When streaming data with modbus the reading rate returns to a slow rate after update of baudrate.

[EdHarris]

Hi,

I am having problems with streaming data with the attached VI. It concerns the inner FOR loop in frame 7 of the flat sequence. The times between readings were more than the specified 100ms timer so I upped the buad rate from 9600 to 19200 this improved the timing down to about 125ms. But after a few runs the time increased again to about 800ms. I updated to 38400 and the performance was perfect but then after starting the VI a couple of times it went back to roughly 800ms again. I suspect this is something to do with Visa because I have found generally that if you stop a VI when it is running you get unusual com port addresses in the comport list which when cleared gets rid of communications problems. But clearing those in this case doesnt help.

I have the same issue on another similar set up and changing the modbus client pc, also with a new installation of Labview community, doesnt help either. 

I hope you can help.

[santo_13]

Please share your VI, it may also be with how you implemented the code inside the loop causing it to slow down over time, a common mistake is accumulating data over time in array and writing to file in the same loop as the reading part.

[EdHarris]

Sorry I attached my VIs before but didnt upload

[EdHarris · Accepted solution]

The  solution is here. Not eally a solution more like an outcome.

What-could-change-after-a-baud-rate-increase-to-slow-down-serial