Trace moisture detection in oil filled transformer by ceramic sensor

This paper reports on the suitability of thin film nano porous.-alumina sensor for sensing parts per million (ppm) moisture present in transformer oil. Transformer oil degrades slowly by weathering, causing dielectric break down voltage of the oil to fall down. For improving this break down voltage, water must be removed from the transformer oil. Flash point of the transformer oil ranges from 150 degrees C to 200 degrees C. When the oil is slowly heated up to 75 degrees C water vapour comes out from oil which is detected by ceramic sensor. The sensor is prepared from organo-metallic precursor by sol-gel process. Gold coated a-alumina substrate was dipped within the alumina hydra-sol and a thin film of.-alumina formed on the substrate. The sensor capacitance was measured as a function of ppm moisture level. The circuit produces an output voltage which is precisely related to the absolute value of the capacitance of the dielectric material. In order to improve the sensitivity, parallel electrode structure was patterned on the nano porous dielectric. The response is sufficiently linear in extremely low ppm level moisture. A prototype hygrometer was built for detection of trace moisture in transformer oil. Porous alumina can be produced at a relatively low cost and in a variety of structural configurations. Sol-gel processing of alumina allows superior control on pore morphology, phase formation, purity and product microstructure compared to the more traditional techniques like Anodic oxidation of alumina sheets, tape cast by different sizes of alumina powder etc

Nano structure metal oxide ceramic thin film for detection of trace moisture using CMOS timer

A trace moisture analyzer is described below which consists of a moisture sensor with nano porous thin film sol-gel processed γ-Al2O3 dielectric and active circuit. The thinner layer pore geometry enhancing the entrapment of water molecules makes it high wet to dry capacitance ratio. A simple dual-CMOS timer has been developed to detect moisture by controlling the monostable pulse width. Monostable pulse correlates the ambient moisture. The sensor is tested in combination with the circuit. Excellent quasi linearity is observed over the range from 0-50 ppmv. An experimental graph shows resolution better than 1% and accuracy of 2%. The response time is less than 2 minutes

Trace Moisture Response Property of Thin Film Nano Porous g- Al2O3 for Industrial Application

Nano porous thin film g-Al2O3 is prepared by sol-gel method by heat treating process at 5500C.The samples are made of various coating thickness and investigated as trace moisture sensor at room temperature within the range of –720C to –420C dew point (DP). It is found that at a particular coating thickness the sensitivity and response time are found to be suitable for commercial application. The capacitance change over the dew point (DP) range from –720C to –420C is found to be prominent for making a sensitive device

Trace moisture response property of thin film nano porous gama-Al2O3 for industrial application

Nano porous thin film γ-Al2O3 is prepared by sol-gel method by heat treating process at 5500C.The samples are made of various coating thickness and investigated as trace moisture sensor at room temperature within the range of –720C to –420C dew point (DP). It is found that at a particular coating thickness the sensitivity and response time are found to be suitable for commercial application. The capacitance change over the dew point (DP) range from –720C to –420C is found to be prominent for making a sensitive device

Pore size optimisation of humidity sensor - a probabilistic approach

Moisture adsorption in ceramic sensors undergoes a series of different chemical and physical mechanisms with respect to humidity of the incident gas mixture. Pore size of the ceramic specimen is one of the major parameters which contribute significantly to the condensation. Since the free path of the incident water vapour molecules alters with the changes in the vapour content in the carrier gas, an optimum pore size that would be comparable to the free path of the wayward vapour molecules is always desirable under all humidity conditions. A probabilistic model has been presented in this paper for pore size optimisation of ceramic under simplified assumptions. Model results have been presented for a variety of carrier gases for which the Brownian motion gets restricted and the associated energy attains a minimum so that the vapour adsorption becomes most likely. The pore size works out in the nano range. The overall pore size equates 80.91 nm at normal pressure. Under increased pressure the experimentally determined pore size for ceramic samples tallies well with the pore size computed from the model. The probabilistic treatment of mean free path of vapour molecules in this study accommodates for the basic limitations of classical kinetic theory of gas. (C) 2002 Elsevier Science B.V. All rights reserved

High temperature humidity sensor for detection of leak through slits and cracks in pressurized nuclear power reactor pipes

The leak before break (LBB) concept is well known to nuclear power reactor. The problem is common to water power reactor. This is based on the premise that a detectable leak will develop before catastrophic break occurs. The main purpose of the present study is to develop tape cast MgCr2O4+35mole% TiO2 and gel cast γ-Al2O3 humidity sensor for use in LBB applications at 3000C. The material capacitance varies with transient injection of water vapour adsorption. In actual plant, the sensors are placed on a steam pipe surrounded by heat insulation. The pipe unites the nuclear reactor and power generator. The analysis of humidity distribution in the annulus is calculated assuring leak rate 0.1gpm in a 30 m long tube. In this paper, analysis is done on the basis of the two types of sensor using AC frequency. Performance characteristics are observed for the LLB application

Development of commercial nanoporous trace moisture sensor following sol-gel thin film technique

A simple laboratory technique for the routine preparation of gamma-alumina (Al2O3) thin films on gold electrodes coated on an a-alumina substrate (10 mm x 20 rum x I mm) is described here. Prepared thin films and porous electrodes are dried at 100 degrees C and sintered at 400-550 degrees C for 4 h to achieve the gamma-Al2O3 phase. Further the temperature is shifted to 950 degrees C for 1.5 h for curing the electrodes. Microstructure of the films are analysed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM). The studies suggested that doubly coated gamma-Al2O3 led to an increase in the surface roughness of the deposited film which provided a unique sensor sensitive to trace moisture on a ppm level by volume (ppm(v)). (C) 2007 Elsevier B.V. All rights reserved