labview - 缓冲数据然后保存到excel文件

Question

My question is with respect to a labVIEW VI (2013), I am trying to modify. (I am only just learning to use this language. I have searched the NI site and stackoverflow for help without success, I suspect I am using the incorrect key words).

My VI consists of a flat sequence one pane of which contains a while loop where integer data is collected from a device and displayed on a graph.

I would like to be able to be able to buffer this data and then send it to disk when a preset number of samples have been collected. My attempts so far result in only the last record being saved.

Specifically I need to know how to save the data in a buffer (array) then when the correct number of samples are captured save it all to disk (saving as it is captured slows the process down to much).

Hope the question is clear and thanks very much in advance for any suggestions. Tom

Answer 1

Below is a simple circular-buffer that holds the most recent 100 readings. Each time the buffer is refilled, its contents are written to a text file. Drag the image onto a VI's block diagram to try it out.

As you learn more about LabVIEW and as your performance and multi-threaded needs increase, consider reading about some of the LabVIEW design patterns mentioned in the other answers:

• State machine: http://www.ni.com/tutorial/7595/en/
• Producer-consumer: http://www.ni.com/white-paper/3023/en/

Answer 2

I'd suggest to split the data acquisition and the data saving in two different loops using a producer/consumer design pattern. .

Moreover if you need a very high throughput consider using TDMS file format. Have a look here for an overview: http://www.ni.com/white-paper/3727/en/

Answer 3

Screenshot will definitely help. However, some things are clear:

Unless you are dealing with very high volume of data, very slow hard drives or have other unusual requirements, open the file before your while loop, write to it every time you acquire a sample (leaving buffering to the OS), and close it afterwards.

If you decide you need to manage buffering on your own, you can use queues. See this example: https://decibel.ni.com/content/docs/DOC-14804 for reference (they stream data from disk, buffering it in the queue, but it is the same idea)

My VI consists of a flat sequence one pane of which

Substitute flat sequence for finite state machine (eg http://forums.ni.com/t5/LabVIEW/Ending-a-Flat-Sequence-Inside-a-case-structure/td-p/3170025 )