Use Cylinder Switches to verify completed motion, coordinate multiple actuators, count cycles, or simply to confirm operation. The use of 'timing algorithms' might seem like a way to save money, but they can cause a machine to crash if the air flow dips, or some other unexpected event causes a cylinder to delay or stop? With cylinder switches, the machine can always cycle as quickly as possible without fear of undesirable motion or mechanical conflict.
Cylinder switches are normally used at the ends of travel of the cylinder to signal that a particular motion is complete. These signals usually feed back to a PLC (or other controller) and are used to provide cylinder position indication, cycle count, or to confirm operation. It is also possible to use cylinder switches mid-stroke for more sophisticated operations. In the case packing example at right, cylinder switches are used to confirm the extension and retraction strokes of the two cylinders. If Cylinder B is not fully retracted before Cylinder A extends, then a crash will occur; cylinder switches are used to prevent this.
Cylinder switches require a magnetic piston in order to sense the piston position. Even if you aren't sure you will need a cylinder switch for a particular cylinder, it might be a good idea to spec the magnetic piston in case a cylinder switch needs to be added later.
The two basic types are Reed Switches and Electric Switches, see the chart below to understand why AutomationDirect doesn't sell Reed Switches.
|Case Packing Sequence|
|Cylinder A||Cylinder B|
|Return to Pos 1||Retract||Retract|
Two solid state magnetic sensing technologies used for pneumatic cylinder position are GMR (Giant Magnetoresistive) and AMR (Anisotropic Magnetoresistive). Both sensing technologies consist of layers of ferromagnetic material that change in electrical resistance when exposed to an external magnetic field. AMR based switches have a higher sensitivity and narrower sensing field compared to less expensive GMR based switches. AMR switches are a better choice for cylinders with short strokes.
NITRA cylinder position switches are available in 3-wire DC, PNP normally open, PNP normally closed, and NPN normally open electronic solid state configurations. Switches include integral cable with either an M8 or M12 wiring connector or wire leads. Integral LED indication provides switch status for speedy switch positioning and troubleshooting. Pre-tested for use with NITRA pneumatic cylinders, these switches are also suitable for use with other brands of cylinders with magnetic pistons.
|Reed Switch vs. AutomationDirect CPS Series Electronic Switch|
|Mechanical Reed Switch||AutomationDirect CPS Series Electronic Switch||Details|
|Durability||low (1-2 million cycles typical)||high (virtually unlimited number of cycles)||Reed switches can stick, break, bounce and are prone to wear|
|Repeatability||low||high||Mechanical wear of reed switches can lead to switch point drift|
|Response time||low||high||Reed switches have a slower response time than electronic switches, resulting in lower switch accuracy|
|Sensitivity to magnetic fields||low||high||Electronic sensors are more sensitive than reed switches, and operate reliably even with weak magnetic fields|
|Temperature stability||high||high||Both switch technologies are extremely stable over the entire temperature range|
|Longevity||low||high||Electronic sensors are insensitive to long term effects of magnetic fields, reed switches can become permanently magnetized over time.|
|Response sensitivity||medium||high||Electronic sensors have small hysteresis and are exceptional for short stroke cylinders|
|Price||low||low||Some vendors charge more for Electronic Switches. AutomationDirect offers electronic cylinder position switches at reed switch prices|
Cylinder position switches are available in many mounting styles with accessories to fit many different styles of cylinders or actuators. The switches are designed for general purpose applications on most popular cylinder brands with sensor grooves or slots, on round body cylinders using mounting bands or on tie rod cylinders using tie rod adapters. Stainless steel mounting bands are also available if needed for harsh duty applications.
Here are ALL the Cylinder Switches offered by AutomationDirect: