How can I use 2530B and 4065 to measure resistance between two selected pins?

[jrenzas]

I want to be able to select 2 pins on a test fixture with 2530B and measure the resistance between them with a 4065 DMM (all PXI). The pins in question are each in different 32-pin blocks, so I can match them to a 32x1 quad or 64x1 dual setup if necessary. I'd then measure resistance between several different sets of pins, like pin 0 to pin 33, pin 0 to pin 34, and pin 0 to pin 35, then pin 1 to pin 34, pin 1 to pin 36, etc. 

I understand how to measure resistance between any given pin and ground using the 2530B/4065 using the NI-DMM/Switch Express wizard, but it's not clear whether I can tell it to measure resistance between two different user-selected pins. I'm a labview newbie, usually write things in C#, so this may be something very trivial (I hope). 

Any ideas? 

Thanks,

- Russ

[Now_With_Underscores]

Hey Russ,

As you've by sure seen by now, the 2530B has a flexible architecture, allowing it to be one of multiple different multiplexers or any of a select few matrices.  The full list is available in the NI-Switch help.  You'll need to decide which topology best fits your needs, or if you want ultimate control, you can't go wrong with the native, independent topology.  Caveat: the native topology provides ultimate control, but that's not always a good thing if you don't know what you're doing.  For initial programming, I recommend connecting series resistors (say, 100 Ohms or so) to prevent the learning curve from damaging your new hotness 2530B module (e.g. if you short external power to ground).

Based on your post, I suspect the best 2530B topology for your application is the 1-wire dual 64x1 multiplexer topology.  Connect the common terminal of the first multiplexer to DMM+, and the common terminal of the second multiplexer to DMM-.  Then short each matching channel on both multiplexers together (e.g. 1a and 1b, 2a and 2b, etc).  Why?!?  If you truly want to connect any channel N to DMM+ and any channel M to DMM-, this is the most efficient method.  Of couse, a 2x64 matrix requires the same number of relays, but that's not a supported 2530B topology.  If you don't want to manually short each external connection and your channel count is low enough, you could also use the 1-wire 4x32 matrix, but you'd only be using two rows (unless you get creative and add another DMM and parallelize your testing (did someone say SwitchExecutive ;))?

It sounds like you're building a cable tester... if so, let me know and I'll tell you how to maximize your algorithm from N^2 to N... your relays will be happy cause they don't have to switch so much, you'll be happy because your test system will scale without the dreaded exponential, and your customer will be happy because it won't take hours to test a cable with tons of leads... but I'll hold off for now until you confirm your application... whatever it is, I can probably help you optimize your routing team... I'll just have to dust off my 'topology' hat, which is one of my favorites.

Also, if you're more comfortable using test-based languages, you can use most of our hardware sans LabVIEW (gasp_).  There are C++ examples installed on your computer already.  The NI-Switch Help (also located on your computer) walks you through the specific locations/functions.  

Happy clicking.

[jrenzas]

Looks like this is possible with the dual setup and all I've got to do is program it explicitly rather than via the express wizard. I suppose I'll have to watch out with triggering to ensure both multiplexers have completed their switch over to their new positions. Do I accomplish this with two separate switch lists (one for each multiplexer), or can I do it within one?

To use the 2530B, I need only implement an initialization (by topology?) of the switch, init the DMM, feed a switch list to a switching function within some kind of test loop, trigger the DMM after both switch events have occured, pass the DMM value to some kind of data structure (array, I suppose), trigger the next loop iteration, then once all the data is stored I just stash it into a file (csv, likely)?

Not quite a cable tester, though I did work in that industry once before. If I can't work it out myself, we've got a guy writing a larger labview app for us that we can have take care of it. The help is much appreciated though - the more comfortable I can get with labview the more I can consider it for projects in the future as well. 

- Russ

[Now_With_Underscores · Accepted solution]

Hey Russ,

I recommend starting with the following Example (located in the Example Finder (Help»Find Examples):
Hardware Input and Output»Modular Instruments»NI-Switch»niSwitch Dmm Switch Handshaking.vi

Since you're using a scan list, you can just drop both connections into the same entry and then the switch will wait for both to settle before sending a trigger to the DMM... problem solved.  For example, to connect CH1 to Com0 (DMM+) and CH93 to Com4 (DMM-), then take a measurement, then connect CH38 and CH120 to the DMM, you'd use the following scan list entry:

ch1->com0 & ch93->com4; ch38->com0 & ch120->com4;

Note you can only have one scan list entry per switch module.  Also, you can only have one scan advance and one measurement complete per switch module.