GB1246154A - Standard resistance thermometer - Google Patents

Abstract

1,246,154. Resistance thermometers. ROSEMOUNT ENG. CO. 2 Jan., 1969 [22 Jan., 1968], No. 349/69. Heading H1K. The main element of a standard resistance thermometer consists of parallel lengths 25, 27, 29, 31 (the middle of the runs 27, 29 is left out of the drawing) or platinum wire threaded through aligned holes in spaced insulator discs and connected in series to form a single "coil" by sharp-angled U-links 26, 28, 30, 32 at one end and at the other end by turns round the insulation 16 which hold the discs 15 apart. The U-links 28, 30 stand out further from the end disc 15 than the links 26, 32 so that adjacent links do not contact one another if accidentally bent. The insulator discs 15 and spacing insulators 16 are held together by a platinum wire 17 passing through axial apertures and being provided with blobs 21, 22 to retain the insulators. In use, measurement between this central wire and one end of the main element gives an indication of insulator leakage resistance. The assembly is mounted in one end of a sealed and gas-filled silica tube, the greater part of the tube being occupied by the lead-out assembly. Each end of the main element is connected by two small gauge wires 37A-40A to two lead-out wires. (Only two 37, 38 of the four lead-out wires can be seen in Fig. 6.) The use of small gauge wires gives high thermal resistance. The lead out wires pass through insulator tubes which hold apart further insulator discs. Details of the external connections to the thermometer are illustrated in Fig. 1 (not shown). To minimize radiation transmission along the thermometer the silica tube is externally sand blasted in its lead-out section, the insulator discs in the leadout section are roughened on the side away from the element and polished on the side facing the element, and the insulator discs in the element section are polished on both faces.