Evolving Sensor Technology: Smarter Solutions for Pneumatic Cylinder Position Detection

Modern pneumatic cylinders are compact, dependable, and cost-effective prime movers used in a wide range of automated equipment, including machinery, material handling, assembly lines, robotics, and medical devices. OEMs, integrators, and end users often struggle to reliably detect whether a cylinder is fully extended, fully retracted, or in an intermediate position – all critical information required before initiating machine movement.

A widely used method for detecting cylinder position is using magnetically actuated sensors. These are either mounted to the cylinder with brackets or inserted into a built-in slot on the cylinder body. The sensors detect the magnetic field of a magnet embedded in the moving piston, sensing it through the aluminum cylinder wall.

The choice of sensor depends on your application and the specific data you need to collect.

Magnetic sensor types

Reed switches

The reed switch is one of the simplest and most often used end-of-stroke sensors. It contains two flat, ferromagnetic reed elements (made of nickel and iron) sealed inside a glass tube. The hermetic seal protects the elements from moisture and reduces compact arcing. When a magnet aligned with the switch axis approaches, it magnetizes the reeds, causing them to attract and close the circuit.

AMR and GMR sensors

Most cylinder manufacturers and OEMs now use anisotropic magnetoresistive (AMR) or giant magnetoresistive (GMR) technology. Both types detect changes in magnetic resistance. A key advantage is their compatibility with axially magnetized magnets and, in some cases, radially magnetized ones as well.

GMR sensors are typically smaller than the AMR sensors, while offering greater sensitivity, precision, and improved hysteresis. Many models also include built-in protections against reverse polarity, overload, and short circuits.

Although AMR or GMR sensors may initially cost slightly more than reed sensors, the difference is minimal, especially when considering the cost of downtime resulting from reed switch failure. Unlike two-wire reed switches, AMR and GMR sensors are three-wire devices with no moving parts, making them a more durable and reliable long-term solution.

Position detection sensors for both C-slots and T-slots

Pneumatic cylinders typically feature either a C-slot or T-slot integrated into the cylinder body. Many sensors are designed with matching housing profiles, allowing them to be easily mounted – either by being dropped into the slot from above and secured with a screw, or by sliding in from the end if no end plate is present.

For round or tie rod cylinders, mounting brackets are available that can use either C-slot or T-slot sensors. This enables OEMs and end-users to use the same sensors across multiple applications, thereby reducing the number of part numbers and simplifying inventory management.

More options for piston positioning and sensor advancements

Today, more options are available than ever for detecting piston position in pneumatic cylinders, including a variety of sensor housing styles to fit different cylinder extrusions. Some now offer two sensors – one for the extended position and one for the retracted position, sharing a single four-pin connection. These magnetic sensors are also available now with weld field immunity for use in harsh welding environments.

Sensor technology has also advanced. You can now program modern cylinder sensors to trigger at specific points along the piston’s stroke. To set a switching point, the user simply moves the piston to the desired position and presses a button. This teachable sensor can also connect to IO-Link, allowing for up to eight configurable switching points for increased flexibility across various applications.

Over time, many users have moved away from reed switches due to their higher failure rates, opting instead for mechanical or inductive sensors to detect pneumatic cylinder position. AMR and GMR offer a better alternative: they are smaller, faster, easier to integrate, and significantly more reliable. Recent advancements in sensor technology make AMR and GMR sensors the preferred solution for cylinder position detection.