Position Sensing Hydraulic Cylinders

Position feedback sensors, used for hydraulic and pneumatic cylinders, have a multitude of uses in technologies today. Most commonly, cylinder position sensors are utilized in magnetostrictive (MLDTs), variable resistance (pots), and variable inductance sensors (LVITs). While they can be found in other sensor technologies, hydraulic cylinders with piston sensors are most commonly found in these three technologies and are the ones you are most likely to run into in your practice.

When implementing these cylinder sensor technologies, a systems integrator must determine the needs of the application and what technology will be best suited, considering installation costs and performance basis. With the strengths and weaknesses of all three types of position-sensing hydraulic cylinders, we are comparing the three to help you decide when repairing hydraulic cylinders. Let’s dive right in.  

How Do the Cylinder Position Sensors Work?

The three hydraulic cylinder position sensor options operate in different ways. Their differences are best suited for various applications. Here's how they each sensor hydraulic cylinders.

LDT Hydraulic Cylinder Sensors

Magnetostrictive sensors, referred to as LDTs or MLDTs, use a magnetic field and torsional straining to provide cylinder position measurements. For this process, short pulses of current are applied to the probe, and when the current reaches the magnet, it causes twists to occur. These twists travel back down the probe as a wave, at which point the sensor measures the time it takes for each pulse to be sent and the wave to be received to sense the distance of the magnet.

Potentiometric Cylinder Sensors

Potentiometric sensors are a more cost-effective solution, but also a bit less accurate when determining position. These sensors operate by measuring the level of resistance to the current. This system relies on a sliding contact that runs along the probe installed in the cylinder, with the resistance of the contact determining where it is along the probe.

LVIT Sensors

Linear variable inductance transducer (LVIT) sensors have accuracy comparable to LDTs, but with more tolerance for shock and vibration. This is ideal for mobile equipment and is more durable than variable resistance potentiometers as they don’t come in contact with the reciprocating surfaces.

These sensors work by applying resonant frequency to the probe. As the probe moves in or out, the frequency is affected and the change is measured to determine the position of the probe as it relates to the cylinder.

Which Position Sensor Is Best for Your Application?

To ensure the most accurate sensing capabilities, selecting the best hydraulic cylinder sensor for your system is essential. Here’s where each is best utilized.

LDT/MLDT Sensors

The magnetic position sensor for hydraulic cylinder uses is usually preferred in high-accuracy applications. These sensors use a stainless-steel tubular probe and a short cordial permanent magnet installed in a counterbored recess in the piston. Typically, the sensor's electronic housing is threaded into an O-ring port at the back of the cylinder, with the probe inserted into the rod’s bore. Using the “time of flight” principle, this sensor determines position with high accuracy and moderate response time.

In practice, a torsional mechanical pulse is reflected using the magnet, reflecting along a wire inside the probe. With this process, the LDT sensor uses a small amount of power and can withstand a good amount of shock and vibration issues.

Potentiometric Sensors

Variable Resistance Potentiometers, referred to as pots, are used when the budget is a bigger consideration and accuracy isn’t as pressing. With this sensor, a resistance pot is embedded into the rear end cap of the cylinder and uses an insulated round carrier attached to the end of the cylinder rod. This supports an electrically conductive wiper that contacts the surface of the plastic probe, and as it moves, the resistance changes. With linear changes, it makes it simple to find the carrier’s position, and subsequently, the rod.

While their ruggedness is a big perk, these sensors are prone to wear out, especially when used at a high frequency.

LVIT Cylinder Sensors

A linear position sensor hydraulic cylinder (LVIT) operates by measuring the oscillator circuit of an inductive probe’s relative frequency. The probe's inductance is buried based on the position of the gun-drilled rod. These sensors are highly regarded as a middle ground between the two aforementioned sensors, with a high level of performance and better ruggedness, all at a more affordable price.

Conclusion

With different hydraulic position sensor options to choose from, which is right for your system? At Cylinders, Inc, an expert sensor cylinder repair company, we can assist in finding the right sensor for your cylinder, replacing an old one, or implementing a new sensor to help your hydraulic cylinders run smoothly.

For more information on our cylinder position sensors and repair offerings, contact us today.