Research programs in the field of automatic sensor systems can help with monitoring arms reduction and peace keeping. Such sensor systems must be able to detect heavy military vehicles by exploiting signals that are generated by them. The ultimate goal of a sensor-monitoring system is to detect these signals, pre-process them, and to extract the relevant information. A system aiming at these requirements was developed by a group working on signal processing and pattern recognition at the Institut fuer Informatik der Humboldt-Universitaet zu Berlin.
The station contains newly designed as well as commercial parts. The most important characteristics of the station are the dynamic range of 120 dB for the received signals and a sampling rate of at least 20 kHz. The sensor station consists of several modules: analog input modules, digital modules with two processors, power supply, and several interfaces for peripheral devices and external communication. The global tasks for the analog input modules are the adaptation of the impedance, amplification, filtering, and sampling and holding of the analog sensor signals. The amplifier is a switchable true differential amplifier with a high common-mode rejection ratio up to the upper frequency range, the filter and the sample-and-hold modules were realised with discrete analog components.
The concept of the developed ADC is that the conversion is done in two parts. First, the amplified signal is transmitted to the 16-bit ADC on the signal-processor module (principle of successive approximation, conversion time 5 µs). The result is the mantissa of the digital value. This mantissa is then combined with the 4-bit exponent in the digital signal processor (TMS320C32) which also has to collect the data of all four channels, to time stamp them, and to transfer the data to the microprocessor. The architecture of the signal processor includes a variable-width external-memory interface, fast instruction cycle time, power-down modes and a 2 channel DMA co-processor. The single board computer with a microprocessor (Pentium MMX 233 MHz, 64 MByte RAM, two serial RS-232 ports, one parallel port, PCI and ISA busses, 10/100-Mbit/s Ethernet adapter) reads and saves blocks of data from the 4 channels, inserts them into a transmission control protocol, and sends the signal packages via Ethernet to an external computer (main computer) using a transmission rate of up to 10 Mbit/s.
Recommendations are made for improving the station. So it should be possible to reduce the distortions caused by the switching power supply of the analog modules and different digital components. The next generation should consist of only one digital signal processor. If the microprocessor is eliminated the power consumption would be less than 5 W allowing a solar panel for power supply.
© Beate Meffert