Simple measurement instrument of moisture content for Indonesia coffee powder based on capacitive sensor

Abstract

Moisture content is one of the most important parameters for coffee commodity especially related to quality and taste. However, research on measurement instruments which capable to measure moisture content directly from a coffee sample is still very rare. Therefore, in the current study, this prototype is realized by utilized a capacitive sensor made from couple of copper plates to measure capacitive signal from the sample, which subsequently converted to a voltage signal by an oscillator and comparator, and then finally converted to the moisture content by a microcontroller which can be shown on an LCD screen. An accuracy testing is carried out by comparing the moisture content measured from the oven heating reference method and the prototype. The results show the average of measurement errors is 0.08 % and 0.22 % for coffee evaporated sample and coffee-water mixed sample respectively. Based on the maximum permissible error stated in OIML International Recommendation of R-059, this prototype meets the requirement of moisture meter of Class I.