What Is The Difference Between Optical Fiber Sensor And Photoelectric Sensor?

An Optical Fiber Sensor and a photoelectric sensor, as two typical sensors, are widely used in production measurement, what is the difference between them? 

1. Different definitions

Optical fiber sensor: Optical fiber sensor is a sensor that converts the state of the measured object into a measurable optical signal. The working principle of the optical fiber sensor is to send the light source incident beam through the optical fiber into the modulator, the interaction between the modulator and the measured parameters outside, so that the optical properties of the light such as light intensity, wavelength, frequency, phase, polarization state change, become the modulated optical signal, and then through the optical fiber into the photoelectric device, after the demodulator to obtain the measured parameters.

Photoelectric sensor: Photoelectric sensor is a device that converts an optical signal into an electrical signal. It works on the basis of the photoelectric effect. The photoelectric effect refers to the phenomenon that when light is irradiated on certain substances, the electrons of the substances absorb the energy of the photons and the corresponding electrical effect occurs.

2. Different performance

Photoelectric sensor:

⑴ Wide range of transient response and strong ability of harmonic measurement. The quality of transient characteristics is an important parameter to judge whether a transformer can be applied in the power system, especially the cooperation with the relay protection operation time. Due to the existence of an iron core, the traditional electromagnetic transformer has poor response characteristics to high-frequency signals and can not reflect the transient process of the primary side correctly. However, the measurement frequency range of the CT is mainly determined by the electronic circuit, and there is no problem with core saturation, so it can accurately reflect the transient process of the primary side. Generally can be designed up to 0.1Hz to 1MHz, special can be designed up to 200MHz bandpass. The structure of a photoelectric sensor can measure harmonics on high-voltage power lines. The electromagnetic induction transformer is difficult to reach.

(2) Digital interface, strong communication ability, because the photoelectric sensor down is the optical digital signal, easy interface with the communication network, and there is no measurement error in the transmission process. At the same time, with the widespread use of computerized protection and control equipment, the photoelectric transformer can directly provide the digital quantity to the secondary equipment, which can eliminate the converter and A/D sampling part of the original protection device, greatly simplify the secondary equipment, and promote the research of new protection principles.

(3) Small size, lightweight, easy to upgrade, to meet the requirements of substation miniaturization, and compact, because the photoelectric sensor is based on the sensor head and electronic circuit signal acquisition and processing, small volume, weight is generally less than 1000kg, easy to integrate in AIS or GIS, this will greatly reduce the area of the substation, Meet the requirements of substation miniaturization and compactness. At the same time, the optical transformer is connected to the secondary equipment through a small number of optical cables, which can greatly reduce the cable trench and cable.

Optical fiber sensor:

⑴ It has the properties of anti-electromagnetic and atomic radiation interference, fine diameter, soft quality and lightweight

(2) Electrical properties of insulation and no induction

(3) Water resistance, high-temperature resistance, corrosion resistance, and other chemical properties, can reach the place, or be harmful to people in the area (such as nuclear radiation area), play the role of people's eyes and ears

(4) It can transcend the physiological boundary of human beings and receive external information that cannot be felt by human senses.

3. Different working principle

First of all, from the working principle of the two, the photoelectric sensor is based on the principle of the photoelectric effect to work, that is to say, when the light shines on the photoelectric sensor made of semiconductor, it will emit photoelectrons, which can be converted into electric energy. For example, photoresistors, photodiodes, and phototransistors commonly used for light control are based on this effect.

Working principle of photoelectric sensor

The optical fiber sensor works by the principle of total reflection of light. The principle of total reflection of light is learned in middle school physics. For example, Snell's law of refraction and reflection of light is clearly expressed by mathematical relations. So we can use the light transmission characteristics of the optical fiber to convert the measured into changes in the characteristics of light, such as changing the frequency, wavelength, intensity and phase of light.

4. Different materials

Photoelectric sensors are mainly made of semiconductor materials or metal materials with photoelectric effects. For example, the manufacturing materials of photodiodes and photodiodes generally include silicon materials or germanium materials, and photosensitive resistors are made of cadmium sulfide or indium antimonide materials.

Optical fiber sensor is composed of glass fiber with high light transmittance (mainly quartz glass), the composition is relatively simple.

5. Different Structure

A photoelectric sensor is relatively simple, such as a photodiode that has a pin, shell, tube core, and glass condenser parts.

The structure of optical fiber sensors is relatively complex, in addition to optical fiber and some complex peripherals as auxiliary control.

6. Different ranges of measurement

The range measured by the photoelectric sensor is relatively small, which generally includes light intensity, illumination, velocity, and strain displacement.

The optical fiber sensor measurement range is relatively wide, about can measure more than 70 physical quantities, such as pressure, vibration, speed, current, temperature, flow, and magnetic field, so the future development of optical fiber sensor potential is huge, can be said to be a latecomer.

7. Different applications

Photoelectric sensor: photoelectric sensor with the photoelectric element as a sensitive element, its variety, and wide range of uses. The output properties of the photoelectric sensor can be divided into two categories: convert the measured into a continuous change of photocurrent made of photoelectric measuring instruments, which can be used to measure the intensity of light and physical quantities such as the temperature of the object, light transmission capacity, displacement, and surface state. For example, the measurement of light intensity illuminance meter, photoelectric pyrometer, photoelectric colorimeter and turbidimeter, and photoelectric alarm to prevent fire, constitute the inspection of the diameter, length, ellipticity, and surface roughness of the processed parts and other automatic detection devices and instruments, the sensitive elements are photoelectric elements. Semiconductor optoelectronic devices are not only widely used in civil industry, but also play an important role in the military.

For example, a lead sulfide photoresistor can be made into an infrared night vision instrument, infrared camera, and infrared navigation system; Converting the measured photocurrent to continue changing. A variety of photoelectric automatic devices are made by using the characteristic of "with" or "without" electrical signal output when illuminated by light or no light. The photoelectric element is used as a switching photoelectric conversion element. For example, electronic computer photoelectric input device, switching temperature regulation device, and speed measurement digital photoelectric velocimeter.

Optical fiber sensors: application of interference gyroscopes and grating pressure sensors in urban construction of Bridges, DAMS, oil fields, etc. Fiber optic sensors can be embedded in concrete, carbon fiber-reinforced plastics, and various composite materials to test stress relaxation, construction stress, and dynamic load stress, so as to evaluate the structural performance of the bridge during the short construction phase and long-term operation. In the power system, it is necessary to measure the temperature, current and other parameters, such as the temperature detection in the stator and rotor of high-voltage transformer and large motor. Because electrical sensors are susceptible to electromagnetic interference, they cannot be used on such occasions, so only optical fiber sensors can be used.

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