Improvements in or relating to means for measuring or controlling the relative humidity of a gaseous atmosphere

Abstract

Abstract 804,421. Electric measuring systems. ELLIOTT BROS. (LONDON), Ltd. June 15. 1955 [March 15, 1954], No. 7525/54. Class 40 (1), Apparatus for determining the relative humidity of an atmosphere comprises a bridge (Fig. 1) having a resistor 3 sensitive to the dry temperature in one arm, a resistor 2 sensitive to the wet temperature in an adjacent arm, the remaining arms containing fixed resistors 6, 7, and the two branches being interconnected by potentiometers 1, 4, the unbalance current being taken from the sliders 8, 5 of the potentiometers and causing a motor 10 to drive the slider 8 of potentiometer 1 to balance the bridge, it being shown that when a specified relationship exists between the resistances in the circuit the position of slider 8 at balance is indicative of the relative humidity when the slider 5 is manually located in accordance with the ambient dry temperature, or a relative humidity value which is to be maintained constant. The movements of sliders 8, 5 are stated to be linearly related for small variations in temperature, so that both sliders may be driven by the motor 10 if the potentiometers are correctly proportioned, to obtain automatic compensation for small temperature variations. To obtain more accurate temperature compensation the potentiometers may be non-linear, and variable resistors may be introduced in series with the temperature-sensitive resistors 2, 3 whose values can be adjusted in accordance with the ambient temperature manually or automatically by a secondary, temperaturemeasuring bridge. In an alternative arrangement (Fig. 3) resistor 4 is replaced by variable resistor 14, which is also manually or automatically adjusted in accordance with the ambient temperature. The humidity of a number of different gases may be measured using separate bridges with common potentiometers 1, 14 connected to measure the humidity of the desired gas by a multiple switch.

Inventors

• 👤 Sydney William Wade

Bibliographic Details