Isothermal reference apparatus

摘要

1, 014, 418. Automatic temperature controL DE LA RUE REFRIGISTON Ltd. June 11, 1964 [July 12, 1963], No. 27809/63. Heading G3R. The temperature of a cold junction thermocouple is automatically maintained constant by locating it in an elongated tube which is closed at its lower end and immersed in a chamber containing liquid, freezable at a temperature close to that to be maintained, which is cooled by thermoelectric means under the control of a detector sensitive to the proportion of frozen liquid. In Fig. 1, a large number of varnished thermocouple cold junctions 4 are housed in a long tube 1 of thin stainless steel having a copper end cap 2 or a similar tube 11 having a lower portion 21 of copper, silver, gold, aluminium or beryllium oxide and an upper portion 31 of thermally insulating material. The tubes, which contain heat conducting liquid such as silicone oil or mercury at their lower ends, are mounted in a chamber 6, e.g. of copper or aluminium, containing, e.g. triply distilled water, which is frozen by a Peltier device 8 the cold junctions of which are in thermal contact but electrically insulated from chamber 6, and the hot junctions make similar contact with heat sinks 9 clamped in position by a band 22 and attached to cooling fins 10. The heat sinks 9 may, alternatively, be water cooled. Chamber 6 is surrounded by a casing 12 containing foamed plastic heat insulating material. When the proportion of water frozen has a predetermined value, a beryllium copper bellows 16 operates a switch to de-energize the A.C. input to a rectifier (not shown) supplying the Peltier device which is thereafter operated intermittently to maintain the proportion of frozen water between predetermined limits. If desired, the time constant of the on-off cycle may be increased by increasing the wall thickness of chamber 6 or delaying the operation of the switch. The energization of the Peltier device may, alternatively, be reduced periodically to a value above zero. In a modification, a switch responsive to low ambient temperature changes the manner of operation so that the Peltier device is switched between cooling and heating instead of cooling and off. In this arrangement a further switch may be operated to increase the energization of the Peltier device when starting up or when ambient temperature is high. Use of a flexible diaphragm or mercury plug instead of bellows 16 is referred to. Cooling of the portions of the tubes outside chamber 6 by an auxiliary Peltier device is also referred to.