What is a capacitive sensor? In the field of engineering, sensors are applied as one of the indispensable devices in measuring. Because they bring high precision, automated systems, precision. Each type of sensor has different characteristics and operating principles.
Capacitive sensors are solutions that are applied on many industrial devices. Sensor devices are important, highly applicable, but few people understand the nature. So, what is a capacitive sensor? What is the working principle and application of this type of sensor? The following article plctop.com will help readers clarify information about this type of sensor.
1. Capacitive Sensor
What is a capacitive sensor? Capacitive sensors are also known as dielectric sensors. This is a device used to measure the dielectric constant in the medium and the surrounding environment. Usually they are used to detect the level of liquids, solids, solutions in tanks, tanks, silos or even in piping systems. They will detect this medium and convert the measured signal into 4 – 20 mA, 0 – 10V analog signals or as On/Off.
With the advantage of measuring the dielectric constant to determine the level of the medium, they are applied in many different fields. Environments where other sensor lines are difficult, but for capacitive sensors, it’s all worth it. Such as environment: Flammable, high temperature and pressure, … can completely be used to measure clean water level, measure acid level, report chemical, oil level…
2. Structure of the Capacitive Sensor
With the ability to work in such harsh environments, I don’t know how they are structured? What is the question that thietbikythuat.com.vn receives a lot in the process of consulting solutions for customers. By the way in this article, I will understand it together.
+ Signal Transducer:
This is an equally important part. All the modern technologies of capacitive sensors are in this section. This unit is used to convert capacitance to analog electrical signal (4-20mA, Relay On/Off). We can think of the transducer as the limbs of the variable cmar, the signal transducer as an intelligent brain. This brain will transfer the signal to the PLC, controller or display unit to perform the system control process.
+ Sensor:
What we see every time we see this electrical sensor device is the sensor head. They are designed with a round cylindrical shape (like a wand). This is the most important part of the capacitive sensor. They are responsible for detecting the medium in the measuring medium. With each different measurement environment, they have different materials. In a less corrosive environment, use SUS304. For high corrosive environments, use 316SS material.
+ Sensor Cover:
This cover is also a pretty important part for the capacitive sensor. They help protect the transducer from elements that corrode the metal rod oil. This helps the sensor to have a longer, longer service life.
3. Principle of Capacitive Sensor
In the capacitive sensor, there is a part that changes the capacitance C of the plates. They work based on the change in capacitance of the capacitor. When any object passes in the sensitive area of the sensor, the capacitance of the capacitor will increase. This change also depends on many different factors such as distance, size, dielectric constant of the object… Inside there is a circuit using DC power to create oscillations for the current sensor, the current sensor will output a current. The electric current is proportional to the distance between the two poles.
Principle of Capacitance
To make it easier to imagine, you can understand that around the sensor there are always a lot of electrodes connected in series between the sensor and the wall of the tank. When the level of liquid or solid comes into contact with the sensor’s electrode, the amount of electrode will increase. The signal is sent to the microprocessor and returns the results so that we can determine the level of fuel in contact with the sensor.
Tapered capacitive sensors will typically have a measuring range of 2mm to 50mm. Their common outs are PNP/NPN/NO/NC… Each different material has a different level of conductivity, so we need to use a sensor to suit each medium. For example, RO water or distilled water will have very low conductivity, very few types of capacitive sensors can measure.
4. Classification of Capacitive Sensors
Capacitive sensors are designed to measure a wide variety of environments and different applications. Usually they are divided into the following forms:
Liquid Continuity Sensor
It is the leading application in liquid measurement and monitoring systems. This sensor is usually mounted on the top of water tanks, silos, storage tanks. This type usually has a rather long probe. This is the direct contact with the liquid. Looking at the illustrations below you can immediately see their application.
+ With a scale of 0-2m, this device is widely used in industrial and civil environments. The principle of operation of the continuous measurement capacitive sensor is when the water level rises and comes into contact with the probe. The probe processes this signal and sends it to the central processor to convert it into 4-20mA, 0-10V analog electrical signals. One way to understand it is that when the water rises, they sense it and convert to an electrical signal.
+ Note: is that for a scale larger than 2m, we should not use this type but must use an ultrasonic sensor.
Liquid level sensor
If you only need to report the initial level or empty level in the tank or tank, this is the most suitable solution for you. Why do I say the most suitable, anyone know?
That’s because this sensor line is much cheaper than the continuous measurement sensor line that I just mentioned above. The principle of this level sensor is that when the level of the conductive liquid touches rises and touches the sensor’s probe. Then immediately the sensor will signal to the processor and convert this signal into current in the form of On/Off relay, this signal we can install them in the form of NO, NC for each application. In case the chamber is full, the chamber is dry.
Solids level sensor
Solids measurement is also one of the outstanding applications of this sensor line. Many of you wonder what is the solid here? Why measure solids level?
To measure these particles in the form of particles, conventional mechanical or electrical sensors do not have any ground. Because when this particle level rises and falls continuously in the tank with a large impact force, it is easy to damage the sensor. Therefore, capacitive sensors are widely used here.
5. How to choose a Capacitive Sensor
To buy the right capacitive measurement sensor product line for the application, you need to pay attention to the following factors:
What is the measuring medium?
Accurately determining the measurement environment is an important factor in sensor selection. Normally, the measuring medium commonly seen in industry is water, conductive liquids, etc. In this environment, it is quite easy for us to choose a sensor because this environment has a low level of corrosion.
What is the ambient Pressure and Temperature?
This is a condition worth considering before making a purchase. For the environment where you need to measure at normal temperature and pressure conditions, we don’t need to pay attention.
But for a high temperature and high pressure environment like in a boiler, please note. Common sensors can only handle temperatures of about -30… 80oC and pressure is 1bar. To use the boiler, you must choose appropriate circuit protection standards. trnash case high temperature and pressure go straight to the converter circuit.
How Scale meters?
The scale is a factor we also need to pay attention to. With the longer the scale, their cost also increases accordingly. Normally, the electric sensor lines that use them are applied with a 2-meter refillable scale. This is the most suitable scale for capacitive sensors.
What is the output signal?
The output signal is for the purpose of synchronously connecting with the central controllers of the PLC. Usually the output is in the form of an analog signal that is 4-20mA, 0-10V or an On/Off relay signal.
One case here is that unfortunately you bought a device with an output of 4-20mA, but your PLC can only read 0-10V signal, what to do? Don’t worry because unfortunately if you encounter that situation, use a 4-20mA to 0-10V analog signal converter.
Learn about 4-20mA and 0-10V signal converters.
Learn about analog to Relay On/Off converters.
Is it explosion proof?
This is a factor to consider when measuring flammable substances. As in the environment of Gas, DO Oil, gasoline … In short, substances that just need a small electrical speculative ray to contact them, they can be your plane. For such an environment, you should choose sensor lines with explosion proof standards.
Thank you for reading the article, please comment below the article if you have any questions.
