GB1333517A - Cold-junction compensator for multiple thermocouples - Google Patents

Abstract

1333517 Thermocouple cold junction compensators MERESTECHNIKAI KOZPONTI KUTATO LABORATORIUM 22 May 1972 [10 Aug 1971] 23894/72 Heading H1K A cold junction compensator for a thermocouple consists of an enclosure of high thermal capacity containing a heat distributor on which is mounted a bridge unit producing a compensating e.m.f., the bridge comprising temperature sensitive resistors consisting of a combination of two metals associated with sections of leads of the same materials as the respective limbs of the thermocouple forming part of the connection between the bridge and the thermocouple to improve the transient response. The enclosure comprises a double walled container (1,2) with the wall space filled with heat insulating material (3). The heat distributer comprises a flat plate (4) having high thermal conductivity and capacity on which terminal units (7) are secured to form the cold junctions of thermocouples (8) which extend into the enclosure. A linearized bridge unit (9) is also mounted on the heat distributer and is fed from a stabilized supply (10) to provide an e.m.f. which varies to compensate for the temperature variations of the terminal blocks. As shown, Fig. 2, the bridge unit comprises a ceramic tube 13 on which are wound Pt resistors 11, linearizing Cu resistors 12 and lead sections 14, 15 of the same material as the respective thermocouple limbs. A Cu tube 10 surrounds these components which are connected together with balancing resistors to form a bridge which is fed from an external stabilized source 10 via a current adjusting device 18. The compensating output produced at terminals 17 may be switched by a unit 21 to any one of a plurality of the thermocouple terminal units 7 mounted on the heat distributer (4) and thus being at the same temperature as the bridge sensor units. A suitable measuring instrument 23 is connected in series with one of the bridge outputs to indicate the corrected thermocouple output.