Headspace Resistance Standards for the Shirley Developments Ltd. Micromat Tester

Abstract

High precision headspace resistance standards (HRS) are developed for the Micromat model of the Shirley Developments Ltd. fineness and maturity tester. The Micromat measures cotton fineness and maturity based on the principle of air permeability through a fixed mass of fibers at two different stages of compression. Differential pressures are the quantities measured, and are related to maturity and fineness by appropriate equa tions. HRS are mechanical air flow restrictors: we use narrow diameter tubes, needle valves, and metal frits. Air flow rates through the calibration cotton are adjusted to give the declared differential pressure values, and these flows are exactly "transferred" to the HRS. The calibration transfer coefficient β, defined as the ratio of differential pressure through the HRS material to differential pressure through the calibration cotton, is fixed at β > 1 to increase sensitivity to Micromat drift. Routine analysis of two sets of cottons is presented based on HRS calibration and control. There is no drift in in strumental readings over the 3-week and 6-week periods required to analyze the sets of cottons.