User manual

GMC-I Messtechnik GmbH 7
Setup Procedure
Setup data are processed and forwarded to the respective I/O
controller of the respective function unit. Each setting value for
output voltage, output current or overvoltage protection triggering
is converted to a proportional control voltage by a 12 bit DAC,
and is fed to the respective controller or comparator as a setpoint
or a reference quantity.
Actual output voltage is ascertained by a voltage monitor, whose
automatic sensor switching inputs are connected either to the
output terminals or the sensing terminals.
Actual output current is acquired as a voltage drop at a shunt
situated in the negative output conductor, and is amplified by the
current monitor to a scaled signal.
In order to achieve rapid downward adjustment of output voltage
even with minimal output load, the device is equipped with a
limited sink function (limited to approximately 15 W continuous
power). The sink function is implemented by means of BET
technology (bidirectional energy transfer). This technology assures
charging and discharging of the output capacitor within an equally
short period of time, even at no-load operation. The sink function
is activated as soon as, and for as long as output voltage exceeds
the current setpoint value (also in the event of energy recovery
from a parallel connected voltage source).
The source and sink functions are enabled when the output On /
Off status is set to ON, and the source function is disabled when
the status is set to Off, in which case the sink function is
deactivated after approximately 300 ms (highly resistive output).
Measuring Procedure
Monitor-amplifier output signals, which are proportional to actual
output voltage and current, are fed to an analog multiplexer (MUX)
which switches one of the two signals to the input of the analog-
digital converter (ADC) depending upon the desired measured
quantity. The converter, controlled directly by the CPU, functions in
accordance with the dual-slope principle and traces measured
value acquirement back to a time measurement (meter reading).
The actually measured decimal value is calculated based upon this
data, and is stored to RAM. Depending upon the circumstances,
the measured value display is refreshed, an extreme value
comparison is performed for the Min-Max function or the measured
value is made available at the computer interfaces’ data output
buffer.
Monitoring Functions
– Control Mode Recognition and Overload
An electrically isolated digital signal is derived from the output
signals of the voltage and current regulators, which indicates
the currently active control mode (constant voltage or constant
current mode), as long as overload operation is not active.
“Overload” indicates that power limiting has been triggered as a
result of selected parameter settings and prevailing load. These
operating conditions are evaluated by the CPU (e.g. for OCP
function), are indicated with LEDs and are used to generate
status and event registers for computer control.
– Overvoltage Monitoring
After bypassing the voltage monitor, device output voltage is
additionally compared to an adjustable limit value within a range
of 3 V to 120% nominal voltage by a comparator, and the
output is deactivated if the limit value is exceeded and an OVP
message is generated (“CV” LED blinks, status and events
registers).
– Overcurrent Monitoring
Overcurrent monitoring can be activated and deactivated.
Response time is defined with the delay parameter. If, with
activated OCP function, the device is in the current regulating
mode for at least the duration of the selected delay time (“CC”
LED is illuminated), the power output is switched off and an
OCP message is generated (“CC” LED blinks, status and
events registers).
–Temperature Monitoring
Temperature is acquired by means of PTC resistors at
representative points (circuit breaker heat sink), and is
converted into a proportional electrical signal. As of an initial
threshold temperature of approximately 70C, fan voltage is
increased in a linear fashion as temperature increases. The
device can be operated at any output load up to the maximum
specified operating temperature after the fan has been
activated. If ventilation is impeded, or at excessive ambient
temperatures, temperature at the sensor may reach the upper
threshold of approximately 90C. If this is the case, an
overtemperature message is entered to the status and event
registers. The output is deactivated by the CPU after 5
seconds, and OTP triggering is indicated by the blinking
“Pmax” LED. After sufficient cooling has occurred, the status
message is cleared and a ready for operation message is
entered to the event register. If the POWER-ON function is set
to “Recall”, the output is reactivated automatically. If the
POWER-ON function is set to “Standby” or “Reset”, the output
remains deactivated and can only be reactivated by pressing
the OUTPUT key, or by means of a command from the control
computer. After actual temperature has fallen to below the
lower threshold value, fan speed is reduced automatically.