There is a consistent demand for machines with increased power and functionality which also translates to a higher need for sensors as prerequisite instruments in developing these machines. One example is the use of sensors in hydraulic and pneumatic cylinders as a feedback device. Currently, there are three common position sensor technologies used in this
There is a consistent demand for machines with increased power and functionality which also translates to a higher need for sensors as prerequisite instruments in developing these machines. One example is the use of sensors in hydraulic and pneumatic cylinders as a feedback device. Currently, there are three common position sensor technologies used in this type of application. This article aims to compare these three technologies so that engineers can determine the more suitable option to ensure optimum performance and minimise installation costs.
Magnetostrictive position sensor
For applications that require high-accuracy measurements, magnetostrictive position sensors are generally the preferred technology. Many position sensor manufacturers like http://www.positek.com manufacture transducers using this type of technology. A magnetostrictive position sensor consists of a stainless-steel tube and magnet assembly. The installation process involves putting the corresponding electronic parts of the sensor in a port behind the hydraulic cylinder. This type of sensor works when the magnet emits a mechanical pulse being transmitted along a waveguide.
Manufacturers usually devise their style in fabricating the magnetic mechanism included in the sensor. Magnetorestrictive sensors use an ample amount of power to operate. Although it has high accuracy, it can be prone to the effects of vibration and shock.
A variable resistance potentiometer is a suitable option when the hydraulic or pneumatic installation does not prioritise accuracy but endeavours to reduce the acquisition cost. Instead of a port mounting, a potentiometer is typically installed in the rear end of the cylinder. The mechanism consists of a conductive wiper that comes into contact with the plastic probe. The wiper movement results in a resistance change which translates to the position.
When potentiometers are applied in hydraulic and pneumatic cylinders, they offer an excellent stroke-to-length ratio and relatively high robustness. However, the main disadvantage of a potentiometer is its susceptibility to wear and tear. Moreover, the embedded installation also makes it more challenging to replace a worn potentiometer; hence, raising the cost and often leading to the acquisition of a new cylinder.
Linear variable inductive transducers
Although LVITs are relatively common when used in cylindrical applications, the recognition is not as extensive as potentiometers or magnetostrictive sensors. But since LVITs feature a non-contact working principle, they bear significant advantages over contacting position sensors like potentiometers. The non-contact technology of LVITs increases the device’s reliability and lifespan. LVITs also have a comparative performance to magnetostrictive sensors in terms of resolution, linearity, and frequency response. Another significant advantage of LVITs is the higher capacity to resist the impact of vibration and shock.
In recent years, the requirement for hydraulic and pneumatic cylinders used in subsea applications has increased dramatically. Some manufacturers specifically fabricate LVITs with pressure sealing that allow for the sensor to perform favourably at extreme depths and in highly pressurised environments.
In conclusion, LVITs appear to be the more superior sensor technology when it comes to ruggedness and performance. In addition to performance, LVITs have also become more affordable and can be used in more mainstream installations. Nevertheless, potentiometers and magnetostrictive sensors are still feasible solutions.