How to synchronize counters and analog input

[orbit]

Hello! This is my first post and I am still trying to familiarize myself Labview. I have an application in which I am reading the velocity of two rotating shafts and an analog input simultaneously. The intent is to execute this VI in a test vehicle. The users will be able to view the waveform chart data and can then choose to record the data. I am using a DaqCard 6036E PCMCIA card with a SC-2345 signal conditioning board.

All three channels are declared in MAX as NI-DAQmx globals. The two counter channels will display and update correctly, but I cannot seem to get the analog input to function in the same loop. I believe I need the counters and analog input to be synchronized so they display correctly (i.e. in the same time domain). The intent is to have the front panel objects update at 100 Hz. I would also like to be able to log to a text file at 100 Hz at anytime (i.e. append to it) while the VI is running.

I have attached a version of my application. I appreciate any suggestions!

Regards...

[orbit]

I realized that the AI was not using the correct DAQmx read vi, which has been corrected. I can view the data simultaneously, but the front panel update seems slower since I have added the analog input. I suppose my question is now slightly revised: What is the most efficient method to synchronize these channels in the display and write the data to file when needed?

Again I appreciate any replies and please forgive my LV ignorance!

[Hal_L]

Hi Orbit,

I took a look at your code and the acquisition looks fine. One thing that could help with your synchronization is to use the error cluster as a means for synchronizing the tasks. Take a look at the Multi-Function-Synch AI Read-Dig Chan example and notice how the error cluster is used. This example can be found in Help >> Find Examples >> Hardware Input and Output >> DAQmx >> Synchronization >> Multi-Function.

As for writing data to a file: that really depends on how often you want to write data. One of the best ways to write data to a file is to use the Write to LabVIEW Measurement File Express VI which is location on the Functions >> File I/O palette. Take a look at this and let me know if this is what you are looking for. I hope that you find this information helpful.

Regards,
Hal L.

[orbit]

Hal - Your reply is much appreciated. Since my last post I have made excellent progress on getting the counters and the analog input channel to update synchronously on the front panel. I believe part of my problem was that I did not know quite the right question to ask! After some trial and error, I was able to find the right combination of AI sample clock frequency, AI read samples per channel, and display loop rate that would update the front panel in sync with the counter frequency channels. I have implemented your suggestion on error grouping and it has made the block diagram much easier to follow. I have also been working with the Write Labview Measurement File Express VI and am getting good results with this as well.

Thanks again for your suggestions.

Orbit