Agilent U1212A, ACA reading was drop to nearly zero but afterward it will rise - Page 1
Forum section: electronics / testgear

author: kamcm
author_rank: Regular Contributor
timestamp: October 12, 2015, 08:10:48 am
content: When I power it on with ACA. The reading was drop to nearly zero but afterward it will rise to 0.16A.Although I can use the null button to get the zero reading.BUT I HAD TO WAIT UNTIL READING IS STEADY. IT TOOK AROUND ONE MINUTE.Anyone had this Agilent clamp meter? Anyone else having the same problem?I wonder to know if it's some kinds of design flaw or it's merely a defective meter?The seller claimed it's in new condition. I have to decide whether to return it for a refund or keep it.Please advice,Thanks.

author: Wytnucls
author_rank: Super Contributor
timestamp: October 12, 2015, 08:27:20 am
content: Why is it a problem?Try it with a real current measurement, as with a live conductor between the jaws and check that the reading is within the manufacturer's accuracy tolerances.

author: kamcm
author_rank: Regular Contributor
timestamp: October 12, 2015, 09:34:34 am
content: Quote from: Wytnucls on October 12, 2015, 08:27:20 amThe AC current reading should be auto zero when there's nothing in the jaw.It's a problem because if you want to get a accurate reading, you have to wait a long time for it to settle down and then press the null button.I don't think the null button is designed for that purpose.I had other brand clamp meter, including fluke, amprobe, UNI-T.All of them never have the same problem.Btw, most of the zero function on the clamp meter is for DC current only.Fluke 374 is a good example, the zero function can be only used in DCA, it will not work in ACA.

author: VK5RC
author_rank: Unknown
timestamp: October 12, 2015, 09:58:37 am
content: Is it close to any mains AC wiring?

author: kamcm
author_rank: Regular Contributor
timestamp: October 12, 2015, 10:34:38 am
content: Quote from: VK5RC on October 12, 2015, 09:58:37 amNo, it's not close to any ac wire.I curious to know if I am the only one having this problem?

author: Wytnucls
author_rank: Super Contributor
timestamp: October 12, 2015, 11:14:08 am
content: I didn't see any auto-zero feature for ACA in the manual.True RMS values are only valid for 2A and above anyway, due to true RMS converter limitations.Random readings before measurement have no effect and shouldn't be zeroed.My true RMS UNI-T UT204 behaves in the same way.'The AC voltage and AC current specifications are true RMS AC coupled, valid from 5% to 100% of range'http://literature.cdn.keysight.com/litweb/pdf/U1211-90001.pdf

author: kamcm
author_rank: Regular Contributor
timestamp: October 12, 2015, 05:09:14 pm
content: Quote from: Wytnucls on October 12, 2015, 11:14:08 amMy other clamp meter able to displayed 0.00A in AC current.In the following video, I will demonstrate it will displayed an incorrect reading when my U1212A failed to zeroed.Although it's usable after zeroed manually but I think there's something wrong with it.Any thought?

author: Wytnucls
author_rank: Super Contributor
timestamp: October 12, 2015, 05:37:17 pm
content: Like I told you, accurate true RMS measurements are only valid above 2A. Shoot the same video with at least 2A going through the wire, without zeroeing the meter and report back.

author: kamcm
author_rank: Regular Contributor
timestamp: October 12, 2015, 06:20:31 pm
content: Quote from: Wytnucls on October 12, 2015, 05:37:17 pmThanks for your reply,Although True RMS values are only valid for 2A and above due to true RMS converter limitations.It only means the RMS converter circuit will not function under 2A.But It doesn't means it will not able to auto zeroed. It doesn't means you must zeroed manually before measuring small current.If this's happening on my UNI-T clamp meter, I can't complaint about it, because all of us knew it's cheap, it's a toy. We can't expect much more.However, for a clamp meter that Agilent selling for $300USD+ . I expected it did much better.If anyone had this clamp meter. Please let me know if you are having the same issue. Thanks!

author: BravoV
author_rank: Super Contributor
timestamp: October 12, 2015, 06:38:39 pm
content: kamcm, I received your PM regarding your question, as I own U1213A.1st, I'm not an expert, but I do own few well known meters, like Agilent U1213A and also Fluke 287s and 87V.Also I happened to read a lot of RMS converter ICs and tecnologies, as I understand it, RMS converter is tricky business. Not like measuring DC, it's accuracy is not linear from bottom range to the top of the range, the "best" accuracy is sort of starting from 20% up to 80% of the range, and a lot of other variations, point is the two corners (lowest and highest) in the range are not the best spot to get the accuracy. CMIIW.Regarding the autozero, I don't think thats a problem, this clamp meter like others, are not designed to measure low current, so those offset actually will fall within the spec. Yes, mine have similar sympton, but not as high offset as yours.Here, a quote from the U1212A's specification, as you can see its valid only from 5% up to 100%.If you still doubting it's accuracy, you can verify it as I did when I was confuse like you for the 1st time, I used the clamp meter, and then put another non clamp meter in series with the measured cable to verify the AC RMS current, and my U1213A actually performs better than it's specification.Also with my limited experience, actually when a meter in RMS mode (either in current or voltage mode), when not connected, since I already get used to see they will flicker, and if its not, I feel like the meter is doing some cheating internally to zero them out, not sure, any experts correct me if I'm wrong.Thats all I can say, and I agree with Wytnucls's comments.Hope this helps.

author: kamcm
author_rank: Regular Contributor
timestamp: October 12, 2015, 07:39:45 pm
content: Thank you very much!I was really confused before, because I didn't know whether it's a normal symptom.I appreciate your opinion on this matter and thanks for the explanation.I just tested it in series with a fluke 287 multimeter and you're right.It actually performs better than my Fluke clamp meterQuote from: BravoV on October 12, 2015, 06:38:39 pm

author: BravoV
author_rank: Super Contributor
timestamp: October 12, 2015, 08:16:32 pm
content: Quote from: kamcm on October 12, 2015, 07:39:45 pmI sort of remember a very good point that I read somewhere, that when it comes to RMS measurement. As its AC, as "Alternating" current or voltage, think about the word "alternating", so when the meter is not measuring, there is no electricity "alternating" at the measured cable/track, hence it will display an offset or sometimes flickering noise at certain acceptable level, which is actually a good sign of "sensitivity" of the meter.If a meter in RMS mode, shows a static zero when not measuring anything, and its like somehow it muted or suppressed "artificially" the display into zero, not sure if this is the right wording. Again, I'm not an expert of this, its just I remember I read it somewhere.Quote from: kamcm on October 12, 2015, 07:39:45 pmLooking at that video, I have a feeling that the two Flukes will start gathering dust sitting inside the drawer.Glad to see you're happy with your new toy.

author: PetrosA
author_rank: Frequent Contributor
timestamp: October 16, 2015, 03:09:12 pm
content: As others have stated, what it shows when unloaded is nothing to worry about. I have two clamp meters, the U1211A and a Hioki 3282 and when measurements count, I use the U1211A

author: macboy
author_rank: Super Contributor
timestamp: October 16, 2015, 03:34:54 pm
content: Quote from: kamcm on October 12, 2015, 09:34:34 amYou must never use the NULL or ZERO function to remove a zero offset for ACA or ACV. The reason is that the reading will add to the noise with a root-sum-of-squares relationship. For example, let's assume that you see a reading offset/noise (no current through jaw) of 0.016 ARMS. Now you clamp a conductor with exactly 1.000 ARMSflowing. The meter will measure the sum of the two currents as:reading = sqrt( 1.0002+ 0.0162)reading = sqrt(1 + 0.000256)reading = 1.00013 ARMS, which displays as 1.000 on this meter.As you can see, the few counts of noise has no significant effect on the reading, when the measured current is at least say 10 times the noise reading. For readings below that, you can to do the above math in reverse to approximate the measured current.The NULL/ZERO button is useful for DC, where everything adds linearly.