Patent GB-498298-A (GB)
Title: Improvements in or relating to the measurement of the electrical conductivity of liquids
IPC: G01N27/04
Filed: 1937-07-01
Abstract: 498,298. Resistance measurements; determining physical qualities of materials ; compensating instruments for temperature errors. SIEMENS & HALSKE AKT.-GES. July 1, 1937, Nos. 18360, 18361, and 18362. Convention dates, July 1, 1936, Nov. 23, 1936, and Nov. 24, 1936. [Class 37] In apparatus for measuring the conductivity of liquids, especially the salt content of solutions a current dependent upon the resistance of the solution to be tested and also upon the resistance of a resistance thermometer responsive to the temperature of the solution acts in only one coil of a measuring instrument, which coil is connected in the diagonal of a bridge having the resistance thermometer connected in one arm whilst the current supplied to the bridge is dependent on the resistance of the electrolyte. In the arrangement shown in Fig. 3, alternating current from a source K is supplied to a bridge containing electrodes E immersed in the solution to be tested. The diagonal current from this bridge flows through a second bridge containing a resistance thermometer Wt. in one arm and a measuring instrument D in its diagonal. The scale may be influenced by connecting a resistance in parallel with the electrodes E and by selecting the other bridge resistances. The beginning and end of the measuring range may be varied by choice of bridge resistances. The instrument D may be for alternating or direct current. In the latter case a rectifier g is employed, which may be a dry rectifier or one of the oscillatory type having its exciting winding g<1> in series with the supply source K. The resistance thermometer Wt may be one having a positive temperature coefficient or one with a negative temperature coefficient such as a liquid resistance or one of uranium dioxide or cuprous oxide. In the arrangement shown in Fig. 4, a single bridge is used. The measuring electrodes E are in series with the secondary winding of the supply transformer T3 and are shunted by a resistance R1 in order to increase the proportionality between conductivity and temperature. The current flowing through this resistance at zero conductivity is compensated by an opposing current from the transformer T3. The temperature-sensitive resistance t1 forms one arm of the bridge. The diagonal contains the measuring instrument and may also include the secondary winding of a transformer T2, which superimposes a current depending on the conductivity of the electrolyte and also on the temperature. In another arrangement, Fig. 6, superimposed potentials are applied to the bridge through two transformers T4, T5. A transformer T6 compensates for the current flowing through the resistance R2, or this compensation may take place simultaneously through the transformer T5. In the arrangement shown in Fig. 7, two bridges I, II are employed, the points shown connected by the dotted line being at the same potential. Alternatively the resistances R4, R5 of the bridge II may be omitted. Fig. 8 shows a modified form of the arrangement shown in Fig. 4, in which the diagonal of a bridge III is connected through the measuring electrodes E to the bridge containing the resistance thermometer t. The current flowing through the shunt resistance R10 is compensated by means of resistances R6, R7. Fig. 9 shows a bridge in which, in addition to the resistance thermometer t1 forming one arm of the bridge, a second resistance thermometer t2 is. connected in the diagonal so as to produce a variation in the sensitivity of the measuring instrument in accordance with the temperature of the solution. The Specification as open to inspection under Sect. 91 comprises also the following subject-matter. The resistance m, Fig. 3 (Cancelled), shunting the electrodes E forms one arm of a bridge B1. A second bridge B2 contains the resistance thermometer Wt. The bridges B1, B2 influence a cross-coil instrument M through oscillation or dry rectifiers g. In another arrangement, Fig. 4 (Cancelled), the measuring electrodes E and shunt resistance m are directly connected to a transformer Tr. The current passing through the electrolyte is supplied through a transformer tr and a rectifier g to one coil of a cross-coil instrument M, the second coil of which is connected in the diagonal of a bridge B containing the resistance thermometer Wt. A zero instrument O, Fig. 6 (Cancelled), may be connected between the sliders of potentiometer resistances P1, P2, in two bridges containing resistance thermometers Wt1, Wt2 respectively. In another arrangement, Fig. 11 (Cancelled), the bridge containing the resistance thermometer t is fed from two transformers T10, T11, while voltages are injected into the diagonal by transformers T8, T9. In the arrangement shown in Fig. 17 (Cancelled), the potential on the secondarv side of a transformer T4 is proportional to the conductivity between the electrodes E and is opposed by a potential derived from a bridge containing a resistance thermometer t3. A thermometer t4 varies the sensitivity of the galvanometer G. The initial current due to the resistance R2 in parallel with the electrodes E is compensated by a transformer T3. The measuring electrodes may alternatively be connected in a bridge circuit. Fig. 18 (Cancelled) shows another arrangement in which a bridge including a thermometer t5 is connected in the measuring circuit by means of a current transformer T3. Transformers T2, T4 compensate for the initial current due to the resistance R3 shunting the electrodes E. The potential across a resistance R4 corresponds to the conductivity. In a further arrangement, Fig. 19 (Cancelled), a potentiometer P is connected in the diagonal of a bridge containing the resistance thermometer t6. Resistances R5, R6 compensate for the initial current flowing through the resistance R7. This subject-matter does not appear in the Specification as accepted.