When switching the High Voltage ON or OFF the voltage changes are made with a fixed set ramp, which defines the maximum
change rate of the output voltage.
Separate security circuits prevent exceeding of the front-panel switch settings for the current I
max
and voltage V
max
limits. A
monitoring circuit prevents malfunction caused by low supply voltage.
The internal error detection logic evaluates the corresponding error signals and the external INHIBIT signal and changes the
output voltage according to the setup. This also allows the detection of short over currents due to single flashovers.
2.2 Digital control unit
A micro controller handles the internal control, evaluation and calibration functions of both channels.
The effective voltages and currents are read cyclically by an ADC with a connected multiplexer. The readings are processed and
displayed on the 4 digit LCD. The current and voltage hardware limits are retrieved cyclically several times per second.
A reference voltage source provides a precise voltage reference for the ADC and the control voltage for the manual operation
mode of the unit. In the computer controlled mode the set values for the corresponding channels are generated by a 18-Bit DAC.
2.3 Filter
A special feature of the unit is a tuned filtering concept, which prevents perturbation of the unit by external electromagnetic
radiation, as well as the emittance of interferences by the module. A filtering network for the supply voltages is located next to
their connectors, the converter circuits of the individual channels are protected by additional filters.
The high-voltage filters are housed in individual metal enclosures to shield even minimal interference radiation.
2.4 Floating HV-outputs
Both HV outputs are related to the same ground HV-0V (HV-GND), provided on the outer connector (screen of HV cable) of SHV
connectors. The channels can be switched independently in polarity, the output voltages, related to HV-0V (HV-GND), are also
independently controlled.
The SHV connectors are mounted isolated to chassis (PE) in order to have a floating HV-0V.
If the floating voltage is increased above 47V a suppressor diode connects HV-0V to PE (chassis) to avoid dangerous voltages
between HV-0V and PE/chassis.
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