34401A long-term accuracy question - Page 1
Forum section: electronics / testgear

author: g0hjq
author_rank: Unknown
timestamp: July 09, 2014, 09:27:06 am
content: Hi All,I've just bought a HP 34401A multimeter on EBay UK for £275.It is one of the earlier models, and is badged "HP" rather than "Agilent". It appears to be in very good condition with manual and probes, a bright display, no self-test errors, and readings on all ranges agreeing closely (zero to 0.3%) with my Amprobe 37XA-A handheld multimeter.The meter calibration message displays that it was last calibrated on 8 Mar 2000 .The manual states that accuracy after 1 year is 0.0035%. Does anyone have any suggestions what I should typically expect after 13 years? Would it be 13 times greater, or is it more likely to have settled down, and not be much greater?Can anyone recommend somewhere in the UK that can calibrate the meter, or is that likely to cost more than the meter is worth?Gary.

author: mzzj
author_rank: Super Contributor
timestamp: July 09, 2014, 09:36:54 am
content: Quote from: g0hjq on July 09, 2014, 09:27:06 amFor voltage ranges You could assume something like sqrt(13)*1year spec (=~4x one year drift) after 13 years. In reality these are even better, I would say that there is >95% probability that you are still within 1 year spec unless your unit is mishandled.34401A current ranges tend to drift bit more but i would bet that you are still within 4x one year spec.

author: TopLoser
author_rank: Unknown
timestamp: July 09, 2014, 09:40:12 am
content: Quote from: g0hjq on July 09, 2014, 09:27:06 amI just had a couple of 2015THD 6.5 digit bench meters calibrated for £45 each by PASS in the UK so it's not that expensive.

author: macboy
author_rank: Super Contributor
timestamp: July 11, 2014, 01:45:44 pm
content: Quote from: TopLoser on July 09, 2014, 09:40:12 amYou are lucky. I had a quote from a local place to do a Keithely 2001, and it was over CAD$400,without adjustments, which would add to the cost if necessary. I didn't do it. Some time later I acquired 3 more 2001's, and they all agree within +/- 3ppm on all voltage ranges, so I have convinced myself that they don't need calibration. All 4 were last calibrated between 12 and 18 years ago, if the cal dates displayed on the units are to be trusted.

author: jpb
author_rank: Super Contributor
timestamp: July 11, 2014, 01:54:52 pm
content: Quote from: macboy on July 11, 2014, 01:45:44 pmPrices seem to skyrocket beyond 6 1/2 digits. 6 1/2 digit meters are included with standard bench meters in the UK and several places seem to offer calibration for under £50 but there are many fewer labs set up for 7 1/2 or 8 1/2 digit meters and there are far fewer people requiring those to be calibrated so those that do get charged a lot.

author: Zucca
author_rank: Unknown
timestamp: July 11, 2014, 06:37:39 pm
content: Quote from: g0hjq on July 09, 2014, 09:27:06 amIn my experience not all the calibration labs change that text... I would not trust it too much, but if you don´t have a calibration sticker then well that´s your best guess.

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: July 11, 2014, 09:16:41 pm
content: I would expect more between £70 and £90 and double if you want adjustment. Ask for uncertainties, might find that given the Cal equipment some ranges have low TUR.

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: July 11, 2014, 09:22:00 pm
content: Some prefer to treat it as adjustment date, and not calibration date. No adjustment was needed therefore date not updated.

author: Zucca
author_rank: Unknown
timestamp: July 13, 2014, 09:20:13 pm
content: Quote from: engineer_in_shorts on July 11, 2014, 09:22:00 pmIn my case there was an adjustment, confirmed by the paper calibration protocol, but the date was not updated.

author: g0hjq
author_rank: Unknown
timestamp: July 24, 2014, 12:55:31 pm
content: I've just got the meter back from Calibration by the local company ServiceCal. Price was £50 (Approximately 90$) + tax for collection, calibration and return. Not bad at allAfter 13 years it's still within the 12 month spec on all ranges, and 5x better on most DC voltage, current and resistance ranges. Massive thumbs-up to Agilent!Thanks everyone for the advice - you were spot-on.Gary.

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: July 25, 2014, 05:20:07 am
content: Hi,Was it adjusted to this, or was it within that spec without adjustment?Did they update the calibration date that is stored in memory?

author: g0hjq
author_rank: Unknown
timestamp: July 26, 2014, 07:42:41 pm
content: No, It was still within the 12-month spec, so they didn't make any adjustments. They did give me a certificate with the expected and actual readings on each range.They've not changed the calibration date string in the firmware, but have put a nice little sticker on it with the calibration date and next due date (in 12 months time).

author: engineer_in_shorts
author_rank: Regular Contributor
timestamp: July 27, 2014, 05:14:04 am
content: great unit - very stable

author: nuno
author_rank: Frequent Contributor
timestamp: April 21, 2017, 08:55:31 pm
content: Quote from: mzzj on July 09, 2014, 09:36:54 amIs that formula generic for some type of semiconductor/voltage reference or specific to those HP 34401A?

author: ap
author_rank: Frequent Contributor
timestamp: April 22, 2017, 06:10:33 pm
content: It is not, and especially do different parts of a meter have different drift rates. So I have often seen meteres with everything fine except a single range being out of spec, sometimes even quite a bid compeared to the rest.It alway surprises me when people spend hundreds of bucks for a 6+ digit DMM, but do not want to spend the money to get it calibrated. Why then having a precise meter? Must be different reasons than why I have mine.If a meter has not been calibrated for a long time, often at least one range is out of spec, experience tells. Having it calibrated, and adjusted (yes, that costs more than just the cal quote most cal labs offer, so be carefull. Sometimes you even pay no fixed fee, but per hour; dont do that), usually fixes it for several years. Older meters have settled more, so drift rates decrease usualy. So my recommendation: Find a cost efficient lab and have it cal'ed.