Strange Problem with Keysight U1253B - Page 1
Forum section: electronics / testgear

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 03:10:23 pm
content: I was going to do a video of this weird problem but since I have a bug and not feeling well I decided to just try and describe it the best I can. During some testing, I discovered a strange problem with the Keysight U1253B multimeter. While looking at a 1KHz sine wave I noticed the meter would register the 1KHz and every 20 seconds or so drop the reading and then immediately display it again. I immediately tried another function generator which worked perfectly! I thought it may have been the Rigol DG4062 so I checked the 1KHz on my Agilent scope from the DG4062 and it was perfect, rock solid. I tried a different multimeter and it was just fine. Curious, I placed 1KHz sine wave from my Rigol DG4062 back onto the U1253B and varied the frequency by just a small amount and it was perfect. I went from 1.000KHz to 1.001KHz and to 99.999KHz which worked just fine. So, I proceeded to check some other frequencies such as 1Hz, 10Hz, 100Hz, 100KHz, 1MHz and 10MHz and curiously they all act in the same manner as the 1KHz only from the Rigol DG4062. But when these same frequencies from 2 other generators are used the U1253B is rock solid. You might think that it could be the DG4062 but I am not quite convinced of that. Outputting the same frequencies from the DG4062 into several other meters, scopes and frequency counters prove to be solid.I am truly puzzled by this...

author: saturation
author_rank: Super Contributor
timestamp: January 11, 2015, 06:12:45 pm
content: My gut reaction is that the DG4062 has a transient amplitude fall during DDS generation causing the counter to lose sync.

author: electr_peter
author_rank: Unknown
timestamp: January 11, 2015, 06:44:36 pm
content: What is the signal level of signal gen? You may be ridding at the edge of detectable limit in your DMM.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 07:22:12 pm
content: Quote from: electr_peter on January 11, 2015, 06:44:36 pm5VPP. I tried all the way to 20VPP. Should be plenty.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 07:23:28 pm
content: Quote from: saturation on January 11, 2015, 06:12:45 pmI don't see that on the scope though.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 07:26:55 pm
content: I have to clarify that the only time the problem shows up is at the 100Hz, 1KHz, 10KHz, 100KHz 1MHz and 10MHz frequencies.

author: cncjerry
author_rank: Unknown
timestamp: January 11, 2015, 08:00:12 pm
content: Do you have test or limit masking on the agilent scope? That would resolve the unit causing the problem. Set the mask for horizontal and vertical separately and run the test.

author: VK5RC
author_rank: Unknown
timestamp: January 11, 2015, 08:13:57 pm
content: @TeraByte What software version have you got?(I also have a U1253B v2.26, its about 4-5 yrs old but I have updated the software)It also reads 0Hz about every 4-7secs on a 1kHz signal from an Agilent 33519 sig gen.PS My OLED is going fine , yours OK?

author: saturation
author_rank: Super Contributor
timestamp: January 11, 2015, 08:19:27 pm
content: Ah, the plot thickens. If another similar model has a periodic pattern its suggesting its in the DMM.Quote from: VK5RC on January 11, 2015, 08:13:57 pm

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 11, 2015, 08:33:54 pm
content: Quote from: saturation on January 11, 2015, 08:19:27 pmIt's strange though, because it doesn't show when you change the 1Khz one Hz up, and I don't think you run both on the same reference. Hmm...

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 09:01:22 pm
content: Quote from: VK5RC on January 11, 2015, 08:13:57 pmInteresting... Other than that, everything else is fine! One of the most accurate DMM's I have with the exception of the my Fluke 289.I am also running 2.26, Did your DMM start doing this right after your upgrade?

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 09:05:43 pm
content: Quote from: cncjerry on January 11, 2015, 08:00:12 pmYes, I do, but further posts suggest a DMM issue. I can try this though.

author: cncjerry
author_rank: Unknown
timestamp: January 11, 2015, 09:35:11 pm
content: I suggest the limit test to eliminate the generator but you sort of did that already. I am struggling with the 1hz variation fixing the problem without a common reference. I have a 1252b and will test that one as well. My DDS can resolve .01hz but without a common reference it can't be that specific to 1000.0 hz.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 09:57:08 pm
content: Quote from: cncjerry on January 11, 2015, 09:35:11 pmI can assure you that it's a 1Hz difference. Here is a picture of 1.000KHz and you can see the meter glitch to 0.0 repeatedly and another picture of 1.001KHz where the frequency display is rock solid for as long as I leave it or until the APO activates.I would do a video if I were feeling better, sorry don't have much of a voice from this bug!

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 11, 2015, 10:26:17 pm
content: Quote from: cncjerry on January 11, 2015, 09:35:11 pmHere is a test Mask I ran for a almost 3 minutes. This should easily capture a glitch in that amount of time. Mask was .05No problems.

author: VK5RC
author_rank: Unknown
timestamp: January 12, 2015, 12:10:51 am
content: Sorry to say that this is the first time I have used the freq counter. The software upgrade fixed a previous poor charging issue, so now battery life from lipo much improved.to me I suspect a sampling issue.As a meter I like it a lot, especially the display. (no fade)

author: lowimpedance
author_rank: Super Contributor
timestamp: January 12, 2015, 12:38:14 am
content: Just for reference I have an U1252a model which I tested with a Stanford DS345 function gen. at 100.0 Hz, 1.000, 10.00, 100.00 kHz and 1.000 MHz sign wave and did not observe any shift from the displayed frequency.

author: VK5RC
author_rank: Unknown
timestamp: January 12, 2015, 12:55:17 am
content: V2.26 according to Keysight fixed-incorrect meter reading when battery v=4.7v-inability to retrieve data when log full- correct default dc filter on mixed ac-dc signalv2.13 I think was the only previous version@lowimpedance what version software do you have?

author: IvoS
author_rank: Frequent Contributor
timestamp: January 12, 2015, 12:56:50 am
content: I also have U1252B, just checked it, no problems.

author: VK5RC
author_rank: Unknown
timestamp: January 12, 2015, 06:06:57 am
content: I have done a bit more exploration, It does the 'blanking' with 1kHz, 1.000,001kHz (or anything in between ) but not 1.000,01kHz or greater.For others who with u125x, does yours do it and what software version?

author: cncjerry
author_rank: Unknown
timestamp: January 12, 2015, 03:05:11 pm
content: I tried my 1252B last night, messed around for about an hour, no blanking, but my counter said I was only getting precision to 1,000.013hz out of that generator. To get finer I would need to test with another DDS I have.I looked last night and the specs on the 1253 freq measure are .02% at less than 600K. This means it is +/- .2 HZ at this frequency (1khz) if i did my math right. This is why I am leaning towards the generator being the culprit even though the testing teaches that it isn't. Without a common 10M reference I am struggling as to how the meter could be reading and acting so precisely. If it was a jitter problem then you would see it as such in the meter so it has to be amplitude to drive it to 0hz.One other data point might be helpful. Does it fail more frequently with a square wave? This is really weird as a counter just conditions the signal, opens a gate, counts or does the reciprocal thing, and displays. Why the hell would it act with such precision?

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 12, 2015, 04:30:17 pm
content: Quote from: VK5RC on January 12, 2015, 06:06:57 amI confirmed my unit. Same thing. Very odd indeed!

author: VK5RC
author_rank: Unknown
timestamp: January 12, 2015, 09:40:40 pm
content: I was wondering if the cpu was 'thinking' while the gate was doing its stuff, so it misses the cycle, says no signal then resets, starts again??? Only happens if gate exactly in time with cpu clock???

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 12, 2015, 09:51:43 pm
content: Quote from: VK5RC on January 12, 2015, 09:40:40 pmBut why those particular frequencies? It should happen with others too! I guess it's possible to have an issue with the CPU clock and timing, but I would think something like this would have been discovered already unless it was due to firmware. You probably did not notice or test this prior to your upgrade, right?

author: VK5RC
author_rank: Unknown
timestamp: January 12, 2015, 10:03:10 pm
content: This is the first time I have used the freq counter on the u1253, I have another frequency counter (a now repaired hp 5342a).You think it would have been found before, but others may be like me or only checked it out very briefly, as it looks ok for a second or 3. The software upgrade has been around for a year or so I think, if that is part of the problem.Mine is out of warranty, is it worth an email to Keysight? Or put it up on the Keysight blogg?

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 12, 2015, 10:11:29 pm
content: Quote from: VK5RC on January 12, 2015, 10:03:10 pmActually, that is what I was going to do. If I can tonight, I may post this to the Keysight forum and see what gives. It's not a mission critical problem because I have way better counters that what's in the U1253B DMM. It's more of an irritant and since I tend to be very picky about my test gear it will bug me until I figure it out. Once I do, I'll post my findings!

author: VK5RC
author_rank: Unknown
timestamp: January 12, 2015, 10:14:47 pm
content: I will be interested as well, kind regards Rob

author: lowimpedance
author_rank: Super Contributor
timestamp: January 12, 2015, 11:50:43 pm
content: Quote from: VK5RC on January 12, 2015, 12:55:17 amOk not sure there are any updates for the 'a' model , cannot find any reference as such. So my meter must have what ever was factory shipped, and will be somewhat different to the 'b' models.Looking at the Keysight firmware update page for handhelds only the U1253b is referred to not the 52, does that mean the update is only for OLED versions?.

author: saturation
author_rank: Super Contributor
timestamp: January 13, 2015, 12:55:22 pm
content: I tried this on a 1252a & 1272a for 1;10;100;1000 kHz to maximum resolution of each DMM then +/- 10 on the LSD of each frequency range. No issues, no blanking. Accuracy on par with published specs, used a Racal 1996 as a reference and an Instek SFG 1003 as source.Since it doesn't affect the accuracy of the count, its not a critical issue compared to the old Fluke 87V GSM interference issue [ which locks up the DMM] or the Fluke 85III that sleeps but not go into low power mode [ thus consuming battery at the non-sleep rate].

author: nanofrog
author_rank: Super Contributor
timestamp: January 13, 2015, 10:46:21 pm
content: Quote from: lowimpedance on January 12, 2015, 11:50:43 pmYes.

author: lowimpedance
author_rank: Super Contributor
timestamp: January 13, 2015, 11:58:03 pm
content: Quote from: nanofrog on January 13, 2015, 10:46:21 pmInteresting, I wonder how different the underlying hardware is apart from the OLED display area of course.It would seem only OLED meters are displaying this behaviour.