KEPCO MBT Series - Manual (Page 110)

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MBTSVC111609
age or current buffer are sent over the IEEE 1118 bus by the Digital Control Board. These digital
signals are also sent to the front panel display to refresh the displayed values of voltage and
current.
4.1.7 VOLTAGE/CURRENT COMPARISON ERRORS
The digital contents of the output voltage and current buffer are also used to make decisions
regarding the dynamic time-out delay and issuing the corresponding error message. The end of
the dynamic time-out is determined by three consecutive “within specified limit window” determi-
nations of the output parameter (voltage or current) that is being programmed. This time-out has
a maximum duration of approximately 20 milliseconds (ten cycles of the main program loop).
Any voltage or current reading at the end of the time-out that differs from the programmed value
(voltage in commanded Voltage mode, current in commanded Current mode) by more than
0.6% of full scale value will trigger a Voltage or Current comparison error message. (For exam-
ple, if Full scale = 100V and Programmed voltage is 20V, 0.6% of 100 = 0.6V; errors occur if the
actual voltage is lower that 19.4V or higher than 20.6V.)
4.1.8 PROTECTIVE CIRCUITS
Error conditions that turn-off the MBT Power Supply generate flags that act on the High Priority
Interrupt line of the microcontroller on Digital Control Board A3. This will result in an immediate
reporting and storing of error messages in the Controller before the MBT DC power is com-
pletely lost. These flags are:
• Crowbar
• Overtemperature
• Power loss
• Path Fault
4.1.8.1 OVERVOLTAGE/OVERCURRENT PROTECTION Among the protective circuits designed for
the MBT Power Supply are overvoltage and overcurrent tracking circuits on the A1 Analog Con-
trol Board. These circuits continuously monitor the output voltage and current and compare
them with the overvoltage and overcurrent Reference Potentials. These two References are set
at approximately 10% of the full scale reading above the references described in PAR.s 4.1.3
and 4.1.4 which are used for error signal generation. If the voltage or current exceeds the pro-
grammed value by the above established limit for longer than approximately 6 milliseconds, a
Crowbar and Turn-off circuit is activated.
4.1.8.2 OVERTEMPERATURE PROTECTION Another protective circuit allows the MBT Power Supply
to detect a temperature increase on the power transistor Heat Sink or on the output capacitor
discharge transistor. An Overtemperature error message is generated if the temperature is
beyond an established limit. If an overtemperature condition persists for 6 milliseconds, the
Crowbar and Turn-off circuit causes an error message to be sent to the controller and shuts off
the MBT Power Supply.
4.1.8.3 POWER LOSS PROTECTION The MBT Power Supply detects a loss of source power after 8
milliseconds. If the power loss continues for more the 6 milliseconds, a signal is provided to
the Crowbar and Turn-off circuit which generates an error message and turns the unit off. This
feature can be disabled by removing Jumper J5 from the A2 board (see PAR. 2.8 and Table 2-
4).