In need of sanity check -- measuring a coin-cell voltage with a Fluke 113 - Page 1
Forum section: electronics / testgear

author: wobbly
author_rank: Regular Contributor
timestamp: June 29, 2024, 07:34:14 pm
content: I recently scored a Fluke 113 for cheap from the interwebs.The first thing I tried was to connect it to my bench PSU and it works well. It can't measure anything below about 0.6V (I suspect because of its elaborate automatic "V-Chek" mode). Decent results up to 30 VDC which is where my PSU stops. Great, I'm pretty happy so far.The second thing I tried was to test a coin-cell (CR2025, 3V Lithium) that was lying around nearby on my desk. Another meter (known good and highly accurate) verifies this cell is about 3.2 volts.When I connect the F113's black lead to the negative of the cell and red lead to the positive, I get NO READING from the meter. Swapping the probes, gives a reading of -1.541 volts. What the heck?I don't quite understand the discrepancy. Is this mismatch due to the "Low Impedance" input of the meter? Is the ESR of the coin-cell interacting with the meter's low impedance input?Is this normal for a low impedance input range on a DMM? And in particular on an F113?

author: RoGeorge
author_rank: Super Contributor
timestamp: June 29, 2024, 08:23:16 pm
content: About the CR2032 measurement, keep the other known-good multimeter connected to the battery, then add in parallel the probes from the Fluke 113, to see if the CR2032 battery remains at 3V, or drops to zero.

author: J-R
author_rank: Super Contributor
timestamp: June 29, 2024, 08:52:36 pm
content: https://www.fluke.com/en-us/product/electrical-testing/digital-multimeters/fluke-1133. Minimum measureable input in VCHEK autorange is 3 VDC. For measurements below 3 VDC, push Range button twice to get to 6 VDC manual range.VCHEK Input impedance (nominal) ~3 kΩ < 300 pFThat model is designed for specific use cases and so I wouldn't consider it ideal as an all-rounder DMM. 3 kΩ is going to drag down the coin cell voltage.

author: wobbly
author_rank: Regular Contributor
timestamp: June 30, 2024, 11:48:39 am
content: Quote from: RoGeorge on June 29, 2024, 08:23:16 pmQuote from: J-R on June 29, 2024, 08:52:36 pmI see, yes the F113's internal impedance does indeed pull the coin cell down to about 1.5V. Then both meters read the same value.Yeah, I guess this meter was designed with some specific profession in mind. Not sure what, electricians perhaps? Perhaps the LoZ mode is handy for testing RCD breakers.Thanks both.

author: tooki
author_rank: Super Contributor
timestamp: June 30, 2024, 12:11:58 pm
content: Quote from: wobbly on June 30, 2024, 11:48:39 amFluke’s handheld meters are essentiallyalldesigned for electricians, other than the automotive model. Look at their marketing material: it always shows electricians in industrial settings. They use the word “industrial” on everything.The only multimeters they make that really are intended for electronics are their bench multimeters, which have been neglected for years. I think they only sell one model now.Quote from: wobbly on June 30, 2024, 11:48:39 amNo. LoZ is for eliminating “ghost voltages” caused by capacitive/inductive coupling in mains wiring.

author: Njk
author_rank: Frequent Contributor
timestamp: July 01, 2024, 08:16:25 am
content: Quote from: tooki on June 30, 2024, 12:11:58 pmWhile some of their test leads such as TL910 are excellent for electronics. Thin and flexible wire that feels like there is no copper inside, thin and sharp needle made of good steel. A model for cheap clones of various quality

author: tooki
author_rank: Super Contributor
timestamp: July 03, 2024, 08:22:20 am
content: Fluke’s test lead subsidiary (Pomona Electronics) makes a lot of electronics test leads, some under the Fluke name, most under the Pomona name, and some are sold under both brands.