Operating Instructions ACU
13.2.1 Switch-Off Threshold
The Switch-Off Threshold. 637 defines the frequency as from which a standstill of the drive is
recognized. This percentage parameter value is relative to the set Maximum Frequency 419.
The switch-off threshold is to be adjusted according to the load behavior of the drive and the device
output, as the drive must be controlled to a speed below the switch-off threshold.
If the motor builds up a stopping torque, it may be possible that the switch-off
threshold stop function is not reached due to the slip frequency and the standstill of
the drive is not recognized. In this case, increase the value of the Switch-Off
Threshold 637.
13.2.2 Holding Time
The Holding Time 638 is considered in stopping behavior 1, 3, 4 and 6. Control to Zero speed
results in the motor heating up and should only be done for a short period in the case of internally
ventilated motors.
Holding time stop function
13.3 Direct current brake
Stopping behaviors 3, 6, 7 and the search run function include the direct current brake. Depending
on the setting of the stop function, a direct current is impressed into the motor either directly or,
when it is at a standstill, after the demagnetization time. The impression of the Braking Current
631 results in the motor heating up and should only be done for a short period in the case of
internally ventilated motors.
I
FIN
: Rated value of frequency inverter
The setting of the parameter Braking Time 632 defines the time-controlled stopping behavior.
Contact-controlled operation of the direct current brake is activated by entering the value zero for
the Braking Time 632.
Time controlled:
The direct current is controlled by the status of the signals Start clockwise and Start anticlockwise.
The current set by the parameter Braking Current 631 flows until the time set by the parameter
Braking Time 632 has elapsed.
For the duration of the braking time, the control signals Start clockwise and Start anticlockwise are
logical 0 (Low) or 1 (High).