Measured And Estimated Motor Speed; Switching Between The Measured And Estimated Speed Values - ABB FSO-21 User Manual

44 Overview

Measured and estimated motor speed

You can use the FSO-21 module either with or without an encoder. When an encoder
is used, the FSO module uses the exact value of the motor speed in the safety
functions. Without an encoder, the FSO module uses an estimated value of the motor
speed. This affects how the safety functions operate (for example, when indications
turn on and off) and how they must be configured. The detailed descriptions of the
safety functions include a separate description when an encoder is used and when it
is not used (encoderless mode).
In some applications, you must always use an encoder, for example, in very low
motor speeds (below 2 Hz). See also section


Switching between the measured and estimated speed values

You can configure how the FSO module reacts when the exact motor speed value
from the encoder is lost (failure in FSE module, safety encoder or its wiring). The
reaction depends also on the status of safety functions:
• Case 1: There are active safety functions in the FSO module.
A monitoring safety function (SLS, SMS, SSM, SDI) is active when the safety
function request is active. A stopping safety function (STO, SS1, SSE) is active,
when the safety function request is active and the safety function is not completed
yet, that is, the completed indication is off.
In this case, the FSO module needs the motor speed value to perform the safety
function correctly and safely.
• Case 2: There are no active safety functions in the FSO module.
There are no active safety function requests, or all stopping safety functions are in
the completed status, that is, the completed indications are on.
In this case, the FSO module does not need the motor speed value to perform the
safety function correctly and safely.
With the POUS and SSM functions, the FSO does not need the motor speed value to
perform safely. The POUS function can be activated only when the motor is stopped.
The SSM function is only for indication purposes. Therefore, the status of these
safety functions does not affect how the FSO module reacts when the motor speed
data is lost.
Use parameter FSE diagnostic failure reaction
There are three alternatives:
1. FSE diagnostic failure reaction
Case 1 and Case 2: With this selection, the FSO module goes into the Fail-safe
mode and actives the FSO STO function immediately when the encoder is lost.
For more information, see section
Encoderless mode
to define the correct FSO reaction.
= STO
FSO modes on page 53.
on page 32.