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SYSTEM CONTROL
Heat reject control: Combination of Single-TEC module & Fan-heat sink assembly
Fan control: PWM signal function of Heat-sink Temperature
Inner temperature control: PWM function of Inner temperature
PID algorithms for FAN and TEC control to maintain the desired temperature at heatsink and container with providing controlled PWM corresponding to voltage require to FAN and TEC
Overall System Power :12V,2A(max),P=24W(max)
Reference values
(Inner)-15*C
(Outer)-32*C
Value of PID used
For TEC
P = 950 I = 0.01 D =0
For Heatsink-fan assembly
P = 300 I = 1 D =0
PID Controller
Here two separate PID control are functioning here one for TEC module and other for dc fan control. The control unit starts when the microcontroller receives the desired temperature set by the user. There is a PID control algorithm implemented inside the microcontroller which output the control signal based on the current temperature detected from analog-based temperature sensor and the desired temperature to control for heat sink cooling with fan attach and another is TEC module for cooling the container. PID controller can provide control action design for specific process requirements by tuning the three parameters. The three parameters are the proportional (P), integral (I), and derivative (D) values. P depends on current error, I on the accumulation of past errors, and D keep track of the trends of future errors. The weighted sum of these three values provides the control signal to the Peltier module.
The value of P, I, D was calibrated by the required specification of the device. The way to get the P, I, and D is to start by calibrating the proportional gain and left the other two zero. After a proper P is set so that the rising time is satisfied for the requirement, D is then modified to smooth the overshooting. By setting a proper P and D, the controller is smooth enough but with a steady-state error of around 3 Celsius degrees. Then Integral gain is modified to eliminate the steady-state error.
PID Controller Flow Chart
