HP3478A DMM, zeroing test leads in resistance mode  - Page 1
Forum section: electronics / testgear

author: gdnichols31
author_rank: Regular Contributor
timestamp: August 16, 2020, 07:34:52 pm
content: I'm embarrassed to have to ask this,but I've looked in the manual and I can't find anything on it. Also looked on this forum.Can someone tell me how to zero out the lead resistance when measuring resistance?ThanksGary

author: Jwalling
author_rank: Unknown
timestamp: August 16, 2020, 07:43:36 pm
content: Quote from: gdnichols31 on August 16, 2020, 07:34:52 pmAre you are using it in 4 wire mode? That's the best mode if you want accuracy...

author: gdnichols31
author_rank: Regular Contributor
timestamp: August 18, 2020, 07:06:35 pm
content: No, I'm trying to figure it out for 2 wire mode. I don't have a set of kelvin clips yet.Gary

author: bob91343
author_rank: Super Contributor
timestamp: August 18, 2020, 07:21:36 pm
content: I think you would just have to measure a short and subtract.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 18, 2020, 08:32:58 pm
content: have you tried the autozero function ?? page 19 of the user manual

author: precaud
author_rank: Frequent Contributor
timestamp: August 19, 2020, 02:44:39 am
content: I think you have to do the Ohms cal in 2-wire if that's what you want. It doesn't store cal constants for both modes and apply which one is being used.

author: Verticon
author_rank: Contributor
timestamp: August 19, 2020, 03:38:21 pm
content: The 3478A has no possibility to calibrate the lead resistance out. The "AutoZero" is not for that purpose. Either you can substract the lead resistance by hand or use 4-wire method (4 normal wires are sufficient).

author: coromonadalix
author_rank: Super Contributor
timestamp: August 19, 2020, 07:01:23 pm
content: Hum there is a project here about the 3478 cpu hack and added functions, not sure if the was a zeroing available ?https://www.eevblog.com/forum/projects/project-extending-hp3478a-functionality/

author: coromonadalix
author_rank: Super Contributor
timestamp: August 19, 2020, 07:05:04 pm
content: you have this thread too about adding a relative mode ??https://www.eevblog.com/forum/testgear/hp-3478a-rom-modification-relative-mode/msg2048623/?topicseen#msg2048623

author: precaud
author_rank: Frequent Contributor
timestamp: August 20, 2020, 02:22:46 am
content: Quote from: coromonadalix on August 19, 2020, 07:05:04 pmLooks like a project that stalled. Too bad, it's a sorely needed feature for the 3478A. It's why I don't use one.

author: Miti
author_rank: Super Contributor
timestamp: August 20, 2020, 10:32:38 am
content: Quote from: precaud on August 20, 2020, 02:22:46 amTake a look at this project. It has everything you need, that’s why HP3478A is my go to bench multimeter.https://www.eevblog.com/forum/projects/project-extending-hp3478a-functionality/

author: gdnichols31
author_rank: Regular Contributor
timestamp: August 30, 2020, 02:35:52 am
content: Quote from: coromonadalix on August 19, 2020, 07:01:23 pmThat's the way I read the manual also. The zero cal only cals the internal parts, doesn't take the leads into account.I guess I need a set of kelvin leads.Gary

author: gdnichols31
author_rank: Regular Contributor
timestamp: August 30, 2020, 02:37:58 am
content: Quote from: coromonadalix on August 18, 2020, 08:32:58 pmThat's what I have been doing, I'm just lazy and would like for the meter to do it for me.

author: Edward3121
author_rank: Contributor
timestamp: August 30, 2020, 02:55:21 am
content: It seem that HP3478 has no NULL function. So, you should use 4W OHM.

author: Miti
author_rank: Super Contributor
timestamp: August 30, 2020, 11:52:16 am
content: Quote from: gdnichols31 on August 30, 2020, 02:35:52 amHP3478 cannot be calibrated in 2 wires and 4 wires in the same time, you have to pick one. Threfore, if your meter was calibrated in 4W, you’re good to go with Kelvin probes. If it was calibrated in 2W, not so much.The project linked above does relative measurements and much more so the leads are accounted for.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 30, 2020, 05:41:27 pm
content: But the OP is lazy loll

author: gdnichols31
author_rank: Regular Contributor
timestamp: September 19, 2020, 11:50:49 pm
content: Quote from: coromonadalix on August 30, 2020, 05:41:27 pmYou got that right!I finally got around to ordering some kelvin leads today.Gary