Rockwell Automation 1771-VHSC , D17716.5.74 Very High S - Manual (Page 64)

Application Considerations C–7
Electromechanical Limit Switch
When using an electromechanical limit switch (the lower circuit in
Figure C.3), you must connect the low speed limit capacitor (C4)
using jumper JPR11. The RC time constant of R31 and C4 will filter
out switch contact bounce. However, this limits the frequency
response to around 100Hz. This circuit would be similar when using
dc proximity switches, but bounce should not occur unless severe
mechanical vibration is present. In either case, source impedance is
very low. If you are using a +12 to +24V power supply keep jumper
JPR8 in the circuit to add the additional 1K impedance.
!
ATTENTION: While the transistor protection circuit
limits the optoisolator current to a safe value, make
certain that the voltage range jumper JPR9 is not in the
circuit. With JPR9 in, you can exceed the 1 Watt
dissipation rating on the 150 ohm resistor (R4) and
cause permanent damage to the circuit.
The 1771-VHSC module contains 4 isolated pairs of output circuits.
Customer supplied power, ranging from +5V to +24V dc, is
connected internally (through terminal Vcc) to the power output
transistors. Refer to Figure C.4.When an output is turned on, current
flows into the drain, out of the source, through the fuse and into the
load connected to the ground of the customer supply (customer
return). Diodes D28 and D32 protect the power output transistors
from damage due to inductive loads.
If local electrical codes permit, outputs can be connected to sink
current. This is done by connecting the load between the power
supply + terminal and the customer Vcc terminal on the field wiring
arm. The output terminal is then connected directly to ground
(customer return). Note that this wiring method does not provide
inductive load protection for the power output transistors.
Figure C.4
Output Circuit Diagram
Q14
Q15
F1
F2
D28
D32
25
26
27
28
Customer
Vcc
Out 0
Out 1
Customer
Return
Drive
Circuit
G
G
S
S
D
D
10693ĆI
Output Circuits