analog trigger

[chen56]

I am trying to find the triggering peak of the index channel of a motor, after I find that peak, I want to record the time of the trigger using basicleveltrigger detection.vi as shown in the attached file. Next, how do I transmit the trigger location (time) to channel A and start counting the number of pulses in channel A at this exact time? My device is called PCI-6014 and it is a E-serie board, also I am using NI-DAQmx and labview 8.0

[Erik_J]

Hi chen,

I believe that we have a great existing example that does what you are looking for.  You can find this example by selecting Help » Find Examples » Hardware Input and Output » DAQmx » Analog Measurements » Voltage » Cont Acq&Graph Voltage-Analog SW Trigger.vi.

I have also attached the example here, I hope this helps!

Regards,
Erik

[chen56]

I looked at the vi that you sent me in detail. What exactly is it doing? Is it triggering a single channel at a specific level? If yes,why does it need several channels? or is it using one channel to trigger another channel? I am a beginner and I have a lot of question regarding this program

What is "when inside window" and "when outside window" and window amplitude in the case structure mean? it says that "inside window" means           data<=window amplitude+level and data>=level-window amplitude(WA),  outside window means data<=level-WA or data>=WA+level. What are these range mean?

Also, when rising edge is selected in the case structure window, it's asking if data<level-WA, if it is true, it is above level, if it is false, it is asking if it is first time called, if that is true, condition is connected to it, which I don't understand, and if it is false, shift register is connected. What does the shift register symbolize in here? Next, inside the case structure window, the true or false switch is turned to false and connected to stop and the next case structure window. What does this false switch symbolize? Next, this false is connected to another case structure, does this mean the case structure is automatically false?

Why is all the rising edge, falling edge, above and below level, inside and outside window connected to the next structure? Does that mean that when these are are true, the trigger is detected? I am very confused about this program and I don't know how to use this program to write a program to meet the requirement that I specified in the first post.

I am very new to labview and this program is frustrating me very much. Could you please answer these questions? Thank you very much.

[chen56]

How do I generate a step function of 5 V DC voltage using DAQmx in LabView for 2 minutes? I need to click on the start button and it starts to run, without entering 5 V everytime. My device number is PCI-6014

[Erik_J]

Hi chen,

The example I posted uses one channel, the index channel, to trigger as many other channels as you like.

"When Inside Window" means that the other channels will acquire data while the index channel is inside a certain window.  For example, if your window is 1 to 2 volts, the channels will acquire when the index channel is between 1 to 2 volts.

"When Outside Window" is just the opposite, the channels will acquire when the index channel is outside a window.  For example, if your window is 1 to 2 volts, the channels will acquire when the index channel is outside 1 to 2 volts.

Since your card does not support triggering on the hardware level, a software trigger must be used.  This is where the Analog SW Trigger VI comes into play.  It will read the current and previous data and will send a software trigger (true or false) if the condition you specify has been met (rising edge, falling edge, above level, below level, inside window, outside window).

For the rising edge, it needs to look at the previous data to see if the new data is above the old data, thus detecting a rising edge.

Why is all the rising edge, falling edge, above and below level, inside and outside window connected to the next structure? Does that mean that when these are are true, the trigger is detected?
Yes, if the condition is true, then the trigger is sent.

I would not be concerned too much with the working details of the Analog SW Trigger VI, just know that if you supply the current data and old data along with a condition, it will output a trigger if the condition is true.

I hope this helps!

Regards,
Erik

[chen56]

Hi Erik, thank you for the explanation. But what is the output graph mean? Does that mean that after index channel is triggered, the channel A that continuously diplaying pulses will start to display the pulses on the graph at that moment? the index channel is periodic, so I need to repeatly trigger the channel A and each time start counting pulses when the trigger is on. Do you know how to achieve this? Thank you.

[chen56]

Erik,

        also, many people from NI recommend me to buy a M series daqmx board to trigger a counter from Channel index, do you think I need that? Thank you.

[Erik_J]

Hi chen,

I would highly recommend a National Instruments M Series card.  I believe that what you are trying to do would be much easier with an M Series card because they have hardware triggering so you will not have to use the complicated software example.

In the software trigger example, the case structure containing the output graph is very important.  Whenever the analog trigger is true, everything in the true section of the case structure will be executed.  So whatever you need to do when the trigger is true, you will want to place in the case structure.

Regards,
Erik

[ClaudeWang]

Hi, Erik:

I found this discussion thread when I have similar need for Software Trigger function. However I do have the PCI-6251 card which supports the analog trigger, but my application is more complicated that I need to have the "triggering events" to ONLY be two successive pulses at an interval of less than a threshold time. When such triggering event occurs, it has to generate some finite samples through Analog Output. Since the hardware analog trigger would keep triggering any single super-threshold pulses (not my desired two successive nearby pulses), I may need the software-trigger function to detect such double pulses. But I couldn't find any example VI about the software trigger for analog output. Could you please help me or you have some better way to tackle my problem? Thanks a lot.

-Claude.