Time loop 中的数组问题

Question

1. time loop 设定每100ms对采集卡的6个通道进行一次单点采样,如果要将每次采集到的数据存到通道对应的数组中,应该如何设计框图?
2. 在time loop 中有一个for 循环,也就是每次对6个通道进行10次采样,10次采样的数据取平均值作为采样数据,为什么每100ms只能进行一次循环?

Answer 1

Hi.
The only way to have a software-timed loop execute faster than 1kHz is to include code in it which will take precisely the time you need to execute, which is very very hard to determine. So, it seems like you would need LabVIEW RT to be able to use the 20MHz computer clock, or some extra hardware.
I once controlled the iteration time of a while loop by doing an analog input task and using the DAQmx Read VI inside the loop set to the correct number of samples to read at a time.
For example, if you set an analog input task to sample at 10,000 samples per second, and then you put the DAQmx Read VI inside the loop, set to read 100 samples at a time, then the loop executes every 10ms (which you could have achieved without the hardware, but is still an illustrating point).
So, if you want a loop to run at 20kHz, you might be able to achieve it by configuring an acquisition at say, 60,000 samples per second, and read 3 samples at a time with each iteration of the loop.
You must be aware though, that usually when you do such an acquisition, you read a lot more samples at a time, precisely to avoid having to execute the loop so often. Therefore, there is still a possibility that the computer might not be able to keep up at such speeds. You can test this method.
I am attaching an image with sample code of what I mean.
I think the cheapest DAQ board NI has is the PCI-6023E, which should work for this application.
Hope this helps.
Alejandro
Attachments:
FasterLoop.JPG ‏20 KB