LabVIEW
Button for saving data using Write to Measurement File
I am new to LabVIEW and I am having some trouble creating a button that would save data from a DAQ device. The goal was to have the button record data that was being graphed on the Front Panel that my team would be able to turn on and off whenever we wanted. However since we need to run the main program and record data for several hours, the Write to Measurement File records too much irrelevant information and we would like it to record a sample of the data every couple seconds or so. In other words we want to see all the data in real time but when we look at it later we would just want to know the "gist of it" (not an average).
So far I have tried to connect a Boolean button to a Write to Measurement File VI in addition to using an Elapsed Time or Time Delay VI with limited success. With an Elapsed Time/Time Delay VI, we would usually encounter endless "Save As" windows while without using the Time VIs we either do not record any data, get only 100 data points (regardless of how long the button has been on), or we would get all the memory-clogging data, all depending on where we connected the Boolean button. Here are two different attempts:The Simulate Signal VI is standing in for the DAQ VI but the problems remain the same. Any ideas on what to do? I have already tried searching on various forums to solve this apparently common problem but there does not seem to be much help since these problems persist or solutions are too vague/out-of-date to be helpful.
As a first step, go back to the tutorial and learn about dataflow. Since you don't even have a toplevel while loop, it seems that you are using "continuous run" mode. That is a debugging tool and not a way to run a VI. Create a proper state machine!
(code 1): it does not make a lot of sense to use the case structure and the "enable" input.
(code 2): Your "simulate signal" probably belongs inside the loop. Currently you are simulating once and writing the same thing over and over to the file. Also, once the boolean is true, you enter the inner loop and the boolean will never be read again and since the loop is set to "continue if true" it will run forever. Your shift register makes no sense, since you never even look at the previous data. Why is it there? Your loop has no timing information and will run as fast as the computer allows. At what rate do you want to acquire data and write to the file?
All you need is an outer while loop that continuously simulates data and condtionally writes to a file. You either need to configure the simulation to "simulate acquisition timing" or place a small wait inside the loop. There is never a reason to run something as a random function of the current computer power. Place a case structure around the "save" code to conditionally save the current data. If the save operation takes long compared to the rest of the loop code, use a queue and save in a parallel loop. It is always better to stay away from express VI, because it does significantly more work. Typically you would open the file before the loop, keep it open while appending, and close it only once the while loop stops.
@ajmarcial wrote:
The shift register was to increase the N number of iterations indefinitely such that the program can run for any number of hours.
You never use the output of the shift register, so it makes no difference. It is also I32, (same as the iteration terminal), so you will run out of numbers (~2^31) at the same time and I don't understand the argument with the "hours" and such. If you delete the "+1" and the shift register, nothing would change. The compiler will remove the associated code parts behind the scenes anyway during "dead code elimination".
