + 3 digits on DCThe GPP4323 is +/-0.03% + 10mv for voltage displayThe meter circuit of the GPP4323 is more accurate than your DMM and it has been calibrated. The cheap Chinese DMM has no calibration certification and is significantly less accurate.Why do you doubt the accuracy of the power supply? Have you ever checked the DMM against a known standard? Until you have a meter with a known accuracy, every measurement you make is of unknown accuracy.It simply defies logic to think an uncalibrated +/-0.5% accuracy meter would be more accurate than a calibrated +/-.03% accuracy meter.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 01, 2021, 02:17:38 pm
content: Thanks all.It reads : 4.900Ok the PSU should be more accurate, this dont say something can be wrong calibrated, maybe someone already returned it before me ?What i seen on this site and reviews is people are happy with the accuracy of the AN8008.Thank you Dieter, i will take a look into this and make more posts about this if it is out of range.Suppose i find some voltage standard, can i calibrate this myself in the menu ?, it also has relays so maybe more voltage standards are needed for each relay setting ?I dont feel like sending this brick back to taiwan for calibration.Suppose i buy a very expensive multimeter to compare it with, it can also be calibrated wrong by someone drunk or out of time.Maybe i should go check how much each channel is different.

author: wraper
author_rank: Unknown
timestamp: February 01, 2021, 02:29:40 pm
content: If you have 7805 vreg IC, check your multimeter against its output voltage. It should read significantly closer to 5V than 4.9V if multimeter works correctly.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 01, 2021, 02:48:06 pm
content: Yes that i forgot to tell, the voltage regulators are measuring good on the 8008.I am searching for a valid meter now, cheaper then having a 600 euro brick thats not good.

author: wraper
author_rank: Unknown
timestamp: February 01, 2021, 02:54:46 pm
content: Then IMHO you should return PSU as faulty.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 01, 2021, 03:13:53 pm
content: Thanks, i will do some more testing and make a movie from all channels and voltages.So 4.900 is out of range ?, ok thanks.

author: Grandchuck
author_rank: Super Contributor
timestamp: February 01, 2021, 04:46:31 pm
content: At 5 volts, the actual value could be from 4.75 to 5.25 volts (that's a guess, as I do not own this supply). My guess is based on a plus/minus 5% specification. Actually, I would expect better performance from a new unit.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 01, 2021, 04:49:02 pm
content: Quote from: WattsThat on January 31, 2021, 08:15:23 pm5 volt to 4.9 volt is 2 whole %, that is alot different then should.

author: TiN
author_rank: Super Contributor
timestamp: February 01, 2021, 11:37:23 pm
content: Again, you cannot claim GPP4323 output in or out of the spec with your 0.5% DMM, it isuselessfor the job. Agreement or disagreement between your DMM and PSU is not really important in your case. You trying to measure more precise and accurate device with less precise meter. It's like you trying to calibrate digital watch to milliseconds by looking at the sun's shadow from a crooked tree.Power supply could be generating perfect 5.0000 VDC but you will never know it unless you have adequate DMM with accuracy better than 0.015% (x2 TUR would be minimum requirement, better is more).Per spec GPP4323 programmed to 5V have readout within 4.9632 to 5.0368 VDC.

author: wraper
author_rank: Unknown
timestamp: February 01, 2021, 11:51:16 pm
content: Quote from: TiN on February 01, 2021, 11:37:23 pmPer spec ≤±(0.03% + 10mV), built it meter should read between 4.988 to 5.012V at 5V of actual output voltage and setting accuracy is exactly the same. So if PSU reads 5.000V exactly, actual output voltage must be within this range. As OP said that his multimeter (4 full digits of resolution) agrees with Vreg ICs he has, IMHO it's way more probable that his PSU is faulty or was improperly calibrated at factory.

author: guenthert
author_rank: Frequent Contributor
timestamp: February 02, 2021, 12:05:08 am
content: Quote from: wraper on February 01, 2021, 11:51:16 pmMoreplausible. There's just not enough data available to us to invoke statistics here.If to Jan the difference between 4.9 and 5V is important for whatever reason, then I think he's best advised to buy, borrow or steal someone else's calibrated DMM or voltage standard. I don't think we can progress here otherwise.

author: bdunham7
author_rank: Super Contributor
timestamp: February 02, 2021, 12:08:20 am
content: Quote from: TiN on February 01, 2021, 11:37:23 pmHe's not calibrating it, he's claiming it is broken. I can infer by the suns shadow of that crooked tree that my watch that tells me it is midnight is wrong. I'm no Aneng fan, but I'd bet money it is off by less than 10 counts from a 'calibrated' 5 volts.

author: wraper
author_rank: Unknown
timestamp: February 02, 2021, 12:11:43 am
content: Quote from: guenthert on February 02, 2021, 12:05:08 amIf you pay ~$600 for PSU, expectation for it to be within spec a pretty serious reason.

author: TiN
author_rank: Super Contributor
timestamp: February 02, 2021, 12:19:43 am
content: QuoteOne can draw any number of digits in resolution. It does not mean anything in terms ofaccuracy. One can have 8-digit meter with bad calibration that will give out 2 digit accurate results, instead of expected 6 digits. This is common misunderstanding and education problem. Thinking that buying 6.5-digit meter will get you 6 digits of accuracy is very incorrect.QuoteWhat is Vreg ICs and what is calibrated (verified) accuracy of their outputs?At this point this thread is pure guesswork. I don't see any possible evidence about PSU being faulty (or working properly either) without actual measurements with better calibrated DVM. But if I'd be guessing, PSU should be ok, unlike 15$ aneng thingy.

author: wraper
author_rank: Unknown
timestamp: February 02, 2021, 12:22:14 am
content: Quote from: TiN on February 02, 2021, 12:19:43 amIt's rare to see genuine 7805 which is more than 50mV off. And usually they are within 20mV.

author: TiN
author_rank: Super Contributor
timestamp: February 02, 2021, 12:26:17 am
content: Maybe Jan Audio got lucky and have non-genuine (whatever that means) 7805 which is 0.2V off.If we look at μA7805C (genuine enough?) it is specified for amazing +/-4%.Useless to even verify aneng DVM own 0.5%, leave alone +/-0.03%+10mV PSU.Next is what, 9V battery with its +/-20% ?It's like putting measurements triangle upside down. Novel, trendy but completely wrong.Proper reference would be something likePentaRefor Ian'sPDVS2 mini.

author: wraper
author_rank: Unknown
timestamp: February 02, 2021, 12:31:34 am
content: Quote from: TiN on February 02, 2021, 12:26:17 amBut you will not have all ICs that far off. Not to say most of 7805 have 2-3% max tolerance at room temperature. But the same as with other components, they seldomly reach tolerance boundaries.QuoteYou can boast about proper metrology as much as you want. But common sense tells that his PSU most likely is the culprit.

author: bdunham7
author_rank: Super Contributor
timestamp: February 02, 2021, 12:36:39 am
content: Quote from: TiN on February 02, 2021, 12:19:43 amWell one or the other isbroken, or at least not performing to advertised specs. Digits and specified tolerances aren't the issue . The fact that the Aneng is specified less precisely doesn't mean it is more likely to not meet that spec.

author: TiN
author_rank: Super Contributor
timestamp: February 02, 2021, 12:40:51 am
content: If OP would want just 3% (for most seldom lucky readings) I'd think he wouldn't create thread?OP didn't post any details about how he tested things, what was the load, measurement points and configuration. Maybe OP used DVM on 1kV rangeEngineering does not work on luck or hopes, it's run by numbers and quantified measured data with known accuracy.Here accuracy of DVM is not enough to verify accuracy of source. End of the story, full stop.

author: wraper
author_rank: Unknown
timestamp: February 02, 2021, 12:42:57 am
content: Quote from: TiN on February 02, 2021, 12:40:51 amMultimeter accuracy spec is enough to tell that at least one of the devices in question is not in spec.

author: bdunham7
author_rank: Super Contributor
timestamp: February 02, 2021, 12:47:05 am
content: Quote from: TiN on February 02, 2021, 12:40:51 amTrue, but you've missed the point entirely. He doesn't need to measure the source to within its specified accuracy to know that it isoutof spec. Confirming something is defective is often different than verifying that it is operational as specified.

author: dietert1
author_rank: Super Contributor
timestamp: February 02, 2021, 08:50:40 am
content: As far as i understand that power supply has built in meters. Do those indicate a similar voltage mismatch? Of course there is a certain risk that they used the built-in meters for calibration - who knows.Regards, Dieter

author: The Soulman
author_rank: Super Contributor
timestamp: February 02, 2021, 09:14:45 am
content: Jan, I could send you a calibrated 7805 in the mail, I can measure it to about 0,01% uncertainty at the moment.The 7805 will likely drift more from transportation and temperature changes but still be good enough to discern 4,900 Volt from 5,000.Send me a pm If you think it will be useful.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 02, 2021, 02:53:18 pm
content: Thank you very much.I attatched the cables straight into the DMM and it was exact correct, I feel very stupid now.I dont know how i got the 4,9 volt ?, maybe a cable or aligator-clip problem in my project.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 02, 2021, 02:57:30 pm
content: Quote from: The Soulman on February 02, 2021, 09:14:45 amSo you bought 100 pieces and measured them all on a very good meter ?Nice one.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 02, 2021, 03:04:05 pm
content: So funny they calibrate gear with a agilent 34461A meter,I almost was thinking i need it, the volt-nuts-disease is real.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 02, 2021, 03:15:02 pm
content: Quote from: dietert1 on February 02, 2021, 08:50:40 amYes this is weird, i forgot to ask.If i dial in 5 volt, the internal-meter says not exact 5,0000 volt.So the meter is not changing the voltage, i thought that was how a switching power supply works, it measures and switches.

author: wraper
author_rank: Unknown
timestamp: February 02, 2021, 03:17:23 pm
content: Quote from: Jan Audio on February 02, 2021, 02:53:18 pmAnd how were they attached if not straight?

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 02, 2021, 03:28:29 pm
content: Now with 1 cable.

author: The Soulman
author_rank: Super Contributor
timestamp: February 02, 2021, 04:50:54 pm
content: Quote from: Jan Audio on February 02, 2021, 02:57:30 pmNo, it means I can measure the output of a random 7805 fairly accurately and can give you that number such as 5,1234V and ifyou remeasure that same 7805 with your aneng meter and it reads for instance 5,120V we can be fairly certain your aneng is operating in spec.But I believe your issues are already solved?Quote from: Jan Audio on February 02, 2021, 03:04:05 pmYes very real, I've started with two 2000 count dmm's that were a few counts apart (both well within spec) but my ocdcouldn't handle it so also got a 30.000 count bench dmm and a 10V vref, life was good for a while until a 20.000 countbench dmm arrived, that was also just a few counts out compared to the other and the vref, but I couldn't be certain If either of them was 100% correct.So a few years and several external calibration rounds later I have one(!) 2.000.000 count bench dmm and 9 vrefs and various thermal sensors/probes with data logging etc. etc...Still use those same 2000 count meters tho, lol.

author: Jan Audio
author_rank: Frequent Contributor
timestamp: February 02, 2021, 05:29:56 pm
content: LoL, i googled OCD.