hp3457a 2nd hand shows CALNUM=535. Is this normal? - Page 1
Forum section: electronics / general

author: onlooker
author_rank: Frequent Contributor
timestamp: April 28, 2012, 02:55:24 pm
content: I bought a 2nd hand 3457a off ebay for $205 including shipping. Everything I have time (1day) to check from the front panel (no meams for HPIB ) seems to be fine or consistent with my 3.5 meters, except CALNUM=535 seems to be high since it means 1 formal calibration for every 2 weeks over a assumed 20 years in service period.This is my 1st meter of this type. Can someone with more experience comment on if this is normal, or give a plausible explanation? Then, is $205 a fair price? The ourside look is good, except for a cracked plastic shell on the I terminal. Thanks.

author: rf-loop
author_rank: Super Contributor
timestamp: April 28, 2012, 04:04:36 pm
content: Quote from: onlooker on April 28, 2012, 02:55:24 pmDo you know why this old professionel equipment manufacturer, Hewlett-Packard have made lot of work for manuals.Read:1. User operation manual.2. If any cal or service related questions, please read service manual.Thumb rule: Do not touch calibration routines becouse.....if you start... well, read manual first. (exept if you really have all what need and exactly know it is nessessary)(You've been kindly warned!)And now this CALNUM?Quote"hp3457a 2nd hand shows CALNUM=535. Is this normal?"Yes, it is normal and this number do not indicate anything what need worry.Maybe it have stay long time after active use without full calibration becouse number is so low.Or they have use long cal cycle."The maximum calibration number which can be stored is 32767. Afterreaching the maximum number, the counter resets to 0 and begins again."This is nice, HP have also think and tell what happend after CALNUM = 32767.

author: codeboy2k
author_rank: Super Contributor
timestamp: April 28, 2012, 09:59:10 pm
content: I find this number pretty useless.So there might be 35 - 50 total calibration points, but each yearly calibration doesn't need to touch every point, so the CALNUM wouldn't be bumped for a point that was still within spec, only the ones the calibration engineer changes to bring it back into spec.So, if you assume on average 25 points are touched for each calibration, then there has been about 21 calibrationsdone.But this useless number tells you nothing, really.

author: free_electron
author_rank: Super Contributor
timestamp: April 28, 2012, 10:20:49 pm
content: that number is useful DURING calibration as thae program that does the calibration can track how far along it is and what the last calstep was. ( it is nonvolatile ) if a calibration step fails the counter would not increment... and that's how you trap such an event.the normal calibration procedure for those machines is automatic. take a fluke calibrator and sme other machinery from agilent , hook it up to an hp900 computer and run the calibration software.

author: codeboy2k
author_rank: Super Contributor
timestamp: May 01, 2012, 11:57:11 am
content: Quote from: free_electron on April 28, 2012, 10:20:49 pmAha, thanks electron. That explains it well.disclaimer: I don't own anything mentioned in this topic

author: onlooker
author_rank: Frequent Contributor
timestamp: May 02, 2012, 12:51:38 pm
content: Thanks for all the replies. I guess I should read 535 as roughly 20 full scale calibrations. I also tested it with the best resistor I have/can find. It is a 82.5k 0.02% 9ppm/C. The read out on the 3457a is 82.5149k (+-4 counts) with the 4 wire setting and NPLC=100 at 20C. My understanding is that this readout is not out of spec yet.