Rockwell Automation 1771-IJ_IK IK ENCODER/COUNTER MODULES - Manual (Page 18)

2–6 Preliminary Adjustments
Publication 1771ĆUM006B-EN-P - June 2002
Table 2.D
Input Configuration Switch Assembly (1771ĆIK) SWĆ2
Switch 1 Switch 2 Switch 3
On PullĆup PullĆdown Filter in (50 Hz)
Off Float Float Filter out (50K Hz)
Certain counting devices may need an input designed to pull current
down through the device. Switch 2 should be set on for pull-down
and switch 1 left off. The module detects a minimum of 7.2V dc at
its input channels as true for a 12V dc external supply and 14.4V dc
at 24V dc external supply. A signal with a maximum voltage of
4.8V dc is considered false for a 12V dc supply and 9.6V dc is false
for a 24V dc supply. Each input channel sinks 10mA at 12V dc and
20mA at 24V dc.
If it is necessary to debounce a contact type of device, such as a
switch, the filter can be added across the inputs by setting switch 3
on. By adding the filter to the circuit, the maximum counting
frequency the module will detect is 50Hz.
Channel B input and the marker input are for open collector encoder
drivers (the channel B input has an internal pull-up) and are not
switch selectable. The marker input reads a signal as high true.
The limit switch input senses a voltage of greater than 10 volts dc as
a logic “1” (on), and less than 5 volts dc as a logic “0” (off). The
input voltage that appears through the switch should be from a 12 to
48V dc external supply that is capable of supplying 10mA of source
current at 48V dc. The limit switch input has a signal delay of 16 ms
(
+7ms) because of the filtering needed to protect against contact
bounce.
The channel B input can be used in the counter mode to select count
direction. If the channel B input terminal is not connected, the
control word in the output program selects the direction of the count.
For external hardware control, the count direction bit in the control
word must be set to count up.
Then if channel B is allowed to float high or is driven high, the
module counts up; if it is pulled low, either through a gate or a
transistor switch, it will count down. Any gate or switch should be
compatible with the external voltage supply (12 to 24V dc).