Short Time Duty - Device Applications

Device Applications

The load can be a maximum power, temperature, revolution speed, torque, acceleration or whatever can influence the mechanical or chemical properties of the device for its correct function: for instance an electrical motor can be driven at a higher revolution speed than for normal (constant) operation (nominal revolution speed), but after a short time it should be driven down or switched out in order to prevent from damage; another example can be the operating temperature of a simple oven which can be raised to the maximum allowed but only for a short time to avoid that the oven begins to burn. Generally at all performances a part of the input energy will be dissipated as heat. The higher the operation power the higher the heat to dissipate. If the performance is too high, the device will not be able to dissipate the heat to its environment and its temperature will raise proportionally to the energy surplus. If the temperature raises too much the mechanical and chemical properties of the device will begin to change causing permanent deformations for plastical material or fractures for brittle materials. Being the energy the product of power and time, either the power (or any to it related physical value) as by normal operation/duty or the time as by short-time duty have to be limited.

A common application is the high current measure (typically up to 10 or 20 A) with multimeters. The maximum time length of short time duty (typically 10 to 30 seconds) is indicated near the corresponding socket (usually the left one) as well as the time to be waited for, before each of such measures might be repeated (typically "each 15 minutes"). Another common application is inflation with air compressors: those become very hot, if used for a too long time and have to be shut down after a certain time (for small compressors such that of the picture a typical time is 10 minutes).