Trying to measure voltage through SCXI-1127/1331 2-wire connection [ Edited ]

[mady]

Hai ,
     this is madhava from LSU,I am working on ERT with  NI hardwares like 1)chasis 1000 2) DMM PCI-4060  3)  SCXI -1331(2 in number)
      I have a system with two large glass plates standing vertically and placed parallel to the user.I am trying to flow different liquids of density through the channel in between.Please  see a attached picture of it.
    There are total of 48 electrodes 24 on each side to which wires are connected. On each side there are 3 rows with 8 electrodes/row, say 1-24 on side A and 24-48 on side B. The medium between the two sides is salt water.
   
     I want to measure the potential in such a manner that  I can calculate the voltage difference between all possible electrode combinations between side A and side B.I have connected a  two end power source to side A and side B, i.e. +ve to side A and  -Ve to side B , so   the  electrode on the A side acts as the "source" and the electrode on the B side acts as "sink".


    I want to use 2 SCXI- 1331 's for this experiment.

    I tried it with 1  SCXI - 1331, but did not get proper values.So what do you suggest shall I continue this with the 1  wire or could you please help me with the two wire experiment, so that I can get more combinations.
           I hope you respond soon and in the affirmative.
With regards
Madhava

[Mark_E]

Welcome to the discussion forums, Madhava!

The optimal solution is to have a 2x48 (or more) matrix so that you could easily choose one point on either plate (column) connected to one lead of the DMM (row0) and another point on the other DMM lead (row1). Since the SCXI-1127 doesn’t support this configuration, you’ll have to try something else with your existing hardware.

Because you can only use a multiplexer setup instead of a matrix for your number of signals, the closest you can get to the above suggestion is to measure one electrode to ground and then read the next electrode to ground and include logic to find the difference between the two voltages. I suggest you start with a LabVIEW shipping example (Help » Find Examples) such as niSwitch DMM Switch Synchronous Scanning.vi or niSwitch DMM Switch Handshaking.vi (found under Hardware Input and Output » Modular Instruments » NI-SWITCH). You will have to modify it to include another SCXI-1127 and set them both up in a 1-wire 64x1 multiplexer topology. Take measurements as quickly to each other as possible on both switches. Again, this is a workaround to what you really should be doing for optimal performance (and the easiest setup).

The last option is to limit your measurements to electrodes directly across from each other (or any other fixed mapping setup) and use a 2-wire 32x1 multiplexer topology. By nature, this is taking a differential signal measurement between two constant points. This would allow you to easily use LabVIEW’s shipping examples without modification.

I hope this helps you get a feel for your options and the consequences of each.