The magnetic switch in pneumatic cylinders is essential for detecting the cylinder’s position and works in conjunction with solenoid valves to control the cylinder’s actions.
Function of Magnetic Switch in Pneumatic Cylinders
The magnetic switch in pneumatic cylinders is a specialized switch used to detect the position of the cylinder’s movement (such as fully extended or fully retracted). With the advent of magnetic switches, it is no longer necessary to set up limit switches and their mounting brackets at both ends of the cylinder’s stroke, nor is there a need to install a bump on the piston rod. Due to the convenience, high reliability, long lifespan, low cost, and fast response time of magnetic switches, they have become widely used.
Principle of Magnetic Switch in Pneumatic Cylinders
Commonly, cylinders are made from materials that have weak magnetism and strong magnetic shielding properties, such as metals like aluminum and stainless steel. When the cylinder operates, a magnetic ring attached to the piston moves along with it, providing a magnetic field that reflects the position of the cylinder piston.
The magnetic switch is installed on the external side of the cylinder. When the magnetic ring on the piston comes close to the magnetic switch, the switch will close as the piston reaches the position of the switch. Once the piston moves away from the magnetic switch position, the switch will open, thus indicating the position of the cylinder piston.
Currently, many magnetic switches utilize electronic components to create contactless switches, also known as active switches. These three-wire switches are more stable in performance and have a longer lifespan. The three-wire switches are divided into PNP and NPN types.
Characteristics of Magnetic Switch in Pneumatic Cylinders
| Space-saving Installation: Since the magnetic switch can be directly mounted on the cylinder, it does not require extra mounting space like limit switches, thus saving space.
| Simple Position Adjustment: Position adjustments for magnetic switches are simpler and easier compared to limit switches.
| Influenced by Surrounding Magnetic Fields: Because magnetic switches operate based on magnetic fields, strong magnetic fields in the vicinity can lead to false triggering of the switch.
Selection of Magnetic Switches
Based on usage experience, careful consideration can be given to the following three aspects:
| Load Voltage Specifications: Choose whether to use DC 24V or AC 220V; the most commonly used is DC 24V.
| Switch Wiring Type: Determine if the switch is a two-wire or three-wire type; the three-wire type includes both PNP and NPN configurations.
| Cylinder Type: When selecting a magnetic switch, consider the type of cylinder, as the magnetic switch is mounted onto the cylinder, which helps in deciding the installation form of the magnetic switch, whether it be bracket mounting, ring mounting, or track mounting.
Considerations for Magnetic Switches in Pneumatic Cylinders
| Vulnerability to Impact: Compared to limit switches, magnetic switches are less resistant to shock. Avoid dropping objects that could hit the switch and do not apply excessive impact forces. Additionally, because magnetic switches operate through magnetic fields, they should not be used in areas with strong magnetic fields to prevent false triggering. When using two or more cylinders with magnetic switches close, maintain a distance of more than 40mm between the cylinders.
| Cylinder Piston Speed: Setting the magnetic switch at a midpoint in the stroke for detecting the piston can be important. If the piston moves too quickly, even if the magnetic switch activates, the action time may be shortened, potentially preventing the load from fully acting.
| Operating Voltage: Ensure the magnetic switch operates within the specified voltage limits. Common operating voltages include DC 24V and AC 100V. For two-wire setups, the power supply voltage is the same as the load voltage.
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