Virtual Bench MSO does not trigger on 2nd falling edge.

[BobB]

I have a pulse waveform input on MSO Ch1 that I acquire 3 waveforms on.  I'm using Analog Edge trigger when acquiring all 3 waveforms.  I allow 2 pulses to occur and then acquire the 1st waveform triggering on a rising edge.  The 2nd waveform is acquired by re-configuring the triggering for a falling edge and it acquires the 2nd waveform on the next falling edge.  The sample rate and acquisition time is then re-configured to acquire the 3rd waveform on the next falling edge.  I've seen the MSO not trigger on the 2nd falling edge but trigger on the next rising edge.  This occurs when I put the MSO to run state when the signal is low.  If I wait until the signal is high and then put the MSO into run state, it triggers properly on the 2nd falling edge.  Why is this?  Attached are waveforms from another ocsilloscope I had connected.  The blue trace is digital output pulses used for debug.  The green trace is the input signal.  Also attached are the Virual Bench MSO waveforms for a proper trigger and a mis-trigger.

[WilliamEarle]

Hi,

I don't see any attachments. Can you try posting them again? Also, are you using the MSO with the VirtualBench application, or with one of the programmatic APIs (LabVIEW or C)?

Regards,

William Earle

Software Engineer

NI R&D

[BobB]

William,

I'm using the programmatic API with LabView 2013 SP1.  I've tried to attach a .zip file with Acquire Switch Waveforms.vi and some screen shots.

Bob B.

[BobB]

William,

This is another attempt at attaching some files.

Bob B.

[Arthur99]

Hi William

I have the same question. Though I managed to make the second trigger working, it is way too slow for my test.

Thank you

Arthur

[bstreiff]

Arthur99:

I'm not quite sure what you're trying to do in that VI. Here's a reinterpretation of what I think you may have been trying to do; maybe it will help.

I have my VirtualBench's ps/+6V channel connected to channel 1 on the MSO. In this VI, I am configuring a rising edge trigger, starting an MSO acquisition, and then enabling the power supply so that I capture the rise of the +6V rail. (I borrowed the settings from your VI-- power supply is set to output +5V, with a trigger point of 4.7V).

After I get that acquisition, I stop the MSO, reconfigure to use a falling edge trigger (keeping the channel and level the same), and acquire again.

I expect that your stimulus was not intended to be the power supply itself, but rather something that you were powering with the power supply, but perhaps that will work as a starting point?

You're doing a full MSO Initialize (with reset), configuration, and then run/read every time you're using the MSO. You can save connection overhead and reconfiguration time by keeping the instrument session around between acquisitions (as you've done with the power supply).

[Arthur99]

bstreiff

Thank you very much. Your solution is exactly what I am looking for.

What I was trying to do is to have the MSO capturing a break of signal sending from an IR beam breaking sensor. That is why I need to catch the falling and raising of the signal in a very short period of time (with in 10ms).

Thank you again. I now have my own VI working as I wanted.

Best regards

Arthur