ABB ACS800 Firmware Manual page 198

198
Index Name/Selection
42.10 LOW REF BRK HOLD Activates a brake hold function and defines the hold delay for it. The function
0.0 ... 60.0 s
Actual signals and parameters
Description
stabilises the operation of the brake control application when the motor
operates near zero speed.
0.0 s = inactive.
0.1 s ... 60.0 s = active. When the absolute value of the motor speed reference
falls below the brake close speed:
- The brake is closed according to the normal stop routine of the brake control
function
- The brake hold delay counter starts after the brake close delay.
During the delay, the function keeps the brake closed despite the speed
reference value and the value of the Start command. When the set delay has
passed, the normal operation resumes if the absolute speed reference is
greater than the brake close speed.
The following figures explain the two different scenarios that can occur in the
LOW REF BRK HOLD function.
Case 1: The absolute speed reference goes above the brake close speed
before the Low Ref Brk Hold time has elapsed.
BRAKE CLOSE DELAY
Speed Ref.
BRAKE CLOSE SPEED
Internal Speed Ref.
BRAKE OPEN CMD
Case 2: The absolute speed reference goes above the brake close speed after
the Low Ref Brk Hold time has elapsed. The brake is opened only after the
speed reference goes above the brake close speed. In this case the brake
immediately opens when the speed ref is greater than the brake close speed,
because the LOW REF BRK HOLD time has already elapsed.
BRAKE CLOSE DELAY
Speed Ref.
BRAKE CLOSE SPEED
Internal Speed Ref.
BRAKE OPEN CMD
* This time is the additional delay until the speed ref goes above the brake
close speed.
LOW REF BRK HOLD
t
BRAKE OPEN DELAY
t
t
LOW REF BRK HOLD
t
*
BRAKE OPEN DELAY
FbEq
100 = 1 s
t
t