| 摘要 |
961,303. Measuring liquid conductivity. PHILIPS ELECTRICAL INDUSTRIES Ltd. July 20, 1960 [July 23, 1959], No. 25305/60. Heading G1N. In a bridge for determining the conductivity of an electrolyte the effect of temperature variations on the electrolyte are compensated for by including in one branch of the bridge circuit a negative temperature coefficient resistor in series combination with a variable resistor and a fixed resistor. With reference to Fig. 2 one branch of the bridge circuit comprises the conductivity cell Rx, containing the liquid under test, the conductivity of which is temperature dependent, in series with a fixed resistor Rm. The outer branch of the bridge comprises a negative temperature. coefficient resistor R2 in series with variable resistor R4 and 10 ohm fixed resistor R5. The variable resistor R4 is connected in parallel with resistors R6, R7 having values in the ratio of 99:1 and to the junction of which is connected a potentiometer type resistor Rp, the tapping 2 of which forms one output terminal of the bridge, the other terminal being at 1. With the bridge arranged as above R4 can be varied dependently upon the temperature coefficient of the conductivity of the electrolyte and in order to carry out the necessary compensation a measurement is first made at 20‹C., the voltage at point 2 being then independent of the value of series resistor R4 at this temperature. The temperature of the liquid is increased to the maximum operating temperature occurring when the resistor R4 is varied so that the same indication is obtained as at 20‹C. |
