The program I've enclosed does what I need it to do quite well for the most part. I'm asking this question because I'm getting more data than I want and it's inconvenient to work with.
In short, I have a sytem setup to record pressure data from an explosion in a very short time period, the entire event is over in less than 100 ms, it typically occurs between 1 and 2 seconds after the ignition signal goes out. Therefore I want to record about 2 seconds of data total. The system has to run in a monitor mode for several minutes before any ignition while I fiddle with various elements associated with the experiment. It DOES NOT record during the monitoring phase but it must be running so I can fiddle with the experiment.
I think have two small issues that are increasing the size of my TDMS file.
- When I hit the big red "STOP" button the system continues to record data for several seconds. I think it has something to do with the queue not being empty. It appears to be stopping at the correct relative time, but the data hasn't been streamed to disk yet. I can live with this but I suspect it's indicative of a bigger problem.
- When I hit "Record" I have a 5s delay built in to engage a FLIR camera which has a variable startup delay (red circle in picture, record button not shown). This shouldn't get recorded because a "true" signal doesn't go to the record case (blue circle) until after the 5s has elapsed.
Example dataset below. To generate this data I started the VI and let it run for 30 seconds (I didn't have to let it run but that is more like a "real" test), after roughly 30 seconds I hit record and it started the 5 second countdown to ignition, I observed the ignition signal and waited to hit "stop" at roughly the 1 second mark on the count up. The VI continued to run until the timer read 8.32 seconds. The signals I recorded are just the TTL pulses that would normally go to my cameras, everything else is unplugged. Awyay, it looks like the system stopped acquirig data when I hit stop but the fact that it kept running tells me my queue didn't empty.
In the sample data the white line is the FLIR TTL signal. It lasts about 1 second (recording at 100 kHz), it should be a 1 second square pulse (or 100000 points), looks like the front got cut off. Sometimes it gets the whole pulse, sometimes it completely misses it. I think it has something to do with when I hit record relative to what is happening with the buffer.
The blue square wave that starts at 5 seconds is the 1/2 second TTL pulse that goes out to the high speed cameras and ignites the explosion. This is actually where the recording should start, where 0 seconds should be. I'm not certain why I'm getting the precursor data. In other words, all the data to the left of 500000 (5s) should not be recorded. The data ends just shy of 1/2 second (~50k points) after the blue pulse ends. This is right around the 1 second mark I tried to hit when I generated this data.
What is the result? Well, I'm recording 10 channels at 100 kHz so I end up with a 50 mb file instead of a 10 MB file and an extra 500k points that I have to strip off. This is tedious and time consuming, it really adds up considering I'll be doing this testing hundreds or thousands of times.
My questons. How do I delay recording until after that first delay is up? What am I missing? Is there some sort of a "TDMS clear queue"command?
Thanks for your time!