Curtis 1297 - Page 108

Curtis PMC 1297 Manual
A-11
APPENDIX A: GLOSSARY
battery voltage is pulled below the threshold by an external load. As soon as the
voltage falls below the undervoltage threshold, the armature current is cut back
linearly until it reaches zero at the cutoff point; normal controller operation
resumes when the voltage rises above the threshold.
During normal operation, the controller duty cycle will be reduced when
the batteries discharge to below the undervoltage level. If the motor current is
such that the batteries are being pulled below the minimum point, the duty
cycle will be reduced until the battery voltage recovers to the minimum level. In
this way the controller “servos” the duty cycle around the point which main-
tains the minimum allowed battery voltage.
If the voltage continues to drop below the undervoltage level to a severe
undervoltage condition (due to battery drain or external load), the controller
continues to behave in a predictable fashion, with its output disabled.
Variable braking
The variable braking feature allows the operator to use the throttle to control the
amount of braking force applied to a moving vehicle—see Section 3A, page 28.
Variable Lift and Lower
The variable Lift and variable Lower features allow the operator to use the throttle
to control the speed of Lift and Lower operation—see Section 3B, page 56.
Watchdog (external, internal)
The external watchdog timer guards against a complete failure of the micropro-
cessor, which would incapacitate the internal watchdog timer. This independent
system check on the microprocessor meets the EEC’s requirement for backup
fault detection.
The external watchdog timer safety circuit shuts down the controller (and
the microprocessor) if the software fails to generate a periodic external pulse
train. This pulse train can only be created if the microprocessor is operating. If
not periodically reset, the watchdog timer times out after 15–20 msec and turns
off the controller. The external watchdog also directly shuts down the PWM
drive to the MOSFETs. It can only be reset by cycling KSI.
The internal watchdog timer must be reset periodically by correct sequen-
tial execution of the software. If not reset, the internal timer times out and the
microprocessor is held in reset. In addition the main contactor, armature
PWM, field, and pump sections are disabled.
Welded contactor check
The 1297 controller checks for a welded main contactor at startup. If a welded
contactor is detected, the controller inhibits its output until the fault is removed
and the keyswitch power is cycled.