Siemens Sinumerik 840D Series Function Manual page 35

10.03
Fail-safe position
Pin assignments
 Siemens AG, 2003. All rights reserved
SINUMERIK 840D/SIMODRIVE 611 digital, HLA Module (FBHLA) - 10.03 Edition
Directly-controlled servo solenoid valves have a fail-safe position, i.e. the control
spool moves to a safe position when the valve is disconnected from the power
supply. The fail-safe position is either "closed" (A, B, P, T disabled) or "open" (A,
B and T connected and P disabled). It should be noted that the "crossed"
switching position is necessarily passed when the valve is switched on and off,
and there can be temporary responses from the cylinder at these moments.
Separate shut-off valves are therefore required in order to implement safety
functions, such as a totally safe cylinder stop.
Pilot-controlled servo solenoid valves, pilot-controlled HR servo solenoid valves
and directly-controlled HR servo solenoid valves do not have a fail-safe position
and thus do not have a safe basic position when switched off. Any safety func-
tions nmust therefore be implemented via separate shut-off valves.
Fail-safe closed
O B
P T
Fig. 2-10 Fail-safe position in the valve graphical symbol
A distinction must be made between servo solenoid valves and HR servo sole-
noid valves.
S
Servo solenoid valves (directly and pilot-actuated): 7-pin round connector
O
B
C
D
100k
I
100k
F
10k
Fig. 2-11 Connector pin assignment on servo solenoid valves
2.3 Configuring the hydraulic drive
Fail-safe open
O B
P T
2.5 AF
+24 V=
Supply
0 V
Reference point for actual
0 V
valve spool value
Setpoint 0..."10 V
Sign.
Actual value spool value
Protective
conductor
Shield
2 Configuration
2-35