schmersal PSC1 - Safety-Related Assessment of the Encoder Types and Their Combination

Installation manual
HB-37420-810-01-25F-EN PSC1-C-100 Installation manual - V2.2.docx Page 70 of 201
Version: 25F
4.2.2.6 Safety-related assessment of the encoder types and their combination
Due to the monitoring functions implemented in the PSC1 series, in applications with encoder
systems there are initially no special requirements on the internal layout of the encoder
electronics, i.e. as a rule standard encoders can be used.
In general, a safety-related assessment of the overall arrangement is to be undertaken. During
this process the information from the manufacturer of the encoder (PFH, MTTF) as well as the
DC from the tables in 4.2.2 are to be used.
On the usage of individual encoders, as a minimum a fault exclusion is required for the
mechanical actuation chain as well as the single-channel part taking into account the applicable
specifications from EN ISO 13849-1. The information in 4.2.2 must also be followed.
PL d and higher according to EN ISO 13849-1 is in general achieved with a combination of two
encoders with essentially different technology and separate mechanical attachment.
The usage of a compact encoder with internal dual-channel layout with different technology is
just as suitable for applications up to PL e according to EN ISO 13849-1, however taking into
account the specific fault exclusions required and their admissibility. As a rule encoders with
proven safety-related properties should be used for this purpose; their safety level should
correspond as a minimum to the level required.
Safety instructions:
• The usage of standard encoders or a combination of standard encoders is permissible.
A safety-related assessment is required for the overall arrangement comprising
encoders, other sensors/switching elements for triggering the safety function, the PSC1
module and the shutdown channel. To determine the safety level achieved, among other
data the information from the manufacturer (PFH, MTTF) and the DC as per the
specifications in 4.2.2 is to be used.
• On the usage of only one encoder, the fault exclusion shaft fracture / fault in the
mechanical encoder connection is required. For this purpose suitable measures are to
be taken, e.g. positive locking of the encoder connection using a slot and key or locking
pin. The applicable information from the manufacturer as well as EN ISO 13849-1 in
relation to the requirement and admissibility of the fault exclusion
must be followed.
• Preferably, only encoders with proven safety-related properties may be used as
individual encoders. This encoder's safety level must correspond as a minimum to the
safety level required for the overall arrangement. The instructions from the manufacturer
in relation to diagnostic measures, mechanical connection and measures for the supply
of power are
to be followed.
• SIN/COS encoders: the internal layout of the sensor system must be designed such that
the output signals for both tracks are generated independently of each other and
common cause failures are excluded. In addition, the mechanical layout is to be verified,
e.g. fastening of the code disc to the shaft. Preferably, encoders with proven safety-
related properties are to be
used.