The purpose of a temperature control system is to maintain a device at a constant temperature. Two types of actuators are commonly used to precisely control the temperature of optics, lasers, biological samples, or other temperature sensitive devices. One is a thermoelectric, or Peltier device. The other is a resistive heater. A precision temperature controller uses a current or voltage source to drive power through these actuators based on feedback from a temperature sensor. The temperature sensors are typically thermistors, RTDs, or linear devices such as the LM335 or AD590.