An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified operating 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 of this range, the device may fail. Aerospace and military-grade devices generally operate over a broader temperature range than industrial devices; consumer-grade devices generally have the lowest operating temperature range.
It is one component of reliability engineering.
Although biological systems do not have a defined operating temperature, individuals are most comfortable when body temperature fluctuations as a result of environmental factors are minimised.
Electrical and mechanical devices used in military and aerospace applications must endure greater environmental variability, including temperature range.
For example, resistors are manufactured in several grades:
These grades ensure that a device is suitable for its application, and may withstand the environmental conditions in which it is used. In the United States, the Department of Defense has defined the United States Military Standard for all products used by the United States armed forces. A product's environmental design and test limits to the conditions that it will experience throughout its service life are specified in MIL-STD-810, the Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests.
The MIL-STD-810G standard specifies that the "operating temperature stabilization is attained when the temperature of the functioning part(s) of the test item considered to have the longest thermal lag is changing at a rate of no more than 2.0°C (3.6°F) per hour." It also specifies procedures to assess the performance of materials to extreme temperature loads.
Commercial and retail products are manufactured to less stringent requirements than those for military and aerospace applications. For example, microprocessors produced by Intel Corporation are manufactured to three grades: commercial, industrial and extended.
Because some devices generate heat during operation, they may require thermal management to ensure they are within their specified operating temperature range; specifically, that they are operating at or below the maximum operating temperature of the device. Cooling a microprocessor mounted in a typical commercial or retail configuration requires "a heatsink properly mounted to the processor, and effective airflow through the system chassis". Systems are designed to protect the processor from unusual operating conditions, such as "higher than normal ambient air temperatures or failure of a system thermal management component (such as a system fan)", though in "a properly designed system, this feature should never become active". Cooling and other thermal management techniques may affect performance and noise level. Noise mitigation strategies may be required in residential applications to ensure that the noise level does not become uncomfortable.
Mammals attempt to maintain a comfortable body temperature under various conditions by thermoregulation, part of mammalian homeostasis. The lowest normal temperature of a mammal, the basal body temperature, is achieved during sleep. In women, it is affected by ovulation, causing a biphasic pattern which may be used as a component of fertility awareness.
In humans, the hypothalamus regulates metabolism, and hence the basal metabolic rate. Amongst its functions is the regulation of body temperature. The core body temperature is also one of the classic phase markers for measuring the timing of an individual's Circadian rhythm.
Changes to the normal human body temperature may result in discomfort. The most common form is a fever, a temporary elevation in the body's thermoregulatory set-point by about 1–2 °C (1.8–3.6 °F). Hyperthermia is an acute condition caused by the body absorbing more heat than it can dissipate, whereas hypothermia is a condition in which the core temperature drops below that required for normal metabolism and is caused by the body's inability to replenish the heat that is being lost to the environment.