The CDA main electronics includes amplifiers
and transient recorders, a control and timing unit, a microprocessor
unit, a bus interface unit, a power input circuit, a low-voltage
converter, and a housekeeping system.
All CSA and electron multiplier signals are separately amplified by
logarithmic amplifiers and then digitized by an analog-to-digital
converter. The data are stored on transient recorders. Only the
recorder connected to the pick-up grids is operated continuously.
All others are activated only by a signal detected at a target or
the acceleration grid. The control and timing unit stores and decodes
information received from the microprocessor and produces all timing
and synchronization signals required for instrument operation.
The microprocessor samples and collects the buffered measurement data,
coordinates the subsystem measurement cycle, controls the instrument
operating modes, processes the data according to a program loaded in
its memory, and outputs data to the spacecraft upon request through the
bus interface unit (BIU). The BIU is the interface circuit
between the spacecraft and the microprocessor and is powered by
the CDA instrument. The power input circuit is the interface with the
spacecraft Power and Pyrotechnics Subsystem (PPS) and contains a filter
circuit and a regulator to produce a d.c. voltage to feed the
low-voltage converter.
The low-voltage converter is a d.c./d.c. converter that provides
different regulated low voltages for the electronics circuits and the
supply voltage for the high-voltage converters. The converters are
synchronized to the 100-kHz clock provided through the BIU from the
Command and Data Subsystem (CDS).
The CDA housekeeping system is a data system that multiplexes,
digitizes, and stores information on the instrument current, the low
voltages, the high voltages, and temperature measurements.
The articulation mechanism (AM) allows the entire
CDA instrument, including the high-rate detectors, the dust analyzer,
the main electronics, and the articulation mechanism electronics, to be
rotated or repositioned with respect to the spacecraft coordinate
system.
The high-rate detectors (HRDs) are two redundant
independent sensors. The electronics for the sensors are contained in
the HRD electronics box, and each sensor has its own electronics,
independent of the other sensor. The HRD will be operated in two
modes: "normal" mode and "calibrate." In the normal mode, the
operational HRD continuously collects dust particle data. In the
calibrate mode, a calibration cycle is initiated, which consists of a
sequence of pulses sent to the HRD by the in-flight calibrator (IFC) to
verify the stability of the electronics.
For additional information, see:
Heidelberg Dust Research Group
