A Flame sensor is a sensor designed to detect and respond to the presence of a flame or fire, allowing flame detection. Responses to a detected flame depend on the installation, but can include sounding an alarm, deactivating a fuel line (such as a propane or a natural gas line), and activating a fire suppression system.
When used in applications such as industrial furnaces, Flame sensors role is to provide confirmation that the furnace is working properly; it can be used to turn off the ignition system though in many cases they take no direct action beyond notifying the operator or control system. A Flame sensor can often respond faster and more accurately than a smoke or heat detector due to the mechanisms it uses to detect the flame.
Infrared (IR) or wideband infrared (1.1 μm and higher) Flame sensors monitor the infrared spectral band for specific patterns given off by hot gases. These are sensed using a specialized fire-fighting thermal imaging camera (TIC), a type of thermographic camera. False alarms can be caused by other hot surfaces and background thermal radiation in the area.
Water on the Flame sensor’s lens will greatly reduce the accuracy of the detector, as will exposure to direct sunlight. A special frequency range is 4.3 to 4.4 μm. This is a resonance frequency of CO2. During burning of a hydrocarbon (for example, wood or fossil fuels such as oil and natural gas) much heat and CO2 is released.
The hot CO2 emits much energy at its resonance frequency of 4.3 μm. This causes a peak in the total radiation emission and can be well detected. Moreover, the “cold” CO2 in the air is taking care that the sunlight and other IR radiation is filtered.
This makes the Flame sensor in this frequency “solar blind”; however, sensitivity is reduced by sunlight. By observing the flicker frequency of a fire (1 to 20 Hz) the detector is made less sensitive to false alarms caused by heat radiation, for example caused by hot machinery.
A severe disadvantage is that almost all radiation can be absorbed by water or water vapour; this is particularly valid for infrared flame detection in the 4.3 to 4.4 μm region. From approx. 3.5 μm and higher the absorption by water or ice is practically 100%.
This makes infrared Flame sensors for use in outdoor applications very unresponsive to fires. The biggest problem is our ignorance; some infrared Flame sensorrs have an (automatic) detector window self test, but this self test only monitors the occurrence of water or ice on the detector window.
A salt film is also harmful, because salt absorbs water. However, water vapour, fog or light rain also makes the sensor almost blind, without the user knowing. The cause is similar to what a fire fighter does if he approaches a hot fire: he protects himself by means of a water vapour screen against the enormous infrared heat radiation.
The presence of water vapor, fog, or light rain will then also “protect” the monitor causing it to not see the fire. Visible light will, however be transmitted through the water vapour screen, as can easily been seen by the fact that a human can still see the flames through the water vapour screen.
The usual response time of an IR detector is 3–5 seconds.
1. can detect the flame or the wavelength at 760 nm to 1100 nm range of the light source, the test flame lighters distance of 80cm, the larger the flame, the greater the distance test.
2. the detection angle of 60 degrees, the flame spectrum particularly sensitive.
3. sensitivity adjustable (shown in blue digital potentiometer adjustment).
4. the comparator output signal clean waveform is good, driving ability, than 15mA.
5. with a precision potentiometer adjustable sensitivity adjustment.
6. Operating Voltage 3.3V-5V.
7. the output in the form: DO digital switching outputs (0 and 1) and AO analog voltage output.
8. a fixed bolt holes for easy installation.
9. small plates PCB size: 3.2cmx1.4cm.
10. using a wide voltage LM393 comparator.
Module for use:
1. the flame flame sensor most sensitive to ordinary light is also a reaction, generally used as fire alarm and other purposes.
2. a small panel output interface can be directly connected with the microcontroller IO port.
3. the sensor and the flame to maintain a certain distance, so as not to damage the sensor temperature of the test flame lighters distance 80cm, the larger the flame, the greater the distance test.
4. small plates analog output mode and the AD conversion process, you can get higher accuracy.
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