Improvements in or relating to moisture measuring and controlling instruments

Abstract

Abstract 668,196. Electric correspondence control systems. STANDARD TELEPHONES & CABLES, Ltd. July 14, 1950. [July 20, 1949] No. 19104/49. Class 40 (i). [Also in Groups XXXV and XXXVI] A hygrometer to indicate or control the relative humidity in an atmosphere comprises a mass of glass fibres 4 (Figs. 1, 2) between two electrodes 1, 2 the electrical impedance between the electrodes being a function of the surface moisture on the fibres produced by the relative humidity of the atmosphere. The electrode discs 1, 2 are stiffened by ribs 6, and perforated by holes 5 to allow free passage of air to the glass fibres 4. An embodiment of the use of the humidity-sensitive element in a bridge circuit for humidity and temperature control is shown in Fig. 6, wherein the four arms of the bridge are the humidity-sensitive element 28, a tapped resistor 26, 27 and the two halves 21, 22 of the centre-tapped secondary of a mains transformer 23, with a thyratron 31 across one half winding 21, and two thyratrons 32, 33 across the other 22, having relays 34, 35, 36 in the respective anode leads. The grids of the valves are connected so that with low humidity, when element 28 has a high impedance, only valve 31 fires, operating relay 34 ; with increased humidity, when the impedance of element 28 is comparable with that of 26/27, valves 31, 32 will fire alternately, operating relays 34, 35 ; and with high humidity valves 32, 33 will both fire, operating relays 35 and 36. Relay 34 opens a vane to admit moist circulating air, relay 35 closes this vane, and relay 36 operates a heater which lowers the relative humidity by raising the temperature.

Inventors

• 👤 Frank Howard Taylor

Bibliographic Details