Cont Acq&Graph Voltage-Analog SW Trigger

[Richard_Z.]

Hi,

In the example Cont Acq&Graph Voltage-Analog SW Trigger.vi it seems to me that if you specifying a channel that the trigger comes in on then this would be a hardware trigger not a software trigger. Why do they call this a software trigger?

I have PCI6071E that I want to trigger by sending in a pulse though one channel (63). Wouldn't that be considered hardware triggering? If it is there an example for this available?

Also I'm not clear on what they mean by the "Window Amplitude/Hysteresis" setting in the Triggering Parameters. Could some one explains this for me?

Thanks!

[Dennis_Knutson · Accepted solution]

It's a software trigger because the detection of the trigger condition is performed by the subVI Analog SW Trigger. This subVI looks at the continuously acquired data on the trigger channel, and if it meets the conditions, the entire acquisition is graphed. DAQmx Read is always acquiring data. This is different with a DAQ board that itself supports triggering. With hardware triggering, the trigger conditions are monitored on the board and if they are not met, the board does not acquire data.

The Window Amplitude/Hysterisis is used differently depending on the trigger condition. If you choose rising edge for example, a voltage below the hysterisis level must be detected and then a voltage above the level setting. If you choose When Inside Window as a condition, it uses the Window amplitude and Level to calculate a window. Any voltage detected within this window will cause a trigger condition.

[CFJ]

Hi Dennis,

I'm trying to use the subVI Analog SW Trigger to detect a falling edge trigger signal from a high speed camera. The voltage signal is stable at 5.5V then falls to 0.25V. The instructions for a falling edge trigger are that the "Falling Edge condition needs to detect a value below the hysteresis level, then watch for a value above the desired level." I don't find this very intuitive, as I thought a falling edge would look for a value below some desired level, for example in my case 5V. In any case, given the instructions, for my case I would think these values should work:  Hysteresis level = any value above 5.5V, Level=any value above 0V.  I've tried many different combinations and can't seem to make it work - do you have any advice?

Thanks, 

Claire.

[Margaret F.]

Hi Claire,

Thank you for posting to the NI Forums! In the future, you may want to start a new thread for new issues and then link this forum since it's two yeards old, but I'll try to help you this time.

Can you please describe for me the behavior of the signal as it drops from 5V to 0.25V? Does it drop immediatly or taper down? This will help us pick the appropriate hysteresis level. Thanks!

[CFJ]

Hi Margaret, thanks for your reply and advice. I have since spent a few more hours and eventually figured it out - if I set hysteresis to 0 and level to 5.2, the software trigger works. However, I'm not clear on what the hysteresis value is doing - do you have a simple explanation?. My falling edge is very sharp, when I sample data at 10kHz, the signal drop occurs over 2 consecutive samples (i.e. the drop takes 1/10000sec). Is there a downside to setting hysteresis at 0?

Thanks, and have a great weekend, 

Claire.

[Margaret F.]

Hi Claire,

I found a Developer Zone article called on hysteresis. I think it provides a thorough explanation. Glad to hear that things are working!