I. Fiber Optic Sensors
A fiber optic sensor is a sensor that converts the state of a measured object into a measurable optical signal. The working principle of a fiber optic sensor is as follows: a light beam incident from a light source is sent through an optical fiber to a modulator. Within the modulator, the light interacts with the external parameters to be measured, causing changes in the optical properties of the light, such as intensity, wavelength, frequency, phase, and polarization state, resulting in a modulated optical signal. This modulated signal is then sent through an optical fiber to a photoelectric device and, after passing through a demodulator, the measured parameters are obtained. Throughout the process, the light beam is guided through the optical fiber, passes through the modulator, and then exits. The optical fiber's primary function is to transmit the light beam, and secondarily, it acts as an optical modulator.
The advantages of fiber optic sensors compared to traditional sensors are that they use light as the carrier of sensitive information and optical fiber as the medium for transmitting sensitive information, possessing the characteristics of fiber optic and optical measurement, and offering a series of unique advantages. These include good electrical insulation, strong resistance to electromagnetic interference, non-invasiveness, high sensitivity, ease of long-distance monitoring of the measured signal, corrosion resistance, explosion-proof properties, and flexible optical path for easy connection to computers.
Sensors are developing towards greater sensitivity, accuracy, adaptability, compactness, and intelligence. They can act as the eyes and ears of humans in places inaccessible to humans (such as high-temperature areas or areas harmful to humans, such as nuclear radiation areas), and can even transcend human physiological limits to receive external information that cannot be perceived by human senses.
II. Photoelectric Sensors
A photoelectric sensor is a device that converts light signals into electrical signals. Its working principle is based on the photoelectric effect. The photoelectric effect refers to the phenomenon where, when light shines on certain materials, the electrons in the material absorb the energy of the photons, resulting in a corresponding electrical effect. Based on different phenomena, the photoelectric effect is divided into three categories: external photoelectric effect, internal photoelectric effect, and photovoltaic effect. Photoelectric devices include phototubes, photomultiplier tubes, photoresistors, photodiodes, phototransistors, and photovoltaic cells. The performance and characteristic curves of photoelectric devices are analyzed.
Photoelectric sensors are sensors that use photoelectric devices as conversion elements. They can be used to detect non-electrical physical quantities that directly cause changes in light intensity, such as light intensity, illuminance, radiation thermometry, and gas composition analysis; they can also be used to detect other non-electrical quantities that can be converted into changes in light intensity, such as part diameter, surface roughness, strain, displacement, vibration, velocity, acceleration, and the identification of object shape and working status. Photoelectric sensors are characterized by non-contact operation, fast response, and reliable performance, and are therefore widely used in industrial automation devices and robots. New photoelectric devices are constantly emerging, especially the advent of CCD image sensors, which has opened a new chapter for the further application of photoelectric sensors.
III. What are the differences between fiber optic sensors and photoelectric sensors?
Fiber optic sensors and photoelectric sensors are two typical types of sensors, and they are widely used in production measurement. So what are the differences between the two? Next, we will analyze the differences between the two from the aspects of principle and application.
(I) Principles
A photoelectric sensor is a sensor that uses photoelectric elements as its detection element. It first converts the change in the measured quantity into a change in a light signal, and then, with the help of photoelectric elements, further converts the light signal into an electrical signal. A photoelectric sensor generally consists of three parts: a light source, an optical path, and photoelectric elements.
Fiber optic sensor: Light from a light source is sent through an optical fiber to a modulator, so that the parameter to be measured interacts with the light entering the modulation region, causing changes in the optical properties of the light (such as light intensity, wavelength, frequency, phase, polarization, etc.), which is called the modulated signal light. After passing through an optical fiber to a photodetector, the parameter to be measured is obtained after demodulation.
(II) Application Aspects
1. Application areas of photoelectric sensors:
Preventing industrial dust pollution is a crucial task in environmental protection. To eliminate industrial dust pollution, it's essential to know the amount of dust emitted; therefore, monitoring the dust source, automatic display, and alarm functions for exceeding limits are necessary. The turbidity of dust in the flue is detected by measuring the change in light intensity during its transmission within the flue. If the flue turbidity increases, the absorption and refraction of light emitted from the light source by dust particles increases, reducing the amount of light reaching the photodetector. Therefore, the strength of the photodetector's output signal reflects the change in flue turbidity.
Applications of photovoltaic cells in photoelectric detection and automatic control: When used as a photoelectric detector, the basic principle of a photovoltaic cell is the same as that of a photodiode, but their basic structure and manufacturing process are not exactly the same. Because photovoltaic cells do not require an external voltage to operate, and possess high photoelectric conversion efficiency, a wide spectral range, good frequency characteristics, and low noise, they have been widely used in photoelectric readout, photoelectric coupling, grating ranging, laser collimation, movie sound reproduction, ultraviolet monitors, and flameout protection devices for gas turbines, among other applications.
2. Application areas of fiber optic sensors:
Measurement of physical quantities such as insulator contamination, magnetism, sound, pressure, temperature, acceleration, gyroscope, displacement, liquid level, torque, photoacoustic, current and strain.
