EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: baoshi on February 15, 2014, 02:26:00 am
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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?
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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?
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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 ?
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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
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Any suggestions what I can check?
I 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 regards
Andreas
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Hi Andreas,
Thanks for the info. I have checked using oscilloscope, and also put a 1K resistor in series, no improvement :scared:
Any suggestions what I can check?
I 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 regards
Andreas
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I have a video showing the initial reading drop.
http://youtu.be/j4AtZpR9pRo (http://youtu.be/j4AtZpR9pRo)
The image below is taken using Agilent GUI data logger application :wtf:
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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.
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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?
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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?
Personally, 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.
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c'mon, even the cheap $2 DMM can display spot on the value on power on.
Don't be so sure. I saw this yesterday (3:06 into video, 1.87V for a Duracell AA).
How to test a Battery with a Cheap Multimeter (https://www.youtube.com/watch?v=W38x9RJs29I#ws)
The problem is obvious, but apparently the person who made the video is not clued in.
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c'mon, even the cheap $2 DMM can display spot on the value on power on.
Don't be so sure. I saw this yesterday (3:06 into video, 1.87V for a Duracell AA).
At least its stable at 1.87 V even its not accurate >:D, 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.
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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?
Personally, 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.
Thanks. I'm sending this back to Agilent. It's nothing more than paper weight now.
Sent from my iPhone using Tapatalk
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Case closed. Received a new one from Agilent
Sent from my iPhone using Tapatalk
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Did they say what was wrong with the old one?
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c'mon, even the cheap $2 DMM can display spot on the value on power on.
Don't be so sure. I saw this yesterday (3:06 into video, 1.87V for a Duracell AA).
How to test a Battery with a Cheap Multimeter (https://www.youtube.com/watch?v=W38x9RJs29I#ws)
The problem is obvious, but apparently the person who made the video is not clued in.
Do 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.
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Did they say what was wrong with the old one?
Nope. They just replaced me with a new set
(http://img.tapatalk.com/d/14/02/26/yqahu4eq.jpg)
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