Using CompactDAQ to acquire correlated force-position data started by a digital hardware trigger?

[cpschnuffel]

Hi there,

until now I use a NI6221 PCI card to acquire time-correlated data from two analog input channels and one encoder (A and B line), i.e. I get two voltages and one position for each sample. The acquisition start is hardware-triggered by a digital PFI line.

To additionally evaluate the inverted encoder lines /A and /B (to eliminate counting errors in harsh environments) I want to migrate this task to a CompactDAQ 9172 with a 9205 (for analog inputs), a 9411 (for differential encoder signals) and a 9472 (for additional static digital outputs) module inside.

My question: Is it possible to use the PFI0 input of the 9205 as digital hardware trigger to perform an acquisition described above? Or how should I continue?

Best regards,

cpschnuffel

[John_P1]

Hi cpschnuffel,

Because of signal routing issues, you may only use the PFI line of the 9205 in a cRIO chassis (see here). What you can do however, is use the 9411 or 9472 to trigger everything the same was you did on your 6221.

You can think of the cDAQ 9172 chassis as an M series device (the modules are essentially front-ends) with the following characteristics:

• Slots 1-4 support correlated digital I/O when using a correlated module in these slots (not important for your application as I understand it, but good to know nonetheless).  This would be equivalent to Port 0 on an M series.

• Slot 5 and 6 support triggering and counters when using a correlated module.  You can think of this as Port 1 and 2 (PFI lines) on an M series.

• Analog tasks and static digital I/O can be performed in any slot on the chassis.

So, putting the 9411 and 9472 in slots 5 and 6 would give you access to the PFI lines and Counters of the 9172 chassis.  Any unused channel may be used to trigger your tasks on the 9172.  For more information about all of this, I would check out the 9172 User Guide and Specifications.  Thanks for posting!

Regards,

John

[John_P1 · Accepted solution]

Let me make a correction to my last post... we actually do have support for the triggers of the 9205 (analog and digital) from any slot in the 9172.  The digital lines still follow the same rules that I mentioned before.

So, you can trigger off of the PFI line of the 9205 in any slot, or off of either digital module in slot 5 or 6.

I'll be sure to edit the KnowledBase article that I referenced once I get the chance to make it more thorough and clear.

-John

[cpschnuffel]

Hi John,

thanks for your quick and detailed reply. 

In the meantime I read your suggested documentation, and many things are now clear to me.

Let me embrace your explanation to make sure that I understand you right : It IS possible to migrate the measurement task to CompactDAQ. I may use the PFI line of the 9205 in any slot as trigger input (in this special case as start trigger with rising edge and as reference trigger with falling edge, because one external signal is used to start and to stop the measurement), or I may use any free input of the 9411 for this (or any free output of the 9472 as additional output trigger) if this module is plugged into slot 5 or 6. With this trigger I am able to start/stop a correlated measurement of two analog channels from the 9205 together with a position information from the 9411.

Is that correct ?

Best regards,

cpschnuffel

[John_P1]

Hi cpschnuffel,

You are correct that you may use the 9205 in any slot of the 9172 to trigger the acquisition (start, reference, or both).

You can also put the 9472 or the 9411 in slot 5 or 6 to gain access to the PFI lines of the 9172.  You can use these lines for the same types of routes that you would use the PFI lines on an M series for (Counter Input, Counter Output, Triggers, Clocks, etc.).  Note that even though these particular modules can only be used for either digital input (9411) or digital output (9472) tasks, you can use either for all PFI routes.  So, you could route a counter output to either module, or you could route a trigger to either module (provided the module is in slot 5 or 6).

You can trigger the 9205 along with the 9411 off of the same source.  You could also use the AI sample clock as the sample clock for your encoder task if you want to synchronize the measurements.  All of these routes are made through the cDAQ 9172 chassis and would not require any additional connections.

-John

[cpschnuffel]

Hi John,

that's perfect. Thanks for your support.

Greetings from Berlin/Germany

cpschnuffel