New a.d. convertor with special application to medium precision platinum resistance thermometry

Platinum resistance thermometers mounted on ceramic formers have a potential uncertainty, after calibration, of 0.01°C over a range exceeding ¿30 to +250°C. To achieve this requires resistance measurements of higher precision than is conveniently available from commercial digital instruments. A new time-interval type of a.d. convertor has been developed for this purpose and incorporated in a simple digital resistance meter with a full scale reading of 300.000 ¿ and an uncertainty of 1 m¿.