9.2. Measuring systems

The purpose of any measuring system, its necessary functionality, technical parameters and characteristics are to a decisive degree determined by the object of study for which it was created. Due to the diversity of the structures of modern IP, dynamic development and the list of tasks to be solved, their classification is currently not fully completed.

Depending on the functions performed, the measuring systems can be divided into three main types:

- measuring systems for measuring and storing information (conventionally referred to as measuring systems for direct use);

- control - measuring (automatic control);

- telemetering systems.

Measuring systems also include pattern recognition systems and technical diagnostics systems that are not studied in the course on radio measurements.

According to the number of measuring channels, measuring systems are divided into one-, two-, three- and multichannel (multidimensional). Multichannel approximation systems are often used for joint and aggregate measurements.

The most rapidly currently being developed and implemented direct-use IP, the main feature of which is the ability to programmatically rebuild them for measuring various physical quantities and change the measurement mode. No changes to the hardware are required.

Measuring systems of direct appointment conditionally divided into:

- information-measuring systems (they are often called the term measuring information systems; the abbreviation is the same - IMS);

- measuring and computing complexes (CPI);

- virtual information-measuring devices (well-established name of the specialists - virtual devices; or computer-measuring systems - KIS).

Information and measuring systems

The widest class of measuring systems for direct use are IIS. The purpose of an IMS is defined as purposeful, optimal management of the measurement process and the provision of adjacent systems of the highest level with reliable information. The main functions of IIS are to receive measurement information from the object of study, its processing, transmission, presentation of information to an operator or / and computer, storing, displaying and forming control actions.

The information-measuring system should control the measuring process or experiment in accordance with the accepted criterion of functioning; perform the functions assigned to it in accordance with the purpose and purpose; have the required performance and characteristics of accuracy, noise immunity, speed, reliability, bandwidth, adaptability, complexity; meet the economic requirements of the methods and form of information presentation, placement of technical means; be adapted to function with measuring information systems of adjacent hierarchy levels and other IMS.

The main function of IIS, like any other technical system, is the targeted conversion of input information into output information. This transformation is carried out either automatically with the help of hardware hardware, or jointly with operating personnel and hardware hardware in complex IMS, CPI and virtual instruments.

The use of modern means of digital circuitry has fundamentally changed the principles of building IIS. In addition, the methods of reasonable distribution and direction of information flows make it possible to reduce their redundancy. This allows us to pose the problem of the maximum possible transfer of the processing of measuring information to the place of its formation, that is, to proceed to the pipeline processing of measuring information in a distributed IMS. In general, such a system consists of the following main parts: a system of primary converters (sensors), devices for collecting and preprocessing information, means for secondary processing of information, control and monitoring devices, communication devices with other systems of the object, storage devices.

According to the organization of the algorithm of operation, the following types of IIS are distinguished:

- by a predetermined algorithm of operation, the functioning rules of which do not change, therefore, they can be used only for research of objects operating in continuous mode;

- programmable, in which they change the algorithm of work on the program, compiled in accordance with the conditions of operation of the object of study;

- adaptive, the algorithm of which, and often the structure change, adapting to changes in the measured values ​​and conditional operation of the object;

- intellectual, capable of reconfiguring in accordance with changing conditions of operation and others to perform all the functions of measurement and control in real time and time scale.

Mathematical, software and information support is included only in IIS with computing systems.

Mathematical software - analytical (mathematical) models of the object of study (measurement) and computational algorithms.

The mathematical model of the measurement object includes a description of the interaction between input and output variables for steady state and transition states, i.e. model of statics and dynamics, as well as boundary conditions and permissible changes in process variables. The form of writing a mathematical model can be different: algebraic and transcendental equations, differential equations and partial differential equations. Transition and transfer functions, frequency and spectral characteristics, etc. can be used. There are 3 main methods for obtaining mathematical models of IIS research: analytical, experimental and analytical.

In recent years, when creating most IPs, mathematical modeling is most often used, which implements a chain: object - model - computational algorithm - computer program - computer calculation - analysis of calculations - research management.

The measurement algorithm can be presented programmatically, verbally, analytically, graphically, or a combination of these methods. The sequence of actions is involuntary, and implements one or another method for solving the problem. In all cases, the task must be formulated so accurately that there is no room for various ambiguities.

Software IIS includes system and general application software, which together form the mathematical software, which is implemented by the software subsystem. System software - a set of computer software used in the IIS, and additional software tools that allow you to work in a dialog mode, to manage the measuring complexes; exchange information within the subsystems of the complex; automatically carry out diagnostics of the technical condition.

Essentially, IIS software is a complementary, interoperable set of subroutines that implement:

- typical algorithms for the effective presentation and processing of measurement information, experiment planning and other measurement procedures;

- archiving measurement data;

- the metrological functions of the complex (certification, calibration, experimental determination of standardized metrological characteristics, etc.).

Information support determines the methods and specific norms of information display of the state of an object of research in the form of documents, diagrams, graphs, signals for their provision to service personnel and a computer for further use in management.

The whole measuring system as a whole covers metrological support (Fig. 1).

Picture 1

The structure of the technical subsystem of IIS includes:

• block of primary measuring converters;

• means of calculating electrical quantities (measuring components);

• a set of digital devices and computer equipment (computing components);

• measures of current time and time intervals;

• block of secondary transducers;

• I / O devices of analog and digital signals with normalized metrological characteristics;

• a set of elements of comparison, measures and elements of description;

• a block of signal converters, digital boards, displays, memory elements, etc .;

• various drives of information.

In addition to these elements, the IMS subsystems may include a number of coordination devices with the standard systems of the object under study, telemetry, etc.

The ergonomic, efficient and visual construction of the display forms and control elements, called the user interface, ensuring the interaction of the operator with a personal (or specialized) computer, is important for the operation of the IMS. In the general case, the interface is called the interface device of a personal computer with measuring instruments or any other external technical systems (sometimes this concept includes the software of the measuring system). The effectiveness of the interface under consideration lies in the rapid development of a simple conceptual model of interaction with IIS for the user, as far as possible. Other important characteristics of the user interface are its visibility, design and concreteness, which is ensured with the help of successively opened windows, drop-down nested menus and command lines with indication of functional "hot" keys.

In a fairly short history of the development of IIS, a number of generations can be noted.

The first generation is characterized by the formation of the concept of IIS and the systemic organization of joint work of means for receiving, processing and transmitting quantitative information. These were mainly centralized cyclical acquisition of measurement information with elements of computer technology. This period (the end of the 50s - the beginning of the 60s of the last century) is called the period of determinism, since the apparatus of analytical mathematics was used for research in IIS.

The second generation of the development and implementation of IIS is associated with the use of targeted information collection and its processing using embedded computers. The element base of such systems is represented by microelectronic circuits of small and medium degree of integration. This period (the 70s of the last century) is characteristic of the solution of a whole series of questions of the theory of systems within the framework of the theory of random processes and mathematical statistics; therefore, it is commonly called the period of stochasticity.

The third generation is characterized by a broad introduction to information-measuring systems of LSI, microprocessors, micro computers and industrial functional blocks that are compatible with each other in information, metrological, design, energy and operational characteristics, as well as the creation of distributed and adaptive IIS.

The fourth generation is distinguished by the emergence of flexible, tunable programmable IIS, which is associated with the development of computer technology. Flexible IISs are distinguished primarily by the freedom of the user in determining the functional purpose of the system. Creates and programs a flexible system is not a manufacturer of its components, and the user, in accordance with their tasks. In the elemental base of flexible IISs, the share of microcircuits of a large and extremely large degree of integration increases sharply.

The fifth generation is booming at the moment, due to the advent of adaptive, intelligent and virtual IIS, built on the basis of personal computers and modern mathematical and software.

Measuring and computing complexes

One of the varieties of IIS are measuring and computing systems. The main signs of the belonging of the measuring system to the CPI are the presence of a computer, normalized metrological characteristics, programmed control of measuring instruments, a block-modular structure of a structure consisting of technical (hardware) and software (algorithmic) subsystems.

By purpose, CPIs are divided into typical, problem and specialized.

Typical CPIs are designed to solve a wide range of typical tasks of automating measurements, tests or studies, regardless of the application.

Problem CPIs are developed to solve a specific problem in a specific area of ​​measurement automation.

Specialized CPIs are used to solve unique problems of automating measurements, for which the development of typical and specialized complexes is not economically feasible.

Measuring and computing systems are designed for the following tasks:

• implementation of direct, indirect, joint or cumulative methods for measuring physical quantities;

• presenting the measurement results to the operator in the required form and controlling the measurement process and the impact on the measurement object.

To implement these functions, the CPI must:

• efficiently perceive, transform and process electrical signals from primary transducers, as well as manage measurement instruments and other technical devices included in its composition;

• produce standardized electrical signals that are input to the means of influence on the object, evaluate the metrological characteristics and present the measurement results in the prescribed form.