Got a HP3458A, not entirely sure why... - Page 1
Forum section: electronics / general

author: amps
author_rank: Newbie
timestamp: June 29, 2018, 10:27:17 pm
content: I spotted a HP3458A for a suspicously low price, so despite my main interst being power electronics, I couldn't resist...Now I've had it for a while and I'm wondering what to do with it? I've been reading around on the subject and have certainly learnt some interesting things ... but that's about it so far. I could just sell it for a profit, but these seem to be holding their value quite well so I guess there's no rush.It seems to be a good unit from the limited testing I've performed. After passing the self test I compared the readings with my HP34401A (cal due 06/17) and they seem to agree to within the error I'd expect from the latter instrument - comparing e.g. battery open circuti voltage, resistors I have lying around. The cal sticker on the 3458A is 2010, which I think puts the uncertainty still below that of my 34401A going by the sqrt rule I read somewhere here(?).Seems to be from the mid 80's, so I've also checked for stability of the CAL? 72 value. Over 8 days (so far) it changed by -0.17ppm/day, so given the spec is <0.43ppm/day that seems pretty good to me.I did find one "worthwhile" experiment to do with the meter. I work with lithium batteries and have in the past used a 7.5 digit meter to measure the open circuit voltage of newly shipped cells, taking 2-3 readings a few days apart then weeding out cells which show a high self discharge. I thought with this meter I might be able to do the same but over a shorter time, so I took a few readings on 5 cells each day over the course of a couple of weeks. But the results seems a little odd - sometimes the cells would actually increase in voltage a little between days, which is what prompted me to check CAL 72. Most likely it was just a temperature effect ... I can post the results if anyone's interested.I also got a quote for calibration from Trescal, just out of interest really. They quoted £137 for "LAB" calibration, which seems a little cheap from what I've read here? I guess I should ask what I actually get for this and which instruments they use? They did confuse me with my university and put their name on the quotation - so maybe there's some discount there. Doubtful though as I've not seen any >1yo instruments in the lab calibrated in the last 10 years...Don't ask me how long I spent getting the picture

author: tggzzz
author_rank: Super Contributor
timestamp: June 29, 2018, 10:52:15 pm
content: Quote from: amps on June 29, 2018, 10:27:17 pmPlease allow me to save you much time, money,andheartache. Allow me to pick it up from you; I'll even give you some money for it, so you won't be out of pocket.

author: dr.diesel
author_rank: Super Contributor
timestamp: June 29, 2018, 11:19:22 pm
content: Welcome to the nut club!

author: bitseeker
author_rank: Super Contributor
timestamp: June 29, 2018, 11:37:41 pm
content: Congrats on getting a deal on a 3458A. If you don't want it, you'll find there's no dearth of takers in this neck of the woods.Nice pic. Would you call that value a centi-pi?

author: TheSteve
author_rank: Unknown
timestamp: June 30, 2018, 12:25:19 am
content: Congrats!!! Always a great toy, I mean tool for the lab. Did you mean mid 90's? Mid 80's is too early for them.

author: amps
author_rank: Newbie
timestamp: June 30, 2018, 12:48:50 am
content: Quote from: bitseeker on June 29, 2018, 11:37:41 pmWell I would be foolish not to consider a good offer, but speaking as a student I'm more keen to keep it initially and see what I can learn, as owning one of these does seem a rare opportunity.Quote from: bitseeker on June 29, 2018, 11:37:41 pmThanks. I'd call it a centa-pi - a centi-pi can be arranged, if you like? For now, here's a whole pi!Quote from: TheSteve on June 30, 2018, 12:25:19 amGiven that the scope I own is only worth about £100 (GDS-1022) this really is a toy! Sorry, mixed up on the dates - based on the serial number I think it's from '88 or '89. If I add the number from CALNUM? to this date, that brings us to the date shown on the last calibration sticker, so it looks like it was calibrated yearly.

author: Mr. Scram
author_rank: Super Contributor
timestamp: June 30, 2018, 01:01:48 am
content: Was this you?https://www.eevblog.com/forum/buysellwanted/the-big-one-that-got-away-hp-3458a-for-$199-bin-(sob)/?topicseen

author: bitseeker
author_rank: Super Contributor
timestamp: June 30, 2018, 01:50:07 am
content: Quote from: amps on June 30, 2018, 12:48:50 amThanks for fixing that.

author: TiN
author_rank: Super Contributor
timestamp: June 30, 2018, 03:58:20 am
content: Quote from: Mr. Scram on June 30, 2018, 01:01:48 amNo, it was not him.ampsI'll save you from spending all your money on precision calibration standards and other 3458A's/5700A's/732's. All you need to do is to sell the meter 4 me, as I'm not coming back to normal EE life anyway :-D.Congratz on meter, let it run 24/7, so you can build up confidence that it is all happy stable. To determine age, you would need to open it up and see datecodes on PCB chips.I'd recommend doing so , to replace Dallas NVRAMs, capacitors on PSU boards and EMI paffner-shaffner-fire-hazard anyway. I heard folkshereandheredocumented the flow already.

author: amps
author_rank: Newbie
timestamp: July 12, 2018, 05:41:57 pm
content: A quick update - I've been recording the CAL? 72 value and over 20 days continuous operation it's drifted by -0.10ppm/day, so within the 0.43ppm/day spec.Given the current heatwave, I also recorded TEMP? values for each ACAL. If I plot CAL72 vs TEMP?, there is agoodcorrelation (R^2=0.96) between it and temperature of -0.56ppm/K. If I compensate the CAL72 values based on this -0.56ppm/K correlation, over my 20 day measurement I get around 0.02ppm/day drift. Of the 10 readings I took, the maximum deviation of any reading from the average is 0.25ppm. All seems pretty good to me.Google sheet here,https://docs.google.com/spreadsheets/d/1515OgYkcfCK3hTnQXVrEw8jEdfPUACMkF5beGhGnTLI/edit?usp=sharingin case you guys consider it useful data. Yes, it is a mess.Quote from: TiN on June 30, 2018, 03:58:20 amThanks for the heads up, still thinking about it. I've been in touch with Trescal and they are now looking for the historic cal certificates for me - will be interesting to see if they made any notes about having replaced parts previously. I've also queried what instruments they use / what I get for their £137 calibration service.