Patent GB-281693-A (GB)
Title: Improvements in hygrometers
IPC: G01N19/10
Filed: 1927-12-01
Abstract: 281,693. Atlantic Precision Co., (Assignees of Allen, A.). Dec. 2, 1926, [Convention date]. Alarm, indicating, recording, and registering apparatus.-Apparatus particularly intended for determining the moisture content, of sheet material in the form of a travelling web, comprise a hygroscopic element which changes it dimensions with changes of moisture content, these changes being arranged to vary the characteristic of an electrical device such a condenser. inductance, &c., and means being provided for indicating the said characteristic. An open-topped troughshaped member 1 contains the hygroscopic material 6, preferably consisting of a number of strands of artificial silk as described in Specification 276,468, this material being ar.chored at one end to a pin 10, and looped at its other end round a. pin 16. In the form shown in Figs. 1 and 3, the pin 16 is connected by links 17, 18 to the movable leaf 19 of a variable condenser of " book " type, this leaf being pivoted at 20 to the fixed leaf 21. With the connection shown elongation of the strip 6 with increasing moisture content increases the capacity of the condenser, but the connection may be such that a decrease in capacity is effected. Adjustment of the strip 6 can be effected by a screw 14 bearing on a bar 11 over which the strip passes. The material 5 of which the moisture content is to be determined is placed, or passes, over the open top of the trough 1 in proximity to the strip 6. A variable condenser of the rotating vane type can be used instead of that shown, the strip 6 being in this case connected to the spindle of the condenser. The variation in the capacity of the condenser may be indicated by including the condenser in a high-frequency oscillating circuit coupled to a second circuit which is tuned nearly to resonance therewith. Such a circuit is indicated in Fig. 9, in which the condenser 71 is arranged in series with an inductance 70 and a coupling coil 80 to form an oscillating circuit, part of the coil 70 being included in the plate circuit of a three-electrode valve. The pick-up circuit comprises an inductance 81 coupled to the coil 80 variable condensers 82, 83 and a milliammeter 84, the reading of which is a measure of the capacity of the condenser 71. Alternatively the condenser controlled by the strip 6 may be used as one of the condensers 82, 83 in the pick-up circuit. The strip 6 may also be used to control other electric devices. For example in the circuit shown in Fig. 9 the strip may control the coupling between the coils 80, 81, the coil 80 being for this purpose rotatably arranged within the coil 81 on a spindle which is connected to the strip 6. In another form either the transmitting or the pick-up circuit may include a variometer consisting of two relatively rotatable coils, the position of the rotatable coil being controlled by the strip 6. In another form, Fig. 8, the strip is connected to an arm controlling a rheostat 115 included in a circuit .containing a source of E.M.F. and an ammeter. In this case the reading of the ammeter depends on the moisture content of the strip. Specification 276,469 also is referred to.