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acqusition delay between channels
vince1970
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07-07-2003 03:37 AM
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"It seems that my question was not very clear. I just want to delay some channels to synchronize the acquisition of my system. I want that the acquition of all signals coming from different sensors or instruments start physically simultaneously.
For example : at t=0 channels 1 to 5 start, and 5s later channels 6 to 10 start, because the elements connected to the channels 6 to 10 have a faster time response and I know it is 5s faster than elements connected to channels 1 to 5.
Doing so I will get synchronize data. At the present I have to switch manually my data after the acquisition. but there are so many data that it is not only long and boring but source of mistakes.
Thanks."
For example : at t=0 channels 1 to 5 start, and 5s later channels 6 to 10 start, because the elements connected to the channels 6 to 10 have a faster time response and I know it is 5s faster than elements connected to channels 1 to 5.
Doing so I will get synchronize data. At the present I have to switch manually my data after the acquisition. but there are so many data that it is not only long and boring but source of mistakes.
Thanks."
rgharrison
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07-09-2003 02:22 PM
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Hi Vince,
It would seem that the easiest way to do this is to use the LabVIEW VI Wait Until Next MS Multiple.vi and set it for 5seconds (5000). To do this, first configure to perform both your acquisitions (initial and then delayed). Then code a Wait Until Next... VI to wait a 5000ms. When it finishes, start your first acquisition and include another Wait Until... VI for 5000ms. When it concludes then you can start your second acquisition.
The reason we have several stages is because the first time you call Wait Until Next ms Multiple.vi it counts from the beginning of the program and not just when it was called first. The second time you call it though, it will be 5000ms from the time you first called the function.
A more accurate way to perform thi
s in hardware is as follows. Start your buffered acquisition on both sets of channels (initial and the delayed group). This will acquire all channels at the same time. When you finish your acquisition, you only need to take your sampling rate and take the inverse of it and you will get the period. Divide this period into 5 seconds and you will get the number of samples that you need to throw away at the beginning of your acquisition. You can even perform this calculation ahead of time and ignore the first X amount of data points and start counting them as valid once you get to that point.
Anyway, hope that helps. Let me know if I wasn't clear.
Ron
It would seem that the easiest way to do this is to use the LabVIEW VI Wait Until Next MS Multiple.vi and set it for 5seconds (5000). To do this, first configure to perform both your acquisitions (initial and then delayed). Then code a Wait Until Next... VI to wait a 5000ms. When it finishes, start your first acquisition and include another Wait Until... VI for 5000ms. When it concludes then you can start your second acquisition.
The reason we have several stages is because the first time you call Wait Until Next ms Multiple.vi it counts from the beginning of the program and not just when it was called first. The second time you call it though, it will be 5000ms from the time you first called the function.
A more accurate way to perform thi
s in hardware is as follows. Start your buffered acquisition on both sets of channels (initial and the delayed group). This will acquire all channels at the same time. When you finish your acquisition, you only need to take your sampling rate and take the inverse of it and you will get the period. Divide this period into 5 seconds and you will get the number of samples that you need to throw away at the beginning of your acquisition. You can even perform this calculation ahead of time and ignore the first X amount of data points and start counting them as valid once you get to that point.
Anyway, hope that helps. Let me know if I wasn't clear.
Ron
