Technical Information

Safety-Related Position Measuring Systems

with purely serial EnDat 2.2 interface for safety-related applications with up to control category SIL 3(according to EN 61508) or performance level PL e (according to EN ISO 13849)
HEIDENHAIN offers encoders that can be used in safety-related applications. These encoders operate as single-encoder systems withpurely serial data transmission via EnDat 2.2. Reliable transmission of the position is based on two independently generated absolute
position values and on error bits, which are then provided to the safe control.
In addition to rotary encoders with different mounting options, absolute sealed linear encoders are also available. Absolute angle encoders
round out HEIDENHAIN’s product program for functional safety.
Safety is becoming increasingly importantin machine and plant construction. Proof ofthis can be seen in new legislation and in
the heightened safety regulations ofnational and international standards. Thesehigh requirements mainly serve to protect
human beings, but material assets and theenvironment are also receiving moreconsideration.
The aim of functional safety is to minimize
or remove hazards that may arise during
both undisturbed and disturbed operationof machine tools and systems. This isachieved primarily with redundant systems.
For example, axes that are moved in safetyrelated applications require redundant
position information in order to perform thecorresponding safety functions. Various
system configurations can be realized inorder to acquire independent position
values. One possibility is the use of two
encoders per axis. In many cases, however,a more economical solution requiring only
one position encoder is preferred. Until
now, analog encoders with sine and cosine
signals were used for this. HEIDENHAIN
offers a purely serial, single-encoder solution
for safety-related position measuringsystems in safety-oriented applications inaccordance with EN 61508 and EN 13849.
This means that safety applications can
now take advantage of all the benefits ofserial data transfer, such as optimization ofcosts, diagnostic possibilities, automaticcommissioning, and rapid formation of theposition value.

11/2019

HEIDENHAIN measuring systems forsafety-related applications are tested forcompliance with EN ISO 13849-1 (successorto EN 954-1) as well as EN 61508 andEN 61800-5-2. In these standards, theassessment of safety-related systems isbased on, among other things, the failure
probabilities of integrated components
and subsystems. This modular approachhelps manufacturers of safety-oriented

systems to implement their complete
systems, because they can begin withsubsystems that have already been qualified.
Safety-related position measuring systems
with purely serial data transmission via
EnDat 2.2 accommodate this technique.
In a safe drive, the safety-related position
measuring system is such a subsystem.

Safety-related position measuring systems

A safety-related position measuringsystem consists of:• Encoder with EnDat 2.2 transmission
component• Data transfer line with EnDat 2.2
communication and HEIDENHAIN cable• EnDat 2.2 receiver component with
monitoring function (EnDat master)In practice, the complete “safe servodrive” system consists of:• Safety-related position measuringsystem• A safety-related control (including theEnDat master with monitoring functions)• Power stage with motor power cableand drive• Physical connection between encoderand drive (e.g. rotor/stator connection)Safety-related position measuring system

Area of application
Safety-related position measuring systems
from HEIDENHAIN are designed to beusable as single-encoder systems inapplications with control category SIL 2 (asper EN 61508), PL d, Category 3 (as perEN ISO 13849).
Additional measures in the control make itpossible to use certain encoders for applications with up to SIL 3, PL e, Category 4.
The suitability of these encoders is indi­cated appropriately in the documentation(brochures / Product Information documents).

The control monitors the functionality ofthe safety-related position measuringsystem through periodically triggered tests.
The architecture of the EnDat 2.2 protocol
makes it possible to process all safetyrelevant information and control mechanisms
during unconstrained controller operation.
This is possible because the safety-relevant
information is saved in the additional
information. According to EN 61508, thearchitecture of the position measuringsystem is regarded as a single-channel
tested system.

Function
The safety strategy of the position
measuring system is based on two mutuallyindependent position values and additional
error bits produced in the encoder andtransmitted over the EnDat 2.2 protocol tothe EnDat master. The EnDat masterassumes various monitoring functions withwhich errors in the encoder and duringtransmission can be revealed. A comparison
is made, for example, between the two
position values. The EnDat master thenmakes the data available to the safe control.

EnDat masterDrive motor

Safe control

EncoderPower cable

The functions of the safety-related position
measuring system can be used fornumerous safety tasks of the completesystem (see also EN 61800‑5‑2).

Power stage

Complete safe drive system

Measured-valueacquisition

Data transmission line

Reception of measured values

In addition to the safety-related position
measuring systems with EnDat 2.2
interface, HEIDENHAIN also offers
safety-related encoder solutions forapplications with DRIVE-CLiQ1) interface.
For details, please refer to the respective
product documentation.
Upon request, HEIDENHAIN can provide
additional data about the individual
products (failure rate, fault model as per
EN 61800-5-2, D16) for the use of standard
encoders (e.g., with 1 VPP output signals)
in safety-related applications.
1)

 RIVE-CLiQ is a registered trademark ofD
Siemens Aktiengesellschaft

Position 1

Position 2

EnDat interface

Safe control

EnDat 2.2
(protocol and cable)

Interface 1
EnDatmasterInterface 2

Catalog of measures

Two independent
position values

Serial data transfer

Position values and error bits
(e.g., via two processor interfaces)

Internal monitoring

Monitoring functions

Protocol formation

Efficiency test

Safety-related position measuring system

Documentation regarding integrationof the position measuring system
The proper use of a position measuringsystem places demands on the control, themachine designer, the installation technician,servicing personnel, etc. The needed
information 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 taskof communicating with the encoder andsafely evaluating the encoder data.
The requirements for integrating the EnDat
master with monitoring functions into thesafe control are described in HEIDENHAIN
document 533095. It contains, for example,
specifications on the evaluation andprocessing of position values and error bits,
and on electrical connection and cyclic testsof position measuring systems.
Supplementing this, document 1000344
describes measures that enable the use ofsuitable encoders in applications with up to
SIL 3, PL e, Category 4.
Machine and equipment manufacturers
need not attend to these details themselves.
This functionality must be provided by thecontrol. Product Information documents,
brochures, and mounting instructions
provide information to aid in the selectionof a suitable encoder. Product Information
documents and brochures contain general
information on the function and applicationof encoders, as well as specifications
and permissible ambient conditions. The
mounting instructions provide detailed
information about installing the encoders.

The architecture of the safety system andthe diagnostic possibilities of the control may
call for further requirements. For example,
the operating instructions of the control must
explicitly state whether fault exclusion isrequired for the loosening of the mechanicalconnection between the encoder and thedrive. Any resulting requirements must berelayed by the machine designer to theinstallation technician and the servicing
staff, for example (also see the information
under "Safety-related characteristic values").

Safety-related characteristic values
Additional parameters, as described below,
become relevant for the use of position
measuring systems in safety-oriented
applications. These parameters are to becomplied with when designing the safetysystem of a machine.
The Probability of Dangerous Failure perHour value (PFH) indicates the probabilityof a hazardous encoder failure per hour.
The failure rate of the encoder is includedin the calculation of the PFH value for thecomplete system.
The error reaction time in the application
depends mainly on the cycle times of thesafety module in the control and theconnected actuators (brake, contactors,etc.). In addition, application-specificsettings (e.g. EnDat clock frequency) can
influence this value. For this reason, theerror reaction time indicated in the control
documentation should be referred to.
The safe position describes the maximum
possible position offset of the encoder until
safe fault detection is ensured. The characteristic value refers to the position value 1
in fault-free operation and is given in theencoder’s unit of measure. It significantly

influences the minimum distance required
to provide protection from pinching (e.g. offingers). The safe position is divided into
the values for the encoder and for the­mechanical coupling.

required for this in many cases. If fault
exclusion is required in the control’s operating
instructions, the information for the safe
mechanical connection is to be taken intoaccount. Otherwise it can be ignored.

The value for the encoder describes themaximum position offset including the­influence of the position value comparisonin the control (algorithm according to­document 536402). Besides quantization
errors, it also includes any position deviations
occurring in the encoder. Depending on thecontrol and the application, the characteristic
value safety-relevant measuring step (SM)may also be relevant for the parameterization of the safety function. The control­documentation includes a corresponding
note in such cases.

For a friction-type connection with fault
exclusion there is no additional mechanicaloffset that would need to be considered forthe safe position.

The characteristic value mechanicalcoupling provides information in case of the“loosening of the mechanical connection”
fault. Table D16 of the EN 61800-5-2
standard for electrical drives defines theloss or loosening of the mechanicalconnection between the encoder and motor
as a fault that requires consideration. Since
it cannot be guaranteed that the control
will detect such errors, fault exclusion isIf the fault exclusion is fulfilled only by amechanical stop with backlash, thismaximum possible offset is to be calculated
into the safe position. This is done byadding the values for the encoder and forthe mechanical coupling.
Important! Fault exclusion can be connected with constraints on the permissiblespecifications. This is to be considered forthe selection of a suitable encoder or typeof mounting. In addition, fault exclusions
for the loss or loosening of the mechanicalcoupling usually require additional measureswhen mounting the encoders or in theevent of servicing (e.g. anti-rotation lock forscrews) that are not necessary in standard
applications. The design engineer of a­machine must strictly adhere to these­additional measures.

Encoders for safety-related applications

The comprehensive product programfrom HEIDENHAIN offers solutions forapplications in which the highest possible
accuracy, reliable reproducibility andrepeatability, safe process management,high machine dynamics, simple operation,and maximum efficiency are required.
These products are therefore used mainlyin the following areas:• Machine tools• Electronics production• Automation facilities• Elevators• Medical technology

Rotary encoders

ExI 1300
SeriesExI 1100seriesECN 1100/
EQN 1100seriesExN 1100/
ExN 1300
series

ECN 400/
EQN 400
seriesECI/EBI 4000 series

Angle encoders

The product program from HEIDENHAIN
also contains numerous encoders forsafety-related applications.
RCN 2000
seriesRotary encoders for servo drives,machines, and larger systems
HEIDENHAIN offers suitable rotary
encoders for a wide variety of applications.
The rotary encoders for safety-related
applications are available in different
versions with absolute position acquisition.
Angle encoders for rotary axes
Angle encoders are characterized by highaccuracy values in the arc second range
and better. The angle encoders for safetyrelated applications are available with andwithout integral bearing, and as sealed
encoders for mounting or as modular
encoders for integration.
Linear encoders for linear axes
HEIDENHAIN offers exposed and sealed
linear encoders for safety-related
applications. These linear encoders areavailable in various sizes, lengths, andaccuracy grades.

ECA 4000 series

RCN 5000series
RCN 8000 series

RCN 6000 series

Linear encoders
LC 400 series

LC 100 series

LIC 4000 series

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596632 · 06 · A · 02 · 11/2019 · PDFAdhere to the information in the following documents to ensure the correct andintended operation of an encoder:• Product Information / brochure and mounting instructions of safety-related position
measuring systems
For implementation in a control:• Specification for Safe Control						533095• Supplementary Specification for SIL 3, PL e, Cat. 4			1000344• EnDat Interface Description						297403• Electrical Connection Directive						231929• Requirements for Position Value Comparison				536402