外文翻譯---高精度溫度測(cè)量裝置的設(shè)計(jì)-展示頁(yè)
2025-01-27 16:34本頁(yè)面
【正文】 one requires nonlinear analog circuit andthe second uses numerical methods that are puted by microprocessor or puter . Analog circuits are frequently used for improving the linearity of the sensor characteristics, which implies additional analog hardware and typical problems associated to analog circuits such as temperature drift, gain and offset error. Using the second method, sensor nonlinearities can be pensated by means of arithmetic operations, if an accurate sensor model is available (direct putation of the polynomials), or use of a multidimensional lookup table. Direct putation of the polynomial method is more accurate but takes a long time for putation, while the lookup table method, though faster, is not very accurate . In recent years, application of ANNs has emerged as a promising area of research in the field of instrumentation and measurement . It provides a neuroputing approach for solving plex problems especially in nonlinear system modeling which the network itself is a nonlinear system. This is extremely useful when the area of interest is absolutely nonlinear including the experimental data that is used for training. One of the most powerful uses of ANNs is in function approximation (curve fitting) . Interpolation based on ANN provides lower interpolation errors when pared with conventional numerical interpolation . In the work we present here, high precision temperature measurement system based on ANN approach is proposed. The calibrating data is obtained by Wavetek 9100 calibration unit that is necessary for the training and the testing phases of the ANN. The hardware and software parts of the system are integrated in a VI used for system operation and calibration. The ANN is matched to the calibrating data by providing a desired final error. The mean square error between calibration and the ANN modeled data is minimized in terms of the structure, number of layers, and number of neurons by the developed software.2 System HardwareA thermocouple generates a voltage proportional to the measurement junction temperature at mV levels while the cold junction temperature is constant. In order to make an accurate measurement the cold junction temperature must be known. Figure 1(a) shows the block diagram of the temperature measurement system designed via an ANN in the operation phase. It consists of a thermocouple (type E) exposed to a desired temperature, including signal conditioning circuit with 16bit analog to digital converter (ADC) and Input/Output interface card interfacing with a puter. The designed signal conditioning circuit has a programmable gain instrumentation amplifier (PGA204BP) with the gain of 1, 10, 100 and 1000, a 16bit ADC (AD976A), an AD595 monolithic thermocouple amplifier with cold junction pensation which is configured as a standalone Celsius thermometer and a 4 channel analog multiplexer (ADG529A) which select the thermocouple or output of Celsius thermometer. The AD976A is a high speed, low power 16bit A/D converter that operates from a single 5V supply. This part contains a successive approximation, switched capacitor ADC, an internal reference and a high speed parallel interface. Accuracy of the system depends directly on step size of ADC. With a 177。10V inputs, one LSB of AD976A is 305μV. When AD595 is used as a Celsius thermometer, the thermocouple is omitted, and the differential inputs are shunted together to mon. In this mode, A
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