Simple chain extension indicator

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The sprocket's summar radius increases when a link extension occurs, as shown in the challenge picture. To detect this increase, you must determine the radius change somehow. An optical slot sensor (optical switch, optocoupler, etc.) is a simple solution; it consists of a transmitter and receiver that respond to beam interruptions caused by opaque external objects. For signal processing, a straightforward approach involves checking whether the beam is interrupted or not using a specific threshold determined by hardware characteristics, which activates the wear indicator via ladder logic without microprocessors. Alternatively, more in-depth processing can involve analyzing dip timing and amplitude, collecting statistical data, and distinguishing incidental triggers. While optical sensors are popular, magnetic or capacitive sensors may be less practical due to their small output signal changes relative to distance changes. Mechanical sensors could also be used, but the slow chain extension process requires thousands of link movements for each micron change in triggering direction, causing significant wear on mechanical contacts. Limit switches with rolling contact are an exception, but they too will wear over time, making their use impractical in many cases.