Thermal cyclers are laboratory instruments capable of generating and maintaining specific temperatures for a defined period of time. Specific devices are similar to either batch heaters or chillers in that they heat or cool only. Unlike large-scale batch heaters or chillers, thermal cyclers are designed to handle a small number of microplates (usually one or two), allowing for uniform temperature maintenance across all samples. As with all devices used with microplates, thermal cyclers are designed to handle either of the microplate sizes (typically 96 or 384); although some varieties can handle both. \
Thermal cyclers use a number of different technologies to effect temperature change. The most types include Peltier cooling, resistance heating, and passive air or water heating.
The Peltier effect is used in many applications for the reliable cooling of sensitive high-temperature components without the need for refrigerants or compressors. Otherwise known as thermoelectric coolers, peltiers are special types of semiconductor that function as a solid-state heat pump. By applying a low voltage DC power source to one side, heat will be moved in the direction of the current (+ to -). The heat is thus pumped from one side of the module to the other, so that one face will be cold while the opposite face will be heated.
Resistive heating energy is applied to the sample through the walls of the thermal cycler. A resistive heating element is simply a coiled wire, very similar to the filament of a light bulb or the element in an electric toaster that gets hot when electricity is passed through it. The heating element presses directly against the sides thermal cyclers and conductive grease makes sure that heat transfers efficiently.
Passive air or water thermal cyclers do not contain heating elements. Water or air is heated outside the thermal cycler and then added to the instrument to heat the sample.