What is a capacitive sensor?
Content
Like some other types of sensors (for example, inductive sensors), capacitive sensors work without physical contact with the object under study. In other words, these types of sensors are non-contact devices. With their help, both electrically conductive and non-conductive materials can be detected. Due to this property, capacitive sensors can be used in places where, for example, inductive sensors are not applicable.
What is a capacitive sensor, its device and mode of operation
This type of sensor is not very complex as a device and usually consists of:
Shells
The case makes it possible to assemble all the elements into one. In addition, it provides reliable protection of elements from external factors that may affect its effectiveness. The housing of the capacitive sensor is usually made of brass or polyamide.
Connector
This is a special resin that protects the sensor elements from moisture or other harmful substances.
Trigger
The trigger creates the necessary power of the switching signal and the hysteresis value (this is the difference in the distance before switching on).
LEDs
LEDs provide quick setup and indicate the position of the switch.
Amplifier
Enhances the output to the desired value.
Demodulator
The demodulator changes the high-frequency oscillations until the voltage changes.
Generator
It creates an electric field that acts on the object.
electrodes
The working surface of a capacitive sensor is usually two electrodes that act as capacitor plates that are connected to the generator feedback circuit. He, in turn, is configured to change his power as it approaches the controlled object.
As a result of these oscillations, when the sensor approaches the object, the generator generates an increasing amplitude, which is processed and creates an output signal.
Capacitive sensors are driven by electrically conductive objects and dielectrics. As the conductive object approaches, the response distance becomes much larger than when the test objects are dielectrics (the reaction distance depends on the dielectric constant).
Using
The use of sensors of this type is extremely large and diverse. They are widely used in industrial process control systems in almost all industries.
They are used in automotive parking sensors and to control the filling of tanks with liquid, bulk and gaseous substances, for circuit breakers on automatic lines, for machine centers, machines, conveyors, alarm systems and others.
Types of capacitive sensors and their application
Proximity sensors
At present, one of the most commonly used capacitive sensors is proximity sensors, which, in addition to being extremely reliable, have a very wide range of advantages.
Sensors of this type are used in almost all areas, as they have a very reasonable cost. They are used to control the filling level of various containers, control voltage, to signal in case of problems on production lines and others.
Capacitive sensors for angular and linear movements
Sensors of this type are used in industries such as engineering, energy, transportation, construction and others.
Inclinometers
Capacitive inclinometers are used on oil platforms in leveling systems, to determine the deformation of supports, to monitor and control the slope of roads and railways during their construction, to determine the quality of cars, ships, elevators, lifting equipment, agricultural machinery to determine the angular displacement of rotating objects, such both shafts, gears and mechanisms, both stationary and mobile.
Capacitive Level Sensors
Sensors of this type are used in monitoring systems, regulation and control of processes in the food, pharmaceutical, chemical and petroleum industries.
They are extremely effective when working with liquids, bulk materials, conductive and non-conductive viscous substances, as well as in harsh working conditions in rooms or places where dust or condensate accumulates.
Capacitive sensors are widely used in industries where accurate measurement of total pressure, thickness of dielectric materials, humidity, linear and angular deformations and others is required.
Classification of capacitive sensors by the method of their implementation
All types of capacitive sensors can be divided into two groups: sensors with one and two containers. The latter are further divided into differential and semi-differential.
Sensors with one capacitance have a simple design and are capacitors with variable capacitance. This type of sensor has several disadvantages that include significant environmental influences such as humidity and temperature.
The disadvantage of sensors with a differential design is that they differ from sensors with a single capacitance, while differential sensors have at least three connecting wires between the sensor and the measuring device to neutralize the negative effects of humidity and temperature.
However, due to this small drawback, differential sensors significantly increase their accuracy and stability and thereby expand their scope.
Pros of capacitive sensors
Compared to competitive optical, inductive and piezoelectric sensors, capacitive sensors have many advantages, including:
- ease of production - cheap materials are used for the manufacture of capacitive sensors, which affects the final price of the product;
- small size and weight;
- low power consumption;
- high degree of sensitivity;
- non-contact (they do not have to be near the object of study;
- long service life;
Easy adaptation of the sensor design to various tasks and measurements.
Disadvantages
Some of the biggest disadvantages of capacitive sensors are:
- a relatively small conversion (transmission) coefficient;
- the need to work at a frequency above 50 Hz;
- dust and moisture can affect performance, and the sensor can detect incorrect measurement;
- temperature sensitivity.
Capacitive sensors are simple to implement, which allows you to create a durable and reliable design. The capacitor parameters depend only on its characteristics and do not depend on the properties of the materials used, if they are correctly selected.
The problem of their sensitivity to temperature can be solved by choosing the appropriate material for the plates and the appropriate insulation for their fastening. It remains only to improve their protection against the harmful effects of dust, moisture and ion radiation, and this type of sensors will have an even wider range of applications.
And finally, we can summarize ...
Capacitive sensors use the very little mechanical force they need to move the moving part, adjust the output of the system, and operate with high accuracy. All this makes these sensors indispensable for the accurate measurement of conductive and non-conductive elements.
Questions and answers:
What are the capacitive sensors? Single-capacitive, double-capacitive. In turn, they are divided into: linear, angular, inclinometers, level sensors, pressure transducers.
What are capacitive sensors intended for and how do they work? In such sensors, the measured parameter changes, due to which the resistance changes. Such sensors are used to convert values of humidity, pressure, mechanical force, etc.
How does a capacitive level sensor work? In such a sensor, due to a change in the measured level, the capacitance of the capacitor also changes (it is formed by the probe and the walls of the reservoir - the more liquid in the reservoir, the higher the capacity).
