Operating temperature

An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the maximum operating temperature (or peak operating temperature). Outside this range of safe operating temperatures the device may fail. Aerospace and military-grade devices generally operate over a broader temperature range than industrial devices; commercial-grade devices generally have the narrowest operating temperature range.

It is one component of reliability engineering.

Similarly, biological systems have a viable temperature range, which might be referred to as an "operating temperature".

Most devices are manufactured in several temperature grades. Broadly accepted grades are:

Nevertheless, each manufacturer defines its own temperature grades so designers must pay close attention to actual datasheet specifications. For example, Altera uses five temperature grades for its products:

The use of such grades ensures that a device is suitable for its application, and will withstand the environmental conditions in which it is used. Normal operating temperature ranges are affected by several factors, such as the power dissipation of the device. These factors are used to define a "threshold temperature" of a device, i.e. its maximum normal operating temperature, and a maximum operating temperature beyond which the device will no longer function. Between these two temperatures, the device will operate at a non-peak level. For instance, a resistor may have a threshold temperature of 70 °C and a maximum temperature of 155 °C, between which it exhibits a thermal derating.

For electrical devices, the operating temperature may be the junction temperature (T_J) of the semiconductor in the device. The junction temperature is affected by the ambient temperature, and for integrated circuits, is given by the equation:

in which T_J is the junction temperature in °C, T_a is the ambient temperature in °C, P_D is the power dissipation of the integrated circuit in W, and R_ja is the junction to ambient thermal resistance in °C/W.

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