using PXIe 5162 (2 channels) NI scope for data aquisition.

[mnprvt]

I was using one of the two channels as a trigger source which is a short pulse of laser. I want to use the external trigger channel so the other two channels can be used for two sets of data. I used signal express to configure the external trigger but I cannot make it work successfully even though it worked well with one of the signal channels as a trigger channel. Do I need to configure the external trigger channel differently? how can I make this work? Thanks.

[James-K]

Hi,

I was able to test a similar setup without any issue.  What type of trigger have you specified?  Also, can you provide some additional details as to what specifically is not working (i.e. are you getting an error message, unable to find where to configure the trigger source, etc)?

[mnprvt]

Hi,

Thanks for replying. I'm using a short pulse laser as a trigger source. The pulsewidth is about 1ns and the amplitude I have is about 20mV which seemed to be sufficient for the regular channel as a trigger source. I had the trigger channel configured at DC coupling, positive edge trigger. I am not getting any error but no data is reported which I'm assuming is because the scope is not getting the trigger pulses. I played with the trigger level but did not help. I tried to use the same trigger level as I was using for the regular channel. I'm not sure if 20mV of amplitude is too small for this external trigger. My typical signals are of the order of few 100 mV.

Thanks

[James-K]

Hi,

If you look at page 16 of the specifications manual (http://www.ni.com/pdf/manuals/373858a.pdf), note the trigger sensitivity specification.  For the 5162, the trigger sensitivity is 3% of full scale.  Assuming you are using a 50 ohm input impedance, this would correspond to 3%*5v=150mV minimum voltage to trigger.  

This link also explains these specifications in a little more detail:

http://digital.ni.com/public.nsf/allkb/AF46FE2038BF2C0186256C3D0078EFF2?OpenDocument

[mnprvt]

Thanks for your reply. I did increase the amplitude to over 200mV but did not help.

[James-K]

Is it possible to try increasing the duration (at least for testing purposes) as well?

[mnprvt]

It seems to be working with 50Ohm termination (externally terminated with a BNC T). Now I'm trying to figure out how to configure the external TRIG channel at 50Ohm termination. I tried to configure the channel using the chan configure VI but does not work. I have tried a few other things in labview to configure this channel at 50 but without any success.

[James-K]

Hi,

You can set the trigger input impedance using a niScope property node with the property 'Trigger Impedance.'

[mnprvt]

I tried doing that but for some reason I get an error. but I figured out my problem. I had to increase the trigger pulse amplitude to close to 2V to be able to get constant trigger.

Thanks