I have a DAQ device which is reading 14 Thermocouples at 1 measurement every 4 seconds. I took around 4 hours worth of readings before stopping the experiment, the last reading was at 12:30 but I didn't stop process until 13:15. The file size is 2.5mb, any reason why it didn't continue to write data or is there a limit to how much can be written to an excel file? Any advice would be greatly appreciated.
What version of Excel are you using? Excel used to have a limit of 65,536 lines (or something around there). What you are describing sounds a lot like you ran into that issue.
Can you share some code? Maybe we can give you a better way to save and view the data.
It might potentially be an issue with the USB port on your computer. What operating system are you using? The USB Power Management in Windows tends to cycle power to the USB port after a period.
You could go into the Device Manager and edit the power management setting of the USB device. There is a setting called "Allow the computer to turn off this devoce to save power" which shuts off things connected by USB after a period. If you deactivate it you might be able to fix your issue.
Also have you included any error handling to see if an error causes the device to stop logging?