Optical encoders are another way to sense rotational movement and are available as incremental encoders, where 2 pulse trains or 2 sine waves indicate that the wheel is spinning – the frequency of the signals corresponds to the speed and the lead/lag relationship between the 2 signals indicates the direction the wheel is turning. A third sensor can be added to indicate each full revolution. If the customer has a dirty wheel or loses power for a moment, bits of the signal can be missed and accurate readings for angular position will not have been obtained. To select an ADC for an incremental encoder, a customer will want to find one with 2 channels for the 2 light sources. Simultaneous sampling and high throughput rates are also important. Encoders resolution ranges from 100 pulses/rev to 5,000 pulses/rev or more.