Change scan list on the fly

[barak]

Hi,

I'm using PXI 1033 with PXI 2532 switches and PXI6602 counters with Labview.

My main task is to close a relay in a matrix for a predefine time exactly 1ms and to be able to repeat this on the fly with different relays..

My first (fail of course) try was to use a NI switch VIs with the following sequence :1) NI switch Close relay  2) (Labview) wait ms (my desire time) 3) NI switch Open relay

The accuracy I got was sometimes 1ms and some times 10ms. It depend on the windows timing.

Then I tried to use the scan list with an external trigger generated from the PXI6602.

Here I have a problem that I was not able to change the list on the fly without effect other relays.

When I tried to use NI switch Close VI and then configure the list again , all VI that were listed in the list changed to open when the close VI finished.

When I didn't used close but try only to change list all relays that are not in the list changed to open.

I would like to know if there is a way to change the scan list on the fly (using external trigger) without effecting relay (Only what is in the list is done and no other effect on relays).

I'm relay stack here, It is very argent for me to find a solution.

[Now_With_Underscores]

Hey Barak

A few notes:

1. The relay operate and release times on the 2532 are 250us, so we need to define what you mean by "exactly 1ms".  If you are comfortable with 750us-1250us, then the mechanical delay is accounted for.

2. The delay between when the trigger is received at the 2532 and when the 2532 commits the change is nonzero, but less than 10us... I just thought I'd mention it because "exactly" means 1.000000ms.

3. Depending on how 'exactly' you need to close the relays, you might need to move to a FET based switch, such as the 2535 or 2536 which has a maximum operate/release time of 16us.  Note that the 2535/2536 won't meet your needs if you're operating above 12VDC/8VACrms.  We do sell other switch modules that could meet your needs, so let us know more about your system if the 2535 or 2536 modules don't meet your needs... 

4.  When we enter scanning mode, the relays are going to reset with each entry unless you place the switch module into 'no action' mode.  'No action' mode means that when you close a relay, it will remain closed until you explicitly open it, and will remain open until you explicitly close it.  To enable 'no action' mode, set the 'scan mode' input of the configure scan list VI to 'no action'.  Now each connection you make will remain connected until you explicitly disconnect.

5. NI switch modules do not support simultaneous software/hardware calls to the module.  You will need to place all scan commands into the hardware scan list.  With the proper scan list, you should be able to achieve what I think you're trying to do.

Let us know if you have any questions.

[barak]

Hi,

Thanks for your answer.

1) the performancce of the 2532 is good for me. what I mean is that 1ms+- 0.1ms is ok, much much better then windows timing!!!!--)

2) I know the no action property, It doesn't help me. I want to reload the list on the fly. when i do this on the fly , all relays are getting open for some reason.

Issue 2 is what  i need help in.

[Now_With_Underscores]

Hey Barak,

Due to the architecture implementation, whenever we load a new scan list, the existing list is reset.  If the list is dynamic and changes based on user input, then we'll need to reload said list each time the scan order changes.  Another method would be to use a realtime operating system with deterministic output, so that we can guarantee execution speed.  Such a system has us execution accuracy.