Sensors are commonly utilized to provide positive feedback to control systems in automated equipment and machinery. Pneumatic cylinders use sensors that locate the linear position of the piston for applications where positive feedback is vital. The most common sensor used by the pneumatic cylinder is magnetic proximity sensors, which can locate the magnetic field of a magnet integrated into the cylinder piston. The sensor is usually attached to the body of the pneumatic cylinder, which will indicate ON or OFF based on how close it is to the magnet. Various types of proximity sensors can be used depending on the different types of applications. This is used to improve performance, space, and reliability.
Reed Sensors
The most common type of pneumatic cylinder sensor is known as the Reed sensor. It is a proven technology that has been used for many years. However, there are two main concerns associated with Reed sensors: lifetime and shock vibration concerns. Reed sensors have a lifetime of over 10 million, and when it is used in high shock or high vibration applications, it is not the first one to fail. Such reasons make reed sensors the most popular and effective pneumatic cylinder sensors.
Electromagnetic Sensors
There are commonly three types of electromagnetic sensors:
- Anisotropic Magnetoresistive (AMR)
- Giant Magnetoresistive (GMR)
- Hall-Effect (HE)
These are solid-state devices and utilize semiconductors instead of mechanical parts. Because of such reasons, they are easier to mount, longer-lasting, faster to react, and more resistant to shock and vibration. Electromagnetic sensors typically operate by converting a measurable physical quantity into an electrical output signal.
Why Use a Sensor for a Pneumatic Cylinder?
The linear position sensors of pneumatic cylinders are used to locate the linear position of the piston during operation. Pneumatic cylinders are typically constructed with a magnet already attached internally to the piston. This allows the use of magnetic proximity sensors if desired. The sensor can detect extension, retraction, or individual positions along the cylinder body depending upon where the cylinder is mounted. You can attach multiple sensors to one pneumatic cylinder for multiple position feedback locations. When pneumatic cylinders are used with position sensors, this adds more security and allows for feedback, ensuring the piston location for vital applications.
Choosing a Pneumatic Cylinder Sensor
Reed sensors, to this date, are the most popular sensors that are used in many applications. Their technology has worked for a long time, and they have excellent vibration resistance with a long-life cycle. For more specialized applications, you need to consider the environment in which your cylinder will be exposed. These considerations could include vibrations and shocks, extreme temperature environments, and the use of enclosed clean environments.
For solid-state devices, you need to consider the importance of switching speed to your application and the type of output signal that your control system requires, which could be PNP or NPN.
The type of sensor that you choose must have switching power and current requirements compatible with your system. It must also have the necessary circuit protections. Mounting options need to be considered depending upon the cylinder type and the magnet's orientation to the piston if you choose an HE sensor or a Reed switch.
It would be best to consider the power supply wired to the sensor because miswiring the sensor can permanently damage it. Reed switches usually have a two-wire configuration, whereas solid-state sensors use three-wire configurations.
