Question
Do the temperature controllers always provide full current to the driven element (a TEC or Peltier device, or resistive heater) when the actual temperature does not equal the set point temperature?
Answer
The short answer is “No, the temperature controller does not always provide full current to the driven element.” The long answer is a little more complicated.
The key point to remember is that the temperature controller will always try to match the actual load temperature to the setpoint temperature. In order to accomplish that goal, temperature controllers regulate the current to the thermoelectric cooler (TEC) based on the parameters of the PID control loop and the heat characteristics of the load.
The parameters programmed into the PID control loop are largely responsible for determining the current driven to the TEC or resistive heater:
| – | Proportional term: the greater the difference between the actual and setpoint temperature, the higher the drive current. As the actual temperature nears the setpoint, the controller will reduce the current in order to minimize temperature overshoot. | |
| – | Integrating term: the longer the actual temperature remains different than the setpoint, the higher the drive current. | |
| – | Derivative term: the slower the thermal response of the load, the greater the drive current. Conversely, if the load responds very quickly the controller will drive a smaller current. | |
The heat load that the TEC is required to pump will also determine the current delivered by the temperature controller. Let’s say the thermal load is a small laser that doesn’t generate much heat. The controller will need to drive only a small amount of current to the TEC in order to maintain the temperature setpoint.