Sensors are fundamental products in the electronic information equipment manufacturing industry and are specialized components among the key emerging electronic components. The sensor industry, recognized both domestically and internationally as a promising high-tech industry, has attracted worldwide attention for its high technological content, good economic benefits, strong market penetration, and broad market prospects. Driven by the booming electronic information industry market, China's sensor industry has formed a certain industrial foundation and made significant progress in technological innovation, independent research and development,成果转化 (technology transfer), and competitiveness, making important contributions to promoting national economic development.
With the advent of the information age, sensors have become the primary means for people to acquire information in the natural and production fields. In modern industrial production, especially in automated production processes, various sensors are used to monitor and control various parameters in the production process, ensuring that equipment operates in a normal or optimal state and that products achieve the best quality. Sensors also hold an even more prominent position in basic scientific research.
Today, sensors have permeated an extremely wide range of fields, including industrial production, space exploration, ocean exploration, environmental protection, resource surveys, medical diagnosis, bioengineering, and even cultural relic preservation. It is evident that sensor technology plays a crucial role in economic development and social progress. Statistics show that the global smart sensor market is growing at a rate of 10% annually. Currently, there are 65 million sensor devices equipped with processors worldwide, and this number is projected to reach 2.8 trillion by 2019.
Key points for sensor selection:
Sensor knowledge is a vast electrical discipline that requires extensive experience to master. We will discuss it further in the future. Today, we will mainly talk about selection.
1. Determine the type based on the measurement object and output conditions.
To perform a specific measurement, the first step is to consider which sensor principle to use, which requires analyzing multiple factors. For example, there are electromagnetic flow meters, vortex flow meters, and ultrasonic flow meters. We need to select the appropriate flow meter based on the specific target. In addition, we also need to consider the required output mode, such as 2-wire or 4-wire current signal, 0-20mA, 4-20mA, 0-10V voltage signal, or a specific communication protocol.
2. Selection based on sensitivity
Generally, within the linear range of a sensor, higher sensitivity is desirable. This is because only with high sensitivity can the output signal corresponding to changes in the measured quantity be relatively large, which is beneficial for signal processing. However, it should be noted that high sensor sensitivity also makes it easier for external noise unrelated to the measured quantity to enter the sensor and be amplified by the amplification system, affecting measurement accuracy. Therefore, the sensor itself should have a high signal-to-noise ratio to minimize interference signals introduced from the outside.
Sensor sensitivity is directional. When the measured quantity is a single vector and its directionality is critical, a sensor with low sensitivity in other directions should be selected; if the measured quantity is a multi-dimensional vector, the lower the cross-sensitivity of the sensor, the better.
3. Determine the frequency response characteristics
The frequency response characteristics of a sensor determine the range of frequencies to be measured, and it must remain distortion-free within the allowable frequency range. In reality, a sensor's response always has a certain delay, and a shorter delay is desirable. A higher frequency response means a wider range of measurable signal frequencies. In dynamic measurements, the response characteristics should be considered based on the signal's characteristics (steady-state, transient, random, etc.) to avoid excessive errors.
4. Based on the stability of the sensor
The ability of a sensor to maintain its performance unchanged after a period of use is called stability. Besides the sensor's own structure, the main factor affecting the long-term stability of a sensor is its operating environment. Therefore, for a sensor to have good stability, it must have strong environmental adaptability. Before selecting a sensor, its operating environment should be investigated, and a suitable sensor should be chosen based on the specific environment, or appropriate measures should be taken to reduce the impact of the environment.
5. The range and accuracy of a sensor are the most difficult pair to coordinate.
Accuracy is a crucial performance indicator for sensors, and it's a vital factor affecting the overall measurement accuracy of a measurement system. However, sensor accuracy is limited by its measurement range; generally, a larger measurement range results in lower accuracy. But high-precision sensors may have insufficient measurement range, which makes high-precision, large-range sensors very expensive. Therefore, it's necessary to appropriately balance these factors when selecting a sensor.
When selecting a sampling sensor, ensure that the device meets the basic operating conditions of the application (refer to the manufacturer's datasheet). The six most important operating conditions include:
1) Temperature range;
2) Specifications;
3) Protection level;
4) Voltage range;
5) Discrete or analog output;
6) Parameter changes, i.e., "Is it beneficial to change the parameters?"
There are six other things to consider when using sensors configured with IO-Link links:
1) Response speed;
2) Sensing range;
3) Repeatability accuracy;
4) Electrical connections;
5) Installation type;
6) Visual display: Does the application need to be visualized on the sensor?
In modern industrial production, especially automated production, various sensors are used to monitor and control various parameters in the production process, ensuring that equipment operates in normal or optimal condition and that products achieve the best quality. Therefore, it can be said that without numerous high-quality sensors, modern production would lose its foundation. The following sections will detail some of the most common sensor types used in manufacturing and provide some application tips and insights.
Most common sensor types
Proximity sensor
Proximity sensors detect the presence of objects in a nearby area without physical contact. They are discrete output devices. Typically, magnetic proximity sensors detect whether an actuator has reached a specific position by sensing a magnet located within the actuator.
Buying an actuator from one company and a magnetic proximity sensor from another is generally not a good idea. While sensor manufacturers may claim their sensors are compatible with X, Y, and Z actuators, the reality is that variations in magnets and mounting locations can cause sensing problems. For example, the sensor may not energize or at all when the magnet is not in the correct position. If the actuator manufacturer provides a proximity sensor that matches the actuator, that should be the preferred choice.
Transistor-based proximity sensors have no moving parts and a long lifespan. Reed-based proximity sensors use mechanical contacts, have a shorter lifespan, but are less expensive than transistor-based sensors. Reed sensors are best suited for applications requiring AC power and high-temperature applications.
Position sensor
Position sensors have an analog output, displaying the actuator's position based on the position indicator of a magnet on the actuator. From a control perspective, position sensors offer significant flexibility. Control engineers can define a range of setpoints to match component variations.
Since these position sensors are based on magnets (such as proximity sensors), it is best to purchase sensors and actuators from the same manufacturer (if possible). The position sensor data can be acquired via IO-Link functionality, which also simplifies control and enables parameterization.
Inductive sensor
Inductive proximity sensors use Faraday's law of induction to measure the presence of an object or simulate its position. When selecting an inductive sensor, the most critical factor is determining the type of metal the sensor will detect, thus determining the sensing distance. The sensing range for non-ferrous metals is reduced by more than 50% compared to ferrous metals. The sensor manufacturer's product manual should provide information on the necessary sample selection.
Pressure and vacuum sensors
Ensure the pressure or vacuum sensor can meet the measurement pressure range in both imperial (pounds per square inch) and metric (bar) units. Specify the optimal dimensions for the allocated space. During equipment installation, consider whether the sensor should be equipped with indicator lights or a display screen for easy operator access. If rapid changes to setpoints are required, consider using pressure and vacuum sensors with IO-Link functionality.
Flow sensor
Similar to pressure and vacuum sensors, flow sensors can be selected based on their flow range, size, and variability in setpoints. Display options can be specified when ordering the sensor. Flow sensors with relatively low flow rates can be selected for applications in a specific area of the equipment or for the entire equipment.
Optical sensors
The most common optical sensors are photoelectric scattering, reflection, and direct beams. Laser sensors and fiber optic sensing devices also belong to the category of optical sensors.
Most photoelectric sensors are presence sensors that detect objects by reflecting or blocking light. Due to their low cost, versatility, and high reliability, these sensors are among the most widely used in manufacturing. Diffuse reflection photoelectric sensors do not require a reflector. They are cost-effective sensors used to detect the presence of nearby objects.
Straight-beam photoelectric sensors offer the longest sensing range. These sensors have a transmitter and receiver mounted at two separate points. Garage door security sensors are examples of beam sensors. When the beam is interrupted, it indicates the presence of a target. Slotted photoelectric sensors are an interesting variation of straight-beam sensors; they mount a transmitter and receiver on a single, compact unit. Slotted photoelectric sensors are used to detect the presence and absence of small parts.
Reflective photoelectric sensors consist of a sensor and a reflector, used for mid-range presence sensing. In terms of accuracy and cost, they fall between diffuse reflection and direct beam sensors.
Fiber optic sensing devices are used for presence and distance sensing. The parameters on these multi-functional sensors can be adjusted to detect various colors, backgrounds, and distance ranges.
Laser sensors can be used for long-distance presence sensing, but they are the most accurate for short-distance measurement applications.
Vision sensors can be used for barcode reading, counting, shape verification, and more. They are a cost-effective alternative to camera systems, which are often expensive and complex. Vision sensors are used for barcode reading, tracking individual components, and executing process steps to match those components. Sensors can verify the number of functional elements present on a part. They can determine whether a specified curve or other shape has been achieved. Because these sensors need to handle light, it is crucial to test them under conditions that closely resemble the operating environment in terms of ambient light and background reflectivity. In most applications, it is recommended to house the vision sensor within a housing to isolate it from external light sources. Seeking assistance from vision sensor manufacturers is a good idea for sensor testing. Additionally, remember to ensure the appropriate fieldbus is selected.
The signal converter will convert the analog output signal of the sensor into a switching signal on the signal converter, or alternatively, into IO-Link process data.
Other sensors
1. Magnetic switch: This is a specific term for a sensor used in cylinders, primarily for detecting the piston position. It is typically provided by the cylinder supplier as part of a package tailored to the customer's needs. As the name suggests, magnetic switches detect targets through electromagnetic induction, therefore, their detection accuracy is quite low.
2. Proximity Switches: Proximity switches are also designed and manufactured based on the principle of electromagnetic induction. Therefore, they can only detect metallic targets, and the detection distance varies slightly depending on the type of metal. Currently, commonly used proximity switch detection distances are approximately 1mm, 2mm, 4mm, 8mm, and 12mm. Proximity switches are generally of two types: embedded and non-embedded. Embedded switches detect only metal targets in front of them, not in the circumferential direction; the sensor head does not need to protrude from the metal mounting bracket. Non-embedded switches detect both metal targets in front and in the circumferential direction; the sensor head must protrude a certain distance from the metal mounting bracket, and there must be no metallic targets within a certain circumferential range to avoid false detections. Proximity switches have higher detection accuracy than magnetic switches. Proximity switches are typically used in applications where positional accuracy requirements are relatively low, such as determining the presence or absence of a product or the positioning of tooling fixtures.
3. Photoelectric Switches: Photoelectric detection methods offer advantages such as high precision, fast response, and non-contact operation. They can measure a wide range of parameters, and the sensors are simple in structure and flexible in form. Therefore, photoelectric sensors are widely used in detection and control. There are generally three types of photoelectric switches: reflective photoelectric sensors, through-beam photoelectric sensors, and photoelectric sensors that use a reflector to reflect light. The latter two detect by blocking light from the target object, while the former detects by reflecting light from the target object. Therefore, the latter two typically have a longer detection distance and higher precision. Due to their high detection accuracy, photoelectric sensors are commonly used to detect the precise position of products or workpieces such as robotic arms, as well as in feedback devices for stepper and servo systems.
4. Fiber Optic Sensors: Fiber optic sensors are also a type of detection element that uses photoelectric signal conversion. Compared to photoelectric switches, they can typically detect smaller targets, have a longer detection distance, and higher accuracy. Therefore, fiber optic sensors are commonly used in more precise detection applications and in positioning feedback devices for stepper and servo systems.
5. Grating: A grating is also a type of sensor that utilizes photoelectric signals. Gratings have a large detection area, so they are often called area sensors. The primary applications of gratings are interlocking between devices and for safety purposes, especially in the protection of people.
8. Thermocouple: Thermocouples are mainly used to detect the ambient temperature around them.
9. Laser measuring instrument: The most important function of a laser measuring instrument is to accurately measure the external dimensions of a target object.
10. Industrial Cameras: Industrial cameras, also commonly referred to as CCD (Charge-coupled Device) in engineering, are primarily used to detect the shape and position of objects. With advancements in CCD technology, high-resolution industrial cameras can now be applied to precision measurement.
11. Encoders : Based on their working principle, encoders can be divided into two categories: incremental and absolute. Incremental encoders convert displacement into periodic electrical signals, then convert these signals into counting pulses, using the number of pulses to represent the magnitude of the displacement. Absolute encoders assign a unique digital code to each position; therefore, their reading depends only on the starting and ending positions of the measurement, and is independent of the intermediate steps. Encoders are typically used in conjunction with stepper motors or servo motors to form closed-loop or semi-closed-loop control systems.
12. Micro switch: A micro switch is a contact sensor that is currently mainly used for the connection between devices or for detecting the status of safety doors of devices.
summary:
Looking back at the development of my country's sensitive components and sensor industry, although it has been rapid, some shortcomings remain, such as low product technology levels, a weak industrial base, a lack of product variety, and weak enterprise R&D capabilities. Therefore, the government is continuously formulating policies conducive to the development of the sensor industry. Furthermore, the continuous emergence of new technologies is also a positive factor for the sensor industry's development. With the research and application of new sensors in fields such as the Internet of Things and the low-carbon economy, the sensor industry will occupy a more important position and play a greater role in the electronic components industry.
Disclaimer: This article is a compilation from China Transmission Network. If it involves any copyright issues, please contact us promptly for deletion (QQ: 2737591964). We apologize for any inconvenience.
