GB779148A - Improvements in or relating to ventilating systems - Google Patents

Abstract

779,148. Electric measuring systems. OCEAN STEAM SHIP CO., Ltd. Dec. 13, 1954 [Dec. 15, 1953], No. 34868/53. Class 40 (1). [Also in Groups X and XII] In a method of comparing the relative humidities of two samples of air (see Group XII), one sample, e.g. atmospheric air, is drawn into a pipe 14, Fig. 1, and passed through a temperature equalizer 12 and a pipe 15 to an electrical humidity sensitive element 10, whilst another sample of air, e.g. air from an enclosed space, is drawn through pipes 17, 18 to the temperature equalizer 12 and through a pipe 19 to another electrical humidity sensitive element 11, a fan 13 exhausting both streams of air to the atmosphere through a pipe 16. Water traps 20, 23 are incorporated in the apparatus. Signals derived from the elements 10, 11 in accordance with the humidities of the two samples of air, are compared in a circuit, Fig. 2, wherein a stabilized alternating current supply across leads 30, 31 feeds two potential dividers, one comprising fixed resistors 38, 39 and the other a potentiometer 40 and a fixed resistor 41. As shown, a full-wave rectifier 42, a coil 43 in the humidity-sensitive element 10, and a common resistor 44, are connected between the common point of the resistors 38, 39 and the lead 30, and a similar circuit including a full-wave rectifier 45, a coil 46 of the humidity sensitive element 11, and the common resistor 44 is connected between the slider of the potentiometer 40 and the lead 30. The outputs of the rectifiers are connected in opposition through a centre zero indicating meter 50, in parallel with an adjustable sensitivity controlling resistor 51. One end of the common resistor 44 is connected to moving contacts 52, 53 of a double-pole multi-position switch. In operation initially a standard sample, e.g. atmospheric air is caused by operating the valve 24, Fig. 1, to pass through both elements 10 and 11 and the double-pole switch is moved to engage contacts 54, 55 which are connected respectively to the coils 43, 46. The potentiometer 40 is then adjusted until the meter 50 indicates zero. The doublepole switch is then moved to its second position where the coils 43, 46 are replaced by fixed resistors 58 and 59 respectively, the values of which are selected to correspond to a predetermined degree of difference in relative humidities, e.g. a difference corresponding to full-scale deflection of the meter 50 in one direction. The sensitivity control 51 is now operated until the meter 50 indicates the predetermined difference. The valve 24 is now operated to place the pipe 18 in communication with a second sample of air, e.g. air from a space to be ventilated, which is passed through the element 11, whereupon the double-pole switch is moved to its third position to reconnect the coils 43, 44 of the elements 10, 11 so that the meter will indicate the degree and direction of any difference between the relative humidifies of the two samples of air.