1. Working principle of photoelectric sensor
The photoelectric sensor achieves control by converting changes in light intensity into changes in electrical signals. Generally, it consists of three parts: transmitter, receiver and detection circuit. The transmitter aims at the target and emits a beam. The emitted beam generally comes from a semiconductor light source, a light-emitting diode, a laser diode and an infrared emitting diode. The beam is emitted without interruption, or with varying pulse widths. The receiver consists of photodiodes, phototransistors and photovoltaic cells. In front of the receiver, optical components such as lenses and apertures are installed. Behind it is the detection circuit, which filters out the valid signal and applies it.
2. What types of photoelectric sensors are there?
1. Photoelectric sensors are classified according to shell shape: cylindrical type , square shape.
The housing of the photoelectric sensor is currently selected as round or square according to the customer’s installation environment. This is not specified.
2. Photoelectric sensors are classified according to detection methods: through-beam, mirror-reflective, and diffuse-reflective.
Through-beam photoelectric sensors have the longest detection distance among photoelectric sensors, and the distance can reach several meters or even ten meters. The installation must have an emitter and receiver facing each other.
The detection distance of the retroreflective photoelectric sensor is slightly shorter than that of the through-beam sensor, but the installation is much more convenient than the through-beam sensor. It can be installed in a narrow space, as long as it is installed with a reflector. However, the characteristic is that it professionally detects the presence or absence of transparent objects.
The detection distance of the diffuse reflection photoelectric sensor is not as good as the above two, but the installation method and installation location of the diffuse reflection photoelectric sensor are more convenient than the first two.
3. Photoelectric sensors are classified according to light source: visible red light, invisible infrared light, and laser.
The light source of the photoelectric sensor is selected according to the customer’s requirements, the detection object, and the detection environment. Visible red light and invisible red light will change the size of the spot with the distance, but Lasers do not. Lasers do not change the size of the spot due to distance. Lasers are suitable for applications such as detecting the presence of small or micro objects, counting, and positioning.
3. Practical applications of photoelectric sensors
Photoelectric sensors can be used to detect non-electrical quantities that directly cause changes in light quantity, such as light intensity, illuminationtemperature, radiation temperature measurement, gas composition analysis, etc.; it can also be used to detect other non-electric quantities that can be converted into changes in light quantity, such as part diameter, surface roughness, strain, displacement, vibration, speed, acceleration, as well as the shape and working status of the object identification, etc.
1. Barcode scanning pen
When the scanning pen head moves on the barcode, if it encounters a black line, the light from the LED will be absorbed by the black line. , the phototransistor cannot receive reflected light, has high impedance, and is in a cut-off state. When encountering a white interval, the light emitted by the light-emitting diode is reflected to the base of the phototransistor, and the phototransistor generates photocurrent and turns on. After the entire barcode is scanned, the phototransistor deforms the barcode into electrical pulse signals. After amplification and shaping, the signal forms a pulse train, which is then processed by the computer to complete the recognition of the barcode information.
2. Simple photosensitive alarm
When there is no light, the silicon photovoltaic cell generates no voltage. At this time, the silicon photovoltaic cell is equivalent to a resistor connected in series with the amplifier. on the base circuit. When there is light, the silicon photovoltaic cell generates a voltage, which is added to the base of the VT1 tube together with the voltage on R2, so VT1 is turned on, VT2 and VT3 are also turned on, the relay K works, and its contacts are closed , the buzzer sounds an alarm.
3. Product Counting
When the product is running on the conveyor belt, it continuously blocks the light path between the light source and the photosensitive device, causing the photoelectric pulse circuit to follow the movement of the product. Is there any electrical pulse signal generated? Every time the product is blocked from light, the photoelectric pulse circuit generates a pulse signal. Therefore, the number of output pulses represents the number of products. The pulses are counted by the counting circuit and displayed by the display circuit.
4. Photoelectric smoke alarm
When there is no smoke, the light emitted by the light-emitting diode propagates in a straight line, and the photoelectric triode does not receive signals and has no output; When there is smoke, the light emitted by the light-emitting diode is refracted by the smoke particles, so that the triode receives the light, outputs a signal, and issues an alarm.
5. Anti-theft alarm circuit
Install the photoelectric circuit breaker behind the drawer, and set a power switch in a hidden place. When anti-theft is needed , turn on the switch. Usually, because the baffle is inserted into the slot, the photoelectric triode only has dark current, BG does not conduct, and relay J does not pull in. When a thief pries open the drawer, the baffle will leave the notch as soon as the drawer is opened. The photocurrent of the phototransistor will generate a voltage close to the power supply on R2, BG will be turned on, and the relay will close, sending out an alarm signal.
6. Bus door closing safety indicator
When the door is closed, the baffle is inserted into the slot of the photoelectric breaker, and the phototransistor has no working current. Its output is high level;When the three car doors are fully closed, three high-level signals are output accordingly. Then the output of the AND gate is high level and the green light is on. If one of the doors is not closed (or not closed tightly), the AND gate output is low, causing the red light to turn on.
If the website content violates your rights, please contact us to delete it。
