Automating Manufacturing Systems - Process Control and ...

continuous sensors - 23.7
Quad input A
clockwise rotation
Quad Input B
Note the change
as direction
is reversed
total displacement can be determined
by adding/subtracting pulse counts
(direction determines add/subtract)
Quad input A
counterclockwise rotation
Quad Input B
Note: To determine direction we can do a simple check. If both are off or on, the first to
change state determines direction. Consider a point in the graphs above where both
A and B are off. If A is the first input to turn on the encoder is rotating clockwise. If
B is the first to turn on the rotation is counterclockwise.
Aside: A circuit (or program) can be built for this circuit using an up/down counter. If
the positive edge of input A is used to trigger the clock, and input B is used to drive
the up/down count, the counter will keep track of the encoder position.
Figure 23.5
Quadrature Encoders
Interfaces for encoders are commonly available for PLCs and as purchased units.
Newer PLCs will also allow two normal inputs to be used to decode encoder inputs.