Letter Circular 1026:

Abstract

This paper reviews the art of testing and calibrating hygrometers. It describes and discusses instruments which may serve as primary and secondary standards. The use of precision humidity generators for producing atmospheres of known humidity is outlined. The methods and techniques of obtaining fixed humidity points are given. Recommendations are made concerning further research to insure consistency and accuracy in hygrometric measurements. CONTENTS 1. GENERAL INTRODUCTION 2. HYGROMETER STANDARDS 2.1 Primary Standard 2.2 Secondary Standards 3-PRECISION HUMIDITY GENERATORS 3*1 Pressure Humidity Apparatus 3.2 Two-Temperature Humidity Apparatus 3.3 Divided Flow Humidity Apparatus 3-4 Apparatus Employing Combined Principles 4.