PID control for temperature stability in LC

 

As reported in elog 3256 the tension in wires was sometimes causing an elevated temperature. So pid control for temperature has been implemented. The temperature was observed for both LCs with the laser on and was found to be fairly stable. This has been done for a temperature of 30 degrees. 

 

The PID parameter for both LCs are shown in the table

 

The method to implement

 

1. P: I and D were made zero. P was made as low as 0.1. We see oscillations between two ranges of values. This was tuned so that the oscillations were faster and also the values were not over or undershooting. 

 

2. I: starting from 0 and increasing by a factor of 0.01 to reduce the height of fluctuations (this will reduce the range of values between which the temperature fluctuates)

 

3. D: this reduced the time duration between which the temperature fluctuated between the two values. Also, decide for how long the value stays in the desired value place without deviating. 

 

4. I and D were tuned till the least or no oscillations were observed. Although we had a logic to keep the temperature stable the temperature was deviating +/-0.09 deg. But now after PID control our temperature deviated +/-0.01 deg. We can see changes in temperature for every 0.01 change in PID parameters. 

 

5. After tuning the LC stays at the set temperature for more than 2 minutes at 0V. (deviates to +/-0.01 for <5s)

 

In PID control we intend to constrict our state (temperature in our case) to a desired value and tune the range of fluctuation and time between which fluctuation happens. Also, the PID control will help us change between temperatures without any overshoots and faster. This has also made cooling down faster. 

 

Note: because we don't need to change these parameters all the time this was done using the VIs with independent control for TC and has not been implemented in the integrated VI.