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W A R N I N G
EXTERNAL BRAKES NEEDED
Estimated speed is calculated only when the drive is in RUN state, that is, when the drive is operating.
If external forces can cause acceleration to the motor when the drive is not in RUN state, use, for example, external brakes to
stop the motor and to keep it in standstill.
W A R N I N G
OPEN-LOOP CONTROL AND EXTERNAL FORCES
If the drive operates in open-loop control and there are external forces that can cause acceleration to the motor, the drive can
pull out (that is, the motor is not under control). This situation can cause estimated speed to be invalid.
W A R N I N G
USAGE OF ONLY ONE SPEED SENSOR
If only one encoder is used for safety monitoring and closed-loop control, the fault model detachment of the encoder from the
motor shaft must be analyzed.
Make sure that the fault model detachment of the encoder from the motor shaft is analyzed.
See 3.6.7 Usage of Only One Speed Sensor.
When estimated speed is used, the speed value from an external speed sensor is compared against the calculated value from the AC
drive. If the two values differ from each other more than the value of Allowed Deviation of Speed Sources, during a time set with
Speed Deviation Timer, a reaction as described in 3.6.3 Speed Discrepancy with Multiple Speed Sources is executed. See Illustration
15.
Speed difference > Allowed deviation of
speed sources
Speed deviation timer
Speed deviation timer
Reaction
Speed difference > Allowed deviation of speed sources
e30bi373.10
Illustration 15: The speed difference of estimated speed and the speed measured by a sensor does not stay within the set limits and causes a
comparison fault
When the AC drive is not in RUN state, estimated speed is not calculated, and the motor is assumed to be coasting to stop. During
that time, the comparison between estimated speed and the speed measured by a sensor is not made. The comparison is activated
again when the value of Coast Stop Time passes, or once the speed of the encoder goes below the value of Allowed Deviation of
Speed Sources. If the speed sensor indicates rotation that is not permitted by Allowed Deviation of Speed Sources, a fault appears.
See Illustration 16.
AQ319736045637en-000101 / DPD01798 | 41Danfoss A/S © 2021.06
Overview of the System
VACON® NXP Advanced Safety Options
Operating Guide
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