182 Safety functions
Safe speed monitor (SSM)
The SSM function provides a safe output signal to indicate whether the motor speed
is between user-defined limits. There are four separate SSM functions
(SSM1...SSM4) with separate monitoring limits and indications. Several SSM
functions can be active at the same time.
You can configure the SSM function to be permanently on or off, or to be activated
externally from the FSO module I/O or from a safety PLC.
You can use the SSM function with a safety encoder or with a safe speed estimate.
With an encoder, the FSO module is always aware of the exact motor speed. Without
an encoder, the speed information is valid only when the drive is modulating (see
section SSM with a safe speed estimate on page 184).
Note: If there is a fault in the speed data and the SSM function is the only active
safety function, this does not trip the drive. This only removes the SSM indication and
generates a warning to the drive.
The operation of the SSM function is described in the time diagrams and tables
below. The SSM1 function is used as an example. For configuration, see section
Configuring SSM on page 387.
A SSM1 limit positive (parameter SSMx.13)
B SSM1 limit negative (parameter SSMx.12)
SSM limits (A and B)
SSM1 state &
indication
SSM1 request
Motor speed
Time
A
4
1
B
2
3
5
6
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