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An examination is made of the basic types of measuring and monitoring instruments utilizing externally modulated fiber-optic sensors with built-in microprocessors, making it possible to achieve a considerable improvement in their metrological characteristics and also to lower the apparatus costs and reduce the overall dimensions and power consumption. The basic algorithms for the functioning of these instruments are presented and the circuitry required for implementing them is considered.The appearance of microprocessors of various architectures and of peripheral large-scale integrated circuits having a low power consumption enable a considerable improvement to be made in the user properties and metrologieal characteristics of the majority of measuring instruments. The advanced structure of modern built-in program-controUed single-crystal microcontrollers makes it possible not only to implement in measuring instruments such classical microprocessor functions as statistical processing of the results obtained and linearization of the transfer characteristic, but also to increase the accuracy at minimum cost and to compensate uninformative factors of the primary transducers themselves which was previously done using "hard" logic and was therefore not widely adopted.The authors consider that the most important effect of using microprocessor insmmaents may be in devices utilizing sensors having an individual conversion function. These include externally modulated fiber-optic sensors [1].Noncontacting devices for measuring displacements are among the simplest measuring instruments utilizing fiber-optic sensors. They include a radiation source and a transmission light guide along which the light flux is conveyed to the measurement zone, two receiving channels (light guides transmitting the flux refl6cted from the object to photodetectors) and a processing unit. The photodetector signals carry information on the distance from the monitored object and depend on the light flux losses due to reflection and propagation (see Fig. 1).The basic algorithm for compensating the uninformative factors of such fiber-optic sensors makes provision for dividing the signals formed in the two receiving channels. The resulting characteristic is theoretically independent of the influence of factors which proportionally reduce or increase the magnitude of the flux incident on the photodetector channels. This makes it possible to practically exclude multiplicative components of the sensor error due to temperature and time-dependent instability of the radiation source and the dependence of its light flux on the power supply voltage, and also errors caused by a change in the reflection coefficient of the object, surface roughness, and the state of the medium in the gap between the end of the light guides and the object when the monitoring point is displaced. However the technical implementation of the operation of dividing analog signals usually introduces an additional error and to a considerable extent determines the frequency and dynamic ran...

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