• I S Williams

      Articles written in Pramana – Journal of Physics

    • An automated high precision calorimeter for the temperature range 200K–400K. Part 1: Design and performance

      I S Williams R Street E S R Gopal

      More Details Abstract Fulltext PDF

      A fully automated calorimeter has been designed and tested over the temperature range 200K–400K. The system may be used for measurements with an absolute accuracy of 0.2% of samples of approximate mass 50g and thermal capacity 15 JK−1. The temperature of the sample is determined by a quartz crystal thermometer of resolution 100 µK which is not in direct thermal contact with the sample. The performance of the system is illustrated by results obtained on high purity copper, distilled water and K2PbCu(NO2)6 which exhibits very sharp first order phase transitions at about 273.4K and 281.8K.

    • An automated high precision calorimeter for the temperature range 200 K–400 K. Part II. Design of temperature controllers

      H Heck I S Williams E S R Gopal S Jyothi

      More Details Abstract Fulltext PDF

      The design and construction of precision temperature controllers, capable of tracking the temperature of the samples to within 1 mK for ramp heating rates from 0.05 to 10 K per hour, are discussed. A tutorial section on the evolution of the control loop configuration is first given. This is followed by an outline of the refinements of the basic control loop desirable in the actual implementation of the electronic controller. The novel features of the present system and its performance are then briefly discussed. Finally the inadequacy of the conventional PID controllers for this application, the estimation of the time constants of the physical system needed in the design of the electronic controllers and the pitfalls in using a simple model of the heater plus thermometer assembly with a single pole are also discussed.

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