Safety Integrated - Industry - Siemens

Safe Standstill Detection and Safely Reduced Speed with
F-CPU and MASTERDRIVES in Category 3 of EN 954-1 or
SIL 2 of IEC 62061
Ex. No.
12 Automation Function
Description of the functionality
Introduction
To ensure, that a drive is not causing any hazards, it must be
detected safely when it is in standstill mode (speed n=0). Only
when the state of safe standstill is reached, must actions be
performed, as during normal operation they would otherwise
be detected as hazard and cause the actuator to be switched
off. Such actions may consist of:
■ Entering a danger zone
■ Opening a safety door
■ Enabling further technological processes
Apart from safe standstill and normal operation this example
also illustrates the "safely reduced speed" (Sicher reduzierte
Geschwindigkeit = SG) operating mode (in this document
referred to as "safe speed (SG)").
When does a "safe standstill" take place?
Within an applicative solution a safe standstill is referred to if
■ a speed n=0 of the drive is recognized and
■ this result is confirmed by a further evaluation of the operating
mode of the drive (independent of the first evaluation).
Functional example
This functional example illustrates two independent methods
of determining drive speed, and safe standstill in comparison
with speed n=0.
■ Method 1: Determining speed via PROFIBUS
■ Method 2: Determining speed via standard count module
■ The following overall functionalities are prepared:
■ Emergency stop
364 Functional Example No. AS-FE-I-012-V10-EN
■ Simulation of a safety door
■ Operating modes normal, "safe speed" (SG) and "drive
standstill"
The actual speed value is determined in two different ways.
The speed values determined this way are checked for plausibility
in the operating modes "normal" and "safe speed" (SG).
If one or several errors occur in "safe speed" (SG) mode, the
drive is switched off fail-safe.
The plausibility check includes:
■ the actual speed value determined in two different ways
■ the comparison of the actual speed value with the N_MAX
speed value, whose value must not be exceeded.
■ To illustrate these functionalities, the example consists
mainly of three parts:
■ DP master CPU
■ DP slave (I-Slave)
■ DP slave (MASTERDRIVES)
These three blocks as well as the mentioned functionalities
are described in greater detail below.
Note
The PFH-Calculation is not a part of this example.
DP master CPU
Determining speed with PROFIBUS (method 1)
A CPU S7-400, connected with MASTERDRIVES via PROFIBUS,
is used as DP master. In the master CPU the operation related
switching is realized:
■ Start the drive
■ Stop the drive
■ Acknowledgement (e.g. after an error)
To forward these commands to MASTERDRIVES, the master
CPU describes the bits of the control word.
To detect the state of MASTERDRIVES, the master CPU reads
the bits of the control word.