Hybrid control and acquisition system for distributed sensors for environmental monitoring

In this paper we describe the architecture and the performances of a hybrid modular acquisition and control system prototype we developed in Napoli for the implementation of geographycally distributed monitoring and control systems. The system, an improvement of a VME-UDP/IP based system developed by our group for interferometric detectors of gravitational waves, is based on a dual-channel 18-bit low noise ADC and 16-bit DAC module at 1 MHz, managed by an ALTERA FPGA, that can be used standalone or mounted as mezzanine (also in parallel with other modules) on a motherboard. Both the modules and the motherboard can send/receive the configuration and the acquired/correction data for control through a standard EPP parallel port to an external PC, where the real-time computation is performed. Experimental tests have demonstrated that this architeture allows the implementation of distributed control systems, using a standard laptop PC for the realtime computation, with delay time Dt < 30 ms on a single channel, that is a sustained sampling frequency fc > 30kHz. Each module is also equipped with a 20-bit slower ADC necessary for the acquisition of an external calibration signal. The system is now under extensive test in two different experiments, i.e. the control of a Michelson Interferometer to be used as Velocimeter for Seismic Waves in Geophysics and the control of the end mirrors a suspended Michelson Interferometer through electrostatic actuators, a prototype for mirror control for Interferometric Detectors of Gravitational Waves.