Schematic

Connecting Sensors and Actuators to Input/Outputs
54 Advanced Digital Motor Controller User Manual V1.8, August 28, 2017
counter in the application. Quadrature encoders have dual channels, A and B, which are
electrically phased 90° apart. Thus, direction of rotation can be determined by monitoring
the phase relationship between the two channels. In addition, with a dual-channel en-
coder, a four-time multiplication of resolution is achieved by counting the rising and falling
edges of each channel (A and B). For example, an encoder that produces 250 Pulses per
Revolution (PPR) can generate 1,000 Counts per Revolution (CPR) after quadrature.
1 Pulse
= 4 Transitions
= 4 Counts
A Channel
Count Up Count Down
B Channel
Quadrature
Signal
FIGURE 3-16.Quadrature encoder output waveform
The figure below shows the typical construction of a quadrature encoder. As the disk ro-
tates in front of the stationary mask, it shutters light from the LED. The light that passes
through the mask is received by the photo detectors. Two photo detectors are placed side
by side at so that the light making it through the mask hits one detector after the other to
produces the 90o phased pulses.
LED light source
Stationary mask
Photodetector
Rotating
encoder disk
FIGURE 3-17. Typical quadrature encoder construction
Unlike absolute encoders, incremental encoders have no retention of absolute position
upon power loss. When used in positioning applications, the controller must move the
motor until a limit switch is reached. This position is then used as the zero reference for all
subsequent moves.
Recommended Encoder Types
The module may be used with most incremental encoder modules as long as they include
the following features:
• Two quadrature outputs (Ch A, Ch B), single ended
• 3.0V minimum swing between 0 Level and 1 Level on quadrature output
• 5VDC operation. 50mA or less current consumption per encoder
More sophisticated incremental encoders with index, and other features may be used,
however these additional capabilities will be ignored.
The choice of encoder resolution is very wide and is constrained by the module’s maxi-
mum pulse count at the high end and measurement resolution for speed at the low end.