1. Fiber Optic Sensors
Fiber optic sensors are devices that transform the state of an object being measured into a detectable optical signal.
The working principle of a fiber optic sensor is to direct light from a source through an optical fiber into a modulator.
Within the modulator, the light interacts with the external parameters being measured, causing changes in optical properties such as intensity, wavelength, frequency, phase, and polarization state.
This results in a modulated optical signal, which is then transmitted through the fiber optic into photonic devices and, after demodulation, yields the measured parameter. Throughout the process, the light beam is channeled into and out of the modulator through the optical fiber.
The primary role of the optical fiber is to transmit the light beam, and secondly, to function as a light modulator.
Compared to traditional sensors, fiber optic sensors have several unique advantages. They use light as the sensitive information carrier and the optical fiber as the medium for transmitting this information.
This endows them with the characteristics of both fiber optics and optical measurements, such as excellent electrical insulation, strong resistance to electromagnetic interference, non-invasiveness, high sensitivity, long-distance monitoring capabilities, corrosion resistance, explosion-proof properties, and flexible light paths that are easily connected to computers.
Sensors are evolving to be more sensitive, precise, adaptable, compact, and intelligent. They can operate in places inaccessible to humans, such as high-temperature areas or hazardous zones like radiation areas, serving as extensions of our senses.
Moreover, they can surpass human physiological limits, capturing external information beyond our sensory perceptions.
2. Photoelectric Sensors
Photoelectric sensors are devices that convert optical signals into electrical signals. Their operation is based on the photoelectric effect.
The photoelectric effect refers to the phenomenon where electrons in certain materials absorb the energy from photons and produce a corresponding electrical effect.
The photoelectric effect is categorized into three types: external photoelectric effect, internal photoelectric effect, and photovoltaic effect.
Photonic devices include phototubes, photomultiplier tubes, photoresistors, photodiodes, phototransistors, and solar cells, among others. These devices’ performance and characteristic curves have been analyzed.
Photoelectric sensors use photonic devices as conversion components. They can detect non-electrical physical quantities that directly cause changes in light amounts, such as light intensity, illumination, radiometric temperature measurement, and gas composition analysis.
They can also detect other non-electrical quantities that can be converted into changes in light amounts, such as part diameter, surface roughness, strain, displacement, vibration, speed, acceleration, as well as the shape of objects and the identification of their operational status.
Photoelectric sensors are non-contact, fast-responding, and reliable, making them widely used in industrial automation and robotics.
The continuous emergence of new photonic devices, especially the advent of CCD image sensors, has opened a new chapter for the further application of photoelectric sensors.
3. What are the Differences Between Fiber Optic Sensors and Photoelectric Sensors?
Both fiber optic sensors and photoelectric sensors serve as two typical sensors widely used in production measurements.
The distinctions between them will be analyzed in terms of principles and applications.
(1) Photoelectric Sensors:
These sensors utilize photoelectric components as detection elements. They first convert measured changes into changes in optical signals, then use the photoelectric components to further transform the optical signals into electrical ones.
Photoelectric sensors generally consist of a light source, an optical path, and photoelectric components.
(2) Fiber Optic Sensors:
These sensors transmit light from a source through optical fibers to a modulator.
The parameters to be measured interact with the light entering the modulation region, leading to changes in optical properties like intensity, wavelength, frequency, phase, and polarization state.
This is referred to as the modulated signal light. After being transmitted through the optical fibers to a light detector and demodulated, the measured parameters are obtained.
(1) Applications of Photoelectric Sensors:
Dust Turbidity Monitoring:
One of the vital tasks for environmental protection is preventing industrial dust pollution. To mitigate industrial dust pollution, one must first determine the amount of dust emitted, thus necessitating monitoring the sources of smoke and dust for automatic display and exceeding alarm limits.
The turbidity of the flue gas is detected by the change in light transmission within the flue. If turbidity increases, the light emitted by the light source is absorbed and refracted more by dust particles, reducing the light reaching the detector.
Consequently, the output signal strength from the light detector can reflect changes in flue turbidity.
Use of Photocells in Photodetection and Automatic Control:
When used for photodetection, the basic principle of a photocell is similar to a photodiode.
However, their fundamental structures and manufacturing processes are not entirely identical.
Photocells don’t require an external voltage when operating; they have a high photoelectric conversion efficiency, wide spectral range, good frequency characteristics, and low noise.
Thus, they are extensively used in photoelectric reading, optoelectronic coupling, optical grating ranging, laser collimation, film sound reproduction, UV light monitors, and flameout protection devices for gas turbines.
(2) Applications of Fiber Optic Sensors:
Fiber optic sensors are employed for measuring various physical quantities such as insulator contamination, magnetism, sound, pressure, temperature, acceleration, gyroscopes, displacement, liquid level, torque, photoacoustic effects, current, and strain.