Rockwell Automation 1771-PM , D17716.5.18 U MNL 1771-PM CLUTCH/BRAKE MOD - Manual (Page 56)

Field Wiring Arm Connections
Chapter 6
6Ć4
Install at least one E-Stop switch at each operator station. Then, any
operator who sees a problem can press an E-Stop switch to stop the press.
Also when either voting processor detects a fault, it de-energizes its seal
relay to stop the press.
Opening any E-Stop switch or de-energizing either seal relay removes AC
power (3L1) from main valve solenoids A and B, auxiliary valve
solenoids A and B, dump valve solenoids A and B, crowbar relays A and
B, and seal relays A and B, as shown in Figure 6.1, Figure 6.3 and
Figure 6.4 or Figure 6.5, Figure 6.7 and Figure 6.8. When either voting
processor detects that 3L1 is off, it immediately commands its seal relay
to remain de-energized. If either voting processor detects that 3L1 is still
on after commanding its seal relay to de-energize, it energizes its crowbar
relay. This shorts 3L1 to 3L2, which blows the 3L1 and 3L2 line fuse or
fuses.
Crowbar tests inputs, shown in Figure 6.1 or Figure 6.5, allow the voting
processors to test their crowbar relays without blowing the 3L1 and 3L2
line fuse or fuses. This test occurs while you push the START button
shown in Figure 6.1 or Figure 6.5.
To allow for the crowbar test, you should press the START button
(break-before-make pushbutton switch) for more than one-half second.
As you begin pressing the START button, its two sets of N.C. (normally
closed) contacts open first, isolating crowbar A and B relay contacts from
3L2. As you press the START button all the way in, its N.O. (normally
open) contacts close, applying 3L1 power to module group 3, slot 0.
Before you release the START button, each voting processor briefly
energizes its crowbar relay and checks, through its crowbar test input, that
the relay turns on then off. Each voting processor energizes its seal relay
only after its crowbar relay is tested as working correctly. At any time
after you release the START button, either crowbar relay can blow the
3L1 and 3L2 line fuse or fuses shown in Figure 6.1 and Figure 6.5.
Crowbar Test Inputs