DAQmx Switch Problems

[Munk100]

Hello,

I have a PXI-1042 rack with a 8106 controller and a 2567 (independent topology) switch card running LV 8.5.  I want to control the relay outputs to turn a bank of external relays on and off individually according to the LV application.  I've used the examples shipped with LV as a basis for my app.  I chose the DAQ mx switch over NISwitch because it seems that DAQmx is Real time ready; this app will eventually loaded to a RT target. 

My problem is that I can turn each relay on and off individually, but when I turn two relays on in succession (first one then the other) I cannot turn them off individually.  If I set my boolean logic to turn both off, then both relays open.  I'm using the +5v supply and ground from the 2567 to operate two small external signal relays.  I've tried renaming the sub VIs  for the opening and closing of the relays with no success.  I've attached the program for your review.  Viewers will note that the renamed relay VIs are missing; I can send those later.

Thanks, Tad     

[Munk100]

I note that opening the VI may not work well since I've created some new (or renamed) VIs. Attached is a jpeg of the program.

[chericks1]

Hi Munk100,

I edited your example to accomplish what I believe was your initial goal: controlling the relay outputs to turn a bank of external relays on and off individually.  Looking at your code, I was confused as to the operations you were attempting to perform. 

The edited example I attached below also includes the functionality to do nothing when the Boolean state of your controls stay the same from one loop iteration to the next.

Hope this helps!

Chad Erickson

Switch Product Support Engineer

NI - USA

[Munk100]

Hey Chad,

Thanks for your rapid and helpful response!  I'm sorry to say that I still see the same response from your code as I did with mine: when both of the switches are closed, I cannot open them individually.

This phenomenon makes me start thinking about the hardware.  Could we have an issue of the FETs on the same ground influencing one another?  k0 and k1 share a common ground.  Could we have enough current leaking back through the FET to keep it on?  I'm using the +5V and ground from the 2567 card to operate my external signal relays.  I was thinking if I connect a pull up resistor across the relay card outputs I may be able to reduce any current leakage through the FET.  Does this make sense to you?

I just may try using other relays on the card, but I'm not sure if all of the FETs share a common ground.

Thanks again for your help!

Munk (aka Tad)

[chericks1]

Hi Tad,

The FETs were designed to share a common ground.  Note PXI-2567 Example Configuration.JPG.  Please confirm your configuration is connected in the same manner:

+5V - PIN 58

ground - PIN 42

ch0 - PIN 40

ch1 - PIN 60

I've also attached the PXI-2567 Pinout in case it needs to be referenced in the future.

Let me repeat the phenomenon to verify that I understand:

You can close k0 and k1 independently.  However, if both are closed, then attempting to open only one of k0 or k1 results in the other opening as well.

If this is correct, I've never heard of this problem occurring in the past.  Can you provide information on the external relays you are driving?

I'm not against using a resistor across the channels, except you don't want to have the opposite problem where you close k0 and k1 also closes.  

Let me know if you see the same problem when using other channels on the card.  Just so you know, all the FETs share a common ground (there are 8 Common Ground Return lines available because we didn't want customers to attempt using only one ground pin for all return paths). 

Thanks!

Chad Erickson

Switch Product Support Engineer

NI - USA

Message Edited by Chad PSE on 09-25-2008 02:03 PM

Message Edited by Chad PSE on 09-25-2008 02:08 PM

[Munk100]

Hello Chad,

Thanks for your continued help.  

I can close and open both relays independently.  When I close both relays I cannot open either relay independently using my code or your code. If I make both boolean cases false, then both relays open.  

Also, I confirmed that the wires are connected as follows:

+5v - Pin 58

Ground - Pin 42

ch0 - Pin 40

ch1 Pin 60

I'm still puzzled.

Thanks,

Tad 

[Munk100]

Hi Chad,

I  worked with an EE here and we found the problem.  I was using incorrectly using a prototype board to mount the signal relays.  The NC contact of one relay was connecting the coil of the other relay to gound acting as self-latching circuit.  Oooops, my fault.  

After we corrected the wiring, we can use your code and mine to independently control both relays.  

Once again, I greatly appreciate your valuable help.

Tad 

[chericks1]

Hi Tad,

I'm very happy to see you've solved the problem and are once again on your way! 

Best of luck!

Chad Erickson

Switch Product Support Engineer

NI - USA