Triggering and simultaneous measurements
Hi everybody
I've written a Vi to to acquire data simultaneously from 7 devices. I'll be using cDAQ9178 with NI9203. The vi will acquire current values 4 to 20mA. Could you please check the attached file and let me know if I need to improve it.
I have some question and I should be grateful if anyone can help me to answer them.
1. How to open the binary file from write to measurement file by EXCEL?
2. Is it better to use write to spreadsheet for data logging, if yes how to include the time column??
3. I'm going to use external signal for triggering through PIF0 port, is it Ok to do that through dag assistance?? I've not tried yet but it seems straightforward?
4. Finally I have another vi for valve control that should be triggered with the measurement vi, is their any way to do that?? I was thinking about notifiers but I don't know how to use them ?
Sorry for asking to much I really in urgent need of all of this. I should finish my data acquisition system by Tuesday
Best Regards
Solved!
Go to Solution.
Attachments:
triggering and simultaneous measurements.vi 97 KB
1. How to open the binary file from write to measurement file by EXCEL?
If you select TDMS as the file format in the write to measurement file, you should be able to open it directly from Excel if you install the TDMS Excel Add-In. Be aware that at 1kHz data rate, you will exceed the capability of old versions of Excel to read the entire file in about 65 seconds. Newer versions can read more, but anything over a couple thousand points gets difficult to analyze. That is about my limit. Over this, I go to something else for analysis, such as LabVIEW or Mathematica.
2. Is it better to use write to spreadsheet for data logging, if yes how to include the time column??
The write to spreadsheet file is very inefficient for data logging and cannot be recommended. Given your data (an array of waveforms), TDMS is your best bet. The write to measurement file Express VI is the easy way to do this. I, personally, prefer the control I get from using the TDMS API directly. Note that under the hood, the output of the DAQ Assistant is an array of waveforms with individual t0s and dts. The t0s are all different due to the fact that your 9203 is a scanned device, not a simultaneously sampled device. It scans at 200kHz, so the differences are not large, but they are there. I would convert the DDT into an array of waveforms, then use the native TDMS API, but I have a lot of experience. Since you are in a hurry, the Express VI using TDMS is probably your best bet.
3. I'm going to use external signal for triggering through PIF0 port, is it Ok to do that through dag assistance?? I've not tried yet but it seems straightforward?
That should work fine. Given your continuous acquisition, the trigger will only start the acquisition, not gate it or trigger it at later times.
4. Finally I have another vi for valve control that should be triggered with the measurement vi, is their any way to do that?
We do not have enough information to answer this question. Specifically, how is the valve being triggered (boards being used, hardware interface, software interface). The ideal way would be to run it through the same cDAQ 9178 so that it can be synchronized through hardware. Software synchronization cannot be guaranteed better than about ±50ms. Read up on how to synchronize things through DAQmx and you should be good.
Good luck!
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