Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 65)

Application Considerations C–8
A successful installation depends on the type of input driver, input
cable length, input cable impedance, input cable capacitance,
frequency of the input.
The following provides information on these installation factors for
the 1771-VHSC module.
Input Cable Length
Maximum input cable length depends on the type of output driver in
your encoder, the kind of cable used, and maximum frequency at
which you will be running. With a differential line driver, 250 feet or
less of high quality, low capacitance cable with an effective shield,
and an operating frequency of 250KHz or less will likely result in a
successfully installation.
If you use an open collector, or other single-ended driver, at
distances of 250 feet and frequencies of 250KHz, your chances of
success are low. Refer to the table below for suggested desirable
driver types.
Desirable Adequate Undesirable
5V Line Drivers: such as
DM8830,
DM88C30,
75ALS192 or
equivalent
Balanced SingleĆEnded: any AC or ACT family part
or
Discrete, balanced circuit
or
OpenĆCollector: suitable for frequencies of < 50KHz
Standard TTL or
LSTTL Gates
TotemĆpole Output Devices
Standard TTL totem-pole output devices, such as 7404 and 74LS04,
are usually rated to source 400 microamps at 2.4V in the high logic
state. This is not enough current to turn on a 1771-VHSC input
circuit. If your present encoder has this kind of electrical output
rating, you cannot use it with the VHSC module.
Most encoder manufacturers, including Allen-Bradley, offer several
output options for a given encoder model. When available, choose
the high current 5V differential line driver.
Application
Considerations