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Proper Name/DIY Circuit For A DMM Switch Bank

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t1d:
My DIY Hobbyist work has become sophisticated enough to require multiple high quality DMMs to read various parts of a circuit all at the same time. I can not afford so many high-dollar DMMs, so I am wondering if there exists a switching bank that could handle multiple/6-8pairs probe inputs, to one/two outputs, wherein the outputs post-switch equal the inputs pre-switch exactly for volts, amps and resistance.

What is its proper name? Commercial unit has gotta be expensive, right?

Is it a DIYable circuit? If yes, any suggestions for a good DIY circuit. I can handle fairly extensive DIY manufacturing... KiCad boards, order them, I have a DIY Reflow Oven...

Thank you for your help.

rstofer:
Any 2 pole rotary selector switch can select any 2 inputs and output them to the meter.  HOWEVER, what are the odds that the meter is in the wrong condition (amps versus voltage versus resistance) when you change the switch?  I would expect this arrangement to be a recipe for disaster.  I guess you could disconnect the DMM from the switch output before changing channels but it still isn't a good situation (in my view).

I can't imagine needing to make as many as 8 measurements for any of my projects.  I might possibly get to 3 but it's not an issue because I have several multimeters (digital and analog).

Have you looked at the Aneng 8008?  It is a terrific meter for about $26 at Amazon.  I wouldn't trust the safety ratings (on ANY Chinese meter, for that matter) but, of all the meters I have, it is the one I reach for.  It's just a nice little meter.  Dave did a review and the accuracy was outstanding!

https://www.amazon.com/Alloet-True-RMS-Digital-Multimeter-Voltage/dp/B072JMBLJS



t1d:
Thanks, rstofer, for your help.
- A simple rotary switch is going to add influences to the reading... The significance of those influences will depend on the accuracy required. That's why I thought some negating circuitry might be required.  I guess it could be handled with just math... Determine the resistance the switching system adds and then account for it. But, that's not very efficient.
- You make a v-e-r-y good point about having to be careful about what mode you are in, when you change the switch. I had not thought of that one and it is extremely important, as you said.
- Well the only reason I ask the question, of course, is because I have a present need. For my current project, I could readily use six... It is a LT3081 PSU... So, Supply volts and amps, Output volts and amps, Iset voltage and Mon voltage. The two input DMMs could be read once and moved off, but my Bench PSUs don't have very nice/accurate/digits accuracy and I am curious as to what is going on on that side...
- Good suggestion on the cheap meters. I will look at the links.

I appreciate your interest, input and opinions. Thank you. I will continue to think on it.

rstofer:

--- Quote from: t1d on May 11, 2019, 06:22:59 pm ---Thanks, rstofer, for your help.
- A simple rotary switch is going to add influences to the reading... The significance of those influences will depend on the accuracy required. That's why I thought some negating circuitry might be required.  I guess it could be handled with just math... Determine the resistance the switching system adds and then account for it. But, that's not very efficient.

--- End quote ---

The rotary switch on the DMM itself is nothing more than spring contacts on PCB traces.  Older V-O-Ms used nothing more than a rotary switch.

http://www.electro-nc.com/faq.shtml
https://www.simpson260.com/260-3/simpson_260-3.htm

True, the 260 never had the resolution of a modern DMM but I don't think it was the rotary switch causing the limitation.

Any 'electronic' multiplexing will add complications due to scaling, injection current, limited range and so on.  You can look into analog multiplexers but I don't think it's going to work out unless you want to deal with the current shunt before the MUX.  But it could be done...

t1d:
Good stuff... Thank you.

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