How to delay a trigger with PXI-5122 before routed to PFI line

[Mercredi]

Hi Everyone,

I am using a PXI-5122 in a PXI chassis. I would like to synchronize it with two external devices. The first one will send a trigger (with a 10 Hz repetition rate) to the PXI-5122. Then, the PXI will generate a trigger (with a constant delay time) to the second one.

It seems I need to generate a trigger, then export this trigger to PFI 0 line, but I don't know how to delay the triggers with accurate delay time of 4µs. I have read that there is a slight delay between a trigger on PFI and the first sample. And the cable length is also important factor to be considered.

Could anyone give me some suggestions?

[Mercredi]

I'm using niScope Export Signal.vi to generate a signal (trigger out). Then, use software-based timing to delay the trigger. However, the delay time is unstable.

Here I attach the VI for my application using LabVIEW 2010, Win 7 (32 bit).

Does anyone know if there is something I can do to delay the trigger signal with a certain delay time?

Regards,

John C.

[Henrik_Volkers]

The method I proposed migth have a jitter due to the internal clock ......

what are your specs for the 4µs delay?     Another solution would be pure hardware: use a comperator for the 10Hz trigger (to get a nice stable voltage step) followed by a RC delay and a second comperator.  the delay time can be set by the trigger level of the second comp or make the R a potentiometer. ...

[Mercredi]

Hi Henrik,

My data is colected based on the trigger signals from/to both the devices. The specs for 4µs delay relates to the total record time (12 µs):

Device_1 --> PXI: 0 - 4 µs 

Device_2 --> PXI: 4 - 12 µs 

Thank for your solution. I'm trying it.

Regards,

John C.

[Nathan-P]

If I understand your application, you have two external devices that you want to acquire data from on the PXI-5122, but you need to send trigger signals to them in order to put them into a state to give you valid data?  Can you explain the sequence of events (acquiring, triggers, etc.) a bit more?

If all you needed was to provide a trigger signal that was delayed by exactly 4us, then you could use a delay generator:

http://sine.ni.com/nips/cds/view/p/lang/en/nid/209730

The purpose of this device is to provide an output pulse at a very precise time compared to the trigger input.  

Since I'm still unsure of the sequence of events you are attemping to program, you could also let the hardware (PXI-5122) calculate the 4us based on an acquisition.  Your attempt at using the software trigger is similar to what I'm about to propose.  For the input trigger to the PXI-5122, set it to be the reference trigger, so a record won't acquire until it's received.  Then configure the acquisition to acquire 4us of post trigger samples.  Then use the Export Signals.vi to export the "End of Record Event" 

http://zone.ni.com/reference/en-XX/help/370592N-01/digitizers/5122_state_model/

For example, if you configure the 5122 to 100MS/s, then with the default 50% reference position, you need to aquire 800 samples (400 pretrigger, 400 post trigger) 400 samples @ 100MS/s = 4us.

I hope this helps.

Nathan

[Mercredi]

Hi Nathan,

This is the sequence of events in my application:

Device_1 (send a trigger @ 10 Hz) --> PXI-5122 (acquire data from Device_2) --> PXI-5122 (wait 4µs) --> PXI-5122 (output a trigger to Device_2)

My current system is using a Digital Delay Generator (DG535) for this purpose. However, I would like to make the system more compact.

In addition, my system can be configured as follows:

Device_1 (send a trigger @ 10 Hz) --> PXI-5122 (acquire data from Device_2) --> PXI-5122 (wait 50ms) --> PXI-5122 (output a trigger to Device_2) --> PXI-5122 (acquice data from Device_2)

All I need is to provide a trigger signal that is delayed by exactly a constant delay time (I prefer from 4µs to 50ms). Please suggest me a suitable solution.

Regards,

John C.

[Nathan-P · Accepted solution]

Mercedi,

Thanks for the drawings, that helps a lot!  One way I see this working (how I would configure the digitizer):

1. Configure the record length to be 12us (4us pre-trigger samples, 8us post-trigger samples).  If the sample rate is 100MS/s this would be a record length of 1200 samples.

2. Configure the record reference position to 33%.  This is how the digitizer breaks up the 1200 samples into 400 pre-trigger and 800 post-trigger samples.

3. Configure the reference trigger to immediate.  Doing this will allow the acquisition to trigger the moment it has acquired the 400 pre-trigger samples.  

4. Export the "Reference (Stop) Trigger" to send to Device_2.  This output pulse has a variable width, so if you want consistency, you will need to have Device_2 trigger from the rising edge of the pulse, not the falling edge.  Once the 400-pretrigger samples are acquired, this pulse will be sent, and then the digitizer will immediately move into post-trigger sampling.

5. Configure the Input trigger from Device_1 (10Hz trigger), as the "Advance Trigger" and "Start Trigger".  This will make the digitizer wait for this pulse before starting the pre-trigger sampling of the next record.  We need to configure both, the start trigger for the 1st record, and the advance trigger for all subsequent records.  

This setup should allow for some pretty decent synchronization, but please test it out to be sure it will be sufficient for your application.

Regards,

Nathan

[Mercredi]

Nathan,

Thanks for your excellent solution. I'm ordering the Aux100 cable (9-Pin DIN to two BNC Female) to export the trigger signal from the PXI to the Device_2. I will test the program (Echo_Mode_PXI_5122.vi) to be sure it will be suitable for my application.

Another problem, when my system is working on ultrasound Pulse-echo mode (Pulse_Echo_Mode_PXI_5122.vi), the input trigger must be set a delayed trigger acquisition (by setting the trigger delay to, for example 3µs) to remove the signal of power source. Could you please tell me how I can configure the digitizer in this case?

Regards,

John C.

[Nathan-P]

Mercredi,

For Reference triggers, you can easily configure a trigger delay using the "niScope Configure Trigger.vi".  Unfortunately this will not work for your application as I described, since we rely on immediate reference triggering.  

Since the 10Hz signal is being used as a Start/Advance Trigger, there is no way to perform the delay in hardware.  Therefore, you will just have to acquire the power source signal as well, and just remove it in software after you have fetched it.

I hope this helps.

Nathan

[Mercredi]

Nathan,

Yes, I can remove the power source signals during data processing. So I will keep following your solution.

However, I have a problem. When I configure the reference trigger to immediate as your sugestion, I don't know how to configure the Input trigger from Device_1 to the PXI-5122.

Could you please help me correct the program in the attached file? I'm using LabVIEW 2010, Win 7 (32 bits)