Abstract.A new comparison system has been constructed for the calibration of capsule-type standard platinum resistance thermometers (CSPRTs) below 273.16 K at the National Institute of Standards (NISEgypt). The system can compare two CSPRTs at once. A gold plated comparison block, in which CSPRTs are mounted for calibration, is made from oxygen-free high-conductivity copper. A description of the system and the comparison block along with the comparison method is given. The standard uncertainty related to the temperature control of the system is estimated to be 0.04 mK. The calibrated values for CSPRTs and obtained using the comparison system are in good agreement with those obtained by the direct realization of the low temperature fixed points of the ITS-90 within the combined standard uncertainty.

(2013)]. The system can calibrate two CSPRTs at once. The compartment is accommodated in an adiabatic calorimeter. With a special technique, the calorimeter could go down to a temperature of 52 K using liquid nitrogen and special pumping system.

(2014)]. The main target of this work is to get the lowest possible uncertainty in calibrating Capsule Standard Platinum Resistance Thermometers (CSPRTs) under adiabatic conditions. The full system is composed of a metallic-sealed cell and an improved adiabatic calorimeter to increase as much as possible the thermal resistance between the cell and the inner adiabatic shield of the calorimeter. It gives also a reliable calculation of the heat capacity of the cell and the comparison copper block which accommodates several CSPRTs. With this new system the reproducibility of metallic-sealed cell was found to be 0.7 mK as described below. reproducibility of metallic-sealed cells is found to be less than 0.7 mK.