Heat detectors may be defined as devices that respond to a rise in ambient temperature.
Are essentially of two types:
- Detectors thermostatic
- -Rise detectors.
The detectors are fitted with a thermostatic element sensitive calibrated for a given temperature. They are activated when the temperature of the sensor reaches the calibration value as a result of an increase of the ambient temperature. At the instant of the intervention, the temperature of the sensitive element will be more close to that of calibration, the slower was the variation of the temperature in the neighborhood of the detector. They can be used as a thermistor sensing element or a fuse or a bimetallic strip or the thermal expansion of a liquid.
The detector thermostatic is completely insensitive to the gradient of the temperature environment until this is maintained below the calibration value.
This reaction could be an advantage in cases where a rapid variation of the ambient temperature depends on normal conditions of user such as those typical of kitchens and boiler rooms, while if the defect is a rapid increase in temperature is related to a situation of fire.
Another defect that appears in the detector thermostatic resides thermal inertia of the sensitive element, so that even in case of high temperature gradients, the ambient temperature can significantly exceed the calibration value of the sensitive element before the detector intervenes.
Therefore, the use of this type of detector finds its optimal location in the detection of open burners with flames and in all situations where it is expected, in the event of an accident, a fast rise in temperature.
The detectors have a sensitive element-rise calibrated for a given temperature gradient, measured in ° C / min.
The principle of operation according to which they operate refers to the precise characteristics of the thermistors or the electrical resistance of the cables or the principle of expansion of the liquids.
They are activated when the temperature gradient, which is subjected the sensitive element, reaches the calibration value, as a result of an increase of the ambient temperature. The trip time is a function of temperature variation and is much more short and more rapid is its variation.
The detectors are insensitive to changes in lens-rise of temperature for a compensation effect between the sensitive element of measurement in contact with the outside and the reference.
This is a positive feature in applications where the ambient temperature varies slowly under normal conditions within the limits very extended.
-Rise detectors are an optimal protection in environments with risk of fire to flame.