Industrial-Type Cryogenic Thermometer with Built-in Heat Interception

Abstract

CERN is a major user of cryogenic machinery and its ancillary instrumentation. Many of these apparatus are assembled by subcontracting firms that do not have necessarily a very good knowledge of cryogenic techniques. This can result in cryogenic sensors malfunctioning with a loss of information that can be crucial during the commissioning or operation of cryogenic equipment. In particular cryogenic temperatures measured under vacuum conditions are often unreliable because of a poor thermal anchoring. In order to improve the performance of such temperature measurements a new thermometric block has been developed. It is fabricated by Prototype Circuit Boards (PCB) techniques and is thus well adapted to large-series production, it includes the thermalization of the leads and a cavity to insert a commercial temperature sensor. The main design goal was to manufacture a thermometer that can be installed by non-qualified personnel. For validating the design, prototype thermometers were mounted on an isothermal substrate as the temperature of the current and sensing leads was increased and they were exposed to thermal radiation. A temperature of 1.8 K was measured to within 50 mK when using copper leads of 2 mm diameter and about 100 mm long heated to 170 K on one end. This demonstrates the good performance of our thermometer blocks under extreme environmental conditions.