From Big Medical Encyclopedia

SENSORS (primary measuring converters) — structurally isolated link of the measuring device or information channel which is carrying out power communication of a controlled object with measuring system. Are intended for perception of controlled size and its transformation to a signal convenient for transfer on the secondary (registering) equipment for the purpose of its transformation, processing, representation and management. The secondary equipment represents electric, pneumatic and hydraulic devices are more rare.

In the medical practician D. use at various medical - biol, researches for measurement fiziol, the indicators of an organism which are expressed directly through corresponding physical. sizes (temperature, pressure, speed, etc.), registration of power manifestations biol, the processes and acts which do not have unambiguous physical. equivalents (pulse, peristaltics, swallowing, blinking, etc.), definitions of properties biol, fabrics and structures (color, conductivity, transparency, etc.), and also specific biol, indicators (sensitivity, biochemical, processes, etc.).

The first D. represented various removable devices transforming preferential mechanical signals in pneumatic then there were D. with an electric exit — the wipers closing an electric chain in response to the movements of an object (aktografichesky D.), microphones for phonocardiography (see), thermocouples for measurement of temperature (see. Thermometry ). D.'s improvement began in the 20th years in connection with implementation in practice fiziol, researches of the secondary measuring equipment, intensifying and universal oscillographic equipment (see. Oscillography ). Among modern recorders the main place is taken by the electric and electronic package (see. Elektrodiagnostika ). Therefore transformation of sizes various physical. the nature produce hl. obr. in the voltage or current that provides precision and bystry measurement, transfer on distance (see. Telemetry ), versatile information processing, and also its use for automatic control biol, processes.

the Schemes of the principles of operation of some sensors characterizing power bonds of an object of a research with a sensitive element of the sensor (examples of a clinical use): and — an object of a research is a natural energy source, the sensor measures a power flow of own energy source of an object; 1 — an object of a research (heart) with an energy source (the vibrating structures of heart), 2 — a power flow (sound vibrations in body tissues), 3 — a sensitive element of the sensor (a membrane of the phonocardiographic microphone); — an object of a research is the carrier of the energy introduced from the outside (for example, 131 I), the sensor measures a power flow from an object of the research depositing the carrier of energy; 1 — an object of a research (thyroid gland) with an energy source (the entered radioactive material, For Example 131 I), 2 — a power flow (radoactive radiation), 3 — a sensitive element of the sensor (the detector of radoactive radiation); in — an object of a research is the converter of the power flow arriving from an external source, the sensor measures intensity of the power flow transformed by an object; 1 — an object of a research (blood vessels of a finger of a hand), 2 — a sensitive element of the sensor (the device reacting to the fluctuations of intensity of light caused by a pulsation of vessels), 3 — a power flow (a flow of light), 4 — an external energy source (an electric bulb); — an object of a research — the pulsing body surface (1); depending on approach or removal of a pulsation from a sensitive element of the sensor (the measuring instrument of high-frequency current — 4) the energy flow (3) going from an energy source (a high-frequency generator — 2), changes the intensity that is perceived by a sensitive element and is transferred to the chart recorder.

Experiences various external influences (warmly, light, vibrations, humidity, gravitation etc.), but has specific sensitivity to (entrance) signal perceived by it representing a power flow of this or that physical. the nature (mechanical, electric, thermal, light, etc.), in each separate case variously created in time and on intensity (fluctuations, impulses, a series of impulses etc.). Character of the perceived information significantly depends on a form of signal transmission, edges is defined by interaction of an energy source, object of a research and the sensor. Allocate three main forms of information transfer at which D. perceives power manifestations of an object (organism) — bioelectric potential (see) and biocurrents, pressure and expenses, forces and movements, sound pressure (fig., a) etc.; the energy introduced in an object from the outside (radioactive — fig., thermal, etc.) and used for quantitative and quality standard of various processes, including for studying of the movement of a flow and distribution of substances in an organism; the power flow from an external source which passed through an object and characterizing its transfer properties — transparency (fig., c), color, electric or acoustic resistance, electric capacity (fig., d), etc.

According to a type of energy of an entrance signal (electric, mechanical, thermal, beam, chemical, light etc.) D. characterize as mekhano-, thermo - photo or hemoelektrichesky. With their help perceive information on the phenomena and properties corresponding to these types of energy (tab).

Some kliniko-physiological methods of a research of an organism based on transformation and measurement of its various physical quantities by means of sensors

Is an entrance link of the measuring information device (system) and quality of the obtained information depends on it. Therefore high metrological requirements from which main thing is accuracy (static and dynamic) — quantitative compliance of value of an output signal to entrance size are imposed to D. Static accuracy is expressed through two main metrological characteristics — the range and an error of measurement. Understand area of values of entrance size as range, in limits the cut is provided its measurement with the set (passport) error characterizing a deviation of result of measurement from a true value of the measured size. The error is usually expressed percentage of the range of measurement (the given error) and characterizes a class of the measuring device (1% — the first class, 2% — the second class etc.). High requirements are imposed also to quality of measurement of rapidly changing sizes (dynamic accuracy) — the sound phenomena, pressure, forces, expenses, etc. The major dynamic characteristics is the amplitude frequency characteristic determining the frequency range of change of an entrance signal the error of transformation on amplitude keeps within Krom in the set limits.

High precision (a small error) is provided, as a rule, by multistage transformation of a signal. Therefore modern D. produce in the form of the uniform block of converters. A structural basis of D. is the measuring channel serving for perception and transformation of the signal arriving from an object. May support also channel of formation of a power flow if for measurement use an external energy source; the created power impact on a live object shall be below a threshold of its sensitivity to this influence.

The main links of the main measuring channel D. are the sensitive element, or the detector, and the intermediate converter. The sensitive element perceives a signal from an object in its natural power form and will transform it to the parameter or the size convenient for the subsequent transformation. The intermediate measuring converter transforms a signal of a sensitive element to the form convenient for strengthening and formation of an output signal.

In which energy of an entrance signal will be transformed by means of a sensitive element (e.g., photo or a piezoelement) in tension or current, call power. The role of the intermediate converter is carried out in this case by the amplifier creating an output signal. In which energy of an entrance signal is used only for change of passive parameter of this or that scheme (e.g., turns a rotor of the variable resistor or condenser), call parametrical. The intermediate converter in these D. changes resistance or capacity in tension or current.

In medical practice D. are widely applied to measurement or registration of parameters of blood circulation as power (piezoelectric, induction, ionization), and parametrical (capacity, resistive, inductive) (see. Blood circulation, methods of a research ), breath, muscular activity (see. Ballistokardiografiya , Cardiography , Pletizmografiya , Sfigmografiya ), and also active reductions of heart, skeletal muscles and muscles of band bodies (see. Dinamokardiografiya , Pneumography ).

May contain also logical, decisive, adjusting, compensation and other links and chains. The channel of formation of a flow usually includes a radiator of energy and the shaper of a power flow. If as the detector of energy the reversible converter, napr, a piezoelement is used, then it at the same time can perform also function of a radiator.

Alarm communication of D. with an object is carried out via receivers — catheters, probes, pneumoreceivers etc.; for communication with the secondary equipment there is a cable (pipeline). For D.'s orientation in relation to an object supports, devices for mechanical scanning, tracking, etc. are used.

Information transfer from an object on the perceiving link of the device in some cases is subject to accidental indignations owing to activity of a live object, instability of conditions of signal transmission in a zone of contact of D. with an object and under the influence of other factors leading to distortion of data (artifacts). Set of these factors defines a so-called methodical error of measurement. For increase in accuracy of measurement of D. or its perceiving link is placed directly on body or in cavities in which it is necessary to execute measurement, applying applications: or sounding. However these interventions are not indifferent for an organism. Therefore the most rational solution of the problem of accuracy and safety of researches by means of D. is, on the one hand, increase in accuracy of nontraumatic methods of a research (a phonocardiography, a tetrapolar reografiya, etc.) by correction of errors, with another — the profound analysis and automatic processing of the obtained data by means of the COMPUTER for the purpose of allocation of the most important signs (the analysis of a cordial rhythm, signals of electric activity of muscles, spirogramm etc.). These two ways define development of such high-informative and safe methods of a research as thermovision, chamber pneumography, a light-beam and electrocapacity aktografiya, and also rather small and traumatic methods — a sound interoskopiya and gamma topography. Development of means of primary information retrieval opens ample opportunities for equipment of medicine the equipment with use of the microminiature D. entered or implanted in bodies, the equipment for contactless researches and exact multipurpose measuring complexes.

Bibliography: Ageykin D. I., Kostina of E. N and To at z N of e of c about in a H. H. Sensors of control and regulation, M., 1965; B and - with to and y E. B. Use of the principles of electric registration of mechanical sizes in physiological researches", in book: Sovr, methods issled. functions serd. - a vessel. systems, under the editorship of E. B. Babsky and V. V. Parin, page 5, M., 1963; Turi-ch and A. M. N, etc. Electric measurements of not electrical quantities, L., 1975, bibliogr.

E. K. Lukyanov.