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 distributed monitoring and control systems. The system, developed by our group within the framework of R&D for interferometric detectors of gravitational waves, 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 is designed to be used standalone or mounted as mezzanine on a motherboard, in parallel with other modules. In particular, the modules can send/receive the configuration and the acquired/correction signal for control through a standard EPP parallel port 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 a sustained sampling frequency up to , using a standard PC for the control signals 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 being extensively tested in on a prototype of suspended optical interferometer for gravitational wave detection we are developing at the INFN in Napoli, made of three superattenuators of the same class of the TAMA Interferometer.

I. Introduction

The design of digital control systems, both for industrial application and for R&D experiments, needs the definition of requirements on control band, sampling frequency, computing power, ADC and DAC characteristics. In many cases, the implementation of a control system becomes just a matter of choice of standards, technologies, control algorithms already described in literature or available on the market, often very reliable and effective. The design of non-standard control systems, like high performance control systems, adaptive control systems or distributed control systems is different. In this case the required large computing powers, distributed controlling actions, large control bands (of the order of kHz or larger) are not easily satisfied by commercial embedded or open systems, without using expensive and complex architectures (e.g., Digital Signal Processors (DSP) to be integrated in the acquisition and control system). The control system of the Interferometric Detector of Gravitational Waves Virgo [1], [2] is a typical example. In fact, this system is based on DSP VME boards designed and implemented to satisfy the specific requirements for computing power and data transfer of the Virgo detector control system. This solution, although very efficient, requires large investments, also in terms of manpower, for the design, implementation, test, maintenance and upgrade of the control system.