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Parker Hannifinvisit website position switches monitor hydraulic cylindersParker Hannifin is launching new position switches for providing a simple, accurate and reliable method of monitoring the stroke position of hydraulic cylinders, thereby enabling machine performance, functionality and productivity to be enhanced. magnetically-actuated switches are being introduced initially for use with Parker's high-performance HMI and 2H steel cylinders and will offer engineers an effective alternative to traditional and often unreliable position sensing mechanisms.

To date, the stroke position of hydraulic cylinders has generally been measured using external end-of-stroke limit switches, which are vulnerable to damage and cannot be used to indicate mid-point positions of the piston. Alternatively, double-rodded cylinders that trip mechanical switches, or external sensors activated by magnetic pistons inside aluminium or non-ferrous cylinders, can be used. These methods are, however, far from ideal. They can, for example, increase overall cylinder dimensions or be located in exposed positions where they can easily become misaligned, resulting in loss of accuracy; additionally, aluminium or non-ferrous cylinders have a relatively low pressure rating, which limits their potential application.

In contrast, the new Parker switch has been designed as a low-profile external device that can be used on conventional steel-bodied cylinders operating at full rated pressures.

How they work

Cylinders fitted with switch technology incorporate powerful magnets that are mounted around the circumference of the piston. During initial setup, the magnets are used to 'format' the cylinder body, simply by completing a full extension and retraction cycle of the piston, which imparts a residual magnetic field to the steel body. switches can then detect the position of the piston magnets as they pass beneath each switch, as the piston magnets create a stronger magnetic field with opposite polarity to that of the residual magnetism of the cylinder body. Each switch can therefore be located in the exact position required, with external red and yellow LEDs making it quick and simple to determine the precise sensing point before the switch is then locked firmly in place.

In operation, switches offer good repeatability, to within 0.5mm, and can be used with Parker's HMI and 2H cylinders at speeds of up to 0.5m/s and at pressures of 210bar. As the sensing point is at the end of the switch, it enables each device to provide absolute end-of-stroke positioning when used at the cap end of the cylinder and within a maximum of 3mm of the end of stroke at the head end; this level of performance is said to be equivalent to, or better than, most conventional end-of-stroke switches.

Unlike traditional methods of position sensing, single or multiple position switches can be placed anywhere along the stroke length and do not affect the overall dimensions of the cylinder. In addition, the non-contact design has no moving parts so a long and reliable operating life is assured, while setup, operation and, if required, reconfiguration are straightforward, with electrical output being via standard switch connectors.

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