OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = VEGA1 INSTRUMENT_ID = SP2 OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "DUST PARTICLE DETECTOR" INSTRUMENT_TYPE = "ACOUSTIC SENSOR" INSTRUMENT_DESC = " The acoustical detector consists of three piezo-electric elements mounted on a mem- brane (3), two of these sensors (4) are connected to two identical recording circuits in order to improve the overall reliability of the system; the third element (5) is used as a stimuli source for calibration purposes. The membrane is mounted in a frame (l) which damps the mechanical oscillations and improves the counting rate. The detector assembly is fixed to the electronics box (6) by means of three acoustical insulators (2). Each piezo-electric element delivers a signal which is fed into a narrow-band amplifier working at a frequency of about 160 kHz. The output signal is split into l6 channels, which have their sensitivity thresholds logarithmically distributed across the whole dynamic range. Four identical impact plasma detectors are mounted at the periphery of the acoustical detector. They are associated in pairs and connected to identical electronic circuits. The entrance to each detector is protected against the environmental plasma by a system of deflecting electrodes and grids (7,8). The ions and electrons generated by each particle impact are separated and collected by a grid (9) and a target (10), bet- ween which a potential difference of 2 kV is applied. The electron pulse detected by the lower electrode constitutes the input signal, which is analysed in several channels with different sensitivity thresholds. The threshold sensitivity of the dust particle acoustic detector in terms of the transferred momentum is given by Pmin ~ 2x10**-5 gcm/s. Taking into account that the recoil momentum may exceed the particle momentum mV by 5 to 10 times, the minimum mass of recorded particles is < 3x10**-13 g. The measurement range n (> m)x3x10**-13 to ~ 2x10**-6 g is divided into 16 channels. With the relative width delta/m ~ 2.82, sensitive area S = 500 cm**2, accumulation time for one spectrum is 1 s, which corresponds to the spatial resolution ~ 80 km over the flyby trajectory. The counting rate of small mass particles is about 4095 1/s. The ionization detector is capable of recording particles with mass 3x10**-16 to 3x10**-11g. The number of channels is 6, with relative width delta/m = 10, sensitive area - 40 cm**2. The limit counting rate of small mass particles is ~ 65,500 1/s. The accumulation time for one spectrum is 1 s. The characteristic features of SP-2 are listed in the table below. --------------------------------------------------------------------- Table. Dust Particle Impact Detector characteristics Detector Piezo-electric Impact plasma --------------------------------------------------------------------- Total sensor area 500 cm**2 40 cm**2 Maximum count rate 4095 s**-1 65500 s**-1 Integration time 1 s 1 s Mass resolution,m/deltam 2.82 10 Number of channels 16 6 Dynamic range 2x10**-6 -3x10**-3 g 3xl0**-16 -3x10**-11 g --------------------------------------------------------------------- " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "ESA-SP1066" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END