Agilent 34401A Jitter. - Page 1
Forum section: electronics / testgear

author: TopGunPk
author_rank: Contributor
timestamp: January 21, 2013, 09:13:12 pm
content: Hi.One of my dad's friend is about to sell his Agilent (HP) 34001A 6.5 Digit Benchtop DMM, he heard about me and offered me to have a look just incase i wanted to buy it before he can toss it out. So i had a look.Looks pretty decent, though it might have seen better days. One peculiar issue that i noticed with it is a bit strange seeming, however i thought i will ask if anyone on the forum can guide me, as i have not used Benchtop DMMs much.The problem starts in the mV range of the meter. Upon switching the meter to mV range, the digits AFTER the decimal point start fluttering between between 0.3589 ~ 0.3791 and something like that. I do not mean that this is the exact number it flutters between, but it is usually 0.3xxxx. Please note, i did not connect any probes to the meter, since my dad's colleague needed some time to dig them out from his stuff.Didnt seem normal to me, so i thought i would ask if any one knows what the problem is, and if it can be rectified without much hassle, or sending to HP / Agilent.Thanks.Zeeshan

author: M. András
author_rank: Super Contributor
timestamp: January 21, 2013, 09:16:09 pm
content: if you short the inputs and goes to zero then its fine btw it has a selftest routinedig up the manual for from the agilent website

author: TopGunPk
author_rank: Contributor
timestamp: January 21, 2013, 09:20:14 pm
content: Thanks Andras.Yes i have downloaded the manual and just reading the Self-Test procedure details, however i did not have the manual back when i was playing with the meter.I did short out the Ohms and LO jacks in the resistance mode with a short wire, and it showed close to 0.000x, so i am guessing the Ohms range is OK, however i did not check that in the mV range - nice point ! Will do tomorrow.Thanks once again.

author: free_electron
author_rank: Super Contributor
timestamp: January 21, 2013, 09:25:12 pm
content: on millivolt range it is normal for that machine to show a few hundred millivolt of nothing is connected.

author: TopGunPk
author_rank: Contributor
timestamp: January 21, 2013, 09:32:19 pm
content: Thanks Free_Electron.However, i was of the view that, being a high resolution precission DMM, it should not do such a thing, that puts a buyer off the track.Is there any mention in the manuals , perhaps in User manula or Service manual ?I have downloaded both and trying to go through them, however quite a few pages worth, so just inquisitive if any of the forum readers have faced such an issue OR can verify this with their own DMMs, OR if any one knows such a thing mentioned / referenced in the manuals.Will be a BIG help.Thank you once again for your reply.Cheers.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 21, 2013, 09:46:46 pm
content: my keithly 199 drifts to like 2 volts but the measurements it makes are good. It's because its a very high impedance.When you have a floating gigaohm impedance then any noise is really picked up, i think?

author: vtl
author_rank: Regular Contributor
timestamp: January 21, 2013, 09:47:53 pm
content: Bench DMMs have a very high input impedance in the mV range (in the order of tens of Megaohms or even higher). This causes charge to build up at the input terminals and causes readings to appear when nothing is connected.

author: ftransform
author_rank: Frequent Contributor
timestamp: January 21, 2013, 09:51:10 pm
content: Actually when shorted my keithly 199 shows a offset of 0.007 mV.My Agilent 34401a shows an offset of 0.003 mV.These measurements were taken 5 minutes after instrument start up after being in a cold room.I think that this is acceptable.

author: free_electron
author_rank: Super Contributor
timestamp: January 21, 2013, 09:56:53 pm
content: the 34401 has an almost infinite input resistance... ( ie : you can't measure it ) you need to specifically turn on '10M' mode ....

author: ftransform
author_rank: Frequent Contributor
timestamp: January 21, 2013, 10:01:05 pm
content: Quote from: free_electron on January 21, 2013, 09:56:53 pminb4 pa4tim

author: JoeyP
author_rank: Frequent Contributor
timestamp: January 21, 2013, 10:14:26 pm
content: I just tested 3 Agilent 34401A meters. Two of them are of identical vintage, and each settled at -0.070mV open circuit, toggling about +/-0.010mV. The third meter is a few years older, and settled at +0.020mV, also toggling about +/-0.010mV. These readings were about 30 seconds after power up. All were within +/-0.003mV with the inputs shorted.All of the meters tested seem to default to 10M input impedance at power up. Maybe there's a way to set the default to 10M on/off at power up, and maybe yours defaults to 10M not enabled, which would give very different results.

author: TopGunPk
author_rank: Contributor
timestamp: January 21, 2013, 10:20:30 pm
content: Thanks for the explanation.Will try to set the Input impedance to 10M for DC mV measurement.

author: StubbornGreek
author_rank: Frequent Contributor
timestamp: January 21, 2013, 11:34:17 pm
content: Quote from: TopGunPk on January 21, 2013, 10:20:30 pmThis won't change the behavior much. What are you trying to accomplish? Does it stabilize when you short the leads? It is the measurement that should concern you; go ahead and check some known sources to ensure the device is functioning properly.