US 3168829 A
Description (OCR text may contain errors)
Feb. 9, 1965 D. E. NELSON CONTROL APPARATUS Filed Oct. 5, 1961 4 3 N ,IIII m MY Lm ww A o .u. tu? .,bvv/Pfvvv www5/hvj.. hol 1 INVEN TOR.
DAVID E. NELSON BY ATTORNEY United States Patent O 3,168,829 CONTRGL APPARATUS David E. Nelson, Minneapolis, Minn., assigner` to Honeywell lne., a corporation of Delaware Filed Oct. 5, 1961, Ser. No. 143,070 3 Claims. l (Cl. 73--336.5)
The present invention is concerned with an improvement in a humidity responsive device; in particular, a capacitance type element is made by placing a conductive coating on both sides of a material having a dielectric which changes with moisture.
Humidity responsive devices, which are connected in an electrical circuit provide a resistance change in the circuit as the humidity in the surrounding air changes, are broad- 1y old. One particular element is made by coating a resistance material with a thin sheet of gold so that a base contacting one side of the material and the gold coating can be connected in series in an electrical circuit. As the moisture passes through the thin gold iilm, the resistance of the material changes whereby the resistance between the two electrical connections is indicative of the moisture content of the air surrounding the unit. Such devices have not proved to be too satisfactory since the resistance characteristics are quite undependable especially as the ambient temperature changes.
In the present invention, a thin sheet of material having a dielectric which changes with moisture content is coated on both sides by a conductive material. The coatings are connected to an electrical circuit whereby the capacitance of the device is indicative of the moisture content of the coated material. The electrical resistance of the device is very high, but the capacitance of the device is used in a conventional bridge circuit to indicate or control -in response to variations in the humidity of the space surrounding the device.
An object of the present invention is to provide an improved humidity responsive element having a dielectric material which is used in a capacitance type element so the variations in dielectric as a function of moisture provides a capacitance indicative of the moisture content of the air in the space surrounding the device.
Another object of the present invention is to provide an improved humidity sensor having a Delrin sheet coated with a thin iilm of gold on each side so that when the gold coatings are connected to two terminals of an electrical circuit and moisture passes through the gold coating into the Delrin, the capacitance of the unit is a function of the moisture content of the surrounding air.
These and other objects of the present invention will become apparent on the study of the following specication and drawing of which:
FIGURE 1 is a schematic representation of a typical control system using the present invention wherein the humidity responsive element controls the operation of a valve.
FIGURE 2 is an enlarged sectional view of the element of the humidity responsive device shown in the crosssectional portion of FIGURE 1.
FIGURE 3 is an enlarged cross-sectional side view of the humidity responsive element showing the sheet of material coated on each side and connected to provide two terminals for a capacitance type sensing element.
FIGURE 4 is a front view of the element looking t0 the right of the element shown in FIGURE 3.
Referring to FIGURE 1, a schematic representation of a typical control circuit using the humidity responsive element or device is shown. A bridge 11 of the conventional Wheatstone type hastan A.C. voltage source or source of power 12connected between terminals 13 and 14. A irst circuit comprising resistor 15, terminal 2t?,
and resistor 21 connected in series is connected between lii Patented Feb. 9, 1965 terminals 13 and 14. A second circuit comprising conductor 22, element 1Q, conductor 23, a terminal 24, a condenser 25 connected in Vseries is connected between terminals 13 and 14. Terminal 24 is connected to a ground 30 so that an output from network circuit 11 is available between ground 30 and terminal 2t). Terminal 2t) is connected by a conductor 31 to a conventional amplifier relay 32 of the type shown in the A. P. Upton Patent 2,423,534. A second input terminal of the amplier relay is connected to a ground 33. The amplifier relay has a source of power 34 and an output circuit 35 which is connected to the energization circuit 40 of a valve 4I. The phase sensitive amplifier relay is adjusted so that upon a predetermined output of network circuit 11, the energizetion winding 40 of the valve 41 is energized.
Element 10 comprises a case having two half sections or cup-shaped members 50 and 51. A thin sheet 52 of a linear acetal polymer of unbranched polyoxymethylene averaging 100() or more in molecular weight, which is commonly known by the trade name Delrin, is coated on each side by a thin conductive material coating such as gold to form two plates 53 and 54 on opposite Sides of sheet 52. The coating of gold is very thin to be pervious to moisture. One particular coating thickness of 2.0 10" centimeters or approximately 50 angstroms has been found to provide good results. The coating 53 eX- tends across the sheet material, but the coating stops short of the edges around the periphery of the sheet material to maintain an electrical isolation between coating 53 and the case section 5t). The coating 54 is spaced from the center portion 60 of the sheet material. When the assembly 49 of the sheet material and coatings is mounted between the assembled halves Si) and 51 of the case and an appropriate seal 61 is provided, coating 54 contacts the half section 51 of the case.
A cross section of the element including the material 52 with the coatings 53 and 54 is shown in FIGURE 2; however, due to the very thin dimension of the coatings 53 and 54, a scaled cross-sectional view of the element would be impractical. The moisture from the surrounding space actually passes through the coatings to enter dielectric material 52.
As shown in FIGURE 3, coating 53 is connected to terminal 70 and coating 54 is connected to terminal 71 so the device 10 can be connected to conductors 22 and 23 of the network circuit 11. The specific construction of the element is more completely shown in FIGURE 3. The half sections 50 and 51 of the case have holes 80 to allow moisture from the air surrounding device lll to move into the case to inally arrive at a material 52. The spacing of the holes in case 50 is shown in the front view of FIGURE 4; however, the particular size and number of the holes is selected depending upon the needed response of the element.
As shown in FIGURE 3, conductive terminal 71 which is a sleeve on insulator member 82 is connected to the half section 51 of the case and coating 54 is connected to the case at the'junction of the two halve sections. In this manner, an electrical connection to one side of the capacitance type element is provided between terminal 71 and coating 54. Terminal 71 has an enlarged section 83 which is butted against an insulator 84 so that when a screw 85 having a washer 90 under its head is passed through coating 53 and sheet 52 into the conductive center portion 91 of member 82, the coating 53 and sheet portion 52 are squeezed between washer 90 and insulator 84. Portion 71 is connected to terminal 70 to provide an electrical connection to coating 53.
Material 52 is selected to have an extremely high electrical resistance and an electrical resistance which is not affected in any manner by moisture. The material has a dielectric characteristic which changes with moisture 3 1 so that the capacitance of the condenser formed by material 52 and the coatings 53 and 54 has a capacitance which changes as the moisture of material 52 changes. When device is placed in a space which changes in moisture content, thev moisture moves through the holes 30 into the case to be absorbed by material 52 after passing through the previous gold coatings 53 and 54. The moisture content of material 52 will meet the equilibrium level depending upon the moisture of the space surrounding the element. A humidity responsive device or elcment of this type having a capacitance which varies with moisture content of the surrounding space has a greater dependability and accuracy than devices which measure the resistance heretofore common in the prior art.
While the invention has been described in one specic manner as applied to one embodiment, the intention is to limit the scope ofthe invention only by the appended claims in which I claim:
1. A humidity responsive element which varies in electrical capacitance with variations in humidity in the surrounding space comprising, a thin sheet of material which has a dielectric characteristic depending upon changes of moisture content and has a high electrical resistance characteristic unaffected by humidity changes, a thin coating of gold on each side of said sheet, said coating being suiciently thin to permit moisture to reachsaid sheet from the surrounding space, a case comprising two half sections, said case having openings to permit moisture to pass to and from said case, means forV attaching said half sections with said coated sheet therebetween. so that said sheet is held around its periphery by a junction of said half sections, one side of said sheet having a portion of said coating cut away to not electrically `contact said case, a capacitance responsive apparatus, and terminal means for connecting said coatings on each side of said sheet to said responsive apparatus so the capacitance between said coatings is indicative of the air humidity.
Vand circuit means connecting said coatings as a condenser whereby the capacitance between said coatings is a function of the moisture in the space surrounding the device.
3. A humidity responsive element which varies Vin electrical capacitance with variations in humidity in the surrounding air comprising a thin sheet of material which has a dielectric characteristic depending upon changes of moisture content and has a high electrical resistance characteristic unaffected by humidity changes, aconductive coating on each side of said sheet having a low' electrical resistance, at least one of said coatings being sufficiently thin to permit moisture to reach said sheet from the surrounding space, a case comprising two half sections, said case having openings to permit moisture to pass to and from said case, means for attaching said half ysections with said coated sheet therebetween so that said sheet is held around its periphery by a junction of said half sections, said one side of said sheet having said coating cut away to not electrically contact said case, and circuit means adapated to connect said coatings in a circuit to re-v spond to a capacitance change of the element as humidity changes.
References Cited in the tile of this patent UNITED STATES PATENTS 2,177,558 Callan Oct. 24, 1939r 2,884,593 Miyata Apr. 28, 1959 2,943,488 Strobel et al July 5, 1960