KEB COMBIVERT F5, Reference Manual

Page: 199 / 349

199
LT - Timer Parameters
This timer delays the drop of the brake when one of the outputs is assigned as
Brake Control or Drive On and that output is actually used to control the brake.
The LT10 Brake Drop Delay timer begins after the Direction input has been
dropped and the speed command has reached zero speed.
The Brake Control output will turn off when the Brake Drop Delay time has
expired.
This parameter determines how long the drive will maintain full current and
control of the motor after the direction inputs have been turned off. During
this time, motor current will continue t
o flow (however the analog input will be
clamped and the speed control gains will be reduced) to allow the motor to
hold zero speed until the brake has set. This timer should be adjusted longer
than the actual required time for the brake to mechanically drop.
The LT12 Current Hold Timer begins after the Direction input has been dropped,
the speed command has reached zero speed, and the LT10 Brake Drop Delay
timer has expired.
The Drive On output will turn off when the LT12 Current Hold Time has expired.
Once the time in the LT12 Current Hold Timer has expired, current will continue
flowing to the motor, but the drive will ramp the motor torque down to zero
over the time adjusted in the LT13 Current Ramp Down Timer. This provides
a smooth transition of the load to the brake and a quiet de-energization of the
motor. This timer should be adjusted such that the drive shuts off the current
before the controller drops the drive enable and opens the motor contactor.
If the drive enable is dropped before the current is shut off, it is possible the
drive will respond with base block protection “BBL” which can prevent further
operation for 1 to 3 seconds, depending on the drive size; likewise, a Drive
Enable Dropped event may be logged. Therefore the times should be adjusted
to prevent this. Additionally during this time the speed control is turned off to
prevent the motor from driving against the brake.
The LT13 Current Ramp Down Timer begins after the Direction input has been
dropped, the speed command has reached zero speed, the LT10 Brake Drop
Delay timer has expired, and the LT12 Current Hold Timer has expired.
The total time between the drop of the direction signals and the turn off
of motor current is the time to decelerate to zero speed + LT10 + LT12 +
LT13. The time delay for dropping the enable (I7) and the opening of the
motor contact should be greater than this sum. If the enable is dropped
prematurely, then current will be cut off immediately and this may be felt
as a ‘clunk’ in the motor.
LT10
Brake Drop Delay
LT12
Current Hold Time
LT13
Current Ramp Down
Time
