Patent GB-160763-A (GB)
Abstract: 160,763. Weston Electrical Instrument Co., (Assignees of Goodwin, W. N.). March 24, 1920, [Convention date]. Addition to 109,046. Thermal current meters; temperature errors, compensating for.-Relates to compensation for temperature errors due to convection currents and surrounding air temperature in thermal ammeters as described in the parent Specification, and describes further means therefor. Compensation may be effected (1) entirely in the conductors of the thermo-couple itself, without the use of auxiliary heat conductors or (2) partly by both or (3) entirely by auxiliary conductors. Fig. 1 shows the cold junctions extended into the air to such a distance as to render the conductors 4, 5 each thermally equivalent to the corresponding half of the heating conductor 2. Thus the temperature of the cold junction varies in correspondence with such variations in temperature of the hot junction as not due to external causes, and the difference between the temperature of the hot and cold junctions gives a true measure of the current in the heating conductor. The Specification describes the application of this method to all the constructions described in the parent Specification. Fig. 6 shows an ammeter in which a number of heating conductors 15 are connected in parallel between two disc termnials 14 and a corresponding number of thermo-couples 19, 20, are connected in series; each cold junction 17, 18, 21, 22 is extended into the air for the purpose of compensation. In another form the hot junctions of a series of thermo-couples are each situated in the centre of one of a number of tubular heating conductors, and the cold junctions extend into the air. In Fig. 8, an auxiliary compensating heat conductor 12 is combined with the means above described. The conductor 12 is in thermal ccntact with both terminals 1. The thermo couple conductors 3 are in thermal connection with its centre and their cold ends 4, 5 are extended into the air. If the thermal conductor 12 is excessive and its connection with the terminals 1 is of negligible thermal resistance, the exposed ends 4, 5 must be thermally equivalent in themselves to corresponding portions of the heating conductor 2, but if it is of small cross-section or of low conductivity, or if the thermal resistance of its connections is not negligible, compensation is effected by making the thermo-couple extensions 4, 5 the auxiliary conductor 12 and its thermal connections with the terminals 1, combined, thermally equivalent to the heating conductor 2. In Fig. 9 the whole of the compensation is provided by an auxiliary thermal conductor 12 and its connections with the terminals 1 which include thermal resistors 80; the cold ends 10 of the thermocouple in this case are in thermal contact with the centre of the conductor 12. This conductor may be of any shape, and it may be divided equally, and the parts used as electrical connections. Fig. 10 shows such a modification. Fig. 11 shows a construction comprising heating-strips 82 in contact with thermo-couples in series, the latter being in thermal connection with thermal conducting bars B so that their cold junctions extend into the air and combine with the bars and their thermal connections to the terminals 81 to afford compensation. This construction is capable of similar modifications in regard to the amount of compensation afforded by the different elements to those pointed out in connection with Fig. 8 above.