Design Of High-accuracy Luminometer

In the architecture, health, film and television industries, luminance measurements are very common, all of these demand measurement of high precision. Consequently, this paper designs a low-cost digital luminometer with high-precision and automatic conversion range.The system regards AT89C51 as the key part of the measurement system, which includes signal gather, signal amplification, A/D conversion, liquid crystal display, key board and RS-232 communication interface parts.In this paper, silicon photocell is chosen as luminometer photoelectric conversion probe with a wide spectral range response, short response time, photoelectric conversion with high efficiency, and large area of PN junction of silicon solar cells as luminometer photoelectric conversion probe and. it creates a separate optical probe, and introduced a v(λ)filter and cosine amendment to separate if from the fuselage, it can be better adapted to the cosine law and improve the measurement precision and scope. Next, the following points are emphasized: (1) The design of photoelectric conversion preamplifier circuit. In order to improve the measurement accuracy of luminometer and ensure linear relationship of the photoelectric, operational amplifiers is designed as current-voltage converter form, on the one hand, it is available to zero-load effect; on the other hand, short-circuit current can be transformed into a voltage volume through the feedback resistor, it is equivalent to voltage drop flowed through a load resistor on the actual effect. (2) Design of automatic conversion range circuit. As visible light irradiation of silicon solar cells at the photocurrent is too wide, in order to guarantee the accuracy of A/D conversion. The 4602 Analog Switches, which produced by MAXIM companies with small channel resistance, is chosen to realize switching between the different range, switching of range is controlled by microcomputer. (3) Design of display circuit. TC1602A LCD module is used in this paper, while LCD illumination does not affect the measurement and LED can Luminescent by itself that had a great influence on the luminance measurements. (4) Choice of scaling transformation. The software is design to control and overcome some shortcomings, which include the high cost of hardware controlling, PCB area occupied, signal scale-transformed is not very accurate, resistance value drifting because of temperature, humidity, and other environmental changes. Finally, the paper presents anti-jamming specific methods and measures of the impact of illuminometer performance. The testing and adjusting of the system indicates that the whole design is feasible and reliable, and the measurement range, resolution, spectral response error basically meet the design requirements.