Siemens SLI-5310 Betriebsanleitung PDF herunterladen (Seite 25)

Safety-related position measuring system

Measured-value

acquisition

Data transmission line

Position values and error bits via

two processor interfaces

Monitoring functions

Efﬁ ciency test

Reception of measured values

Position 1

Position 2

(protocol and cable)

Serial data transfer

Two independent

position values

Internal monitoring

Protocol formation

EnDat interface

EnDat

master

Interface 1

Interface 2

Safe control

Catalog of measures

For more information on the topic of

functional safety, refer to the technical

information documents Safety-Related

Position Measuring Systems and Safety-

Related Control Technology as well as the

product information document of the

functional safety encoders.

Function

The safety strategy of the position measur-

ing system is based on two mutually inde-

pendent position values and additional er-

ror bits produced in the encoder and

transmitted over the EnDat 2.2 protocol to

the EnDat master. The EnDat master as-

sumes various monitoring functions with

which errors in the encoder and during

transmission can be revealed. For example,

the two position values are then compared.

The EnDat master then makes the data

available to the safe control. The control pe-

riodically tests the safety-related position

measuring system to monitor its correct

operation.

The architecture of the EnDat 2.2 protocol

makes it possible to process all safety-rele-

vant information and control mechanisms

during unconstrained controller operation.

This is possible because the safety-relevant

information is saved in the additional infor-

mation. According to EN 61 508, the archi-

tecture of the position measuring system

is regarded as a single-channel tested sys-

tem.

Documentation on the integration of

the position measuring system

The intended use of position measuring

systems places demands on the control,

the machine designer, the installation tech-

nician, service, etc. The necessary informa-

tion is provided in the documentation for

the position measuring systems.

In order to be able to implement a position

measuring system in a safety-related

application, a suitable control is required.

The control assumes the fundamental task

of communicating with the encoder and

safely evaluating the encoder data.

The requirements for integrating the EnDat

master with monitoring functions in the

safe control are described in the HEIDEN-

HAIN document 533095. It contains, for

example, speciﬁ cations on the evaluation

and processing of position values and error

bits, and on electrical connection and cyclic

tests of position measuring systems.

Document 1000344 describes additional

measures that make it possible to use

suitable encoders for applications up to

SIL-3, PL “e”, category 4.

Machine and plant manufacturers need not

attend to these details. These functions

must be provided by the control. Product

information sheets, catalogs and mounting

instructions provide information to aid the

selection of a suitable encoder. The

product information sheets and catalogs

contain general data on function and

application of the encoders as well as

speciﬁ cations and permissible ambient

conditions. The mounting instructions

provide detailed information on installing

the encoders.

The architecture of the safety system and

the diagnostic possibilities of the control

may call for further requirements. For

example, the operating instructions of

the control must explicitly state

whether fault exclusion is required for

the loosening of the mechanical

connection between the encoder and

the drive.The machine designer is obliged

to inform the installation technician and

service technicians, for example, of the

resulting requirements.

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