There is understandably some confusion when it comes to position sensors, especially when it comes to the specific terms or jargon often used when talking about them. For instance, there are different terms which are used to refer to the word ‘sensor’ and these terms include encoder, transducer, detector, and transmitter. Generally speaking, all these terms refer to one thing: a sensor.
Additional confusion ensues when some sensors (especially proximity sensors) are actually switches because they only detect the presence or non-presence of an object. What this means is that they only produce a digital output or on or off output rather than uninterrupted position measurement. Here, we are referring to ‘true’ position sensors instead of mere switches – sensors which can produce signals (often electrical) which are proportional to a particular position on a path of measurement.
More on position sensors
A position sensor can be classified as a speed or velocity sensor. As speed or velocity is the rate of position change, any particular position sensor with a position which is frequently or regularly updated is, generally speaking, a speed sensor. The speed can be determined by a contemporary control system by distinguishing the output of the sensor relative to time or by simply counting the changes in position in relation to time.
Position sensors have a further classification: absolute or incremental. If there is a position change, the output from a sensor which is incremental will undergo a corresponding change as well. In the meantime, the signal from a sensor which is absolute will be in proportion or relation to its true position and whether or not it is moving or stationary. To determine whether or not a sensor is incremental or absolute, you should consider what happens when it is powered up. An absolute sensor will produce a signal of true position without any motion.
Choosing the right sensor
In choosing the right sensor for your specific application requirements, there are many factors to be considered, including resolution, accuracy, and repeatability. But these factors are sometimes not properly thought of or determined, which can result in an incorrect selection of sensor, or less than optimal sensor selection. If the chosen sensor is incorrect, this could result in an extremely costly sensor for the requirement or a system which does not rank high in performance.
Whilst accuracy is often a strong requirement for position sensors, especially for a linear position sensor, there are some additional considerations as well. For example, when looking for a position sensor for an industrial-flow meter, the sensor’s linearity is not an essential requirement, as the flow property of the fluid will not be linear. For this use, repeatability is more essential. Another example is when looking for a position sensor for a CNC machine. For this, precision and accuracy are the most crucial requirements, but high resolution and repeatability should also be considered since it will be used in an extreme (dirty and wet) environment with little maintenance.