Industrial Sensors Overview

Thanks to semiconductors, even the smallest devices can be equipped with accelerometers, motion sensors, and capacitive touchscreens that make using smartphones and tablets easier than ever before.

However, proximity sensors and switches are also essential in industrial environments and processes. They not only ensure the safety of the machines but also of the people who operate them.

The term ‘sensor’ typically refers to any technical component that independently detects certain physical or chemical parameters or properties of either objects or the environment. For example, this could include temperature, brightness, or acceleration.

In this sense, they resemble our own sensory organs, with the key difference being that they can register things that would otherwise remain invisible or hazardous to humans.

An important property of sensors is the ability to convert measurement data into signals or visual displays. These can then be meaningfully interpreted by either an operator or an electronic device.

In other words, a sensor is also always a transducer – a device that converts one form of energy or stimulus into another.

A motion sensor, for example, can be integrated into industrial machinery and wired to a safety switch. This provides safe shutdown in the event of the detector signalling an abnormal mechanical movement to the switch which, if it were permitted to continue, may damage the equipment, or pose a danger to nearby operatives.

This is an example of measurement being converted into a signal for input into another non-human device, but of course, many sensor-based systems convert the measurements into scales or displays intended for a human operator.

The mercury-in-glass thermometer, for instance, is a familiar form of temperature sensor which converts the expansion or contraction of a small mercury bulb into a readable scale (Celsius or Fahrenheit). As the mercury expands or contracts, it rises or falls inside a narrow, hollow filament within the glass, which has a calibrated temperature scale engraved on its outer surface.

Within the temperature ranges it is designed to measure, the thermometer displays an important feature required of all sensors – linearity. In other words, the physical changes in the detector material – in this case, mercury – are directly proportional to changes in the object, force, movement, or radiation being measured.

Another type of sensor, the thermocouple, will similarly respond to temperature changes in a linear fashion, in this case generating changes in output voltage that are proportional to changes in heat. To ensure accuracy, sensors are carefully calibrated to conform to established, tried-and-tested scales.

In today’s electronics-oriented world, sensors play a pivotal role in ensuring the proper functioning of a vast number of machines, gadgets, vehicles, and manufacturing processes. Sensor technologies are behind a vast number of day-to-day items, such as the accelerometer, which ensures that the display on a mobile phone is always the right way up no matter how the device is moved or rotated. They are widely used in medical equipment, aerospace engineering, automotive safety, robotics, and innumerable manufacturing processes.

A certain degree of sensor impact is inevitable in most situations, but care should be taken to ensure the effect is minimised wherever possible. One solution is to aim for as much miniaturisation as possible in sensor design. The smaller a sensor is physically, the less physical impact it will have on its medium.

Microelectromechanical Systems (MEMS) technology is transforming sensor manufacturing, enabling the construction of micro-detectors that are microscopic in scale. These sensors are typically faster in their response times and considerably more sensitive than their larger counterparts.

In engineering, sensor solutions are used in the most ingenious ways to improve efficiency and reduce labour costs. For example, RFID sensors have not only helped to create cardless payment systems when integrated into smartphones but have also greatly simplified security procedures. This is achieved by enabling the automation of gate and door opening systems in secure areas when the required RFID chip is presented. They have also helped to revolutionise logistics and transportation, as well as cross-docking processes.

Industrial sensing solutions are used in many different types of applications, as detailed below:

• Accelerometer sensors are not only used to auto-rotate device displays. They are also widely used in the navigation systems of modern aerospace equipment
• Infrared sensors are often built into heavy machinery and electrical equipment, where they activate safe shutdown in the event of abnormal and potentially dangerous temperatures
• Infrared sensors (and thermal imaging cameras) are also used for preventive maintenance
• Motion sensors, when wired to shutdown switches, perform a similar function by detecting potentially hazardous movement in mechanical parts. This may suggest faults such as worn bearings, which could have significant cost implications if not deactivated swiftly
• Motion sensors are also widely used in commercial security systems for intruder detection
• Temperature sensors such as thermocouples are regularly used in chemical engineering plants. They can withstand very high temperatures and are ideal for monitoring small heat changes indicative of chemical reactions. The developing field of nanothermometry has enabled the measurement of temperature differentials between nanometre-sized particles
• Photoelectric sensors are used to detect solid objects with one-way light barriers in freight elevators, for example
• State-of-the-art smart sensors are indispensable in industrial automation and IoT applications