NI USB 6525 Delay timer

[sahani]

Hi,

I am using the NI USB 6525 DAXmx for digital input and digital output, but I am introducing a Delay in between when the triggers the input and gives true state to output. the program is running ok in labview but when I am using the same program and connecting a another data aquisition kit to check the actual delay in ms , i am getting more delay than the delay i have input.

I am using this program in windows PC, can anyone help me if  why the actual dealy i am getting is more than the delay I want .

I have attached a screen shoot of the VI i am using.

Thanks

Veer

[herrlin]

Veer

First, you chose an interesting method for sharing you code, most people attach a VI.  I believe why you are seeing the difference is because of you use of express VIs, express VIs have a certain amount of over head associated with them because they have to create and run the task.  Also, the method you are trying to implement is a software based trigger.  I imagine that this method is not only inaccurate as you described but also not that precise, meaning the delay varies a good amount from run to run.  I am not sure your device supports it but what you need to do is configure the trigger so that it is hardware based.  If I have time later I will try to see if you device can do this and post an approximate example, in .vi format, for a starting point.

Regards

[sahani]

Hi Herrlin,

Thanks for the information, yes the delay vaires from run to run and it varied a lot .

it would be helpful if you can figure out how i can improve the dealy timing.for your refernce i have attached the VI.

Thanks

Veer

[herrlin]

Veer

From you code I believe you are trying to generate a logic high signal on your output line a certain amount of time (a delay), after a high signal is received on an input line.  Unfortunately I looked up you device and it doesn’t support triggering or hardware timing, both features would be needed to do this with any kind of accuracy and precision.  Here is a good example if you had these features, https://forums.ni.com/t5/Example-Code/Start-a-Task-with-a-Specified-Delay-After-a-Trigger-Using/ta-p.... 

A work around with your device would be to implement some code that continuously polls your input then upon the desired state start a task that will output your desired signal.  Unfortunately, since this is method is dependent on software timing you will not be able to achieve very good accuracy and precision.  Do you have any idea of the kind of accuracy and precision you need?  If you need sub seconds’ accuracy and precision then I would recommend getting a different DAQ, something with hardware timing and triggering capabilities.  I use a USB-6353 a bit and believe this could do what you are looking for but an NI rep could direct you better if you had some requirements to work from.

https://www.ni.com/en-us/shop/model/usb-6353.html - usb-6353

https://www.ni.com/en-us/shop/model/usb-6525.html  - usb -6525 notice no triggering abilities under specs

Regards

[sahani]

Hi Herrlin,

I want the delay to be as precise as 1ms accuracy, because where I am going to use this application depends all on the delay.

Is it possible to use the same hardware but trigger by the software input using a virtual channel in the input and then after a delay to get the output or I  need to buy a new harware to trigger it correctly.

I was trying to work the delay trigger Vi provided by you but it is not working with my hardware, it comes up with an error as  Physical channel specified does not exist.

Thanks

Veer

[herrlin]

If you are looking for 1ms accuracy you should consider new different hardware.  The reason you are getting an error is because you hardware does not support triggering in this fashion as i believe i mentioned in my early post.

Good Luck