Typically, a capacitor sensor is a kind of proximity sensor that uses the electrical field it creates to detect items close nearby. Although being limited to short ranges, usually less than 1 cm, a basic capacitive sensor has been commercially available for many years for the detection of nonmetallic items. An overview of capacitive sensors and their uses is provided in this article.
What is a Capacitive Sensor?
A capacitive sensor is an electronic device that uses no physical contact to detect targets such as liquids or solids. The capacitive sensor will generate an electrical field from its detecting end in order to detect these targets. This sensor can identify any object that has the ability to interrupt this electrical field. Wood, paper, plastic, glass, and fabric are among the solid things that a capacitor sensor can sense. A capacitor sensor can also detect liquids such as paint, water, oil, etc.
Capacitive Sensor Working Principle
A capacitive sensor functions similarly to a typical capacitor. This sensor uses a metal plate inside the sensing face that is electrically connected to an oscillator circuit. The target that is detected can serve as the capacitor's second plate. A capacitive sensor creates an electrostatic field instead of to an electromagnetic field like an inductive sensor does. The capacitive sensor's block diagram is given below.
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| Photo credit: elprocus.com |
This sensor consists of a high-frequency oscillator with two metal electrodes forming the detecting surface. When an object gets near the sensing surface, it enters the electrodes' electrostatic field and changes the oscillator's capacitance. Consequently, once it reaches a specific amplitude, the oscillator circuit will start to oscillate and alter the sensor's output condition. The oscillator's amplitude will decrease as the target moves away from the capacitive sensor, returning the sensor to its initial position.
The normal detecting range of this sensor is around 1 inch or 25 mm, while some sensors have a range of up to 2 inches.
Types of Capacitive Sensor
Capacitive sensors provide target detection without need of contact. These sensors are capable of detecting pressure, flow, spacing, liquid level, and other factors in addition to whether a target is present or absent. This is easily accomplished for many materials in various sectors. Capacitive sensors come in a variety of forms, such as the following.
Miniature- The smallest spaces may accommodate this kind of capacitive sensor, which comes in cylindrical or wafer shapes. These sensors function similarly to detectors used for task counting and are primarily used to monitor and control machine activities. Small sensor heads require an external amplifier to fit in compact areas as well as possible. This external amplifier's potentiometer allows for sensitivity adjustment.
Cylindrical- Compared to the Miniature type sensors, this cylindrical capacitive sensor is larger in size. This sensor primarily includes flush and non-flush mounting options, a range of housing diameters, and an adjustable sensing distance. Level detection or contact-free proximity detection are the primary functions of these sensors, which can also be used straight across a container wall.
High Temperature- When the sensor head is exposed to extremely high temperatures, high-temperature capacitive sensors are utilized. Even under the most extreme conditions, these sensors can detect liquid temperature levels and bulk products even when they are in direct touch with hot materials and temperatures.
Analog Capacitive Sensor
The analog capacitive sensor functions similarly to other capacitive sensors, but depending on how it is used, it offers various advantages. For instance, compared to other applications, these sensors are excellent for material selection, thickness monitoring, and concentration differences.
Characteristics of Capacitive Sensor
1. Mechanical limit switches are unable to detect small or light items, but these sensors can.
2. When used in product counting-based applications, these sensors offer a maximum switching rate for an instant response.
3. Through nonmetallic barriers like glass, plastic, etc., they are able to detect liquid targets.
4. Compared to more traditional sensors like strain gauges and LVDTs, these sensors offer a greater mix of linearity, precision, stability, bandwidth, and resolution.
5. They have an almost infinite number of operating cycles and a long operational life.
Advantages
- Non-metallic targets are detected by these sensors.
- It is easy to construct.
- A capacitive sensor can be adjusted to work with a variety of materials.
- These sensors are also capable of detecting liquid and solid targets.
- It requires very little energy to run and has a great sensitivity.
- Its resolution and frequency response are good.
Disadvantages
- The performance will be impacted because it is highly sensitive to variations in external factors like temperature, humidity, etc.
- Compared to measuring resistance, measuring capacitance is more difficult.
- When compared to inductive-type sensors, these sensors are less accurate.
Applications
The most common usage for these sensors is to detect changes in the position of a conductive target. But these sensors can also be very good at monitoring thickness, density, presence, and the location of non-conductors. The dielectric constant of non-conductive materials, like plastic, differs from that of air. Fluid level, humidity, acceleration, displacement, location, and closeness can all be detected or measured with capacitive sensors.
