Are there different kinds of calibrations (for Agilent/HP/Keysight gear)? - Page 1
Forum section: electronics / testgear

author: hp3310a
author_rank: Regular Contributor
timestamp: October 10, 2025, 02:30:48 pm
content: I sent my Agilent 34411a to calibration last week and it came back today with a PASS calibration certificate. It lists all the different ranges, test values and readout values, percentages of acceptable deviations and so on. Every single range and test value passed. I guess that is good.However, I was kind of expecting the calibration also to adjust the meter in such a way that deviations from test values get as close to zero as possible. Also I had expected the cal message and cal count to be updated, but those did not change.So, my question is: The type of calibration that also adjusts the meter, how is that called? Is that something only Keysight will do (the lab I sent it to wasn't Keysight)?

author: Grandchuck
author_rank: Super Contributor
timestamp: October 10, 2025, 02:36:21 pm
content: I have read here it is called calibration plus adjustment.

author: coromonadalix
author_rank: Super Contributor
timestamp: October 10, 2025, 02:48:30 pm
content: in my towncalibration does include adjustment, you can have it NIST / traceable or just printed reports as : the before and after / tolerances and outside of company tolerances by xxxx,if outside of tolerances, they will ask if you want to try the nearest possible adjustment to approach the company tolerances in the highest or lowest limits ... or unattainable ?they will tell you witch range is calibrated and the one(s) who can't be ... they will stamp the equipment accordingly ...certification will only give results as passed or failed with reports if asked

author: mzzj
author_rank: Super Contributor
timestamp: October 10, 2025, 05:11:51 pm
content: Quote from: hp3310a on October 10, 2025, 02:30:48 pmAs already commented it is called calibration with adjustment.And you don't need to send it to Keysight for adjustment. Most of the "better" labs should be able to adjust the 34411A. Expect to pay anywhere 200...800 usd for calibration with adjustment.Did they list calibration uncertainty or reference equipment used?

author: hp3310a
author_rank: Regular Contributor
timestamp: October 10, 2025, 07:29:28 pm
content: Thanks for the clarification guys, looks like I didn't ask for the right thing. Now I still don't know which of my two 6.5 multimeters is closer to the truth.Quote from: mzzj on October 10, 2025, 05:11:51 pmThey listed the equipment used (Fluke 5520A and 5730A) and measurement uncertainties for each measured value (in the range of 10e-3 to 10e-6).

author: Stray Electron
author_rank: Super Contributor
timestamp: October 10, 2025, 11:19:03 pm
content: FYI, I've had very poor results from some of the small independentlabscompanies that claim to "calibrate" HP gear (Can you say E-bay??) They not only didn't calibrate it but some of the readings were worse when the units came back than they were when I sent the stuff in! If I ever get anything recalibrated again I'm going to make them give me a detailed statement of the specs that they guarantee that it will meet when they finish.

author: J-R
author_rank: Super Contributor
timestamp: October 11, 2025, 03:44:51 am
content: Definitely do some reading in the Metrology section:https://www.eevblog.com/forum/metrology/Assuming the cal lab is legit, the calibration data should tell you how close to "the truth" the 34411A is.Some people prefer having the DMM adjusted each time, while others prefer to never adjust. Default is typically not to adjust unless a measurement falls out of spec.There has been some variance with regard to terminology over the decades. So the best solution is to discuss expectations with the cal lab before shipping the DMM off.You should add some references that you can separately ship off for calibration to your workflow, in addition to the DMM calibration.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 11, 2025, 04:05:44 am
content: Yeah, some people think calibration includes adjustment, but those are typically separate. I always ask if adjustment is included or not.

author: mzzj
author_rank: Super Contributor
timestamp: October 11, 2025, 10:33:33 am
content: Quote from: hp3310a on October 10, 2025, 07:29:28 pmYou got all the information needed to calculate the true or corrected reading of your 34411A. Take error from your calibration certificate and correct your reading according to that.---Sounds like you got reasonable calibration certificate.1. You have actual measurement results (instead of just pass/fail compared to mystery spec with mystery uncertainty)2. Fluke 5730 should be good enough for 6½digit meters3. Having measurement uncertainty gives some hopes that cal lab knows what they are doing.

author: free_electron
author_rank: Super Contributor
timestamp: October 11, 2025, 09:58:43 pm
content: typically you do not want adjustment, unless the range is out of spec. if the range is in spec they will not touch it. The reason being that, if it is adjusted, subsequent measurements in the same setup will have a deviation from previous ones.Let's say you have an automated test setup where a meter is measuring parameters on hundreds or thousands of items under test.The meter undergoes adjustment. This will create a shift in results on any device that is tested after the adjustment was done. this gives problems with process control. you have a statistical discontinuity in data before and after adjustment.If the machine is not out of spec you do not want to adjust it to avoid these problems in process control.If it is out of spec you need to be able to regress and find out in your collected data when the machine started going out of spec.That's the reason adjustments are only done if the machine is out of spec.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 11, 2025, 11:46:13 pm
content: That's correct; adjustments are only needed when something is out of spec.The terminology is crazy because calibration really means verification, but sounds more like it means adjustment.

author: J-R
author_rank: Super Contributor
timestamp: October 12, 2025, 04:02:51 am
content: The 34410A/11A could be +/- 35 counts at 10V DC and still be in spec. For a hobbyist using this on the bench, anything beyond about 5-10 counts seems like more trouble than it's worth. Are you really going to check the cal data printout for EVERY range and function when taking a measurement? Or always trashing the last two digits if you only get a "pass" from the cal lab and no data because you have no idea where it is within the specifications? Seems unlikely.Companies with "procedures" can make up anything they want, but it may not be always the best answer. If you're already doing the statistics on your calibration data, whether it's adjusted or not won't matter. It's just another number in your data/formula. If the unit has to be adjusted back in to spec while at the cal lab, then you also still have to track that data. Better to use multiple DMMs during production. If a DMM suddenly drifts between calibration intervals, you have a problem otherwise. I've seen mention of "oh, you have to go back and retest products from this date to this date if the DMM comes back out of cal." That is crazy. Have multiple DMMs and references to ensure you have the correct reading at all times. Just my opinion, though.I have specifically mentioned previously a reference I sent for calibration and it turned out the company only had one device to use for this. Many years I had no troubles, but suddenly one year I had serious reservations after receiving the reference back and ultimately it was determined their equipment had drifted in between its calibrations. Not good.There could be some plausible reasons for splitting out the adjustment in the current agreed upon meaning of calibration. If the adjustment is not 100% closed case, then there is the chance of disturbing something, so it's better to just document rather than adjust. There is also the cost involved for an adjustment, whether it's closed case or not.There can still be some disagreement on terms, such as Keysight's ACAL (autocalibration) which literally adjusts the displayed output to compensate for temperature drift, and some companies calling an adjustment a repair.I think it could also be slightly open for debate on whether it's safe to call a calibration a verification because some equipment has the "performance verification" split out from the calibration procedure.

author: KungFuJosh
author_rank: Super Contributor
timestamp: October 12, 2025, 05:12:48 am
content: Yeah, it's all crazy.

author: free_electron
author_rank: Super Contributor
timestamp: October 14, 2025, 07:53:18 pm
content: Quote from: J-R on October 12, 2025, 04:02:51 amI Never said you need to retest. You need toregressyour dataset.This is important if you are doing SPC. Check if there is a gradual deviation or if it is a jump. Find out if and where it has altered data.On automated lines, the calibration report's deviation data was entered in the data collection software. If a machine was swapped this was noted and the associated parameters as well. If questions arose later on they could trace back to the machine swap.

author: J-R
author_rank: Super Contributor
timestamp: October 15, 2025, 03:54:37 am
content: Quote from: free_electron on October 14, 2025, 07:53:18 pmWas referring to some other users' posts in the past.