Acquire multiple analog signals continuously with pretrigger

[riks]

Hi,

I am very much new to Labview and DAQ. I have a PCI-MIO-16XE-10 board. I want to acquire 4 analog signals with one of them as a trigger signal. I also need pretriggering and continuous data acquisition. I found pretriggering in reference trigger but I was forced to give the number of samples to acquire. I need a start trigger with pretriggering. As soon as the trigger signal crosses say 1 volt, it has to start acquiring all analog signals till the user hits cancel/stop button. Along with this, I need few samples just before the trigger occured.

Please let me know how to do this. This may be very simple but I started working with labview just yesterday.

Thanks in advance,

riks

[Salvador_Santolucito]

Hi riks,

What you are trying to accomplish (start triggering with a specified number of pretrigger samples) is unfortunately not possible. What is available is using the reference trigger with a finite number of samples (and pretrigger samples). This means that you will have to specify the number of samples before and after the trigger (you cannot do continuous sampling after the trigger comes).

Another option is to do just plain analog continuous acquisition and filter out your data in software. You can to continuous acquisition and test the incoming data until the trigger level is achieved. There is a subVI in the Analyze >> Waveform Monitoring function pallette called "Basic Trigger Level Detection." You can use this to monitor your data to see when and where the trigger occurs.

-Sal

[Jeremy_C]

As Sal stated, you cannot perform a hardware reference trigger and then proceed to acquire continuously. Additionally, you cannot perform a hardware reference trigger with multiple channels in the scan list. You will have to perform some software manipulation in order to achieve your desired goal. However, there is an NI-DAQmx example that ships with LabVIEW 7.0 or higher that looks like it may work for you. The example is called Cont Acq&Graph Voltage-Analog SW Trigger.vi. In the LabVIEW Example Finder, navigate to Hardware Input and Output >> DAQmx >> Analog Measurements. In here you will find this example. If you take a look at the subVI called Analog SW Trigger.vi, you can see that this is performing some software analysis looking for a trigger point, similar to what Sal mentioned. I haven't used this example much, but if you delete the wire branch from the Analog SW Trigger.vi subVI to the Compound Arithmetic OR, then the VI should run continuously, even if you specify a number of pretrigger scans > 0. I hope this helps.