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Capacitive Sensor Explained | Different Types and Applications

Learn about how capacitive sensors work, different types of capacitive sensors, and some examples of how these sensors are used with automation.

In this article, we will be talking about capacitive proximity sensors. We will explain what a capacitive proximity sensor is and how they work.

We will also talk about some of the different types of materials these sensors can detect, explain the main parts of these sensors, talk about some of the different types of capacitive proximity sensors, and we will give some examples of how these sensors are used with automation.

What is a capacitive sensor?

A capacitive sensor is an electronic device that can detect solid or liquid targets without physical contact.

What-is-a-capacitive-sensor

To detect these targets, capacitive sensors emit an electrical field from the sensing end of the sensor. Any target that can disrupt this electrical field can be detected by a capacitive sensor.

Types of materials capacitive sensors can detect

Some examples of the solid materials a capacitive sensor can detect are all types of metal, all types of plastic, wood, paper, glass, and cloth.

Types of materials capacitive sensors can detect

Capacitive sensors can also detect liquids like water, oil, and paint.

Types of liquids capacitive sensors can detect

Some capacitive sensors can be used to detect material inside a nonmetallic container. The capacitive sensors used to do this have an adjustable sensing range. We will explain how to adjust these types of capacitive sensors with an example in just a bit.

Detecting-material-inside-a-nonmetallic-container

Capacitive sensor main parts

Capacitive sensors have four main parts, the sensor’s body, the sensing face, the indicator light, and the cable or cable connection end.

Capacitive-sensors-main-parts

Adjustment screw

If the sensor has an adjustable sensing range, it will also have an adjustment screw to adjust the sensing range.

Sensor adjustment screw

1) Sensor’s body

Inside the sensor’s body is where the circuitry is that makes the sensor work.

Sensor’s-body

2) Sensing face

The sensing face is the part of the sensor that is used to detect the targets. 

3) Indicator light

The indicator light is on the other end of the sensor from the sensing face. This light turns on when a target is within the sensors sensing range and turns off when the target is out of sensing range.

Sensing face and Indicator light

Sensing range

The sensing range of a capacitive sensor is the max distance a target can be detected from the sensor sensing face.

Sensing-range

An example of being within the sensors sensing range would be if the target is six millimeters away from the sensing face and the sensors sensing range is twelve millimeters.

Within-the-sensor-sensing-range

The sensors sensing range can be found on the datasheet of the sensor, or you can look it up on the manufacturers’ website.

Sensing-range-on-the-datasheet

4) Sensor connection

These sensors can be purchased with a cable already attached to them or they can have a connector that the cable screws into.

Sensor connection.

In this cable, you will find four wires. The colors of these wires are brown, blue, black, and white.

1) The brown wire gets connected to twenty-four volts DC positive.

2) The blue wire gets connected to twenty-four volts DC negative.

3) The black and white wires are the sensor output wires. The black wire is the sensor’s normally open output wire. The sensor will send out a signal on the black wire when it detects the target. The sensor stops sending this signal when it does not detect a target.

Normally open output

4) The white wire is the sensor’s normally closed output wire. The sensor will send out a signal on the white wire when it does not detect a target. The sensor stops sending this signal when the target is detected.

Normally closed outputv

Capacitive sensor’s outputs

A capacitive sensor’s outputs can be a positive signal (or PNP) or a negative signal (or NPN). Depending on how the sensor outputs will be connected will determine what style of sensor outputs are needed.

Capacitive-sensor’s-outputs-signal

Adjustable sensing range

If the capacitive sensor has an adjustable sensing range it will have an adjustment screw. Turning the screw clockwise increases the sensitivity of the sensor and turning the screw counterclockwise decreases the sensitivity of the sensor.

Adjustable sensing range

Capacitive sensor mounting

Mounting a capacitive sensor can be easy, it mostly depends on how the sensor is going to be used and where it’s going to be located.

Some styles of capacitive sensors can be mounted by just bolting them into place. Other styles of capacitive sensors can be mounted by drilling and tapping a hole the same size as the sensor and sometimes using a bracket to mount the sensor is the best solution.

Capacitive-sensor-mounting

How to set up a capacitive sensor

Now we will explain how to set up a capacitive sensor to detect water in a nonmetallic container. In this example, we will use a drinking glass made out of plastic for the container and a capacitive sensor with an adjustable sensing range that is mounted on a post to detect the water.

How-to-set-up-a-capacitive-sensor

Notice when we put the empty drinking glass next to the sensor, the sensor’s indicator light turns on. This means the sensitivity of the sensor is set to high and will need to be adjusted.

To adjust the sensitivity of the sensor, turn the sensitivity adjustment screw counterclockwise until the indicator light turns off.

Sensor sensitivity

Now we will fill the drinking glass with water up to the sensor. Notice the indicator light turns on.

If we remove some of the water to where the level is below the sensor, the indicator light will turn off. This means that the capacitive sensor is adjusted correctly.

Adjusting sensor sensitivity.

Capacitive sensor applications

Capacitive sensors can be used in many ways. They can be used for part detection on workstations, conveyors, and robots.

Capacitive sensor applications

They can also be used for counting and checking liquid levels.

When these sensors are used for part detection, the sensor just sends a signal to the workstation, conveyor, or robot so they know when the part is there.

A capacitive sensor can be set up on a conveyor to trigger a counter so that it can count how many parts have been built.

Use of Capacitive sensor for counting

Capacitive sensors can also be used to check for high or low tank fluid levels and to trigger alarms for each.

Checking-liquid-levels-using-Capacitive-sensor

Summary

In review, by reading this article, you have learned about capacitive sensors. That they detect most solid or liquid targets without physical contact by creating an electrical field.

You learned the four main parts of a capacitive sensor and that they have many different options to fit the needs of most applications.

Please let us know if you have any questions about capacitive sensors, or about sensors in general, in the comments below and we will get back to you in less than 24 hours.

Got a friend, client, or colleague who could use some of this information? Please share this article.

Adam Stykemain

Adam Stykemain

Automation Engineer

Posted on Jul 14th, 2021

Adam Stykemain

Adam Stykemain

Automation Engineer

Posted on Jul 14th, 2021

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