Abstract
For the purpose of developing a compact and light weighted measurement system for the concentration of electrolytic solution, a new technique with the application of transmittancy membrane is devised.
It is known that a liquid densitometer (conductivity meter) is commonly used for the measurement of electrolytic solution concentration. For the purpose, there are DC and AC (below several KHz) bridges and either of which has merits and demerits. Especially when AC bridge is used, apparent solution impedance obtained is containing both surface and solution impedance. In order to eliminate the influence of the surface impedance, it is better to increase the measurement frequency up tot some MHz order, however, RF bridge is not easy to operate and is apt to include some stray error. A resonance method by a Q meter for measuring RF impedance is the most easy way.
This is the way of utilizing characteristics of a solution transmitted and diffused into pure water through a control plate and cellophane membrane since the solution concentration varies in the pure water. Namely, continuous measurement by a Q meter has been tested regarding Q variation of a detector coil which is installed in pure water. The most remarkable feature of this method is an indirect measurement by diffusing and transmitting solution into pure water through membrane rather than direct measurement on the solution. It is possible to obtain many kinds of information. A spiral coil which is printed on a board by photoetching technique is used as a detector. It has several advantages that the sensor becomes rather small and light weighted so that it occupies less space which turned out less quantity of solution under sample and the coil parameters are stable.
Experiments have been conducted for various types of solution and for the extent of influence of the control plate. It has been found out that each solution has a proper curve for different value of concentration with the optimum condition of a control plate. Analysis on each curve resulted fundermental characteristic values which can be used for the identification of solution.
