Applications of Pressure Sensors: Used to measure pressure below atmospheric pressure at a given location; used in meteorological instruments, aircraft, vehicles, and other machinery that have implemented pressure functions; used in systems to measure other variables, such as fluid/gas flow rate, velocity, water level, and altitude.
4.Temperature Sensors
Temperature sensors are devices that collect information about temperature from a source and convert it into a form that other devices can understand. They are a common category of sensors that can detect temperature or heat and measure the temperature of a medium.
The main types of temperature sensors used in automation include digital temperature sensors and temperature-humidity sensors.
Digital Temperature Sensors: Digital temperature sensors are silicon-based temperature-sensing ICs that provide accurate output by digitally representing the measured temperature. Compared to methods involving external signal conditioning and analog-to-digital converters (ADCs), this simplifies the design of control systems.
Temperature-Humidity Sensors: Temperature-humidity sensors combine temperature sensors and humidity sensors, attributing the measured digital signal output. By utilizing this technology and temperature, as well as limited digital signal acquisition for humidity sensing, high consistency and excellent long-term stability are ensured.
Applications of Temperature Sensors: Continuous measurement of temperature in air, soil, or water; used for measurements in complex industrial applications; used for measurements in harsh working conditions.
5.MEMS Sensors (Micro-Electro-Mechanical Systems)
MEMS industrial automation sensors convert measured mechanical signals into electrical signals.
Important sensors used in industrial automation are MEMS accelerometers and motion sensors.
Accelerometers: MEMS accelerometers are one of the primary inertial sensors and possess dynamic sensor capabilities with a broader range of sensing abilities.
Motion Sensors: MEMS motion sensors use data processing algorithms designed for motion interaction platforms, which integrate numerous low-cost MEMS motion sensors with ZigBee wireless technology. This allows for personalized interaction when working with machines. The sensor signal processing system mainly addresses issues such as noise elimination, signal smoothing, gravity influence partitioning, coordinate system changes, and position information recovery. It is widely used in the automotive industry's ABS technology.
Applications of MEMS Sensors:
MEMS sensors have a wide range of applications, spanning industries such as industrial, entertainment, sports, and education. For example, they are used to trigger airbag deployment or monitor nuclear reactors. They are also used to measure static acceleration (gravity), object tilt, dynamic acceleration in aircraft, vibrations in objects within cars, as well as vibrations in mobile phones, washing machines, or computers. Additionally, they are used for motion detection and more.
6.Proximity Switches
Proximity switches are also designed and manufactured based on the principle of electromagnetic induction. Therefore, they can only detect metallic targets, and there is a slight difference in detection distance for different metals. The commonly used detection distances for proximity switches are approximately as follows: 1mm, 2mm, 4mm, 8mm, 12mm, etc.
There are usually two types of proximity switches: flush-mounted and non-flush-mounted. Flush-mounted means that the sensing head of the proximity switch does not detect metallic targets in its circumferential direction but only detects metallic targets in front of it. In other words, the sensor's sensing head can be hidden within the metal mounting bracket. Non-flush-mounted means that the sensing head of the proximity switch detects metallic targets both in front of it and in its circumferential direction. Therefore, the sensor's sensing head must protrude from the metal mounting bracket by a certain distance, and there must be no metallic targets within a certain range around it to avoid incorrect detection.
The detection accuracy of proximity switches is higher than that of magnetic switches. Proximity switches are commonly used in situations where position accuracy requirements are relatively low, such as determining the presence of a product or whether a fixture is in place.
7. Photoelectric Sensors
The photoelectric detection method has the advantages of high precision, fast response, and non-contact. Moreover, it can measure a wide range of parameters, and the sensor structure is simple with diverse forms. Therefore, photoelectric sensors are widely used in detection and control. The photoelectric switches we commonly refer to are generally of three types: one is the reflective photoelectric sensor, another is the through-beam photoelectric sensor, and the third is the photoelectric sensor that uses a reflector to reflect the light beam.
The latter two types detect objects by the target blocking the light, while the first type detects by the target reflecting the light. Therefore, the latter two usually have longer detection distances and higher precision. Due to the high detection precision of photoelectric sensors, they are commonly used to detect the precise position of products or robotic arms and as feedback devices in stepper and servo systems.
Since the U-shaped photoelectric sensor is the most commonly used in automation design, it is introduced in detail here. Different brands of U-shaped photoelectric sensors have different installation forms, which will not be discussed in detail here. As shown in the figure below, this is a plug-in type U-shaped photoelectric sensor from a certain company. When selecting this type of U-shaped photoelectric sensor, it is important to ensure that there is enough space at the tail to insert the plug. Of course, this is something to be mindful of when selecting electrical components in general. Additionally, when designing short-stroke modules, it is essential to consider whether there is enough distance within the stroke to set up three U-shaped photoelectric sensors. If the distance is insufficient, U-shaped photoelectric sensors can be designed on both sides of the module.
Generally, a module is equipped with three U-shaped photoelectric sensors. Two of them are the limit photoelectric sensors for the two ends of the module's stroke, and the middle one is the U-shaped photoelectric sensor for finding the module's origin. The following mainly explains two ways to find the origin:
(1) The photoelectric switch senses the reflective plate, and the motor continues to move to find a program-set origin within one rotation of the motor as the module's origin. This method has high positioning accuracy, mainly affected by factors such as the lead screw, the motor itself, and the coupling. It is mainly influenced by the module's own parameters, with high positioning accuracy that can reach 0.01 mm.
(2) After the photoelectric switch senses the reflective plate, the motor starts to brake until the entire system stops, which is considered the module's origin. The accuracy of this method is affected by temperature, lighting conditions, and the response speed of the photoelectric switch, resulting in lower positioning accuracy, generally around 0.05–0.1 mm.
8. Fiber Optic Sensors
Fiber optic sensors are also detection elements that utilize the conversion of optical and electrical signals. Fiber optic sensors generally need to be used in conjunction with fiber optic amplifiers. They are slightly more expensive in terms of price, but in terms of nature, they are fundamentally different from the previously mentioned photoelectric and proximity sensors. They can perform qualitative measurements. In other words, they can quantitatively detect, such as measuring a distance in millimeters.
Compared to photoelectric switches, fiber optic sensors can usually detect smaller targets, have longer detection distances, and higher precision. Therefore, fiber optic sensors are commonly used in more precise detection scenarios and as positioning feedback devices in stepper and servo systems.
The working principle of fiber optic sensors is to send the light beam from the light source into the modulator via the fiber optic cable. Within the modulator, the light interacts with the external measured parameters, causing changes in the optical properties of the light, such as intensity, wavelength, frequency, phase, polarization state, etc. The modulated light signal is then sent into the photoelectric device via the fiber optic cable and demodulated to obtain the measured parameters. Throughout this process, the light beam is guided through the fiber optic cable, which not only transmits the light beam but also acts as a light modulator.
When designing fiber optic sensors, it is important to consider the protection of the fiber optic head to prevent collisions, usually by designing a bracket to protect the fiber optic head. Additionally, whether it is a through-beam photoelectric sensor or a through-beam fiber optic sensor, they are less affected by the surrounding environment compared to ordinary reflective fiber optics. This needs to be carefully considered during the design process.
9. Displacement Sensors
As the name suggests, these are sensors that detect changes in the position of the target object.
Displacement sensors, also known as linear sensors, are linear devices that belong to metal induction. The role of the sensor is to convert various measured physical quantities into electrical quantities.
In the production process, the measurement of displacement is generally divided into measuring the size of physical objects and mechanical displacement. Depending on the form of the variable being measured, displacement sensors can be divided into analog and digital types.
Analog types can be further divided into property-based and structure-based types. The commonly used displacement sensors are mostly analog and structure-based, including potentiometric displacement sensors, inductive displacement sensors, synchros, capacitive displacement sensors, eddy current displacement sensors, Hall effect displacement sensors, etc.
An important advantage of digital displacement sensors is that they can easily send signals directly into computer systems. These sensors are developing rapidly and are increasingly widely used.
10. Light Grids
Light grids are also sensors that utilize optical and electrical signals. Light grids have a large detection area, so they are also commonly referred to as area sensors. The main application field of light grids is interlocking and safety between equipment, especially for the protection of people. They are commonly used in stamping machinery, shearing equipment, metal cutting equipment, automated assembly lines, automated welding lines, and mechanical conveying and handling equipment.
11. Laser Measurement Instruments
The primary function of laser measurement instruments is to accurately measure the external dimensions of the target object.
12. Industrial Cameras
Industrial cameras are also commonly referred to as CCDs (Charge-coupled Devices) in engineering. They are mainly used to detect the shape and position of the target object. With the improvement of CCD technology, high-resolution industrial cameras have been applied in the field of precise measurement.
13. Encoders
Encoders can be divided into incremental and absolute types according to their working principles. Incremental encoders convert displacement into periodic electrical signals and then transform these signals into counting pulses, using the number of pulses to represent the magnitude of displacement. Each position of an absolute encoder corresponds to a specific digital code. Therefore, its display value is only related to the starting and ending positions of the measurement and is independent of the measurement process. Encoders are usually used with stepper motors or servo motors to form closed-loop or semi-closed-loop control systems.
14. Micro Switches
Micro switches are contact-type sensors. They are currently mainly used to detect the connection between equipment or the status of safety doors on equipment.
15. Smart Sensors
The last type of sensor may also be the most important one for the future of industrial automation—smart sensors.
The new generation of advanced smart sensors will become the heart of industrial automation. A "smart factory" refers to a digital factory that, based on digital technology, uses Internet of Things (IoT) technology and equipment monitoring technology to enhance information management and services. It aims to clearly understand the production and sales process, improve the controllability of the production process, reduce human intervention on the production line, timely and accurately collect production line data, and reasonably arrange production plans and schedules. The technologies that a smart factory can implement include wireless sensing, networked control systems, and wireless industrial communication, such as weighing sensors.
For certain product quality indicators (e.g., viscosity, hardness, surface finish, composition, color, and taste), rapid direct measurement and online control can be achieved. Sensors integrated with smart technology will be able to effectively address the aforementioned issues.
Currently, industrial production is indeed shifting towards automation on a large scale. However, with the continuous commercialization of IoT and cloud platform applications, the development of automation in the industrial field is trending towards a higher level of upgrade, namely intelligent production.
