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What are the Basic Principles of Photoelectric Sensor?

Author: Apogeeweb Date: 13 Apr 2021  466

how does a photoelectric sensor work

Introduction

Photoelectric sensor is a sensor that uses a photoelectric component as a conversion element. In electronics, the photoelectric sensor converts the light intensity into the electrical signals. It is generally composed of three parts: transmitter, receiver and detection circuit.
The transmitter emits a light beam to the target, and the emitted light beam is generally a semiconductor light source, such as a light emitting diode (LED), a laser diode, and an infrared emitting diode. The beam is emitted continuously, or change the pulse width to accomplish it. The receiver is composed of a photodiode, a phototransistor, and a photocell commonly. In front of the receiver, optical components such as lens and aperture are installed. Behind it is the detection circuit, which can filter out the effective signal and make actions.

What is Photoelectric Sensor?

Catalog

Introduction

Ⅰ Photoelectric Sensor Basic

1.1 Photoelectric Sensor Characteristics

1.2 Photoelectric Effect

1.3 Optical Signals into Electrical Signals

Ⅱ Photoelectric Sensor Applications

2.1 What are Photoelectric Sensors Used?

2.2 Example: Infrared Photoelectric Sensor Switch

Ⅲ Photoelectric Sensor Development

3.1 Advantages

3.2 Smart Photoelectric Sensors


Ⅰ Photoelectric Sensor Basic

1.1 Photoelectric Sensor Characteristics

Photoelectric sensors can be used to detect non-electrical physical quantities that directly cause changes in light, such as light intensity, illuminance, radiation temperature measurement, gas composition analysis, etc., and can also be used to detect other non-electrical quantities that can be converted into light quantity changes, such as part diameter, surface roughness, displacement, vibration, speed, acceleration, as well as the recognition of the shape and working state of the object. It has the characteristics of non-contact, fast response, reliable performance, etc., So it is widely used in industrial automation devices and robots.

1.2 Photoelectric Effect

The principle of photoelectric sensors is usually divided into three categories: 
(1) The phenomenon that can cause electrons to overflow the surface of an object under the action of light is called external photoelectric effect, such as photoelectric tube, photomultiplier tube, etc.
(2) Under the action of light, the change of resistance is called the internal photoelectric effect, such as photoresistor, phototransistor, etc.
(3) An object generates a certain directional electromotive force under the action of light is called the photovoltaic effect, such as photovoltaic cells.

1.3 Optical Signals into Electrical Signals

Photoelectric sensors that use photoelectric components based on photoelectric effect as sensing parts have a wide variety of applications. According to the nature output of the device, it has two principles:
1) A continuously changing photocurrent can be used to measure the intensity of light and physical quantities such as temperature, light transmission ability, displacement and surface state of the object. For example: illuminance meter for measuring light intensity, photoelectric pyrometer, photoelectric colorimeter and turbidity meter, photoelectric alarm, automatic detection device for quality testing products. Semiconductor optoelectronic components are not only widely used in the civil industry, but also have an important role in the military. For example, lead sulfide photoresistors can be made into infrared night vision devices, infrared cameras and infrared navigation systems.
2) Convert the measured stuff into a continuously changing photocurrent. Various photoelectric automatic devices are made with the characteristics of "with" or "without" electrical signal output when photoelectric elements are irradiated by light or no light. The photoelectric element is used as a switch-type photoelectric conversion element. For example, the photoelectric input device of the electronic computer, the switch type temperature adjusting device and the digital photoelectric speed measuring instrument, etc.
Based on the above mentioned, the sensing types of photoelectric sensor include through-beam arrangement, reflective arrangement, laser-reflective, and diffuse type.

electronic photoelectric sensors

Ⅱ Photoelectric Sensor Applications

2.1 What are Photoelectric Sensors Used?

1) Smoke and Dust Concentration Monitor
Preventing industrial smoke and dust pollution is one of the important tasks of environmental protection. To eliminate it, we must first know the amount of smoke and dust emissions. Therefore, the source of the smoke and dust must be monitored, automatically displayed and alarmed for exceeding the standard. The turbidity of the smoke and dust in the flue is detected by the size of the change during the transmission of light in the flue. If it increases, the light emitted by the light source is absorbed and refracted by the soot particles, and the light reaching the photodetector decreases. Therefore, the strength of the output signal of the photodetector can reflect the change of flue turbidity.

2) Barcode Scanner
When the scanning pen moves on the bar code, if it encounters a black line, the light of the light-emitting diode will be absorbed by the black line, and the phototransistor will not receive the reflected light, present a high impedance and be in a cut-off state. When encountering the white interval, the light emitted by the LED is reflected to the base of the photosensitive triode, which generates a photocurrent to conduct. After the entire bar code is scanned, the phototransistor deforms the bar code into electrical pulse signals, which are amplified and then reshaped to form a pulse train, and finally processed by a computer to complete the identification of the bar code information.

3) Product Counter
When the product is running on the conveyor belt, it continuously shields the light path from the light source to the photoelectric sensor, so that the photoelectric pulse circuit generates an electrical pulse signal. Every time the light is shaded by products, the photoelectric sensor circuit generates a pulse signal. Therefore, the number of output pulses represents the number of products. The pulse is counted by the counting circuit and displayed by the display circuit.

4) Photoelectric Smoke Detector
When there is no smoke, the light emitted by the LED travels in a straight line, and the phototransistor does not receive a signal. When there is no output, but having smoke, the light emitted by the light-emitting diode is refracted by the smoke particles, so that the triode receives the light, a signal output sends an alarm.

5) Measuring Speed
Coated with black and white on the rotating shaft of the motor. When rotating, the reflected light and non-reflected light alternately appear. The photoelectric sensor correspondingly intermittently receives the reflected light signal, and outputs the intermittent electrical signal, which is amplified by the amplifier and the shaping circuit. The square wave signal is shaped and output, and finally the motor speed is output by the electronic digital display.

6) Photocells in Photoelectric Detection and Automatic Control
When photocells used as photodetectors, their basic principles are the same as photodiodes, but their basic structures and manufacturing processes are not exactly the same. Since the photovoltaic cell does not require an external voltage when working, it has the advantages of high photoelectric conversion efficiency, wide spectral range, good frequency characteristics, low noise, etc. They are widely used in photoelectric readout, photoelectric coupling, grating ranging, laser collimation, film sound recovery, UV monitors and flameout protection devices for gas turbines, etc.

2.2 Example: Infrared Photoelectric Sensor Switch

Uses the blocking or reflection of the infrared light beam by the measured object to detect whether there is an object under test. When the detected object passes through the detection area, the output state of the infrared photoelectric switch will be change to achieve automatic detection. Moreover, objects that have the ability to reflect and block infrared light can be detected.

Photoelectric Sensor Switch Design: Parameters and Drawings

Parameters

Descriptions

Current Consumption

5mA~30mA

Output Current

DC: less than 200mA  AC: less than 200mA  Relay Outputs, Contact Current: 1A~3A

Response Time

DC: less than 2.5ms AC: less than 30ms

Detect Object

Transparent, Opaque

Opaque

Transparent, Opaque

Opaque

Differential Distance

Less than 20%

 

Less than 20%

 

Pointing Angle

 

3°~20°

3°~10°

 

3°~20°

3°~10°

Environmental Illuminance

Surface Light Intensity: Less than 3000lx (filament lamp)  Less tan 10000lx (sun light)

Insulation Resistance

Over 200MΩ

photoelectric sensor drawing

photoelectric sensor drawing

photoelectric sensor drawing

photoelectric sensor drawing

photoelectric sensor drawing

photoelectric sensor drawing

photoelectric sensor drawing

Ⅲ Photoelectric Sensor Development

3.1 Advantages

① Long Detection Distance
If the detection distance of 10m or more is set in the through-beam type, it can detect remotely that other detection methods (magnetic, ultrasonic, etc.).

② Less Restrictions on Detecting Objects
As the detection principle is based on the shading and reflection caused by the detection object, unlike proximity sensors, which limit the detection object to metal. Photoelectric sensor can detect almost all objects such as glass, plastic, wood, and liquid.

③ Short Response Time
The light itself is high speed, and the circuit of the sensor is composed of electronic parts, so there is no mechanical working time, and the response time is very short.

④ High Resolution
High-resolution can be achieved by using advanced design technology to concentrate the projected light beam on a small spot, or by forming a special light-receiving optical system. It can also detect small objects and high-precision position.

⑤ Non-contact Detection
The detection can be achieved without mechanically touching the detection object, so it will not cause damage to the detection object and the sensor. Therefore, the photoelectric sensor can be used for a long time.

⑥ Color Discrimination
The reflectance and absorptivity of the light formed by the detection object differ according to the combination of the wavelength of the light projected and the color of the detection object. Using this characteristic, the color of the detected object can be detected.

⑦ Easy to Adjust
In the type of projected visible light, because the projected light beam is visible to the eyes, the position of the detection object can be moved easily.

3.2 Smart Photoelectric Sensors

Discover the best Photoelectric Sensors in the future. Smart photoelectric sensors provide essential input for every process chain. They support dynamic, real-time-optimized, and self-organized industry processes. The functions of the smart photoelectric sensor are: self-compensation, self-calibration, self-diagnosis, numerical processing, two-way communication, information storage, and digital output. With the development of science and technology, the functions of smart photoelectric sensors will gradually increase. It will use artificial neural networks, artificial intelligence, and information processing technologies (such as sensor information fusion technology, fuzzy theory, etc.) to enable sensors to have more advanced intelligence, analysis skill, and judgment. So its self-adaptation, and self-learning functions can complete complex tasks such as image recognition, feature detection, and multi-dimensional detection.

 

Frequently Asked Questions about Photoelectric Sensor

1. What is a photoelectric sensor?
A photoelectric sensor is a device that detects a change in light intensity. Typically, this means either non-detection or detection of the sensor's emitted light source.

 

2. How does a photoelectric sensor work?
A Photoelectric Sensor consists primarily of an Emitter for emitting light and a Receiver for receiving light. When emitted light is interrupted or reflected by the sensing object, it changes the amount of light that arrives at the Receiver. The Receiver detects this change and converts it to an electrical output.

 

3. Where are photoelectric sensors used?
Checking objects on production lines or conveyors: photoelectric sensors can detect items' sizes to spot any errors, or simply spot their absence, as well as picking up problems like misaligned caps on bottles. They are widely used in the food and pharmaceutical industries, and in packaging plants.

 

4. What are the three types of photoelectric devices?
There are three major types of photoelectric sensors: thru-beam, retroreflective, and diffused. Each sensor has its own strengths and can be used in a variety of ways.

 

5. What are the two basic components of a photoelectric sensor?
Basically, there are two major components in photoelectric sensor. They are a transmitter (light source) and receiver (sensor).

Ordering & Quality

Photo Mfr. Part # Company Description Package PDF Qty Pricing
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LM335H-NOPB LM335H-NOPB Company:Texas Instruments Remark:SENSOR ANALOG -40C-100C TO46-3 Package:TO-206AB, TO-46-3 Metal Can
DataSheet
In Stock:1498
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Price:
1+: $12.27000
5+: $10.76000
10+: $9.68400
25+: $8.60800
50+: $7.96240
100+: $6.88640
500+: $6.45600
1000+: $6.02560
5000+: $5.72432
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AD7416ARZ AD7416ARZ Company:Analog Devices Inc. Remark:SENSOR DIGITAL -40C-125C 8SOIC Package:8-SOIC (0.154", 3.90mm Width)
DataSheet
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1+: $2.92000
10+: $2.61800
25+: $2.47520
100+: $2.03500
250+: $1.82600
500+: $1.76000
1000+: $1.59500
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LM83CIMQA-NOPB LM83CIMQA-NOPB Company:Texas Instruments Remark:SENSOR DIGITAL -40C-125C 16SSOP Package:16-SSOP (0.154", 3.90mm Width)
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5+: $7.36600
10+: $6.50600
25+: $5.27840
50+: $4.66460
100+: $4.54180
500+: $3.80526
1000+: $3.55975
5000+: $3.31425
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DS18B20Z DS18B20Z Company:Maxim Integrated Remark:Temperature Sensor Digital, Local -55°C ~ 125°C 12 b 8-SOIC Package:8-SOIC (0.154"", 3.90mm Width)
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TCN75-5-0MOAG TCN75-5-0MOAG Company:Microchip Technology Remark:SENSOR DIGITAL -55C-125C 8SOIC Package:8-SOIC (0.154", 3.90mm Width)
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TC72-5-0MMFTR TC72-5-0MMFTR Company:Microchip Technology Remark:SENSOR DIGITAL -55C-125C 8DFN Package:8-VDFN Exposed Pad
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MCP9701AT-E-TTVAO MCP9701AT-E-TTVAO Company:Microchip Technology Remark:SENSOR ANALOG -10C-125C SOT23-3 Package:TO-236-3, SC-59, SOT-23-3
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LM335AZT LM335AZT Company:STMicroelectronics Remark:Temperature Sensor Analog, Local -40°C ~ 100°C 10mV/°C TO-92-3 Package:TO-226-3, TO-92-3 (TO-226AA) (Formed Leads)
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10000+: $0.41600
50000+: $0.39000
1+: $1.07000
10+: $0.95900
25+: $0.91000
100+: $0.74750
500+: $0.61750
1000+: $0.48750
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