NI 5102 external (TRIG) trigger

[Tato]

Old trouble coming back: In both PCMCIA and PCI versions of the 5102 card we are seemingly unable to get the external trigger (TRIG) to work properly. Signals that ch0 or ch1 have no trouble triggering on just fly under the radar there. The triggering pulses are sufficiently wide (>10 samples). We have not been able to get the edge trigger to work on TRIG, and while window triggering does work, after a while the triggering rate slowly drops to zero, giving a timeout condition. This has nothing to do with the triggering source, relaunching the DAQ just repeats the cycle.

Can you help?

[Aaron_W.]

Tato -

Thank you for posting on the NI Forums.  So if I understand correctly channels ch0 and ch1 both trigger correctly, but you have having trouble getting the edge trigger to work on the TRIG? At what voltage are you trying to get your edge trigger to trigger off of? There is a Knowledge Base article: Minimum Voltage that You Can Edge Trigger off of with an NI High Speed Digitizer (5102, 5911, 5112) that might help you determine if your voltage is high enough to trigger off of. 

Message Edited by Aaron W. on 01-21-2009 10:13 AM

[Amirul]

Can someone support me with some idea?

Ive been trying to analyze phase difference between 2 encoder pulse (pulse  A and B). So far no function in labview support this kind of analysis ( please refer attachment ). I need to get "result wave" as in the attachment picture to calculate the value of phase difference between pulse A and Pulse B

Im using PCI 5102 hardware  and input came from encoder with pulse A and Pulse B

[DFGray]

There are several ways to find the phase difference between your two inputs.  The easiest is to use the NI-SCOPE API phase difference measurement to measure it directly.  You can also use the LabVIEW zero crossing functions to determine the zero crossing points of your two waveforms, then subtract the times (gives you time difference - you can get frequency from the pulse measurement VIs to convert to phase).  You can add the two waveforms and use the pulse measurement VIs to get period and duty cycle.  You can use the tone extraction VIs on either the original waveforms or the addition of the two waveforms to give you phase and frequency information, which can be converted to phase difference.

If you need any help with these, let us know.

[Amirul]

Good day,

Thankyou for your kind attention, I am interested in your method "zero crossing"

but I dont have idea how to create that kind of program. Is it possible you provide some example for this related measurement?

Im using Labview 7.1

[DFGray]

The oldest version of LabVIEW I have on my machine is 8.2.1, so I used that for this answer.  Look in Signal Processing»Waveform Measurements»Transition Measurements.vi for a VI which will find the high and low transition points for a square wave.  I think you need a full version or better to get this VI (it is not in the base version of LabVIEW).

If the inputs for this VI look familiar, it is because the code was originally migrated from the NI-SCOPE measurement codebase.  You will get the same result if you use the native NI-SCOPE measurement API (which I would recommend).

[Amirul]

thanks for your reply.., can you help me with the programming ? Im kinda have no idea how to relate the function

[DFGray]

The NI-SCOPE example niScope EX Measurement Library.vi has most of what you need, but you will need to slightly modify it.

1. Open the block diagram and find the property node which sets the levels and the active channel.
2. Right click on the Active Channel item and select Add Element.  This will add another line to the property node.
3. On the new line, left click and select Waveform Measurement»Other Channel.
4. Right click on the input to the new line and select Create Control. This will be used to select the reference channel for your phase info.  The channel you will be measuring is the Active Channel.
5. Concatenate the input channel and the new other channel controls with a "," between them as the input to the channel configuration VI.  This ensures that both channels will be acquired.
6. Save this as a copy of the original so you do not lose your changes or the original VI.  The VI block diagram should look somewhat like the image below (ignore the error cluster property node at the right of the loop, it is a consequence of creating the snippet with a local variable).
7. Close the block diagram and go to the front panel.
8. Select your device from the Resource name.
9. Enter your reference channel in the new control (you may want to move the new control to a convenient spot).
10. Enter the input channel and your new reference channel.
11. Run.

[Amirul]

thanks for your answer., can I use labview v 7.1 to do this block?

[DFGray]

Yes.  That code has not changed since about LabVIEW 6.1.  The icons were updated around LabVIEW 8.0, though, so things may look a bit different.  That particular example goes back many years, so you should be able to find it as a starting point.