A hybrid modular control and acquisition system

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 geographically distributed monitoring and control systems. The system, an improvement of a VME-UDP/IP based system developed by our group within the framework of R&D for interferometric detectors of gravitational wave, is based on a dual-channel 18-bit low noise ADC and 16-bit DAC module at 800 kHz, managed by an ALTERA FPGA. The module can be used standalone or mounted as mezzanine on a motherboard, in parallel with other modules, too. Both the modules and the motherboard can send/receive through a standard EPP parallel port the configuration and the acquired/correction signal for control to/from an external PC, where the real-time computation is performed. Experimental tests have demonstrated that this architecture allows the implementation of distributed control systems with delay time Deltat < 30 mus on a single channel, that is a sustained sampling frequency f_c > 30 kHz, using a standard laptop PC for the real-time computation. Each module is also equipped with a 20-bit slow ADC necessary for the acquisition of an external calibration signal. The system is now going to be extensively tested in two different R&D experiments, i.e. read-out and control of a monolithic accelerometer with interferometric read-out 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.