Estimated Speed - Danfoss Vacon OPTEA Operating Manual

VACON® NXP Advanced Safety Options
Operating Guide
Table 14: Speed Sensor Fault Models and their Fault Exclusions
Fault model as stated in EN IEC 61800-5-2
A loss of an attachment during motion:
• sensor housing from motor chassis
• sensor shaft from motor shaft
• mounting of the readhead
A loosening of an attachment during motion:
• sensor housing from motor chassis
• sensor shaft from motor shaft
• mounting of the readhead
A loss of an attachment during standstill:
• sensor housing from motor chassis
• sensor shaft from motor shaft
• mounting of the readhead
In practice, the solution is over dimensioning against the occurrence of the fault model. The sufficient over dimensioning factor
depends on the connection type and the fault model. In case the drive operates in open loop and the estimated speed is also used,
cross-check with the estimated speed will detect the fault in the encoder. In closed loop with no external accelerative forces, it is
likely that the fault will not be detected. In this case, after the loss of the encoder, the drive will either trigger a fault or the speed of
the motor will not accelerate but will stabilize to a speed value that corresponds to the nominal slip of the motor. See also the
operating instructions of the encoder.

3.6.8 Estimated Speed

It is recommended to use two standard speed sensors or a single certified speed sensor. When it is not possible, a standard speed
sensor can be used with estimated speed measured by the AC drive. The estimated speed is used as a second independent channel
to compare against the value of the speed sensor. Estimated speed is used for diagnostics only and it does not trigger safety func-
tion limit violation on its own.
Estimated speed can be used with a digital pulse encoder or a proximity sensor. With a Sin/Cos type encoder, the estimated speed
offers no benefits because it is limited to SIL2 which an analog Sin/Cos type encoder can fulfill alone.
Estimated speed can be used with these safety functions:
• The STO function
• The SS1 function
• The SQS function (in STO and SS1 mode)
• The SLS function
• The SSR function
• The SSM function
• The SMS function (when the SMS limits have the same value, or when the values of SMS Limit Plus and SMS Limit Minus are
greater than the value of Allowed Deviation of Speed Sources)
Estimated speed cannot be used with these safety functions:
• The SS2 function
• The SQS function (in SS2 mode)
Estimated speed with a speed sensor fulfills the safety requirements, but it is possible that estimated speed is less accurate than a
sensor, especially when sudden changes occur in the load or the speed.
40 | Danfoss A/S © 2021.06
Fault exclusion as stated in EN IEC 61800-5-2 (Annex D Table D.16)
Prepare the Failure mode and effects analysis (FMEA) and prove:
• permanent fastness for formlocked connections
• fastness for force-locked connections
N O T I C E
Overview of the System
AQ319736045637en-000101 / DPD01798