Author Topic: HP3478A DMM, zeroing test leads in resistance mode  (Read 1074 times)

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Offline gdnichols31

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HP3478A DMM, zeroing test leads in resistance mode
« on: August 16, 2020, 07:34:52 pm »
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?

Thanks
Gary :-//
 

Offline Jwalling

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #1 on: August 16, 2020, 07:43:36 pm »
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?

Thanks
Gary :-//

Are you are using it in 4 wire mode? That's the best mode if you want accuracy...
Jay

System error. Strike any user to continue.
 

Offline gdnichols31

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #2 on: August 18, 2020, 07:06:35 pm »
No, I'm trying to figure it out for 2 wire mode. I don't have a set of kelvin clips yet.

Gary
 

Offline bob91343

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #3 on: August 18, 2020, 07:21:36 pm »
I think you would just have to measure a short and subtract.
 

Offline coromonadalix

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #4 on: August 18, 2020, 08:32:58 pm »
have you tried the autozero function ??  page 19 of the user manual
 

Offline precaud

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #5 on: August 19, 2020, 02:44:39 am »
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.
 

Offline Verticon

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #6 on: August 19, 2020, 03:38:21 pm »
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).
 

Offline coromonadalix

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #7 on: August 19, 2020, 07:01:23 pm »
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/
« Last Edit: August 19, 2020, 07:14:27 pm by coromonadalix »
 

Offline coromonadalix

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Offline precaud

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #9 on: August 20, 2020, 02:22:46 am »
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

Looks like a project that stalled. Too bad, it's a sorely needed feature for the 3478A. It's why I don't use one.
 

Online Miti

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #10 on: August 20, 2020, 10:32:38 am »
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

Looks like a project that stalled. Too bad, it's a sorely needed feature for the 3478A. It's why I don't use one.

Take 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/
« Last Edit: August 20, 2020, 10:34:24 am by Miti »
That big spark at power up was by design!
 

Offline gdnichols31

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #11 on: August 30, 2020, 02:35:52 am »
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/

That'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
 

Offline gdnichols31

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #12 on: August 30, 2020, 02:37:58 am »
have you tried the autozero function ??  page 19 of the user manual

That's what I have been doing, I'm just lazy and would like for the meter to do it for me.
 

Offline Edward3121

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #13 on: August 30, 2020, 02:55:21 am »
It seem that HP3478 has no NULL function. So, you should use 4W OHM.
 

Online Miti

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #14 on: August 30, 2020, 11:52:16 am »
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/

That'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

HP3478 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.
That big spark at power up was by design!
 

Offline coromonadalix

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #15 on: August 30, 2020, 05:41:27 pm »
But the OP is lazy   loll   :-DD
 

Offline gdnichols31

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Re: HP3478A DMM, zeroing test leads in resistance mode
« Reply #16 on: September 19, 2020, 11:50:49 pm »
But the OP is lazy   loll   :-DD

You got that right!

I finally got around to ordering some kelvin leads today.

Gary
 


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