8.5 digit DMMs, who needs this much precision? - Page 1
Forum section: electronics / beginners

author: Nasreddin
author_rank: Newbie
timestamp: July 16, 2020, 07:39:36 pm
content: My employer is restructuring and has reduced both its scientific staff and its laboratory space. Some nice equipment from another division was written off and scrapped.Thankfully I had shared my nascent interest in electronics design with a couple people before this started, and they were kind enough to tell me when choice items were being discarded. My home bench is now happily populated with a small collection of power supplies, signal generators, digital multi meters, and a couple analog Tek scopes. I can't really imagine what else I will need.But to my question, one of the multi meters I was gifted was a 3458A and I'm not sure what to make of it. I've never needed more than 5 significant figures in my personal, school, or 10 year professional life.Outside of a metrology or calibration lab, what use do 8.5 digit DMMs have? Are they just an expensive novelty for hobbyists?edit to add a little more detail: My own experiences and needs rarely exceed 10^-3 to 10^6 Hz, 10^-6 to 10^1 Amps, or 10^-3 to 10^2 Volts. Reading this forum and other sources implies the 3458A needs active care and attention to stay stable and calibrated, and I'm wondering if I've inherited a tool that I'll damage through misuse or lack of use.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 16, 2020, 07:46:35 pm
content: The 3458 is still a high end meter. It is not just 8.5 digit resolution, but also fast at 6 or 7 digits. So it could be used in automated test setups for the speed.Even if old they are still quite expensive.

author: dr.diesel
author_rank: Super Contributor
timestamp: July 16, 2020, 07:55:22 pm
content: Quote from: Nasreddin on July 16, 2020, 07:39:36 pmCongrats! One can never have enough 3458As.

author: bdunham7
author_rank: Super Contributor
timestamp: July 16, 2020, 08:06:17 pm
content: That's quite a gift. Most people don't have a need for such a thing, I don't even need a 6.5 digit DMM (but I have two...). They have their uses--calibration, metrology, keeping your other devices accurate, research in areas like batteries and low power systems with wide dynamic ranges, etc etc. The linearity over a wide dynamic range is one of its key features.How old, what brand label (HP, Agilent or Keysight) and what overall condition? You could certainly sell it for a few thousand bucks if you make sure it is clean and operating correctly. But you probably won't--it will still be sitting on your bench a year from now giving you the EXACT state of charge on your 9V batteries.

author: exe
author_rank: Unknown
timestamp: July 16, 2020, 08:21:17 pm
content: It's a very old dmm from eighties. Not worth much, but I can help disposing it for free, just send it to me (I'll pay for postage)

author: Nasreddin
author_rank: Newbie
timestamp: July 16, 2020, 08:48:13 pm
content: Quote from: bdunham7 on July 16, 2020, 08:06:17 pmIt seems to be a 2013 Agilent, at least that's the last year I found a record for calibration on Agilent's website. A couple 34401A's came along with it and I'm much less nervous about using them.Most of my career has been battery research from the chemistry side for which +/- 2mV was good enough. I also salvaged a 3 channel x 7.5nA - 750mA potentiostat for the real cell characterization. This is the instrument I really understand how to use.I was very grateful knowing how prized 3458s are in the electronics community, but I'm also a novice who can barely translate a schematic onto a breadboard. I hope with some hands on tinkering I'll develop a better understanding of the battery management system design.Quote from: exe on July 16, 2020, 08:21:17 pmAll the cool guys are using Flukes now.

author: sokoloff
author_rank: Super Contributor
timestamp: July 16, 2020, 10:55:11 pm
content: If you don't have a use for the 3458A and have a couple of 34401As, you probably do want to just sell the 3458A.It's likely to bring $3.5K or more if you can convince the buyer that it's fully working.With two other decent benchtop meters, you'll probably enjoy the cash more than the meter you're afraid to use.

author: 0culus
author_rank: Super Contributor
timestamp: July 16, 2020, 11:11:56 pm
content: The 3458A is an awesome meter. So awesome, in fact, that Keysight is building them again (RoHS compliant this time). It could be a very useful high speed 6-7 digit meter. It can also be used as a calibration standard for less precise meters. However, to do this, you'll have to keep your 3458A calibrated (moreso if it's not equipped with the higher stability option) and this isn't cheap to do. Owning a 3458A and keeping it in cal is more like renting the damn thing because it's unlikely you'll also have the proper equipment to calibrate it. For this reason, I went with a 3456A instead for my "good" meter because it is far less demanding and you can find them for very cheap if you're patient. Even busted 3458As fetch thousands.

author: 0culus
author_rank: Super Contributor
timestamp: July 16, 2020, 11:21:13 pm
content: Quote from: Nasreddin on July 16, 2020, 07:39:36 pmOn another note, you have a pretty awesome employer to let you take your pick of stuff to take home.A lot of them are wankers these days and will as soon have it all crushed and destroyed as let that happen. Come join us at Test Equipment Anonymous and share pictures of your stuff!https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/

author: WattsThat
author_rank: Frequent Contributor
timestamp: July 17, 2020, 12:42:00 am
content: If you have any plans at all to sell the unit... and if the unit has been calibrated by Keysight, contact their customer care department and get the calibration report history. Explain the situation to KS that you work for the company, better yet, send them an email from your work email and open a Keysight account. You should be able to have Keysight open the permissions to the reports for you but they should all be available online. Download whatever cal history you can, I think KS keeps eight years available online.Cal reports showing the stability over time and can increase the sale price as the stability history is usually a big unknown when buying used equipment. Of it depends on who is buying.It will not be long before you’re hanging out with the VoltNuts.

author: MosherIV
author_rank: Super Contributor
timestamp: July 17, 2020, 07:07:41 am
content: QuoteNothing too hard. Keep the temperature stable. Try to keep the humidity stable too.To get the resolution, the meter needs to be 'warmed up', basically powered up for at least 1 hour for the internal reference to warm up and stablize. Same storage condition for both storage and use.As other have said, you only need to calibrate it if you need traceability, all calibrations do is measure the device for inaccuracy and give you a report.