Rockwell Automation 1734-IK Encoder/Counter Modules User Manual - Manual (Page 13)

Publication 1734-UM006B-EN-P - August 2005
About the Modules 1-3
Example of Counter Mode
Encoder Mode
The encoder mode reads incoming pulses and returns a binary
number (0 - 16,777,215
max
) to the POINTBus. The encoder mode
only accepts 2 phase quadrature inputs. The module senses the
relationship between the 2 phases, and counts up or down
accordingly.
The two basic encoder types are absolute and incremental. A single
output incremental encoder is called a tachometer encoder. A dual
channel incremental encoder with one channel leading the other by
90
° is called a quadrature encoder.
A system using a quadrature encoder may include an optional zero
pulse, or index, serving as a reference mark for system reset. The
principal disadvantage of a system using incremental encoders is that
a power interruption causes the loss of position reference, so a system
must be reinitialized or returned to a known zero position.
Absolute encoders typically have higher speed requirements (200 KHz
typical) for motion control applications. An absolute encoder has a
unique code associated with each position, so the exact position is
always known, even if the system power is turned off.
A Input
B Direction
Z (Store Count)
Single Phase Pulse Generator
1734-VHSC
Input A
Input B
1 2 3
A Input
B Input
Count
(Gate / Reset )
2 1 0
Count Up Count Down
Input Z
0
Outputs
Updated
Continuously