Pressure balanced type membrane covered polarographic oxygen detectors for use in high temperature-high pressure water, (I) Application of guard electrode to improve detector performance at temperatures above 200.DEG.C.

Abstract

A pressure balanced type membrane covered polarographic oxygen detector was developed to determine directly oxygen concentrations in high temperature, high pressure water without cooling and pressure reducing procedures. The detector is characterized by the following features: 1. The detector body and the membrane for oxygen penetration are made of heat resistant resin.2. The whole detector body is contained in a pressure chamber where interior and exterior pressures of the detector are balanced.3. Thermal expansion of the electrolyte is absorbed by deformation of a diaphragm attached to the detector bottom.4. The effect of dissolved Ag+ on the signal current is eliminated by applying a guard electrode. As a result of performance tests at elevated temperature, it was demonstrated that a linear relationship between oxygen concentration and signal current was obtained up to 285°C, which was stabilized by the guard electrode. The minimum 02 concentration detectable was 0.03 ppm (9.4×10−7 mol/kg).