Encoder Modes - Allen-Bradley 1734-VHSC5 User Manual

[B = High, Count = Down; B = Low or floating (not connected), Count
= Up]
The Channel B input may be tied high or low for unidirectional
counting, or toggled for bidirectional counting.
EXAMPLE
Example of Counter Mode
Single Phase Pulse Generator
Count Up
A Input
B Input
Count
0 1 2

Encoder Modes

The encoder mode reads incoming pulses and returns a binary
number (0 - 16,777,215
accepts 2 phase quadrature inputs. The module senses the
relationship between the 2 phases, and counts up or down
accordingly.
There are two basic encoder types, 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.
About the Very High Speed Counter Modules
A Input
B Direction
Z (Store Count)
(Gate / Reset )
Count Down
3 2 1
) to the PointBus. The encoder mode only
max
Publication 1734-UM003A-EN-P - August 2000
1-3
Input A
Input B
Input Z
1734-VHSC
Outputs
Updated
Continuously
0