In today’s digitised environment, the integration of electronics allows engineers to control the motion of hydraulic cylinders with pinpoint accuracy. Hydraulic cylinder sensors make this possible by providing fast, accurate information on cylinder position at all times, which can be used to control and automate cylinder movement with extreme precision and reliability.
When it comes to hydraulic cylinder sensors, there are three main technologies to detect cylinder position which are: magneto-strictive sensors (MLDTs), potentiometric sensors, and variable inductance sensors (LVITs) sensors. In most cases, Hydraulic cylinder sensors usually consist of a long probe or wire inserted into a hole drilled into the end of the cylinder rod. In this article, we’ll discuss the different ways in which these devices detect cylinder position and the pros and cons of each technology.
Magneto-Strictive Hydraulic Cylinder Position Sensors
Magneto-strictive sensors (also known as LDTs or MLDTs) make use of a magnetic field and a phenomenon known as ‘torsional straining’ to give accurate cylinder position measurements. In this technique, short pulses of current are applied to a wire (the probe), and when this pulse of current reaches the location of the magnet it causes a tiny twist to occur, which travels back down the wire as a wave. The sensor measures the fraction of time it takes for each pulse to be sent and for the torsional wave to be received, which tells the sensor the distance of the magnet. This is a very accurate and fast way to determine the magnet’s position, which makes them perfect for applications in which accuracy is a must. On the downside, magneto restrictive sensors are quite sensitive to shock and vibration, which makes them vulnerable in certain applications.
Potentiometric sensors are a more cost-effective, but less accurate method of determining hydraulic cylinder position. These sensors work by measuring the level of resistance to current (the resistance of a conductor is directly proportional to its length). This system features a sliding contact which runs along a probe installed within the cylinder. The resistance of the contact determines where it is along the length of the probe. Thus, by measuring resistance, we can work out the extension of the hydraulic cylinder. Potentiometric sensors are very rugged and have a higher tolerance for shock and vibration. However, because some reciprocating components are in physical contact, this makes them more susceptible to wear and can be vulnerable and this may lead to increased maintenance costs in high-frequency applications.
Linear Variable Inductance Transducer Sensors
Linear variable inductance transducer (LVIT) position sensors have several benefits. They offer accuracy comparable to magnetostrictive sensors, but with better tolerance for shock and vibration, which makes them a great choice for mobile equipment, or fixed plant applications handling extreme forces. They are also more durable than variable resistance potentiometers since they do not come into contact with and reciprocating surfaces.
These sensors operate by applying a resonant frequency to the probe. This frequency is affected as the probe moves in or out of the hole in the hydraulic cylinder and by measuring this change, we can determine the position of the probe in relation to the cylinder. Which means we know the position of the cylinder itself.
As hydraulic system design and technology improves, new advantages are opening up that offer benefits to engineers and designers. These three hydraulic cylinder position sensor technologies offer different ways to exert pinpoint control over hydraulic cylinders. Considering the advantages and disadvantages of each technology and the requirements of the application, it’s up to the system designer to determine which technology is the best option.
Berendsen’s Engineering & Design team has extensive experience designing and commissioning real world hydraulic systems. If you’d like to know more about hydraulic cylinder sensors available, or if you have an application that requires a high level of hydraulic cylinder control, contact our E&D team.