On The Calibration Of Photoelectric Smoke Detector Technology
Current methods of fire detection in the most commonly used are two broad categories, namely, temperature detection and smoke detection. Smoke detection is conducive to early detection of fire, and this “early” is the core of the pursuit of fire prevention, so Fire Monitoring System, use smoke detectors majority. Smoke detectors are divided into ionic and photoelectric type two categories. Early widely used mostly to ionic, photoelectric type, use less. One reason seems to comparison, ion is more sensitive in the “early smoldering smoke” (smoke particle size smaller). Only in respect sensitivity of this point, can be resolved from the sensitivity setting, it is not keen on the early people ion type smoke detector main reason. In fact, people in the radioactive sources ionic worry has always been there, but because ionic Probe The calibration technique is easy to grasp, to achieve a very easy product sensitivity is easy to maintain consistency. The photoelectric-type probe, was initially Environment And stray light interference, when the light source and photo on the tube and light maze solution, the interference problem is basically solved. More troubled by the current general factory calibration technique, compared with ionization smoke detector calibration, the calibration of photoelectric detectors, relatively more difficult, if improper methods, the sensitivity of the product are often scattered yield is also affected. Therefore, many manufacturers are still abandoned development and production of photoelectric and ionic. ?
As economic development, the rapid growth of social wealth, fire prevention more attention. This makes the rapid growth of the number of detectors used, ion probe reprocessing of radioactive sources have become a major concern by people Environmental protection Potential problems. Therefore, when the photoelectric type smoke sensor quality assurance, and the price quite, people will be more willing to use photoelectric smoke detector. So the situation is forcing ionic dominance and give out photoelectric sensor. In particular, the future development of analog Fire Alarm Technology to replace the volume of alarm switch technology or “quasi” (pseudo) analog detection technology, is the general trend. Sensitivity and consistency required to produce the optical line sensor, increasing the rate of qualified products, to master the production of the last pass – high-precision calibration technology has become a problem to be solved.
As a calibration photoelectric system, which is different from the ionic calibration system where the threshold on the concentration of smoke in its simulation. This is because the threshold concentration of smoke, on the photoelectric type is to change the current intensity of light scattering light. In addition to the intensity of photocurrent and the concentration of smoke, but also by the luminous efficiency of LED, the drive current strength, and optical receiver photoelectric conversion efficiency of the tube, even with the LED and receiving control the direction of the launch and receive surface distribution function and the LED and receiver tube installation has great relationship. In short, the impact of too many factors, but also the necessary precision in the context of most of them can not be ignored. The ion type, the smoke into, its direct effect is to change the gate voltage, while the gate voltage is the voltage from the ion chamber and ion chamber of the mechanical structure and the decision of radioactive sources. As the partial pressure ratio can be mechanical parts geometry precision, and accuracy of the sources match made sufficiently accurate (as compared with the optical control type is easier). Threshold concentration of smoke in the simulation, you can simply set the control by the voltage ion chamber, to achieve sufficient accuracy of the simulation. ?
From the above mentioned simulation of the relationship with the smoke can be seen, ion calibration can be done very simply. Calibration, the ion chamber at the top with only required analog voltage. The photoelectric emission drive current If can, LED light-emitting efficiency and intensity distribution of the direction of the surface, the photoelectric conversion efficiency of photoelectric tubes and receive direction, each light and other optical properties of the maze to achieve sufficient accuracy consistency , and the two pipe installation precision and optical properties of an ideal, you can not calibrate. If the optical output signal for the function of various factors as variables, known from the differential theory: the differential output signal (error) will be a function of the variable, and by the individual variable differential (error) of, on the whole , the error is much greater than when a single variable. If only one or two good control, then after a comprehensive tobacco scattering, the uncertainty of the individual electrical simulation of compensation can be taken to reach the sensitivity required. However, in practice, usually there are many aspects of device performance and technology on the discreteness, and they are all significantly affect the sensitivity of the detector, which is difficult to simulate by way of electrical compensation. So the simulation is more difficult.
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