如何编辑和接收来自cRIO的数据？

Question

At my lab I have a testbed that uses cRIO. There are 3 cRIOs connected to multiple sensors. My aim is to manipulate sensor data and see how it affects other processes. The company that installed the testbed wrote a very complex LabView program.

I am new to LabView. I have seen a few answers about making web-services. Will this be useful to edit the data? The engineer says that the data is continuously injected in a loop, so my program would also have to run in a similar manner or to disable the other loop completely. If yes how do I go about creating web services for such a massive project?

Is there an easier way to achieve my goal. A man in the middle between the controller and remote(?) IO? What protocol runs there? Do you recommend any Python libraries for this?

Answer 1

Since your existing application has a 'simulation mode' in which the data you want to change can be set manually using controls on the LabVIEW front panel, you can manipulate these controls programatically from another LabVIEW VI using control references. The following LabVIEW snippet sets the value of the control with index 0 in the target VI to the specified value:

We open a reference to the target VI then use property nodes (from the Application Control palette) to return references to that VI's front panel, to all the controls on that panel (as an array), and finally to write to the Value (Signaling) property of the selected control. To make repeated changes you only need to repeat that last property write. Just close the reference when you're finished.

To find out which control has which index, read the Label.Text property for each control reference in the array, giving you the text of its block diagram label - not necessarily the same as its caption on the front panel.

If you prefer to do the automation in Python you should be able to use the method described in this post , using the pywin32 module:

import win32com.client
labview = win32com.client.Dispatch("Labview.Application")
VI = labview.getvireference(r'C:\path\to\target.vi')
VI.setcontrolvalue('Numeric','5')

This sets the value of the control with label Numeric to 5. However the above code will not work if the target VI uses LabVIEW events to respond to control value changes, rather than polling the control values, because it sets the control's Value but not its Value (Signaling) property. Unfortunately the answer from rolfk to my question on the NI forum suggests there isn't a way of doing the latter - you would need to write an intermediate LabVIEW layer and send the data from Python to that somehow. That could use the COM interface to drive the LabVIEW code in the first example above, if you poll value to set (etc) in a loop.

If you want to go beyond this it should be possible to either modify the existing LabVIEW application so you can inject the data you want, or, if you prefer, to replace it completely and handle the sending and receiving of data to/from the cRIOs yourself; but that would be too broad a question to answer without more detail of how the system has been implemented.