P-TEST - computerized instrument for testing of the water vapour and thermal resistance of fabrics

The water vapour permeability of fabrics is presented, along with thermal resistance, the most important characteristic of clothing comfort. The patented measuring method and original facility are briefly introduced. The paper describes a prototype of stand-alone instrument that employs and automates this method. An embedded microcontroller together with appropriate sensors replaces the number of facility devices and greatly simplifies the instrument operation. The concept of analog signal conditioning and conversion is discussed. Firmware is completely written in C language including interrupt handlers. The function of core subroutine that handles A/D converter with channel multiplexing and makes temperature control, averaging, conversion and linearization of integer data to the SI values is explained. Both the measurement process and the formulas are used to compute the results. PC application that supports built-in diagnostics in the instrument through serial link is mentioned. Finally, the experience with the prototype electronics and its calibration is released and future improvements are outlined.