The third way to monitor conveyor speed is to attach an encoder to an encoder measuring wheel that rides on the surface of the belt or one of the rollers if the belt itself is crowded with product. Typically, these wheels are 1 foot in circumference, which makes an easy conversion from RPM to linear speed in feet per minute.
It is important to remember that a follower wheel is a mechanical assembly and can degrade accuracy. Error sources include misalignment and slippage between the wheels and the surface being measured. Applying preload helps prevent that slip but increases bearing wear. Finally, the follower wheel itself can wear, particularly in the case of misalignment. To address this particular problem, some encoder measuring wheels feature dual o-rings on the circumference that can be replaced when necessary, extending the lifetime of the wheel itself. And remember, the follower wheel, not the performance of the encoder, is the limiting error source.
Synchronizing the speed of one conveyor belt with another requires multiple encoders and a master-slave architecture. The motor has an encoder mounted to the shaft as described above. The slave conveyor has an encoder mounted to a shaft originating from a set of rollers on the secondary conveyor. Both encoders are wired back to the controller.
The assembly on the slave controller is purely a feedback system. With that input, the controller can monitor any speed differential between the primary conveyor belt and the secondary conveyor belt. Any time that difference exceeds tolerance, the controller can command the drive to speed up the motor until the speed of the primary belt matches that of the secondary belt.