Temperature control with NI USB-6001 - Huge fluctuation at the setpoint

[Jeon17]

Hi all,

I'm using NI USB-6001 to control the temperature of two rope heaters in the system. But I have a hard time controlling the temperature in two situations:

1. The setpoint for one heater is 280 C. But, it reaches only 270 C and maintains 270 C (applying PID control). I tried to use only P control to check if it reaches a higher temperature when I set a higher setpoint, but it always reached 270 C and was maintained even when the setpoint was 280, 290, and 300 C.

2. The other heater shows huge fluctuation at the high-temperature setpoint (> 270 C). When the setpoint temperature is less than 270 C, the temperature control works well. However, if I set the setpoint to 270 C or higher, it starts to fluctuate with the range of ±20 C. I tried to use P control to see if it reaches a steady-state at the setpoint more than 270 C, but it couldn't reach a steady-state and just started to fluctuate around the set point.

I'm wondering if this is a programming issue or others. I inherited this system from my senior and am quite new to Labview and DAQ systems so any direction would be greatly appreciated.  

[santo_13]

USB-6001 is a generic instrument to acquire/generate analog and digital signals. What those analog and digital signals do is completely dependent on your application and how it is implemented.

Unfortunately, you did not provide all the required information in terms of how things are connected and the source code of the application controlling the 6001 devices to get a better understanding of what is happening.

Please help us understand how the temperature controller is controlled by the 6001 device.