Today's cylinder is a compact, reliable and cost-effective prime mover used in automation equipment. They are used in many applications such as mechanical, material processing, assembly, robotics, and medical. One challenge faced by original equipment manufacturers, integrators, and end users is how to detect reliably whether the cylinder is fully extended, retracted, or positioned at some intermediate point before allowing machine movement. One widely used method for cylinder position detection is to use brackets to connect magnetic inductive switches or sensors to the side of the cylinder, or insert them into the slot extruded from the cylinder body. Magnetic field sensors detect internal magnets mounted on the moving piston through an aluminum cylinder wall. The choice of which type of magnetic sensor to use depends on your application requirements and specific data needs.
Reed switch cylinder sensor
The reed switch cylinder sensor is the simplest and most commonly used end-of-stroke sensor on the market. It consists of two flat ferromagnetic nickel and iron reed elements encapsulated in a sealed glass tube. The tube helps to minimize contact arcing and prevent moisture ingress to the switch elements. When a magnet axially aligned with the switch element approaches, the reed element is magnetized and attracted together to complete the circuit.
AMR and GMR cylinder sensors
Most cylinder sensor manufacturers and OEMs use electronic sensors employing either anisotropic magnetoresistance (AMR) or giant magnetoresistance (GMR) technologies. Both versions are based on resistance changes. One advantage of these sensors is that they can work with axially magnetized magnets, and in some cases, also with radially magnetized magnets. GMR sensors can be physically smaller than AMR sensors. They are more sensitive, more accurate, and have better hysteresis. Versions exist that offer reverse polarity protection, overload protection, and short circuit protection. The initial cost of an AMR or GMR sensor may be slightly higher than a reed sensor, but this cost is decreasing, especially when you calculate the downtime cost of a reed switch failure. AMR and GMR sensors are also three-wire devices, unlike two-wire reed switches. Finally, AMR and GMR sensors are a better solution because they have no moving parts and their lifespan is typically much longer than that of reed switches.
Cylinder position detection sensors for C-shaped and T-shaped slots
Cylinders often feature C-shaped or T-shaped slots in the extrusion of the cylinder body. Many sensor housings have the same outer profile, and cylinder sensors can be either dropped into the slot from above and secured with screws, or slid in from the end of the cylinder body, provided there is no end plate. For round oil cylinders or tie-rod cylinders, additional brackets can be provided that allow the use of C-shaped or T-shaped slot sensors. This allows end users and OEMs to use the universality of the sensors to meet the needs of many applications and reduce the number of sensor components and stock.
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