Fail-Safe Modules
7.5 4/8 F-DI DC24V PROFIsafe Digital Electronic Module
ET 200S Distributed I/O System - Fail-Safe Modules
Installation and Operating Manual, 08/2008, A5E00103686-07
129
Special Features of Fault Detection (Application 3.1 and 3.2)
The following table presents fault detection according to the sensor supply and the
parameter assignment for the short-circuit test:
Table 7- 23 EM 4/8 F-DI DC24V PROFIsafe: Fault Detection (Application 3.1 and 3.2)
Fault detection with internal sensor power supply and
activated short-circuit test for...
Example of fault
Sensor 2-channel equivalent Sensor 2-channel non-
equivalent
Short circuit in DI 0 with DI 1 Yes* Yes*
Short circuit in DI 0 with DI 4 Yes* Yes
Short circuit in DI 0 with DI 5 Yes* Yes*
P-short circuit in DI 0 Yes Yes
M-short circuit in DI 0 Yes* Yes*
Discrepancy error Yes Yes
P-short circuit in sensor supply 1 Yes Yes
M-short circuit in sensor supply 1, or
sensor supply 2 defective
Yes Yes
Short circuit in sensor supply 1 with
sensor supply 2
Yes Yes
Fault in read/test circuit Yes Yes
Supply voltage fault Yes Yes
*: Fault is detected only in case of signal corruption. In other words, the signal read differs from the
sensor signal (discrepancy error). If there is no signal corruption with respect to the sensor signal,
fault detection is not possible and is not required from a safety standpoint.
Requirements for Machine Protection Applications with Category 4
The following requirements apply for applications in machine protection with category 4:
● The wiring between sensors and automation system and between automation system
and actuators must be designed to state-of-the-art engineering and standards to prevent
short circuits
● All short circuits listed in the above table are covered. It is sufficient to locate a short
circuit, because two faults are required for it to occur (both signal lines in short circuit
have an insulation fault). A multiple short circuit analysis is not required.
Procedures for locating all short circuits are also permissible if single short circuits are not
located,
● provided these do not cause corruption of read signals compared to the sensor signals or
● provided they cause corruption of read signals compared to sensor signals in the
direction that ensures safety.
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