From: Dick Moore richiem@hughes.net
To: volt-nuts@febo.com
Hi, Marv – RE my 3458 – It was very clean externally, leading me to think it had been used in a test or lab environment, but it needed a display board and a ROM board, both of which I installed. Then it went to Loveland for calibration. That was last September. Because the ROM board was replaced, there was no “before” data to compare the cal to. It goes back to Loveland this September, and now there will be “before” and “after” data which will provide an estimate of drift in parameters. It is not an -02 high-stability option unit.
The ROM board change essentially made this a good-as-new unit, at least according to Loveland – it passed all pre-cal tests with flying colors and cal'ed without problems.
I believe that Loveland uses a Fluke 572x calibration system, which for DC is at least as good as the 732B. As to AC – well I think it probably is as good as there is right now for cal use outside of labs. The specs for the 3458 reflect the uncertainty of the calibration standards, and the AC specs definitely show that. I bought that 3458 for $1600 on fleabay – didn't want to pay too much more because of the ROM battery problems on older units with the Dallas ROMs that had built-in battery back up. The new ROM board has ROMs that have a snap-on battery which is apparently easy to replace, though I wonder how long they will be available via Agilent….
In any case, the display board was $400+, the ROM board was $500+ and the cal was about $500, so my total investment to this point is around $3100 – a lot, but worth it. I just trust the 3458 without wondering if it is right. It is the only high-res measurer in the shop now, so it is right by definition. As Steve Rooke likes to say, “A man with one clock knows what time it is. A man with two clocks isn't ever sure.”
Best, Dick Moore
Hi Dick,
Something in your post caught my eye. Are you aware that, although performed at Loveland, Agilent's $500 cal is *not* performed in their Standards Laboratory. In order to receive their Standards Lab Cal, you have to specifically ask for that, and the cost is approximately $1350.
Basically their $500 cal is a STE9000 “Service Center” cal, although it's now performed geographically at Loveland. I'm the one who calculated the STE9000 version MU approximately 20 years ago. …And I tweaked the procedure a bit for a little better metrology. The STE9000 version calibration for 3458A was developed for field calibration, hence its inferiority to the Standards Lab cal.
Having intimately evaluated the two versions of 3458A cal, I would briefly summarize the situation as follows:
If you only need a “go / no go” status for your 3458A, then the STE9000 cal might be sufficient for you. But if you wish to actually use the supplied test data (that's supplied along with the calibration), then the STE9000 cal is insufficient and you instead want the Standards Lab cal.
Put another way, if you just want to depend on your 3458A performing within its published specifications, then the STE9000 cal is probably sufficient. But if you want to track or trend your 3458A by parameter - or to use its calibration test data as correction constants in your processes - then you must have the Standards Lab cal. (The MU of the STE9000 procedure is too high for the supplied test data to be of much value for those purposes.)
Knowing what I know, I'd rather send my 3458A for Standards Lab cal on a 3 year cal interval, instead of a one year cycle for STE9000 cal.
…apology if you already know this information… …Just putting out the info in case otherwise. I do know, in the past, confusion over this issue has “tricked” many customers into ordering the wrong 3458A cal based on a misunderstanding of what version calibration they're receiving.
Best, Greg
From: “Dick Moore” richiem@hughes.net
To: volt-nuts@febo.com
Sent: Thursday, August 26, 2010 1:29 PM
Subject: Re: [volt-nuts] HP 3458A cal
@Greg Burnett – thanks so much for that info – I certainly did not know that, and the folks at Loveland never articulated that difference either. What a difference. I really appreciate your information. Now, to find the rest of the cash somewhere…..
I'm assuming the STE9000 cal is automated – do you know whether they use a Fluke 5720 or 21?
Dick Moore
Hi Dick,
Agilent's online descriptions for 3458A calibration and services makes no mention of the Standards Lab calibration option. So no wonder so many customers order the wrong calibration. Yesterday in a phone conversation with their Call Center, I again gave my feedback that they should add a line item describing their Standards Lab Cal. They show that line item on their internal system, on their side of the firewall, but it doesn't show to external customers.
Yes, the STE9000 cal is automated. (STE9000 is an internal HP/Agilent test platform.) It supports the Fluke 5700, Fluke 5720 and Datron/Wavetek 4808. Because the published specs for these multi-calibrators are not tight enough to verify 3458A performance, the multi-calibrators are used only as short-term stable “power supplies”. The way it works is that, just prior to testing the UUT, STE9000 derives calibration correction constants for the multi-calibrator (being used as a stable power supply) by measuring it against a 'golden' 3458A (which is re-calibrated in the Loveland Standards Lab every 90 days). STE9000 also corrects these derived constants according to the Standards Lab's supplied data for the particular 'golden' 3458A. Because correction constants are used, basically this process traces back to the Standards Lab's original MU + 90 day drift of the 'golden' 3458A + 15 minute drift of the multi-calibrator + noise, thermals, etc. STE9000 monitors internal temperatures of both the UUT and 'golden' 3458A - the test aborts if either device deviates more than +/- 1deg C for the duration of the tests. The combined uncertainty of this process at least makes it possible to calibrate a 3458A in the field, but remains significantly inferior to calibration of your 3458A directly in the Loveland Standards Lab.
The question has always been, “How do you calibrate a state-of-the art DMM, and how do you come up with the right equipment/process to do it?” The answer is not easy.
Best, Greg