[volt-nuts] HP 3458A

Dick Moore richiem at hughes.net
Fri Aug 5 19:12:53 UTC 2011

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...


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: < 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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