Installation manual

Danaher Motion Kollmorgen 08/04 System Operation
SERVOSTAR S Installation M-SS-001-01 Rev. T 71
7.3.4 CURRENT SAMPLING
The current loop receives corrective feedback from the current
sampling circuitry. The current sensors use closed-loop hall
sampling techniques in all units.
The current sample is used by the current loops to regulate the
current in each of the three motor phases. Two phases (A and C) of
the current signal are sampled by the microprocessor at a 16 kHz
rate. The momentary A phase current and C phase current can be
monitored by examining the IA and IC variables, respectively. The
microprocessor calculates the equivalent absolute current, which
can be monitored as I. This value can be averaged for 2, 4, 8, 16,
32, or 64 samples.
7.4 Foldback
The SERVOSTAR offers two types of FoldBack protection for both
the motor and the drive. The drive’s microprocessor monitors the
current feedback signal and develops a RMS value of this signal for
the purpose of providing a value that represents the current in the
motor. The system is similar to an I-squared-T accumulator.
7.4.1 DRIVE FOLDBACK
The FoldBack algorithm monitors current feedback and will
decrease the system’s current to the ICONT level if the feedback
exceeds the continuous current rating of the drive/motor
combination (ICONT). For example, under a step command input
condition the FoldBack algorithm will allow maximum peak current
(IMAX) output from the drive for 2 seconds. After 2 seconds the
drive enters FoldBack mode (FOLD = 1) and begins an exponential
FoldBack to the system’s continuous current. It will take
approximately six seconds for the exponential decay to drop from
the system’s peak current to its continuous level.
For drive currents that exceed ICONT, but are below IMAX,
the system period before FoldBack occurs is extended
beyond two seconds. Two seconds is the shortest time
period that will elapse before the drive enters FoldBack and
only occurs when maximum peak current (IMAX) is drawn.
This FoldBack feature is designed to protect the drive
electronics, not the motor. The Configurable Output, O1,
(pin 12) can be configured to indicate a drive FoldBack
condition.