Colorimeter circuit

In industries such as metallurgy, chemistry, papermaking, and textiles, it is necessary to identify the color, whiteness, turbidity, and density of objects. Direct
observation with human eyes is time-consuming and inaccurate. In response to this problem, colorimeter, whiteness meter, turbidimeter and density
meter that use silicon photovoltaic cells instead of human heels have emerged. This type of instrument is popular because of its small size, easy operation and accurate measurement.
    As shown in Figure 9-4 3a, when a beam of parallel monochromatic light passes through a parallel container containing a solution with a concentration C, the optical density is expressed by the following formula:
    D = aCI.
In the formula, D is the optical density, sometimes called warm luminosity or extinction.
Light value; A is the solution absorption coefficient; C is the solution concentration;
J is the emergent light intensity.
    In general measurements, expressed in common logarithms. ,
it can be seen from the formula that as long as d and I remain unchanged and the incident light intensity remains
unchanged, then CccD, this is the working principle of the colorimeter
. That is, the color of the substance solution to be measured or
the chromaticity of the colored solution generated after adding a color developer
is directly proportional to the substance content. Therefore, from the intensity of light absorption of the colored solution reflected by the output of the photovoltaic cell , the amount of matter in
the solution can be known .     Figure b shows the schematic circuit of the instrument . The circuit consists of silicon photovoltaic cells, differential amplifiers and power supplies. When the monochromatic light passes through the sample and is projected onto the photocell, the photocell has a signal output, which is amplified by the differential circuit and read directly on the microammeter. In the figure, RP1 is the zero-adjusting potentiometer , and RP2 is the standard sample full-scale potentiometer . During testing, a standard solution is used for calibration, so that the concentration value of the solution can be read directly from the microammeter.