Pyroelectric sensor basic knowledge and use of common problems

Pyroelectric infrared sensor can detect a person or animal and output signals emitted infrared sensors. As early as 1938 , it was proposed the use of pyroelectric effect detecting infrared radiation, but not taken seriously until the sixties, with the rapid development of laser , infrared technology , was also promoted to the pyroelectric effect of research and pyroelectric crystals for applications. Pyroelectric crystals have been widely used infrared spectroscopy , infrared remote sensing and thermal radiation detectors , it can serve as an ideal infrared laser detectors. Its goal is being widely applied to various automation control device . In addition to our well-known automatic switch in the corridor , burglar alarm has been applied on the outside , the more promising areas of application . For example: In the room that no one will stop automatically when the air conditioner , water dispenser . TV viewers can judge no one watching or shut down automatically after the agency has to sleep. Turn the monitor or on the application of automatic doorbell . Combined with a video camera or digital camera automatically records the animal or human activity , and so on ...... . You can according to their whim , in combination with other circuits develop more excellent new products. Or automated control devices.

Pyroelectric sensor basics

Pyroelectric effect is similar with the piezoelectric effect , is due to temperature changes caused by the phenomenon of crystal surface charge . Pyroelectric sensor is a temperature-sensitive sensors. It consists of ceramic oxides or piezoelectric crystal components, the component made of two surface electrodes , is within the range of sensors to monitor temperature change ΔT , the pyroelectric effect will be on the two electrodes produce a charge ΔQ, ie generating a weak voltage ΔV between the two electrodes . Because of its high output impedance , there is an impedance transformation for an FET in the sensor . Charge ΔQ pyroelectric effect is produced by the disappearance of the combined air ions , ie when the ambient temperature is stable and unchanging , ΔT = 0, then the sensor is no output . When the body enters the detection zone , because the body temperature and ambient temperature difference , resulting in ΔT, there ΔT output ; if the body does not move into the detection zone, the temperature does not change , there is no output of the sensor . Therefore, this sensor detects the human or animal activity sensor . Experimentally proved that the sensor without the optical lens ( also known as Fresnel lens ) , for detecting distance is less than 2m, and the coupled optical lens , its detection distance may be greater than 7m.

Use should note the following:

First, the DC voltage must comply with values too high and too low will affect the performance of our modules required , and requires a well- regulated power supply must be filtered , such as computer USB power supply, cell phone charger power supply , older 9V laminated battery modules are unable to meet the job requirements , we recommend that customers use the power transformer and after a three-terminal voltage regulator chip and then back through the power supply filter capacitor 220UF and 0.1UF .

Second, as far away from the body when debugging sensitive area , sometimes in front of the body , although not in the module , but too close to the body when the module from the module can also be sensitive to the cause has been output , and do not touch the circuit debugging body part will also affect the module , more scientific approach is the output end of an LED or a multimeter , the module is covered with newspapers, people leave the room , such as two minutes later to see if there is an output module or been ?

Third, when the module is not connected to the load can work, after work load connected disorder , one reason is because the power supply capacity is relatively small load power, voltage fluctuations caused by the load at work cause the module to malfunction , and the other reason is that the load will produce electrical work interference, such as inductive loads such as relays or solenoids back electromotive force generated when the 315M will emit electromagnetic radiation , such as board work will affect the module . Solution is as follows : A, the power supply section plus inductor filter . B, using load and voltage module using different methods , such as : load using 24V operating voltage , the module uses 12V operating voltage , during a three -terminal regulator isolation. C: using a higher capacity power supply .

Fourth, the human body sensing module can only work in the room and the work environment should avoid sunlight , direct exposure to intense light , if the work environment has a strong radio interference shielding measures can be used . In case there is a strong air flow interference, doors and windows closed or blocked convection. Sensing area to avoid facing the heat and appliances and objects easily windblown debris and clothing.

Fifth, the human body sensing module is recommended to install in a sealed box , or it may have been the output signal.

Six , if the requirements of the human body sensing module detection angle less than 90 degrees, you can use opaque tape blocking lenses or cutting narrow lens to achieve.

Seven human body sensing module with dual element probes , the body's limbs and head movement direction and sensor sensitivity are closely linked , and the characteristics of the infrared module can not determine the precise control of the sensing distance .

Eight , in the probe module (PIR) can be assembly and welding the other side of the circuit board . The probe can also be used to extend the two-wire shielded cable , the length should be less than 20 cm for good