Objective measurement of equipment parameters is an essential activity in nuclear power plant. The testing needed is extensive and often requires very fast data collection and processing.
The introduction of the VXI specification made it possible to use universal plug-in meters for modular systems. The flexibility of these instruments meets the demands for high speed measurements while maintaining the accuracy required by international standards. The range of these devices, their serial production and consequently their affordability are higher than with similar CAMAC systems, used before. The inherent flexibility of the VXI bus also brings the possibility of obtaining a universal device which purpose is only encoded in programs.
The VXI bus provides a modular foundation for automated measuring and testing systems. The standard specifies in detail both the mechanical and electrical parameters that the equipment must meet. This allows devices of different manufacturers to be used together in one VXI instrument box. Subsequently, such a measuring system can be reconfigured and expanded to include the most suitable instruments for the application.
The VXI standard is based on the VME computer architecture, to which it adds new features for timing, synchronization, and instrument power. It also defines methods and protocols how instruments communicate each other. Addressing allows presence of up to 255 devices on the bus, but most of the enclosures are designed for a maximum of 12 devices plus a controller. The controller is located in the first position (position 0) of the instrument panel and is responsible for communication with an external computer that controls measurement and evaluates data. Often a PC, Macintosh, microVAX, or Unix workstation is directly used as the controller. The controller at position 0 also controls instrument timing and system resource allocation.
As VXI standard becomes a widely accepted industry standard, the flexible systems of this standard become the ideal basis for building measurement systems to meet today’s and tomorrow’s requirements.
Based on VXI instruments, our company designed and supplied a system for non-standard measurements at the power plant reactor. The described system consists of products of renowned companies (Tektronix and Hewlett-Packard). The VXI architecture used and the fact that the system’s properties are largely determined by the program, provide the user with an important feature – easy extension and modification of measurements as requirements change over time. Also advantageous is the compactness of the solution, which allows to carry the complete measuring device.
The supplied system consists of a 88 measuring point switch, a digital voltmeter, 240 digital I / O and a control module.
Two-wire switch 88 input channels to 1 output (multiplexer) has a maximum switching frequency of 80 channels per second, insulation resistance> 10 GΩ, contact life> 107 switchings, crosstalk between channels -105 dB. From the program point of view, individual channels can be referred to instead of numbers using the selected four-character names. Self-test is a matter of course for all VXI modules.
The digital multimeter has DC voltage range 30mV to 300V, switchable in decades. The resolution at the lowest range is 10nV, at all 6½ digits. Sampling frequency 5/s to 1500/s, with higher sampling frequencies decreasing resolution. The input is resistant to overvoltage 300V (in all ranges). Mains voltage suppression is 54dB. The multimeter is also equipped with AC voltage measurement (30mV to 300V, 6½ digits) and resistance (3Ω to 3GΩ, 6½ digits). Up to 4096 transducers can be recorded in the multimeter memory.
Three aditional DIO modules contain a total of 240 digital inputs / outputs, controllable bit by bit.
The controller slips into the chassis zero position and controls operation on the VXI bus. It also includes a GP-IB connector, which is used for connection to a computer.
Modules are located in a chassis, which contains 13 slots for inserting modules, of which 7 slots are occupied by measuring technology and 6 slots remain free for future expansion of the system. The chassis ensures that all modules are supplied with all necessary voltages and cooling air.
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