2569 timing sequence

[Ali M]

Hello,

The best recommendation would be to look into hardware timing as earlier suggested by John. According to the nature of your application, using hardware scanning would definitely povide you with

determinism and eliminate most of these latencies. Perform a test using a predefined scan list onto the switch, then use hardware triggers/digital pulse to determine when the module advances to connect the next set of relays.  To gain access to a scanlist example, LabVIEW demonstrates how to scan a series of channels and take measurements (replace the DMM functions with a digital pulse)using synchronous scanning (LabVIEW 8.2»Help»Find Examples»Click on the search tab and search: synchronous»Switch Scanning with DMM-Synchronous.vi).

Thank you,

Regards,

Ali M

Applications Engineer

National Instruments

[Ali M]

Message Edited by Ali M on 04-02-2010 05:27 PM

[MI-CAL]

I'll look, but it seems you haven't answered my first question.  Long story short, if I am only calling for 1 channel to activate at time X and another channel to activate at time Y, the timing is fine, but if I call for 10 channels to activate at time X and 10 other channels to activate at time Y, it seems YOUR A/D on the board can't handle it.

I am struggling how a counter will alleviate this concern.   I'm happy to send you a .vi for you to look at if you wish.

[Ali M]

Hello MI-CAL,

We are currently looking further into your inquiry, I will post an update of the results (also, feel free to post your VI).

Thank you,

Regards,

Ali M

Applications Engineer

National Instruments

Message Edited by Ali M on 04-06-2010 06:56 PM

Message Edited by Ali M on 04-06-2010 06:58 PM

[Ali M]

Hello,

The solution attached demonstrates how to incorporate the counter on your 6225 card to send a trigger to initiate hardware synchronous scanning. The first scan list entry is a ‘;’ to tell the switch to connect nothing when we start. In order to obtain about 7ms gap between successive relay closures for the first and second relays, adjustments to the frequency value (front panel control) were made, in this case approx 142 Hz (t = 1/f). Since we expect the relays to take around the same time to physically close, we would send one pulse to the switch to engage the first relay, followed by another pulse 7ms later to switch to the next configuration. As you brought up earlier, using a software timed solution will exhibit longer delays when connecting additional relays simultaneously due to the reliance on the communication between the computer and hardware. With a hardware timed solution, the computer to hardware communication is limited and the determinism is greatly improved.

Ali M

Applications Engineer

National Instruments

Message Edited by Ali M on 04-08-2010 04:17 PM