Using non-contact sensors for various applications that require precise measurements is rapidly increasing. Many factors contribute to this increasing trend, and two of the primary reasons are: end users demand more accurate readings, and the assembly is subject to difficult working conditions. In some instances, the device can’t be touched during operation, such as in applications in the medical and food manufacturing sectors.
This increasing demand is pushing manufacturers to develop and perfect new sensor technologies that will cater to these unique needs. Nevertheless, these new sensor technologies take into account existing principles and improve them to improve sensor performance. As such, it is also essential to have a thorough knowledge of the advantages and disadvantages of each kind of non-contact sensor to select the most suitable sensor required for the task.
In practice, there are many different types of non-contact sensors. In displacement measurement, for example, manufacturers can assemble a non-contact rotary position sensor, linear sensor, and submersible angle sensor by using the underlying working principles that define a non-contact transducer. For this article, we will take a closer look at four specific principles of non-contact sensors – the eddy-current, capacitive, and laser triangulation.
Eddy-current sensors use an inductive measurement technology by extracting energy from a rotating circuit. A coil receives AC from a source and results in a magnetic field surrounding the coil. Once an object capable of electric conduction is placed within the magnetic field range, this action induces eddy currents. In turn, this creates an electromagnetic field which reacts in contrast with the coil’s magnetic field. The device controller will then calculate the impedance as the sensor’s final output.
In sensors that operate using the capacitive principle, the object and the sensor work similar to a parallel plate capacitor. This type of sensor is capable of achieving ideal sensitivity and linearity to metals. This sensor technology is also stable even when subject to varying temperature. But this method is only suitable for dry and clean applications.
Laser triangulation principle
In sensors that work using the laser triangulation principle, there is a corresponding laser diode which emits a laser beam pointing directly to the object. This process will result in back-scattered light which is reflected and projected to a CCD array using a lens system of high-quality. If the target object moves, the reflected light’s movement is analysed to produce an output corresponding to the object’s position. These sensors are typically coupled with a controller which converts the output into an analogue or digital signal.
These non-contact sensor technologies have many desirable characteristics which make them the ideal solution for various industrial applications. Higher measurement accuracy, as well as robustness, make these sensors compatible with applications in mining, consumer electronics, laboratory devices, robotics, transportation, and manufacturing. While many process control engineers today consider adopting non-contact sensors over contact sensors, the selection still depends on a variety of factors including cost. If the application is cost-prohibitive and is not subject to vibration or shock, other less expensive and simpler contact sensors may have comparable function and performance.