There are many factors to consider when selecting the best inductive proximity sensor for an application. William Darby, Managing Director of Carlo Gavazzi UK, outlines his top five tips to ensure the best sensor for a particular application.
Inductive proximity sensors are commonly used in machine design and automation where a more traditional switch might prove problematic or impossible to use, such as in an application where lots of water and dirt are present.
There are three primary components to an inductive proximity sensor: an inductive coil with an oscillator, an evaluation circuit, and an output circuit. When an oscillating signal is applied to the coil, a magnetic field is created. The presence of metal nearby disrupts this magnetic field. This is detected by the evaluation circuit, which energises an output signal.
Inductive proximity sensors allow the non-contact detection of both ferrous and non-ferrous metals. They are wear-resistant, maintenance-free, waterproof, widely resistant to chemicals and insensitive to moderate levels of dust and dirt collection. What’s more, they have excellent resistance to shock and vibration, and their solid-state output provides for bounce-free switching over a long lifetime.
Material | De-rating Factor | Type of Metal |
Steel (Fe360) | 1.0 | Ferrous |
Chrome-nickel (CrNi) | 0.6 to 0.8 | Non-Ferrous |
Brass (CuZn) | 0.35 to 0.5 | Non-Ferrous |
Aluminium (Al) | 0.3 to 0.5 | Non-Ferrous |
Copper (Cu) | 0.25 to 0.3 | Non-Ferrous |
The combination of these properties enables inductive proximity sensors to be used for numerous applications, including gear tooth detection, speed monitoring, end of travel detection and positioning/closure detection in industries including food and beverage, transportation, agriculture and packaging.
There are numerous inductive proximity sensors available, so how do you select the best sensor for a particular application? I’ve listed my five top tips below:
Determine the sensing range required
It is critical to identify the physical size and material properties of the target to determine the sensing range required.
• Target Size: even though inductive sensors detect metal, the target must be large enough to disrupt the sensing field. The minimum target size is defined according to EN 60947-5-2.
• Target material: Technical data and specifications for inductive sensors are based on ferrous steel according to EN 60947-5-2. Most metals, however, are compounds, so a reduction factor will need to be applied to the sensing range – see Figure 1
• Sensing distance: The sensing distance for inductive sensors ranges from 1mm to 40mm, depending on the target metal. For example, a standard inductive sensor listed as having a 10mm sensing range (based on a ferrous steel target) would have a range between 2.5 mm to 10mm, depending on the composition of the metal being sensed.
• Speed: inductive sensors offer faster switching speeds compared to capacitive sensors, and they can be as fast as some photoelectric sensors.
Understand the integration requirements
Integration is determined by the set-up of the application and components which cannot be changed, so the sensor needs to be selected accordingly.
• Supply Voltage: Inductive sensors are available for use with input supply voltages of AC, DC, or even AC/DC applications.
• Sensor Output: Common output options available include Normally Closed (NC) and/or Normally Open (NO), NPN and/or PNP (DC), SCR (AC), MOSFET (AC), NAMUR, or IO-Link communication.
• Sensor Installation: Inductive sensors are available in threaded cylinder and rectangular housings. The most common body style is threaded cylindrical in M8, M12, M18, and M30. If more than one inductive sensor is to be installed, ensure the sensors will not interfere with each other. There are inductive sensors available which can be programmed to operate without interference for this type of application.
• Termination Style: Typically, inductive sensors are connected using a quick disconnect (M8 or M12) or a cable with flying leads. Larger sensors are occasionally offered with terminal connections.
Consider the operating environment
The operating environment of an inductive proximity sensor can greatly narrow the selection options. Exposure to oils, chemicals, wash-down conditions, noise, extreme shock or vibrations might require specialised sensor capabilities.
• Housing material: Inductive sensor housing materials are nickel-plated brass, stainless steel or polycarbonate. The durability of metal housings means that these are the most common. Plastic housings can be beneficial when exposed to certain chemicals.
• Operating temperature range: Consider the minimum and maximum temperature the sensor will experience during operation.
• Environmental ratings: IP ratings establish the conditions a sensor can operate under, indoors or outdoors. Similarly, a sensor needs to be appropriate for operation in hazardous environments. For mobile equipment and automotive applications, often an E1-type approval is required due to the extreme conditions and public road safety.
Plan for the future
Digitisation capabilities enable data to become valuable information. Some manufacturers, such as Carlo Gavazzi, offer sensors with IO-Link communication. This allows the user to program the sensor output, implement custom time delays, and use logic functions.
Select a reputable sensor manufacturer
Hopefully, the above tips will help identify the issues to be considered when selecting an inductive proximity sensor for a particular application. My final tip is to talk to a sensor manufacturer and experienced automation expert, such as Carlo Gavazzi, so that your project can benefit from 50 years of global application experience and sensor knowledge.
