Vestil EPT-30 - Manual (Page 68)

68
Curtis PMC 1207/1207A Manual A-13
APPENDIX A: GLOSSARY
Undertemperature
When the controller is operating at less than -25
°C, the current limit is cut back
to approximately one-half of the set current. The operating PWM frequency is
shifted to 1.5 kHz when the controller is operating at undertemperature.
Undervoltage protection
Undervoltage protection automatically disables the controller output if battery
voltage is detected below the undervoltage point at start-up, or when the battery
voltage is pulled below the undervoltage point by an external load. The undervoltage
cutback point is set in ROM, and is not adjustable.
During normal operation, the controller duty factor will be reduced when
the batteries discharge down to less than the undervoltage level. If the motor
current is such that the batteries are being pulled below the minimum point, the
duty factor will be reduced until the battery voltage recovers to the minimum
level. In this way the controller “servos” the duty factor around the point which
maintains 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.
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 150 msec and turns off the
controller. The external watchdog also directly disengages all contactors and
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 sequential
execution of the software. If not reset, the internal timer times out and the
microprocessor is “warm booted.” This causes the microprocessor to shut down
its outputs (thus shutting down the controller) and attempt to restart.