The logarithmic amplifier gives a voltage response proportional to the ratio of the current i 1 to the i 2, where i 1 is a current set to 500 μA with a 3-terminal adjustable current source. The calibration is achieved from two variable voltage dividers the values of these voltages are used like an offset to adjust the values of optical density displayed to the values of a calibration density strip tablet with the National Institute of Standards and Technology (NIST) traceability. A microcontroller performs the calculation of optical density and its display in a low-power consumption liquid crystal display (LCD). The acquisition and signal conditioning are achieved by implementing a circuit with the well-known integrated logarithmic amplifier LOG102. The instrument consists of a light source, viz., light-emitting diode (LED), a tiny aperture through which the light is directed and a light detector (photodiode) to measure the light intensity transmitted to the film.
An overview of the system framework of the transmission densitometer is shown in Figure 1. In other fields, a similar technique has been used with good results as those presented here. Even other instruments have been constructed for this purpose, but the technology is old or they do not cover a wide range of optical density.
The range of OD measured by the instrument is between 0.15 and 4.0 with an uncertainty of ☐.02 OD.
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