Precision temperature measuring equipment

The paper describes the development of a resistance thermometer of high accuracy together with its associated bridge circuit. The thermometer is of the dual-element type in which two coils of metals having different temperature coefficients of resistance are incorporated in the sensing head. The change in the resistance ratio of the two coils gives a unique indication of temperature. The bridge circuit developed for use with the thermometer employs the transformer ratio arm method which allows highly accurate and stable ratios to be produced. A modified potentiometer recorder automatically balances the bridge and provides direct read-out. A further refinement is the addition of a shaft digitizer which gives a record of the temperature in a form suitable for automatic data logging. The whole apparatus is stable and robust and can be used in industrial applications.