Patent GB-847537-A (GB)
Title: Improvements in or relating to apparatus for controlling the moisture content of materials being fed through a conditioning chamber
IPC: F26B25/22
Filed: 1957-10-22
Abstract: 847,537. Drying fabrics in long lengths. EICKEN, H. Oct. 22. 1957 [Oct. 26, 1956], No. 32952/57. Class 34(1) [Also in Groups XXXV, XXXVI and XXXVIII] Apparatus for controlling the moisture content of a material comprises a moisturechanging chamber, means for developing three electrical signals representing respectively the moisture content of the material leaving the chamber (for verification only), the moisture content of the material in the chamber, and a reference level, means for comparing the second and third of these signals and accelerating or decelerating the feed of material through the chamber according to which signal is greater, and variable delay means for delaying the 'acceleration of the feed, after stoppage of the mechanism, for a time corresponding to the non- conducting period of an electrical device and determined by the difference between the second and third signals above. The apparatus is particularly suitable for controlling textile material to a given degree of dryness, measurement being made of its electrical conductivity while it is passing between conductive rollers located in the drying chamber. The rollers are connected to terminals 116, 117 (Fig. 2), and the varying resistance produces a signal at the grid of the cathode-follower 118'; this signal is amplified and displayed on the meter 120<SP>1</SP>, which is calibrated by means of the various potentiometers shown to read directly in terms of moisture content of different materials, e.g. wool or cotton. The anode current of the amplifier also flows through the windings B5. and B5' of magnetic amplifiers T1 and T2 to produce in each a flux in opposition to that from windings B4 and B4' energized by the preset reference source 129. Normally there is no A.C. output from the windings B1 and B1<SP>1</SP> but if the opposing fluxes are unequal a signal U<SP>1</SP> will be passed to the accelerating thyratron 134 or a signal U to the decelerating thyratron 133 according to which flux is greater. The feedback windings B3 and B3' ensure that only one signal is generated at a time. The thyratrons are biased negatively on their grids and are normally non-conducting, but when a signal U or U<SP>1</SP> is present the negative half-cycles are passed by rectifier 158 or 159 to lower the cathode potential of the thyratron and allow it to fire and charge the capacitor 135 or 137. Relay 154 or 156 is then operated and cuts off the thyratron by contacts 154a or 156a until the capacitor has discharged. The thyratron thus generates pulses of frequency proportional to the magnitude of the signal U or U<SP>1</SP> and the relay 154 or 156 will energize the deceleration or acceleration circuits of the drive motor accordingly (not shown) via contacts 154c or 156d. This automatic operation occurs if the switch CR is closed. When the switch is opened, the operation of the thyratrons gives via relay contacts 154b and 156b an indication at the lamps J, R and V and the necessary control is done manually. If the machine is stopped, a switch CM is closed to energize a delay thyratron 139 which receives the "acceleration" signal from line 38. When the machine re-starts, the switch is opened but the thyratron remains blocked until the capacitor 142 has discharged, so that relay 180 is not energized and the "acceleration" pulses cannot pass the contacts 180a. The delay time thus depends on the magnitude of the signal U<SP>1</SP> and hence on the moisture content of the material. Fig. 3 (not shown) contains the stabilized power supply circuits and the "verification" measuring circuit which is the same as that of Fig. 2 except that it is isolated from earth. Since the material leaving the chamber may have picked up a static charge the measuring rollers are modified to allow for this. The upper one (joined to the H.T. line) is a uniform conductive roller, but the lower one (Fig. 4) is made of alternate conducting and insulating segments 72, 74 respectively. The negative charge on one side of the material is neutralized by the upper roller, but the lower side is charged alternately positive and negative by the segments of the lower roller. A pulsating current is thus taken off by a brush and transmitted through the material to the measuring apparatus, and this current depends on the moisture content of the material irrespective. of any inherent static charge. If the moisture content is very low or if the material must not be compressed, a single roller is used with alternate conducting and insulating laminations along its length (Fig. 5, not shown). Specification 737,145 is referred to.