6 - Application of sensors
6.6 - Household
Temperature control in appliances
The simplest household application is the temperature control used in kitchen machines: microvawe and normal ovens. The temperature vs. time curves of the different kind of meals are definied by the manufacturer or programmed by us according to our gustation. The oven will use it, and make the meal. This solution is also widely used in industrial applications: soldering, temperature curing processes, etc.
Smoke detectors
Ionization smoke detector:
The detector operates on the ionization principle: the detector respond to the first traces of fire in the form of visible smoke or invisible products of combustion. The detector consist of self compensating dual ionization chambers. One chamber detects the presence of combustion product, the second chamber serves as a reference. In case of fire the sampling chambers current is reduced.
Linear Beam detector:
The detector consist of a transmitter (IRLED) which emits an IR pulse. The pulse traverses the protected area to reach the reflector prism. The reflected beam detected by silicon photodiode. The attenuation of the IR pulse by smoke particles via scattering and absorption, results in an alarm condition.
The detector operates on the ionization principle: the detector respond to the first traces of fire in the form of visible smoke or invisible products of combustion. The detector consist of self compensating dual ionization chambers. One chamber detects the presence of combustion product, the second chamber serves as a reference. In case of fire the sampling chambers current is reduced.
Linear Beam detector:
The detector consist of a transmitter (IRLED) which emits an IR pulse. The pulse traverses the protected area to reach the reflector prism. The reflected beam detected by silicon photodiode. The attenuation of the IR pulse by smoke particles via scattering and absorption, results in an alarm condition.
Sensors for fire detection
NTC linear heat sensor
The NTC based sensor contains a negative temperature coefficient polymer as insulator between the wires, whose resistance changes as a function of temperature. Linear heat sensors can detect temperature changes along the sensing cable, triggering fire alarm when temperature exceeds a predetermined value.
Melting linear heat sensor
Melting type linear heat sensors use a thermoplastic material as insulator between the electrode wires. The insulator melts at a predetermined temperature, causing short circuit triggernig fire alarm.
Optical linear heat sensor
In fibre optic based linear heat sensors laser light pulses generated from control unit are launched into the fibre. When pulses encounter a temperature change at a point on the fibre, the pattern of back-scattered light alters and is analyzed to provide a real-time temperature profile. Exceeding a predetermined temperature value is triggering fire alarm.
Pneumatic heat sensor
Pneumatic heat detector consist of a sealed stainless steel tube containing pressure sensitive switch and a core material releasing an extremely large volume of gas, when any section of the sensor is heated to a particular temperature. When the temperature around the detector rises to preset level, the gas pressure within the tube increases and closes the alarm switch.
Triple IR based flame detector
Triple IR based flame detectors are sensing three infrared wavelength to distinguish flame from other IR sources, e.g. sunlight or electric bulbs. Most of flame's radiant energy falls within the IR region and the CO2 peak at 4.3 mm is caused by the combustion of hydrocarbons. Triple IR system operates by monitoring this peak, and two other, non-flame-sensing wavelengths.
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