Short time duty
Encyclopedia
The short time duty indicates an operating mode of increased performance but for a shorter length of time. Commonly it is also referred to the maximum load (the performance) at which and the related maximum length of time a device can be operated without to failure.
, 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.
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A common application is the high current measure (typically up to 10 or 20 A) with multimeter
s. 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).
in electrical devices (for instance in a halogen lamp
to prevent damage from use of too high power bulbs) or in form for instance of a pressure relief valve in hydraulic devices (e.g. a pressure cooker); many others have no protection (most hair-dryers) and the user realizes that the duty short time is over after for example the overheating has already damaged the device.
.
The best example is the radiation exposure (X-rays, gamma-radiation
or particle radiation
) for which a maximum short-time-, as well as a cumulative year-, and a life-dose are well defined for every type of radiation in order to avoid cancer (e.g. maximum number of dental X-rays per year). In this case the maximum load of the definition is represented by the dose
(see also Radiation Safety
). A controversial field is the uses of mobile (cellular) phones, for which there are not yet proven damages has for smoking or drugs.
Another simple example of well defined short time duty are the exposure times of sunscreen lotions (in this the case the load is also the electromagnetic radiation dose but its energy is just weaker and its frequency is shorter, i.e. ultra-violet light UV
).
A last good example are allergies
: in this case the load is the concentration of the allergic substance and the short time duty is depending on many factors like age, genetics, medical condition and so on.
Besides this somatic examples many everyday situations can influence the correct operating of human beings: a stressing situation (an annoying noise or even mobbing at work) can be tolerated for a certain short time "duty" (some seconds or days depending on its impact and on patience), but thereafter it can make irritable or bear to a serious depression.
Only by psychological aspects the short time duty is very different from human being to human being depending on their culture and religion (to sneeze in a far east country will rapidly irritate the companionship while just causing commiseration in a west country).
Device applications
The load can be a maximum powerPower (physics)
In physics, power is the rate at which energy is transferred, used, or transformed. For example, the rate at which a light bulb transforms electrical energy into heat and light is measured in watts—the more wattage, the more power, or equivalently the more electrical energy is used per unit...
, temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, revolution speed
Rotational speed
Rotational speed tells how many complete rotations there are per time unit. It is therefore a cyclic frequency, measured in hertz in the SI System...
, torque
Torque
Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
, acceleration
Acceleration
In physics, acceleration is the rate of change of velocity with time. In one dimension, acceleration is the rate at which something speeds up or slows down. However, since velocity is a vector, acceleration describes the rate of change of both the magnitude and the direction of velocity. ...
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
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...
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.
Multimeter
A multimeter or a multitester, also known as a VOM , is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance...
s. 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).
Protection
Only in some cases there is a built-in device protection in form for instance of a fusibleFuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
in electrical devices (for instance in a halogen lamp
Halogen lamp
A halogen lamp, also known as a tungsten halogen lamp, is an incandescent lamp with a tungsten filament contained within an inert gas and a small amount of a halogen such as iodine or bromine. The chemical halogen cycle redeposits evaporated tungsten back on to the filament, extending the life of...
to prevent damage from use of too high power bulbs) or in form for instance of a pressure relief valve in hydraulic devices (e.g. a pressure cooker); many others have no protection (most hair-dryers) and the user realizes that the duty short time is over after for example the overheating has already damaged the device.
Standardisation
Many producers indicates this short time duty only in the instruction handbook of the device, other indicates it on the very device. At this time (2007) there is no international identifier for this property. In Germany for instance it is indicated with KB (Kurzzeitbetrieb = shor time operating/operation ) and the time in minutes, in France there is no abbreviation but it is referred to as service temporaire, in Spanish it is indicated with servicio temporal, in Italian with servizio di durata limitata, and so on.Human applications
The concept of short time duty is easy to understand when referred to human beings in medical applications both somatic (body) as well as psychological (mind). The analogy with devices is useful to better understand both type of applications and should not be underestimated as if human beings were much better than their machines or devices: in this case a short time duty prevents from diseasesIllness
Illness is a state of poor health. Illness is sometimes considered another word for disease. Others maintain that fine distinctions exist...
.
The best example is the radiation exposure (X-rays, gamma-radiation
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
or particle radiation
Particle radiation
Particle radiation is the radiation of energy by means of fast-moving subatomic particles. Particle radiation is referred to as a particle beam if the particles are all moving in the same direction, similar to a light beam....
) for which a maximum short-time-, as well as a cumulative year-, and a life-dose are well defined for every type of radiation in order to avoid cancer (e.g. maximum number of dental X-rays per year). In this case the maximum load of the definition is represented by the dose
Dose (biochemistry)
A dose is a quantity of something that may impact an organism biologically; the greater the quantity, the larger the dose. In nutrition, the term is usually applied to how much of a specific nutrient is in a person's diet or in a particular food, meal, or dietary supplement...
(see also Radiation Safety
Radiation Safety Officer
In the United States, the person within an organization responsible for the safe use of radiation and radioactive materials as well as regulatory compliance...
). A controversial field is the uses of mobile (cellular) phones, for which there are not yet proven damages has for smoking or drugs.
Another simple example of well defined short time duty are the exposure times of sunscreen lotions (in this the case the load is also the electromagnetic radiation dose but its energy is just weaker and its frequency is shorter, i.e. ultra-violet light UV
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
).
A last good example are allergies
Allergy
An Allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen. These reactions are acquired, predictable, and rapid...
: in this case the load is the concentration of the allergic substance and the short time duty is depending on many factors like age, genetics, medical condition and so on.
Besides this somatic examples many everyday situations can influence the correct operating of human beings: a stressing situation (an annoying noise or even mobbing at work) can be tolerated for a certain short time "duty" (some seconds or days depending on its impact and on patience), but thereafter it can make irritable or bear to a serious depression.
Protection
The human body has also some built-in protections but only to a moderate extent (there is no fusible which can be simply exchanged in case of overload). The best protection for human beings is on the one side health education, which is equivalent to a handbook of its own body (body side), and love, friendship and politeness in case of human relations (mind side).Standardisation
All human beings have a similar resistance to most biological agents and exposures with some exCEptions (e.g. UV-rays short time duty or allergies) but the human gene sequences are remarkably homogeneous, so that there is a quite good standardisation and all human beings recognize their similars as such and automatically know which short time duties they can withstand.Only by psychological aspects the short time duty is very different from human being to human being depending on their culture and religion (to sneeze in a far east country will rapidly irritate the companionship while just causing commiseration in a west country).