Two independent but synchronized pulse outputs

[Plasmaexp]

Hi everyone,

I have a NI cDAQ-9174 with a NI9401 card (4 counters, 8 DIOs). I want to do the following:

I want to have two pulse outputs on different terminals, both completely adjustable (i want to set pulse widths and delays independently for both of the pulses) but the timing between these two should be well defined, as in the jitter should be as small as possible. I managed to get two independent output pulses with the attached VI but the timing unstability is within 1 ms or so which is too much for my purpose. Might be a stupid question but I'm new to this DAQ stuff and couldn't really find an answer here. Is it smarter to combine the two to one task maybe?

Thanks,

Nico

 

[Alexander_Sobolev]

What is the frequency of input source pulses? These counters can be triggered by different input source pulses.

You can trigger the second pulse by the first one. Usefull feature: I am not sure if cDAQ has advanced terminals (Ctr0InternalOutput). Right click digital terminal -> I/O name filtering -> include advanced terminals.

Another option is to use daqmx routing (if it works on cDAQ): disconnect (DAQmx Disonnect Terminals.vi) route linking input trigger and both terminals, then start both tasks, and DAQmx Connect Terminals.vi

If you need to constantly run 2 your pulses for each input pulse, use property Retrigger task, stop on button, not when task done. In this case you can modify their delays and widths in run-time

[Agamemone]

What is the overall application of this to give me a better idea of what needs to be focused on to help you better. Are you having two independent pulses generated simultaneously? What do you mean about the timing between the pulses being "well defined"?

[Plasmaexp]

Hi Agamemone,

I have a pulsed laser system with 1 kHz repetition rate and want only a couple of laser pulses come through. Therefore I want to control two successive laser shutters with two independant TTL pulses being sent to the shutters by hitting a "GO" button. With controllable delay and pulse widths of both TTL pulses I can control how many laser pulses come through. To always have the same amount of laser pulses behind the shutters I need the delay and pulse widths of the TTL pulses to be as reproducable as possible..

Thanks,

Nico

[Plasmaexp]

Hi Alexander,

triggering the second pulse with the first one might be a good idea, but then there will be an intrinsic delay, right? Why not use a common trigger source? Anyways, I am gonna try that. I couldn't find the advanced terminals you are speaking about but I am not sure where to look either. Where should I right click digital terminal?

The input pulses have a frequency of 80 MHz but could be anything. The output pulses dont have a frequency, I just need a single pulse on both channels whenever I press a "GO" button.

Thanks,

Nico

[Alexander_Sobolev]

advanced terminals (for PCI-6602):

Input trigger pulses arrive at 80 MHz, basically it is not a trigger, it is software start. You need to pause these triggers, start both tasks, then resume triggers. In this case counters will have common trigger source, it is my second option - use DAQmx routing (disconnect/connect terminals).

The intrinsic delay between 2 pulses, one triggers the other, will be 25 ns (minimum 2 low ticks 80 MHz cDAQ clock), but it will be constant. If you need smaller separation, it can be 3-d counter that starts both tasks, or routing, or fixed adjusted delay using cable (1.5 ns / foot).

Do you need to synchronize to 1 kHz pulses or pulse pick seed (80 MHz pulses)? If you need 1 kHz pulses, you need to synchronize to them, you do not need 80MHz input, 25 ns delay between pulses is nothing.

For pulse picking 80 MHz pulses these counters are not enough, you will pick +/- 1 pulse