Encoders for Functional Safety
Safety is – not least since the EU Machinery Directive 2006/42/EG – an “integral part of the construction of drives”.
When choosing the right encoder for functional safety the principle applies that safety is achieved through the intelligent combination of encoder, controller and actuator.
Sendix SSI absolute encoders, with an additional Sin/Cos incremental output, and Sin/Cos versions of incremental encoders are available with certification.
But safety goes further than this: safe components are characterised by a robust reliable interface and by the ability to cope with high mechanical and electronic loads.
Encoders for functional safety
Safe Incremental Encoder Function
In order to achieve safe incremental information with the encoder, the controller must monitor the validity of the analogue, 90° phase-shifted sine/cosine signals with the help of the function: sin² + cos² = 1
Safe Absolute Encoder Function
In order to obtain safe information with the encoder regarding the absolute position, the controller counts the incremental pulses and compares the result with the absolute positions also provided by the encoder.
Safe mechanical connection
A 100% reliable mechanical connection is required for a safe function in the applications. Suitably sturdy fixing elements can help eliminate the risk of faults.
Compliance with Safety Standards
According to DIN EN 13849-1 and DIN EN 61800-5-2 up to SIL3/PLe/Kat.4 the following safety functions can be implemented with the encoder:
-SS1: Safe Stop 1 – controlled braking, STO after time or standstill.
-SS2: Safe Stop 2 – controlled braking until SOS.
-SOS: Safe Operating Stop – safe operating stop in position control.
-SLS: Safe Limited Speed.
-SLI: Safe Limited Increment of Position.
-SLP: Safe Limited Position.
-SSR: Safe Speed Range.
-SDI: Safe Direction.
-SSM: Safe Speed Monitoring.