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Control measures (safety functions):
• Safe torque off (STO)
• Safe disconnection of the energy supply (SEC)
• Prevention of unexpected start-up (PUS)
Input
Triggering event:
• Light grid interrupted or interlocked safety doors open or not kept closed
Logic
Evaluation of the safety function:
• Switching off the energy supplies
Output
Safety-directed response:
• Disconnection of fluid power supply: PL
and of electrical energy supply: PL
I
L
1
2
3
Fig. 12: Safety-related block diagram, example 3
1
Safety door switch (e.g. PILZ PSEN cs3.1 or PSEN sl-0.5p 1.1)
2
Safety module (e.g. PILZ PNOZ)
3
PLC (programmable logic controller)
4
electrical part of the AV valve system, UA supply via electrical supply plate
For this block, fault exclusion is possible (see
5
Directional valves of the AV valve system
6
Main air valve with position detection (e.g. IS12-PD, ...)
7
Diagnosis "Query of the position of the main air valve"
8
Diagnosis "Valve voltage UA is lower than switch-off voltage (UA < UAoff)"
If fault exclusion is applied for (4), this diagnosis is not required.
3.6.1 Fault exclusion
If the valve system is set up and used as described in the following chapters, the
valve electronics do not have to be included in the calculation of the MTTF values
of a safety-related control chain.
Prerequisite for the application of the fault exclusion is,
• that PL d is applicable as a maximum (PL e must be calculated as in exam-
ple 1),
• that the valve system is built with 1 or more electrical supply plates,
• that the valves which are to be switched off are supplied via these electrical
supply plates,
• that the electrical supply plates are wired according to the wiring concepts 1–
3,
• that the cable for connecting the supply plate contains only the 24 V supply
voltage UA,
• that the cable is laid in accordance with DIN EN 60204.
AVENTICS™ AV | R412018148-BAL-001-AB | English
≥ d => 2-channel
r
≥ d => 2-channel recommended
r
O
4
5
6
7
8
g 3.6.1 Fault
exclusion)
1
2
3
3
1
2
Fig. 13: Valve system and external components
1 Bus coupler
3 Valves (not in the safety circuit)
5 Pneumatic supply plate, - no monitor-
ing (UAoff) required, no active elec-
tronics installed
7 Safety module, corresponds to block
2 in the safety-related block diagram
3.7 Overview of various options for supply
Table 4: Various options for supply
UA supply via bus
coupler
Maximum achievable
b
PL
r
Is fault exclusion pos-
no
sible
Evaluation of diagno-
yes (UAon and UAoff
sis
of bus coupler)
DC
90 % ... < 99 %
Inrush current limita-
yes
tion
Testing possible
no
(cross-circuit)
Inrush current limitation
The very high inrush current of the unit, as normally present with capacitive
loads, is limited to a value of 5 A maximum.
Definition of test pulse
A test pulse is a time-limited change of a signal voltage level to check the func-
tionality of the output or device or to check the transmission path.
[Source: ZVEI - Zentralverband Elektrotechnik- und Elektronikindustrie e.V., Posi-
tion paper "Classification of binary 24 V interfaces with testing in the field of func-
tional safety"]
Testing possible
Safe outputs and/or safety modules generate clock signals or test pulses on their
outputs. If such an output is connected to the electrical supply plate, there is no
misinterpretation of the cross-circuit test. If such an output is used for the UA
supply at the bus coupler, this leads to a misinterpretation of the cross-circuit
test.
Comment
Only the transmission path up to the electrical supply plate can be checked.
3.8 Assignment of the supply voltages in the valve system
The following figure shows the assignment of the supply voltages to the func-
tions within the valve system.
• The UL supply voltage fed to the bus coupler (1) supplies the complete elec-
tronics of the valve system.
• The supply voltage UA fed to the bus coupler supplies the outputs of the DO
module (6) (digital output) and all valves between the bus coupler and UA
supply.
4
5
6
5
6
4
7
7
8 8
2 Pneumatic supply plate
4 Electrical supply plate - corresponds
to block 4 in the safety-related block
diagram
6 Valves (safety circuit) - corresponds
to block 5 in the safety-related block
diagram - the electrical part of the
valves (valve driver) corresponds to
block 4 in the safety-related block di-
agram
8 Main air valve corresponds to block 6
and 7 in the safety-related block dia-
gram
UA supply via electrical supply plate
e
PL
≤ d: yes
r
PL
= e: no
r
PL
≤ d: no
r
(not necessary due to fault exclusion)
PL
= e: yes (UAon and UAoff)
r
Pneumatic supply plate must be equipped
with UAoff monitoring.
90 % ... < 99 %
yes
yes
20
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