Agilent DMM U1241B, needs warmup? - Page 1
Forum section: electronics / testgear

author: baoshi
author_rank: Regular Contributor
timestamp: February 15, 2014, 02:26:00 am
content: I have a Agilent U1241B DMM. Recently it develops a strange phenomenon:1. I measure a 5V voltage stand (AD588 based, +-1mv, 1.5PPM/C, 5.00046V according to HP3458A), if I just turn on the multimeter, the reading is about 5.3V, then it drops continuously until stable at 5.003V after 1-2 hours.2. If I disconnect the voltage stand for a while then reconnects it, the reading jumps up again, then drops slowly. How long it takes to stabilize depends on the how long I disconnect the voltage stand.3. If I leave the testing voltage on and let the meter power off by itself, after several hours if I wake up the meter, the reading is bang-on.It looks as though something in the meter needs charging or discharging? All testing are done in aircon room.Any suggestions what I can check?

author: retiredcaps
author_rank: Super Contributor
timestamp: February 15, 2014, 04:44:30 am
content: I currently have never used an Agilent orange series multimeter so I'm just making general suggestions on what I can find in the manual.1) Does ohm measurements work fine? For example, if you measure a 1k ohm resistor, is it 1k right away or does it take hours to settle?2) Have you tried resetting the multimeter back to factory defaults?3) Are you running the latest version of the firmware?4) Did this 5.3V to 5.003V problem happen on day 1?5) Is the meter in a shared environment where anyone can use it?6) Do you know if the meter was subjected to high voltage?7) Can you post a clear focused picture of the inside?

author: BravoV
author_rank: Super Contributor
timestamp: February 15, 2014, 04:49:39 am
content: Own U1242B which very similar to U1241B of yours, mine doesn't have that symptons, suspect there is something wrong in there.Does U1241B at the lcd display have the meter temperature reading ? does it fluctuate ?

author: baoshi
author_rank: Regular Contributor
timestamp: February 15, 2014, 06:18:33 am
content: Thanks for both suggestions, here are some testing results:1. I tried ohm range. I have one Vishay S102K resistor, 25K000 0.01%, measure result 24.99K, no reading fluctuation.2. Testing are done in aircon room at about 26C, the temperature reading are stable.3. I'm not sure it this happens on day 1, because at day 1 this meter is my only reference. I only noticed this after I get my hands onto a HP3478A.4. I tried to set the meter to default settings, but not recalibrate it. I guess the stability issue is not related to accuracy.I will to let the meter rest for a while then try shot a video of the initial dropping period

author: Andreas
author_rank: Super Contributor
timestamp: February 15, 2014, 12:55:50 pm
content: Quote from: baoshi on February 15, 2014, 02:26:00 amI would check wether the reference voltage is stable with the DMM as load. (Oscilloscope).Perhaps the output oscillates and needs some kind of decoupling with this meter as load.Try a 200 Ohms to 1K resistor in series with the DMM.with best regardsAndreas

author: baoshi
author_rank: Regular Contributor
timestamp: February 15, 2014, 03:10:48 pm
content: Hi Andreas,Thanks for the info. I have checked using oscilloscope, and also put a 1K resistor in series, no improvementQuote from: Andreas on February 15, 2014, 12:55:50 pm

author: baoshi
author_rank: Regular Contributor
timestamp: February 16, 2014, 05:14:47 am
content: I have a video showing the initial reading drop.http://youtu.be/j4AtZpR9pRoThe image below is taken using Agilent GUI data logger application

author: BravoV
author_rank: Super Contributor
timestamp: February 16, 2014, 05:22:12 am
content: My U1242B does not experience that problem, while connected to my 5 volt reference, as soon its powered on, the voltage reading instantly displays spot on at 5.000 volt, and stays there, and sometimes only the least siginificant digit flickering between 0 and 1 which is normal.

author: retiredcaps
author_rank: Super Contributor
timestamp: February 16, 2014, 05:28:37 am
content: Does this long settling problem happen with a simple 1.5VDC AA cell? I'm just wondering if the problem happens below the 5.0V range?If it does, I think it is time to send it back to Agilent for warranty repair?

author: BravoV
author_rank: Super Contributor
timestamp: February 16, 2014, 05:35:38 am
content: Quote from: retiredcaps on February 16, 2014, 05:28:37 amPersonally, I would send it back to Agilent, no need further to test with 1.5V cell, c'mon, even the cheap $2 DMM can display spot on the value on power on.

author: retiredcaps
author_rank: Super Contributor
timestamp: February 16, 2014, 05:43:55 am
content: Quote from: BravoV on February 16, 2014, 05:35:38 amDon't be so sure. I saw this yesterday (3:06 into video, 1.87V for a Duracell AA).The problem is obvious, but apparently the person who made the video is not clued in.

author: BravoV
author_rank: Super Contributor
timestamp: February 16, 2014, 06:14:12 am
content: Quote from: retiredcaps on February 16, 2014, 05:43:55 amAt least its stable at 1.87 V even its not accurate, c'mon, seriously, I think you know what I meant and agree with me here, if a $200 class DMM can not read firmly a simple DC 5 V at power on, something is not working properly there.

author: baoshi
author_rank: Regular Contributor
timestamp: February 16, 2014, 06:40:53 am
content: Quote from: BravoV on February 16, 2014, 05:35:38 amThanks. I'm sending this back to Agilent. It's nothing more than paper weight now.Sent from my iPhone using Tapatalk

author: baoshi
author_rank: Regular Contributor
timestamp: February 24, 2014, 02:05:56 pm
content: Case closed. Received a new one from AgilentSent from my iPhone using Tapatalk

author: retiredcaps
author_rank: Super Contributor
timestamp: February 24, 2014, 05:33:58 pm
content: Did they say what was wrong with the old one?

author: WVL_KsZeN
author_rank: Regular Contributor
timestamp: February 24, 2014, 06:22:59 pm
content: Quote from: retiredcaps on February 16, 2014, 05:43:55 amDo note that the multimeter in the video is showing a low battery warning! it's quite common to show too high readings when battery is low.

author: baoshi
author_rank: Regular Contributor
timestamp: February 26, 2014, 03:20:23 am
content: Quote from: retiredcaps on February 24, 2014, 05:33:58 pmNope. They just replaced me with a new setSent from my iPhone using Tapatalk