[volt-nuts] HP 3458A

Sat Aug 6 06:46:58 UTC 2011

To All,

I would like to comment on “Cal Labs.”

First, a “Primary Lab” is one that has attained a very high degree of accuracy and stability in their in-house standards and their methods of measurement.  Typically, few such Primary Labs actually exist within the context of the word “Primary.”  At this level, the Primary Lab’s main responsibility is to make sure their “standards and methods” are above reproach.  This is done by inter-comparison with other Primary Labs and constant research toward improvement.  No adjustments are made, just the mere recording of delta differences.  Indeed, many “standards” are not adjustable, they merely exist and are known to be stable and repeatable to a very high degree, no matter their actual value.  This level of inter-comparison defines the quality of the Lab.

The “Primary Lab’s” second duty is to bring into agreement all subordinate secondary standards that are utilized by the next { lessor level } Lab under the influence of that particular “Primary Lab.”  That second level “Lab” is a working type Lab where “customers” equipment are calibrated (adjusted) and repaired, if necessary.

This second level Lab will have a high degree of capability, but the emphasis is not on “maintaining a standard” within the meaning of that phrase.  Instead, their aim is service and production (i.e., getting work done) relative to their customers.

The cost of a real “Primary Lab” that covers all the disciplines is beyond extremely expensive.  Besides NIST and some NASA sites, the Navy, Army and the Air Force each have a so-called Primary Lab.  However, they may not all cover every discipline.  The one I am familiar with is the Navy’s Primary Lab that covered just about everything and a Secondary Lab, both here in San Diego, CA.

A true Second level Lab is also extremely expensive, not just because they have to have multiples of equipment for production work, but equally have to have a given level of parts available for repair.  And they would typically have way more people employed than a Primary Lab.

Relative to the Navy system, with which I am familiar with, the hierarchy extended itself below the Secondary Lab by several levels each with different capabilities and responsibilities.  The Navy system’s intent was to service the fleet where and as needed.

Hewlett-Packard (the old company) is no different, as they need to service their fleet of Research Labs and production facilities.  To quantify their high quality instruments, they have no choice but to have some form of a Primary Lab.  However, to service their Research and production facilities, they also need a Secondary Lab that does the actual work of maintaining all the equipment within the HP environment.  Most likely HP has third level Calibration Labs in their system.  Additionally, they also need to serve their customers who want their calibration services.

Fluke also maintains a Primary Lab with capabilities that meet their needs.  I am sure they also have a Secondary Lab to do the work for their general needs and customer requirements.

What do you actually get for a given calibration job ?  It all comes down to the amount of money you want to pay.  For the basic calibration service the instrument would have to meet all of its specifications or be rejected and a repair request from the customer to proceed further.  Beyond the basic calibration service, you are paying for a paper trail on what the instrument was doing before and after, and any special requirements that you, the customer, requests.

The hp-3458A is NOT a Primary Standard !  At best, it can only qualify as a transfer standard at some level within a limited set of circumstances.  If you carefully read the specifications, you will noticed a bunch of conditions pertaining to the specifications.  For the 3458A to reach a given level of quality and reliance the user would have to meet all of those conditions.

The average user, generally, never even comes close to meeting those conditions.  The individual hobbyist never has a chance unless that person is very well off and builds a personal lab at a level few could afford.  First off, it is damn hard to control any reasonable size space to within a 1 degree temperature variance and adjust it to the TCAL value.  The end result is all you can count on is the worse case specifications taking into account all of the error variances which in the end means all those stated numbers get worse.

So, after all of the above, my point is that it does not make sense to spend more then what the basic calibration service offers you.  You would be better served spending money, first { on trying to improve your home lab } and second; buy at least four Fluke 731 or 732 voltage references and some extreme quality standard resistors from which you can use to verify the operation of your fancy meter after you fix the LAB !

Unless you are doing something life threatening with the equipment and need to cover your A** legally, it makes no sense to go crazy in the wrong places.

My two cents;

Bill....WB6BNQ

Steve wrote:

> I went the other way when I found the dates on my ROM board chips was 1994. I bought replacement chips, did an ACAL, desoldered and read the old chips, burned the new ones, installed sockets and the new chips, did another ACAL, and all was well. I've kept the old chips and will read them every now and again to see how long the on-chip cells actually last.
>
> I haven't sent the meter in for calibration yet. Hoping Santa might bring that for Christmas. Our local Agilent rep swore the only difference between the Agilent $550 calibration per incident and the pricier ones offered is the amount of paperwork you receive; the actual calibration is to full specs for all functions and all ranges. The Agilent web site seems to say the same thing, so I'm a bit confused by others saying there's calibration and there's full calibration. I need to go read the information provided by Greg Burnett and then approach Agilent again. When I was in metrology full time, all calibrations were to full specs or you had to clearly note any deviations and get the customer to buy off on them. It was amazing how many would accept things I wouldn't accept for my home lab!
>
> Steve
>
> On Aug 5, 2011, at 2:12 PM, Dick Moore <richiem at hughes.net> wrote:
>
> > Hi Roy -- please see the link posted by Marv, below -- it covers things pretty well.
> >
> > About the ROM board -- You get it from Agilent, and the swap is fairly easy to do, but it requires a new cable because the new board is physically much smaller and the cable needs to be longer. Best way is to order the complete kit (sorry -- I can't find the part number now) which is the board and the cable; it was about $500. Note that changing the ROM board eliminates all previous cal data, so it needs to go for a cal. As noted in the various posts in the link from Marv, I did not know about the difference in cal levels described by Greg Burnett, so I got the STE9000 cal by default.
> >
> > While the 9000 level cal is not up to the full capabilities of the 3458, the test guys do check all of the basic operations of the unit, including the integrity of the various relays which, if they have bad or high resistance contacts, can really mess up stability. I had sent the meter to Loveland, and they called me to tell me that it had a problem with the ROM board and that it needed to be replaced -- bad batteries. The tech said that all the basic tests showed the unit to meet new unit specs except for the battery issues, so that made me confident that the ROM board replacement was money well-spent. I had them send it back to me and I ordered the board. They didn't charge me anything for the first round, which was very nice of them, so I was only out the shipping costs. Then I sent it back to them for the cal, which was another $500 or so.
> >
> > I had a couple of Fluke 732As at the time which I had repaired and had set to 10V using a Datron 1081 in it's high-res 7-1/2 digit mode. When the 3458 came back from Loveland, the 732s both measured within 2ppm of 10V (and in the same direction) according to the 3458, so I guess the old Datron meter was really good. That level of correspondence, while definitive of nothing, gave me a lot of satisfaction and made me fairly certain that I was going to get very good 6-1/2 digit accuracy from the 3458, and as noted on the list, outstanding linearity, which means real trustworthiness over the whole measurement span of each range.
> >
> > The only thing I miss with the 3458 is the extensive math capabilities found in the older 3456, etc., particularly the dB measurements...
> >
> > Best,
> > Dick
> >
> >
> >
> > On Aug 5, 2011, at 9:06 AM, volt-nuts-request at febo.com wrote:
> >
> >> ------------------------------
> >>
> >> Message: 4
> >> Date: Fri, 5 Aug 2011 15:54:03 +0100
> >> From: "Roy Phillips" <phill.r1 at btinternet.com>
> >> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> >> Subject: Re: [volt-nuts] HP 3458A
> >> Message-ID: <3AAC8F9DA58A48AAAAF3368F57865C46 at LapTop>
> >> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
> >>    reply-type=original
> >>
> >> Dick
> >> Re: HP 3458A
> >> Please can you advise me on the replacement ROM board - what is the cost ?,
> >> where did you  purchase it from. Can it be obtained in the UK ?  Is it a
> >> straight swap, or does it have to be installed and re-calibrated by Agilent
> >> ?
> >> Best regards
> >> Roy
> >>
> >> --------------------------------------------------
> >>
> >> Message: 6
> >> Date: Fri, 05 Aug 2011 11:30:08 -0400
> >> From: "Marv Gozum @ JHN" <marvin.gozum at jefferson.edu>
> >> To: Discussion of precise voltage measurement <volt-nuts at febo.com>,
> >>    "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> >> Subject: Re: [volt-nuts] HP 3458A
> >> Message-ID: <6.2.5.6.2.20110805110035.02a6c7b8 at jefferson.edu>
> >> Content-Type: text/plain; charset="us-ascii"; format=flowed
> >>
> >> $3k is sweet.  I've tracked 3458a on eBay for 2 years and the lowest
> >> I've seen it sell for is $1k, today its typically $2-3K, if not
> >> working.  Replacement board costs vary.  The Loveland metrology cal
> >> alone is over $1,000 IIRC.
> >>
> >>
> >> Here's an old chat we had about the 3458a, this is when Dick was just
> >> putting his 3458a together:
> >>
> >> http://www.ko4bb.com/dokuwiki/doku.php?id=test_equipment:hp_3458a_precision_digital_multimeter
> >>
> >
> >
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