Proportional Temperature Controllers use proportional regulation to maintain a constant temperature with no swing in the control temperature. This is accomplished by using a PID algorithm to determine the output value and a pulse width modulation (PWM) output to handle the physical control. Proportional Controllers are often used in heating and cooling systems where the temperature must stay constant (with no change) regardless of the change in ambient temperature. Laird Thermal Systems offers two standard programmable controllers. The PR-59 is mountable at system level and comes with software to connect to PC. Settings can be adjusted while running the thermoelectric cooler assembly, which is beneficial for product development.