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751分光光度计在使用中常见故障之一是,仪器开启后,发现指零表指针在平衡位置附近来回摆动,很不稳定。首先,对此故障进行分析。即对稳压电源、光源、光电管等检查,结果均无问题。为此,初步判断故障发生在光电暗盒内的元件上。从装在光电暗盒内的放大器结构图(见下图)可知,如果放大器输入级的高阻值(2GΩ)电阻R受潮或光电管受潮,均会引起指针不规则摆动。其原因是,光电管输出的光电流十分微弱(10~(-9)～10~(-10)A),经高阻R形成电压信号。该电阻被封装在绝缘材料中,然后置于暗盒内,若暗盒内受潮,这相当于在高阻两
One of the common failures of the 751 spectrophotometer in use is that after the instrument is turned on, it is found that the zero gauge pointer swings back and forth near the equilibrium position, which is very unstable. First, analyze this failure. That is, the power supply, light source, photocell and other inspection, the results are no problem. To this end, initially determine the fault occurred in the photoelectric cassette components. It can be seen from the structure of the amplifier in the photo cassette (see below) that if the high resistance (2GΩ) resistance R of the amplifier input stage is damp or the photo transistor is damp, it will cause the pointer to swing irregularly. The reason is that the photocurrent output by the photocell is very weak (10 ~ (-9) -10 ~ (-10) A), and the voltage signal is formed by the high-resistance R. The resistor is packaged in an insulating material, and then placed in the cassette, if the cassette is damp, which is equivalent to two high resistance