Machine Design

Scanning for ideas: Lights gauge rod position

Reed switches are widely used to measure how far a pneumatic or hydraulic cylinder extends or retracts.

But these switches are prone to failure and aren’t very precise. An alternative, Insight from Motion Controls LLC, Hartford, Wis. (, uses what the company calls quantum volumetric light absorption to determine a rod’s position. The technology places an LED and a light-to-voltage converter or photocell in the bottom of the cylinder. The

Lights gauge rod position amount of light the converter picks up, and therefore its output voltage, is a function of how much reflective surface area there is inside the cylinder, and the amount of reflective surface function of the rod position.

Users can easily set the rod’s travel points using a keypad built into the bottom of the cylinder. And cylinders can be aluminum, steel, stainless steel, and a variety of other metals and composites.

The technology works in pneumatic and hydraulic cylinders. There are no magnets or coils, and it generates little electrical noise, so it is immune to EMI problems from welding. The technology is available on the company’s 1.24, 2.0, and 2.5-in. non-NFPA D Series cylinders and NFPA K Series of 1.5, 2.0, and 2.5-in. cylinders.

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