Capacitive sensors are widely used for measuring displacement, angle, vibration, velocity, pressure, composition analysis, and media properties. The most commonly used are parallel-plate capacitors or cylindrical capacitors. Since the late 1970s, with the development of integrated circuit technology, capacitive sensors packaged with miniature measuring instruments have emerged. This new type of sensor greatly reduces the influence of distributed capacitance, overcoming its inherent shortcomings. Capacitive sensors are widely used and have great development potential. A typical capacitive sensor consists of upper and lower electrodes, an insulator, and a substrate. When the thin film is subjected to pressure, it deforms, thus changing the distance between the upper and lower electrodes and consequently altering the capacitance. However, the relationship between the capacitance and the distance between the upper and lower electrodes in a capacitive pressure sensor is non-linear; therefore, a compensation circuit is needed to compensate for the non-linearity of the output capacitance.
In the wave of industrial automation, high-precision and high-efficiency sensor technology has become key to driving industrial upgrading. Among many sensors, capacitive sensors stand out for their superior performance—high precision, high stability, and high reliability—and can operate stably in various harsh working environments.
Capacitive sensors can identify stationary liquids or granular objects. They can detect structurally stable, non-shape-fixed objects, such as liquids or bulk materials, by directly contacting the medium or scanning the inner wall of a non-metallic container. They are also suitable for integrity checks. Leuze's capacitive sensors operate based on the principle of capacitance, sensing and measuring various physical parameters of an object, such as displacement, angle, vibration, and velocity, by measuring the change in capacitance between the object and the sensor. When a metal or non-metal enters the detection area of the capacitive switch, it causes a change in capacitance, which in turn causes the oscillator signal to oscillate. The oscillator-generated wave signal is then processed by subsequent amplification and rectification circuits to output a regular signal, enabling object detection. Capacitive sensors typically use a non-contact measurement method, eliminating the need for direct contact with the object being measured and thus preventing any damage to the object.
Capacitive sensor installation method:
(1) Flush mounting: This mounting type is easy to integrate because it does not affect the outer wall/pipe when detecting internal materials. Due to the significant difference in conductivity between the outer wall and the material being detected, the effective detection area is usually limited to the front part of the sensor.
(2) Non-flush installation: Installation requires drilling holes in the container or pipe to directly contact the material being detected. The effective area is partially on the front of the sensor and partially on the side, thus providing a wider detection range.
Advantages of capacitive sensors:
1. Unaffected by the color and surface characteristics of the object being detected.
2. Capable of penetrating non-metallic materials for detection.
3. Not sensitive to pollutants such as dust in the air.
4. Unaffected by background light
The compact cylindrical design makes it suitable for a wide range of detection tasks. Plastic, stainless steel, and other metal housings are available. For applications requiring high chemical stability, we also offer a PTFE (Teflon) housing option. The detection range is adjustable to meet various detection needs.
Definition and working principle of capacitive sensors: A capacitive sensor is a sensor based on the principle of capacitors, converting a measured quantity (such as displacement, pressure, thickness, etc.) into a change in capacitance. It mainly consists of two parallel metal plates. When the measured quantity changes, the distance, medium, or area between the plates changes accordingly, resulting in a change in capacitance. By measuring this change in capacitance, the value of the measured quantity can be deduced.
Capacitive sensors have advantages such as high precision, high sensitivity, non-contact measurement, good dynamic response, and strong anti-interference ability, and therefore have been widely used in industrial automation, aerospace, automotive electronics and other fields.
The characteristic of variable-area capacitive sensors is that they achieve changes in capacitance by altering the area of the plates. Specifically, when the measured quantity (such as displacement) changes, one plate (usually called the moving plate) moves relative to the other plate (the fixed plate), thus changing the overlap area between them. This change in area directly leads to a change in capacitance, and the amount of change is proportional to the amount of displacement.
The advantages of variable area capacitive sensors are mainly reflected in the following aspects:
1. Simple structure, easy to manufacture and install.
2. It has high measurement accuracy and sensitivity, and is suitable for measuring minute displacements.
3. It has good dynamic response and can reflect changes in the measured quantity in real time.
4. It has strong anti-interference ability and is less affected by the external environment.
However, variable area capacitive sensors also have some limitations, such as requiring high parallelism between the plates and uniformity of the medium, otherwise the measurement accuracy will be affected.
The main function of variable area capacitive sensors: Variable area capacitive sensors play a vital role in industrial automation and measurement technology. They are widely used in various applications requiring precise measurement of physical quantities such as displacement, pressure, and thickness. Below are some specific application examples:
1. Displacement Measurement: In machining, assembly, and inspection processes, precise measurement of workpiece or tool displacement is often required. Variable area capacitive sensors can provide high-precision displacement measurement data, helping to achieve automated control and quality control.
2. Pressure Monitoring: In hydraulic systems, gas storage tanks, and similar applications, real-time monitoring of pressure changes is necessary to ensure safe operation. By installing a variable-area capacitive sensor at an appropriate location on the pressure vessel, pressure changes can be monitored in real time, and corresponding electrical signals can be output for processing by the control system.
3. Thickness Measurement: In industries such as paper production and plastic film processing, product thickness is an important quality indicator. Variable area capacitive sensors can measure product thickness non-contactly, offering high accuracy and speed, which helps improve production efficiency and product quality.
In conclusion, variable area capacitive sensors, as high-precision and high-sensitivity measuring instruments, play a vital role in industrial automation and measurement technology. With continuous technological advancements and increasing application demands, they are poised for even greater development and application prospects in the future.
