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Temperature Control Methods

Proper temperature level in an appliance is maintained by a thermostat, an automatic control which directly or indirectly turns on or turns off the energy flow. Thermostats control temperature using a hydraulic, rod and tube, bimetal, or electronic type of sensor. Range oven thermostats are a typical application of the hydraulic sensor. Rod and tube thermostats are commonly found in storage water heaters. Room thermostats that control space heating and cooling typically use the bimetal and electronic sensors. All thermostats operate on the principle that certain metals, liquids or gases expand and contract in response to more or less heat or pressure. This expansion and contraction is used to regulate the flow of natural gas in gas appliances.

For food service facility operators, temperature control in range ovens is often critical to the quality of the end product. Even slight temperature variations can produce less-than-desirable results and some dishes require very low oven temperatures.

The range oven thermostat consists of two parts: the sensor and an automatic control valve. In a gas oven, the automatic control valve increases or decreases the flow of gas to the burner in response to a signal from the sensor for more or less heat to maintain the set temperature. Oven thermostats can be the modulating type, cycling type or a combination of both. The modulating control maintains the set temperature by varying the flow of gas to the burner. Since the modulating control always maintains some flow of gas to the burner, the minimum oven temperature is determined by the minimum gas flow --usually 250° to 300°F.

In contrast, the burner turns on and off in thermostats utilizing a cycling control, allowing for oven temperatures as low as 140°F. Usually the cycling control relies on a standing pilot to light a heater pilot which in turn ignites the oven burner, resulting in a short delay between the call for heat and ignition of the burner.

The combination control operates in cycling mode below 325°F and in modulating mode at higher and broiling temperatures.