Development and testing of a hardware platform for measuring instruments based on near-infrared diffuse reflection

• The developed a system has high immunity to interference of external light.
• The amount of reflected light decreases with the increment of moisture in the sample.
• Multivariate calibration may be used to determine substance concentration.
• The temperature control system stabilized the optical sensor at 25 °C.

Generally, the methods which enable the measurement of a given substance concentration in a material are slow and destructive. On the other hand, the near-infrared spectroscopy makes it possible to rapidly determine concentrations in natural state samples, i.e., it is a nondestructive method of analysis. Unfortunately, instruments based on this technology are not easily developed due to the low signal-to-noise ratio inherent to the problem, the need of building optical-electronic systems, the great influence of external factors, among others. This paper presents a hardware and software platform that can be easily adapted to be used in concentration determination of various types of substances. Therefore, fixed mirrors, which do not require alignment, were used. Signal noise was reduced by using EMI filters, active filters and metal shield. In addition, InGaAs sensors were used, which present rapid response and so are more suitable for real time measurements. The developed system was evaluated by the detection of moisture in instant coffee samples. The results show that this equipment is sensitive to variations in humidity, but it can also be applied to detect concentrations of other substances.