trigger delay

[MikeCamer]

I have a digital trigger switch which is connected with an NI module. How can I know the amount of delay from the trigger to the Ni module?

[James.M]

Depends on your device. Each device has a rating on the scale of microseconds.

[MikeCamer]

Here is the data sheet..is this the one saying propagation delay 3 ms? how do I account for ?

[James.M]

That's 3 microseconds. Plus the rise/fall time of 50 nanoseconds.

Do you have something switching that needs to account for that small of a switching time?

[MikeCamer]

I have a data acquisition test that lasts for about 20 milliseconds..Do I need to consider this delay?

[James.M]

That depends on the application. 

3ms is 1/6667th of your trigger time. In everything I've worked on before, this isn't an important amount of time.

[MikeCamer]

Just to clarify, If the trigger is recording on the falling edge we have: 

50 nanoseconds = 0.00005 milliseconds (rise time)

Propagation delay = 3 microseconds = 0.003 milliseconds (propagation delay)

In total, we have a delay of 0.00305 milliseconds. If the test will last only 20 ms from the time the acquisition is triggered, I guess this delay can be considered as negligible?

[James.M · Accepted solution]

Yes.

AKA 0.00000305 seconds out of 0.02 seconds trigger duration.

AKA 305usec out of 20000usec

AKA 0.305nsec out of 20000000nsec

It's up to your application if it's negligible. If the nuclear reactor is going to explode in 2 microseconds unless this digital trigger shuts its down first, you're hosed. Otherwise, good to go.

Nothing is instantaneous, including any input signals you have. The propogation delay is on the rising and falling edge of the signal, so the signal length will still be 20ms, it will just be shifted by the 3us delay.

[MikeCamer]

Thank you very much for solving my question James 🙂