Удосконалення метрологічного програмного тесту вимірювального каналу температури

Abstract

Запропоновано структуру вдосконаленого метрологічного програмного тесту шляхом введення в його структуру нових блоків, що дають змогу враховувати вплив специфічних похибок термоелектричного перетворювача з керованим профілем температурного поля. В такому вигляді він стає придатним для імітації вимірювального каналу, який використовує ТЕП з КПТП і створює можливість дослідження метрологічних характеристик такого вимірювального каналу. Крім того, наведено результати досліджень і дано рекомендації щодо подальшого зменшення похибки вимірювання температури.

Modern measuring channels of measurement and control systems become more complex. This complicates the process of determining metrological characteristics of such systems due to the rapid growth of the amount of experimental investigations. Nowadays the model simulation is often used to solve this problem [1 ... 3] and allows to speed up the metrological investigations. There was suggested the creation of specialized software – metrological software tests (MST) [4, 5]. MST contains blanks simulation models of typical components of measuring channels. These models contain specific errors of relevant components of the system units. They take into account the mentioned above errors effect on measurement results during modeling process. The signal is sent to the corresponding input of MST component. It makes possible the investigation of considered set of components reaction on the corresponding errors and estimate efficiency of the available in the measuring channel means of decreasing of those errors. Thus, the MST allows investigation of the efficiency of methods and means of correcting errors for different conditions and environments. Available MST allows to investigate only measuring channels, in which the error from the acquired thermoelectric heterogeneity of thermocouples is adjusted according to the method considered in [7, 8]. That is why MST should be appropriately modified. The aim of the proposed paper is to improve the MST described in [4, 5] to be able to apply improved MPT for investigations of the measuring channel that use TBS with CPTF. The structure of the proposed MST measuring channel of temperature measurements that uses TBS with CPTF is presented in Fig. 1. The MST similar to the MST is considered to be described in [4 ... 6], the same additive error model of measuring channel components. The structure of the measuring channel itself and digital to analog converters that can directly interact with components of the measuring channel is shown in the top of Fig. 1. The most important part of the MST is the sets forming software located in the middle of Fig. 1. Each MST block simulates only one property of a component of the measuring channel then blocks are grouped by components ( below each component of the measuring channel of the top part of Fig. 1 "its own" blocks of MST). The blocks that simulate main error are located in the top row. These errors are split into components. Additional errors caused by the temperature and time of exploitation are located below. The errors caused by the additional parameters are located in the next row. The only difference is that additional block – block of thermoelectric heterogeneity is built-in structure of conventional MST. If any error consists of separate components, these components are placed below it. The lowest row are blocks of nominal conversion characteristic (CC) of components. The thermocouple is split into two subcomponents (hot and cold junctions). CC of switch is considered to be equal to one. However, the profile of temperature field of the main thermocouple TBS with CPTF is not constantly stable. It changes under influence of: 1. Non ideal design of TBS with CPTF. 2. Errors of built-in multi-channel temperature control subsystem, which supports and stabilizes the profile of the temperature field along main thermocouple of TBS with CPTF. The structure of MST for research of measuring channel that use TBS with CPTF as it was shown in [4, 5], MST consist of three relatively independent units: 1. Software for creating sets of test signals (codes). These codes correspond to output signals of components of the measuring channel, whose work is simulated by MST; 2. Software for providing communication with considered measuring channel that delivers the generated set of test signals to the inputs of the respective components, and also receives and stores the measurement; 3. Software for processing the results obtained during the investigations.