Capacitive Proximity Sensors Explained

‍Introduction

Have you ever marveled at the magic behind the scenes in industrial automation? Amidst the sea of sensors, one unsung hero is stealing the spotlight: capacitive proximity sensors! These nifty little devices bring a touch of magic to the mundane, detecting objects without even touching them. But hold onto your hats because the whole world of applications is waiting to be discovered! From enabling robotic arms to precisely grab materials on assembly lines to tasks like counting products on conveyor belts or detecting materials for further processing while in motion, these sensors are champions of convenience and efficiency. So, let's roll up your sleeves and explore the captivating universe of capacitive proximity sensors!

Prerequisites

It's advisable to familiarize yourself with non-contact capacitance sensors. Knowing their applications will enable you to follow this tutorial more effectively.

What is a Capacitive Proximity Sensor?

A capacitive sensor is your tech-savvy friend who can spot movement or when something's around. Then, it shoots out an electrical signal to let you know what's up.

Capacitive Proximity Sensor Components

Capacitive sensors are all about four key components: the body (like its little house), the face that does the sensing (we'll call it the detection section), a light to show what's happening, and the cable or where it hooks up. And here's the kicker: no moving parts are needed at all!

• Body of the sensor: Peek inside the sensor's body, and you will find all the cool sensing electronics tucked away. Plus, that plastic body? It's like a shield against corrosion.
• Sensing face: It is where the sensor gets its mojo, spotting targets with its oscillating field. It is like the sensor's radar.
• Indicator light: It is at the opposite end of the sensor, keeping an eye out for action. It flips on when something is in the sensor range and off when it's not.
• Sensor electrical connection: These sensors are pretty versatile. Some come ready to roll straight out of the box with a cable already hooked up and equipped with all the necessary wires. Other capacitive sensors have this neat feature where they come with a cordset pre-installed at the factory or a pin connector built right in. So, you can screw the cable right into the connector, making it super easy to set up.

Capacitive Proximity Sensor Working Principle

Imagine the sensing head of a capacitive sensor. It's got two plates that behave like an open capacitor with a particular capacitance. The oscillator within the sensor charges a capacitor plate, thus forming an electrostatic field. This oscillator also produces a specific frequency waveform, establishing a reference point for the sensor's detector circuit.

When a target approaches the capacitive proximity sensor and disrupts the sensing field, two main actions occur. First, the disruption increases the capacitance of the electrostatic field. Secondly, due to the change in capacitance caused by the presence of the target, the frequency of the oscillator shifts. The detector circuit monitors this frequency shift and triggers a response, such as activating the sensor's output when the detected change exceeds a predetermined threshold.

Capacitive Proximity Sensor Target Materials

Capacitive proximity sensors are versatile devices renowned for detecting the presence or absence of objects without physical contact. Unlike many other sensing technologies, capacitive sensors excel in a wide range of materials detection, including all types of metal (copper, aluminum, iron, stainless steel, etc.), plastic, wood, glass, rubber, leather, cloth, etc. The detection of liquids, including water, paint, and oil, is another function of these sensors.

Detection of materials behind non-metallic barriers is another capability of capacitive proximity sensors. They achieve this by detecting variations in capacitance caused by the higher dielectric property of the contained material compared to the container.

Capacitive Proximity Sensor Sensing Range

For a capacitive sensor, the sensing range is like its 'detection zone.' It tells you the farthest distance something can be from the sensor's face to be still noticed.

Some capacitive sensors have a notable control to adjust their 'detection zone.' Why? Because the type of material and even the environment can affect how far these sensors can sense things.

Many of these sensors have a little dial that you can turn to ensure they work perfectly for your needs. Turning it up lets them 'see' from farther away while turning it down makes them only focus on things right up close.

The sensing range of the capacitive proximity sensor is listed in its datasheet or on the company's website!

Capacitive Proximity Sensor Output Connection

Setting up a capacitive proximity sensor with four wires can feel like deciphering a secret code! Don't worry. It is not as complex as it seems. Imagine the wires as teammates: brown and blue are the power couple connected to the positive and negative sides of the power supply, respectively.

The black wire is the sensor's superhero, sending a signal when it saves the day by detecting something (target). This signal disappears when the coast is clear (no target).

The white wire is another superhero with a different power - it sends a signal when there is no trouble to stop (no target). It stays quiet when there is something to sense.

Capacitive sensors have two distinct ways of communicating their detections. Imagine them as party guests, each with a unique way of greeting their host (the control system).

The Outgoing Announcer (PNP): This configuration, like a boisterous party guest, uses a high voltage signal to announce its presence. We call this a PNP (Positive-Negative-Positive) configuration because of the doping types within the sensor itself. When it detects something, the PNP sensor sends out a positive voltage, indicating a change in its environment.

The Subtle Handshaker (NPN): This sensor, on the other hand, prefers a more reserved approach. Like a guest opting for a polite handshake, the NPN (Negative-Positive-Negative) sensor completes a circuit by connecting to the ground when it detects something. It creates a change in voltage relative to the control system, acting as a quieter "hello."

Keep in mind that some of the modern capacitive sensors are equipped with IIoT protocols that may connect in different ways - Ex: IOLink, Modbus, etc.

Here's an example of wiring a 4 wire sensor into a Siemens S7-1200 PLC: Sensor, Push Button & LED Hardware Wiring Tutorial Inputs Outputs S7-1200

Here's an example of wiring a 4 wire sensor into an Allen Bradley PointIO block: Point IO 1734 Allen Bradley - Input Sensor Hardware Installation Wiring Testing Programming Tutorial

Capacitive Proximity Sensor Installation Styles

Capacitive sensors are all about clear detection, and proper mounting is crucial for getting the most accurate readings. Here's a breakdown of how to mount different capacitive sensor styles to ensure a happy sensor and reliable results:

Bolt-on Buddies: These sturdy sensors are your friends for applications requiring a strong and secure mounting solution. They typically have threaded holes in their base designed for screwing them directly onto a flat, stable surface. Make sure the surface is strong enough to hold the sensor firmly and avoid any potential wobbling that could affect readings.

Drill-and-Mount Fans: These sensors prefer a pre-drilled hole for a snug fit. The sensor body will likely have a specific diameter requirement, so consult the manufacturer's datasheet for the exact hole size needed. A perfectly sized hole ensures the sensor sits flush and minimizes any influence on the sensing field.

Bracket Besties: For applications where direct mounting isn't ideal, these sensors shine. They often have slots or holes designed to work with dedicated mounting brackets. The bracket provides additional support and allows for more flexibility in positioning the sensor for optimal target detection. Look for compatible brackets offered by the sensor manufacturer for a seamless installation.

Capacitive Proximity Sensor in Action

These amazing sensors are like invisible helpers in factories, helping with all sorts of tasks. Here are a few ways they keep things running smoothly:

Part Pick-Up: Imagine tiny robot assistants who know exactly when to grab a part! Capacitive sensors on workstations and robots can sense parts and tell the machines what to do next.

Counting: Ever wondered how factories keep track of all those parts? Capacitive sensors on conveyor belts can count them all automatically, making sure everything's accounted for.

Level Detection: Running out of oil for a machine or overflowing a tank can be a big problem! Capacitive sensors can keep an eye on fluid levels and cause an alarm to go off if things get too high or too low.

Conclusion

In conclusion, you learned about the fascinating world of capacitive proximity sensors! These sensors use the magic of capacitance to detect objects without touching them. They boast a wide range of applications, from precisely guiding robots on assembly lines to keeping track of inventory on conveyor belts. You explored the inner workings of these sensors, including their components, how they detect objects, and the different ways they communicate with control systems. Finally, you discovered various mounting styles to ensure optimal performance for your specific needs. With this newfound knowledge, you can confidently step into the world of automation and put capacitive proximity sensors to work for you!