Looking for microohm meter. - Page 1
Forum section: electronics / general

author: alligatorblues
author_rank: Regular Contributor
timestamp: July 16, 2022, 10:59:46 pm
content: I was looking at the Keysight 34420A nanovolt microhom meter. But at the prices they are selling for I suspected the product may be obsolete. I found one posr her e that confirmed that. Are there any other products similar to the 34420A? I need the precision for measuring 1 Ohm to 10ppm. The 3458 can do it, and I have one, but the terminals are not ideal nor the input amplifier.I'm having serious problems with repeatability within a few ppm. Keysight touts 34420A as having very repeatable readings and high linearity! But even it is not ideal. I'd like something with lower LT drift. Otherwise calibration will kill me. It's over $600 per. Whereas the Fluke and Keysight 6.5-digit multimeters are 200-300 USD per.I haven't done a significant amount of metrology work. But this message board has all kinds of stuff no one ever learns in school. I'M flat out amazed. If anyone could put the infirmation into a textbook, it would be the best textbook ever. But I guess it wouldn't really fit in a book, or even a library.

author: TiN
author_rank: Super Contributor
timestamp: July 17, 2022, 01:18:03 am
content: Typically standard shunts in microohm realm use high current resistance bridges, so you can calibrate them at rated nominal currents.So DMM alone is a poor instrument to do microohm metrology in first place, because it has very limited current source capability.But 34420A combined with low-noise current source (e.g. calibrator) would give you decent results.I got some of suchmeasurements done beforeusing 2182A voltmeter and 5725A+5720A as 10A current source.

author: beanflying
author_rank: Super Contributor
timestamp: July 17, 2022, 02:42:13 am
content: Several years ago I got lucky and scored an older Quadtech 1880 Milliohm meter very cheap. It runs rings around my 34401A and 34461A under a few ohms as TiN mentions due to the test current mainly.So add Quadtech, Chroma, Hioki and a few others to your search list along with the usual suspects.Under 2it runs 100mA and under 20m1A. The 100range on a 34401A as a comparison is 1mA.https://82fai3h5wg8220a0l3ilfiz1-wpengine.netdna-ssl.com/wp-content/uploads//2015/09/QUADT1880.pdf

author: Pip
author_rank: Contributor
timestamp: July 17, 2022, 10:30:50 am
content: The Keysight 34420A Nano Volt / Micro Ohm Meter is not obsolete as far as I can tell. It's still available from Keysight.The Keithley 2182A Nanovoltmeter is similar to the 34420A except that you require an external current source e.g. Keithley 6221 (or Fluke calibrator as TiN has mentioned) to measure resistance.You will probably find that the Fluke 8508A Multimeter is a better ohmmeter for measuring 1 ohm than the 3458A. It has a 2 ohm range, on top of the 3458A's 10 ohm range, which provides more resolution and 100 mA of current. The downside of course is the cost involved in purchasing one.What is your desired measuring current? This will help to specify a suitable meter.Do you have a 1 ohm standard resistor that you can use with the 3458A's voltage ratio function? This would be the most economical method along with long-term stability.

author: alligatorblues
author_rank: Regular Contributor
timestamp: September 13, 2023, 08:09:22 pm
content: Sorry for necroposting, but I just spoke to my service rep at Keysight, and the 34420A is a current model, starting at $7,629.00.