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.