Trigger delay of niscope & running multiply tasks on one device

[ASpektron]

Questions:

1. Is there a delay between the trigger and the first sample of the usb5133 scope card? My scope card doesn't seem to start sampling as soon as the trigger occurs or is it caused by the way I have designed my vi?

I've attached my vi showing that I run 'niScope Initiate Acquisition' before the trigger is generated by the usb DAQ device (which is also driving the UUT). I've had a look at the relativeInitialX value, but this seems to display the location of the trigger on the graph.

2. I need to use both the internal counters in the usb6218 device to generate a 10kHz square wave, with output being the inverse of the other. These two counter outputs need to be routed to any of the digital output pins. So far I have only been able to have 1 timer running at a time. An example of this would be useful.

3. Is it possible to setup the usb6218 to simultaneously generate a ramp output on one of the DAC outputs and to measure an analogue voltage on one of the ai pins. I wish to generate a ramp output to drive an input on the UUT then measure the response of the UUT with an analgue input.

[Matt_E.]

Hello,

There is a slight delay between a digital edge trigger on PFI1 and the first sample.  This delay should be no more than 2-3 samples if sampling at 100MS/s.  There is an input to the NIScope configure trigger VI called trigger delay.  You will need to measure the delay in your system and enter the value into this input to correct for the delay.  The reason to do this is that there are other sources of delay besides that of the digitizer itself.  The cable that is connecting your trigger source to the PFI line contributes propagation delay and there may also be a delay between the trigger output of your device and the analog signal you are trying to acquire.

To calibrate the delay connect a BNC T adapter to your trigger source, this will allow you to connect the cable you are using for your analog input and the PFI input to the same source.  You can use the niScope EX configured acquisition example VI to trigger off the digital PFI line and acquire the same signal on channel 0.  Since you are sending the same signal to both inputs you should be able to adjust the trigger delay control on the example VI until the reference position on the fetched data matches point you want.  This trigger delay value is the value you need to calibrate out the cable and digitizer delays.  You may need to tweek this value further to account for delays in your source.

You should post the rest of your questions to the Multifunction DAQ forum to receive a response as quickly as possible.

Hope this helps!

Regards,

-Matt

[ASpektron]

Thanks for the reply, but I fixed the problem it was because I was using the read instead of the fetch command which caused the program to initialise an acquisiton twice.