The 803-B4RB Rotating Cam Limit Switch with Speed Reducer Option is a circuit control device by Allen-Bradley. It is used for control of industrial machines with dedicated cycles of operation, and in applications where the operation motion correlates with the shaft rotation. The 803-B4RB uses a shaft-mounted cam, which actuates contact as the shaft rotates for operation, and it is built for industrial applications like punch presses, injection molding, waterway gate/lock operations, and steel forming/heavy metals. It has 4 control circuits with 10A (1 NC, 1 NO) snap action contact, a spring-loaded cam-roller, and a rotating shaft with over-sized ball bearings, and a base speed of 150 RPM. The 803-B4RB also has 4 independently-operated cams with variable higher and lower cam segments (lobes and valleys), which activate and deactivate the circuit as the shaft rotates. The circuit is activated as the cam lobes push against the cam roller assembly, and the duration of the cam activation (dwell time) solely depends on the size of the cam lobes.

The circuit deactivates as the cam valley passes through the cam-roller. The timing that is measured in degree is the moment the rotating cam activates the circuit, and it is determined by the position of the rotating cam on the shaft, with reference to the Top Dead Center (TDC). The 803-B4RB has both internal timing and dwell time adjustments, which is only done when the machine stops, and like the standard Style B series devices, it comes with a left shaft extension. The 803-B4RB also comes with a speed reducer modification, with a 60:1 gear ratio, and a cast iron side plate, built specifically for the ruffed industrial condition. It has a -30 to 66 degrees Celsius (-22 to 150 degrees Fahrenheit) factory-designated operating temperature range, with a storage temperature range of -30 to 93 degrees Celsius (-22 to 200 degrees Fahrenheit), and it comes in an indoor-rated NEMA Type 1 enclosure. The 803-B4RB has CE, CSA, and UL certifications, and weighs about 10.9 kilograms (24 pounds), with an aggregate volume of 144.5 x 82.6 x 177.8 millimeters (5.69 x 3.25 x 7 inches).