Design, construction and testing of a portable soil moisture meter using a modified gypsum block as sensor

Date

3-1992

Degree

Bachelor of Science in Applied Physics

College

College of Arts and Sciences (CAS)

Adviser/Committee Chair

Nelio C. Altoveros

Abstract

A portable soil moisture meter was designedIciD7gCrle(al constructed and tested using a modified gypsum sensor. The circuit design contains three modules. The first module consists of two voltage regulators which operates in a fixed +12V and -12V output mode. The second module consist of a Wein Bridge Oscillator which serves as an alternating current voltage source for the third module. The third module is a practical bridge amplifier whose output voltage is exponential in a certain range with respect to a change in the moisture content of the gypsum block. A new design of the two-electrode gypsum block was fabricated using a small rectangular mold in order to improve the response time of the block to a change in the moisture level. The output of the fabricated moisture meter ranges from 0 volt (AC) for the saturated condition and 12 volts (AC) for the wilting condition and is readable through an ordinary voltmeter. The instrument is being powered by four (4) 9V batteries and is packaged in a fiber glass case for protection from environmental stresses. The results show an exponential relationship of the voltage readings and the moisture contents of the block between the saturation and wilting conditions. By plotting the natural logarithm of the voltages and moisture contents it was found that the newly-designed gypsum block has 'a wider linear range than the existing block design. the commercial and the fabricated meters were compared and was found that the former is more efficient because it was already been calibrated to different soil types and the latter is cheaper in terms of cost. It was also found that the new design of the block has a faster response time to a change in moisture level than the existing design. It was recommended that the fabricated soil moisture meter be calibrated to different types of soil, be equipped with its own meter-panel (analog or digital) to indicate voltage and moisture levels, and be interfaced with a data logger for continuous field monitoring of soil moisture.

Language

English

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

Thesis

Document Type

Thesis

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