The value of the counter indicates the position of the object quantized to the resolution of the encoder. The simple counter approach does have a few drawbacks that are overcome by the Motion Capture card. These quadrature signals as they are called are either sent out of the encoder directly as analog sinewave signals or squared using comparators to produce digital outputs. To increase the resolution of the encoder, a method called interpolation is applied to either or both the sinewave or squarewave outputs. Interpolation typically results in an increased encoder resolution of 2 to 25 times the fundamental resolution of the glass disk.
Direction is derived by simply looking at the timing of the quadrature signals from the encoder.
A variation on the standard rotary encoder is the hollow shaft encoder. Hollow shaft encoders are self contained encoders without a shaft. Instead of coupling to a shaft to measure position, hollow shaft encoders simply mount over the shaft to be measured. Subsequently, hollow shaft encoders eliminate the resonance associated with couplings and simplify the difficulties of alignment. Linear optical encoders sense linear motion.