US2488811A - Electronic control device - Google Patents

Description

Ndy. 22, 1949 s. b. EILENBERGER 2,488,811

ELECTRONI C CONTROL DEVICE Filed Sept, 20, 1943 il T INVENTOR BYW i ATTORNEYS Patented Nov. 22, 1949 ELECTRONIC CONTROL DEVICE Stanley D. Eilenberger, Kenosha, Wis.-, assignor,

by mesne assignments, to Chicago Coin Machine 00., a corporation of Illinois Application September 20, 1943, Serial No. 503,163 p This invention relates to a system of electronic control, where the controlling factor is a change in the properties of the test material, as, for example, a change in the moisture content of paper. By way of further example, the instrument may also be used as a gauge in deter-- mining the ripeness of fruit, the thickness of one insulating material applied over a second insulatingmaterial, such as, for example, one or more coats of paint on wood or Bakelite, etc.

The presentinvention is an improvement on the invention disclosed in my co-pending application Serial Number 502,843, filed September 17, 1943, now Patent 2,428,700 issued on October The present invention makes use of feedback between two electrodes which are, in part, shielded from each other. The control voltage developed does not depend on absolute capacity change and thearrangement is such that specific control voltages are developed independent of the total mass of the test material, without actually contacting the test material and without having electrodes on opposite sides of the test material.

It is well known in the art that any electronic amplifier will oscillate if the output of said amvention discloses a means for producing a feed-' back voltage, the value of which is a function of the propertiesof the test material but without the limitation implied by absolute values of capacity, inductance or resistance. This is accomplished by the use of two electrodes, one connected to the output of an amplifier and the other, connected to' the input of said amplifier, said electrodes being so shielded from each other that oscillation does not normally occur, with all circuit values so adjusted that for a given condition of the material under test a definite feedback voltage is available at the output terminals of the amplifier, where the value of voltage so Obtained may represent a minimum, a

It is also well known in the art that 3 Claims. (Cl. 315-326) I 2 maximum or any valuebetween said minimum or maximum voltages, this being dependent on the particular application for which the electronic control device isto be used, For this condition a small change in the property of the material undergoing test will'produce a large change in control voltage.

For example, where it is desired to determine the moisture content of paper and to operate external control circuits according to the value of said moisture content, it is entirely practical to have a voltage ratio of :1 with a change in moisture content on the order of 1%. Continuing with this example, it may be assumed that the minimum desired moisture content is 3%, the maximum desired moisture content is 5% and the average moisture content is 4%.

For this hypothetical case the control instrument may be so adjusted as to provide, for example, 10 volts control voltage for amoisture content of 4% and, without resorting to maximum sensitivity, this control voltage may rise to 15 volts for a moisture content of 5% and drop to 5 volts for a moisture content of 3%. Continuing with this hypothetical case, actual control circuits could be arranged to close at any desired fraction of 1% above or below 4%.

It is understood that the foregoing is by way of example and is not to be deemed as restrictive in scope. While the example is confined to moisture content of paper, it is understood that a similar arrangement maybe used in connection with any test material where said test material changes in specific inductive capacity, surface resistivity, volume resistivity or thickness of the test material. It is understood that the thickness of the test material may be made the test factor; I V

This invention will be best understood in consideration of the following detailed description, in View of the accompanying drawing forming a part of the application. Nevertheless, it is understood that the invention is not confined to the disclosure, being susceptible to such changes and modifications as define no material departure from the salient features of the invention as expressed in the appended claims.

In the drawing the single figure represents a complete schematic circuit arrangement of the control instrument, including a cross section view of the test electrode assembly, and including the electronic controlcircuit, where that part of the schematic below the broken line X is the instrument used to develop the control voltage and that part of the schematic above the broken maximum possible sensitivity is, in part, a func-, tion of the voltage gain of such amplifier and,

in part, of the frequencyof oscillation. In the machine, where the minimum moisture content desired is 3%, the maximum moisture content desired is and the average moisture content is 4%. The adjustment of potentiometer 31 for this condition may be made with a. test sample 39 having a known moisture content of, for example, 4%, and, for this known moisture content, potentiometer 31 may be adjusted to develop any arbitrary voltage at terminals 45 and 46. By way of example, this voltage may be taken as direct volts and, by way of further example, it may be assumed that the voltage will increase to direct volts for a moisture content of 5% and decrease present example, the frequency is on the order of 4000 C. P. 3., this factor being largely determined by the design of iron coretransformer 39. and the voltage gain is on the order of 10,000.

Control grid 4 of vacuum tube is connected through a shielded line 85 to metal electrode 4|, which is in turn partially shielded by grounded shield 43, electrode 4| being shown in cross section with the upper plane surface unshielded. Electrode 4| is mounted in a block of insulating material 40, preferably some material having a low dielectric constant, such as, for example, a ceramic material, or polystyrene. Grid resistors 5 and I3, cathode resistors 6 and 4, cathode bypass condensers 1 and I6, screen resistors 8 and 5, screen by-pass condensers 9 and I1, plate resistor H] and coupling condenser II are all of a value normally used in the type of amplifier represented in the lower half of the figure, the actual values being largely determined by the particular tubes employed, and by the plate volt-- age available between negative plate voltage terminal 25 and positive plate voltage terminal 26, this plate voltage being by-passed by condenser l8, and preferably regulated to provide a constant voltage. V

The output of vacuum tube 63 is coupled to diode rectifier 84 by transformer 30, which has a primary winding 3| and a secondary winding 32-33. Vacuum tube 84 is represented as a conventional diode having plate 34 and cathode 35, it being understood that other forms of rectifier may be used in order to provide a direct voltage at terminals 45 and 46. The direct voltage output of rectifier 84 appears across load resistor 22 and is by-passed' by condenser 23, this direct voltage being connected to terminals 45 and 46, the polarity being as indicated. If desired, an indicating meter 2| may be connected in parallel with this voltage and rheostat 20 may be employed to calibrate the reading obtained on meter 2|.

Feedback voltage is taken from terminal 32 of transformer 30, it being understood that terminals 32 and 33 are reversable, actual connection depending on the phase relationship necessary to secure oscillation. This feedback voltage is connected through condenser 36 and potentiometer 31 to electrode 42 which is in the form of a flat plate attached to the lower side of insulating block 40, electrode 42 being shielded on the lower side by grounded shield 44. The adjustment of potentiometer 31 is such that minimum, or zero, oscillation is obtained with no test material, as represented by 39, in the electric field existing between electrode 42 and electrode 4|. For this condition, any test material 39 placed in the electric field will produce an increased voltage at terminals 45 and 46.

An alternate adjustment would be for a condition where test material 39 varies between arbitrary limits. For example, test material 39 may represent paper moving at high speed in a paper to 5 direct volts for a moisture content of 3%.

This direct voltage which appears at terminals 45 and 46 is used to control two gas discharge tubes generally referred to by numerals 41 and 69. These gas discharge tubes are so arranged as to have control characteristics of opposite polarity, where tube 41 is triggered by increased positive voltage and tube 69 is triggered by increased negative voltage, which is equivalent to decreased positive voltage.

Referring particularly to the control circuit represented by gas discharge tube 41, suppressor grid 49 is biased negative in respect to cathode 5| by direct voltage 53. The control voltage appears across potentiometer 52, with polarity as indicated. The plate voltage is obtained from winding 60 of transformer 58, primary 62 of said transformer being connected to a suitable source of voltage 38 which, for purposes of example, may be 60 cycle alternating current. Plate voltage from winding 60 is connected to plate 48 in series with current limiting resistor 59 and relay coil 55, relay coil 55 being by-passed by condenser 54 which is designed to hold relay 55 operative during the negative half of the plate voltage cycle. Contacts 56 of relay 55 are normally open and are connected to terminals 51, terminals 51 being further connected to external apparatus designed to correct the moisture condition, for example, terminals 51 may control the operation of a high frequency induction heating device designed to reduce the moisture content of material 39.

For any given value of plate voltage Epl, a definite positive value of grid voltage E 1 will be necessary to ionize gas discharge tube 41, thus operating relay 55 and closing contacts 56 to operate the external device controlled by terminals 51. In the example given, where the average control voltage was taken as 10 volts, the suppressor grid voltage furnished by battery 53 and the setting of potentiometer 52 are such that gas discharge tube 41 remains de-ionized. Any increase in moisture content of test material 39 will be reflected as an increase in direct voltage at terminals 45 and (l6 and the direct grid voltage Egl will also increase in the positive direction. The actual sensitivity of control will be determined by the setting of potentiometer 52. Assuming that potentiometer 52 has been adjusted for a voltage regulation of 1 volt, gas discharge tube 41 will ionize when Egl rises 1 volt and gas discharge tube 41 will remain ionized until this Voltage Egl returns to its original value, at which time gas discharge tube 41 will de-ionize on the first negative half cycle of plate voltage, thus releasing relay 55, restoring contacts 56 to the normally open position and de-energizing the external apparatus connected to terminals 51.

The operation of gas discharge tube 69 is identical to the operation just described for gas discharge tube 41, except that all polarities are reversed, so that vacuum tube 69 will ionize on a decrease in control voltage EgZ, the actual sensitivity again being controlled by potentiometer 64. The operation of relay 6B, condenser 68, current limiting resistor 63, contacts 6'! and terminals 65 being similar to that previously described. Plate voltage Ep2 obtained from winding 6| of transformer 68 is similar in value to plate voltage Epl obtained from winding 60, any slight difference in value being unimportant as actual ionization voltage will in any event be controlled by the adjustment of potentiometers 52 and 64. The input voltage to primary 62 of transformer 58 should preferably be regulated to provide a constant voltage. Control terminals 65 are in this case designed to control external apparatus for increasing the moisture content of the test material which, for purposes of example, may be accomplished by controlling solenoid valves to increase the water content of the pulp.

The invention has been described for a condition where a minimum and maximum value of the test material was the control factor in operating external circuits in accordance with changes between said minimum and maximum values. While the moisture content of paper was used in the foregoing example, it is understood that a similar arrangement may be used with a wide variety of materials. By Way of further example, a similar arrangement may be used in testing the ripeness of fruit, where the minimum and maximum values are represented by a predetermined degree of greenness and ripeness in said fruit, and for this application the control Voltage is determined largely by said degree of ripeness and is almost totally independent of actual mass of the test items, provided the design of shielded electrode assembly 4 |43 is such that the electric field is confined to an area much smaller than the test item. For example, in testing oranges having a nominal diameter in the range of 2.5 to 4 inches, the electric field existing between electrodes 43 and 4| should be restricted to an area on the order of 1 inch in diameter. For this condition, actual mass will not materially affect the control voltage. By way of further example, the minimum and maximum values may well represent the distance of any object, conductive or non-conductive, from electrode 4|, the average value being taken as the mean distance, with control voltages varying in accordance with minimum and maximum distances. Innumerable other applications of the invention herein disclosed will occur to those skilled in the art.

For the sake of clarity and simplicity, the invention has been described with only a minimum and maximum value represented by two gas discharge tubes as the controlled medium. It is understood that the method is applicable to a single tube for certain conditions or for a multiplicity of tubes for certain other conditions, wherein each tube represents a definite change in the test material, it being further understood that for certain applications this invention may be practiced without any intermediate control device as represented by the gas discharge tubes. For example, where relatively coarse control is required, the change in control voltage may Well be used to operate difierential relays. This method would not provide the close control possible with gas discharge tubes, where control may be realized with a voltage change of 1 volt or less. However, for certain applications, differential relays would provide economy of operation.

The above examples are for the purpose of illustrating some of the methods and means by which the broad purposes of the invention may be carried out and are not to be deemed as restrictive in any manner. Other modifications and alternatives will occur to those skilled in the art without departing from the scope of the invention as defined by the following claims.

I claim:

1. A system for testing a material with respect to a physical characteristic which changes its conductivity, said system comprising a vacuum tube amplifier having an input and an output, a pair of electrodes connected to said input and output respectively and adapted to be disposed in proximity to material to be tested, said electrodes being coupled to each other through said material with the physical state of said material determining the amount of coupling between said two electrodes, said amplifier having a sufl'iciently high gain so as to be unstable and being adapted to oscillate when the coupling between said electrodes exceeds a predetermined value, rectifier means for deriving a direct potential from the amplifier output in proportion to the intensity of oscillation of said amplifier and a relay system fed by said derived potential and biased to change its condition when said derived potential increases or decreases with respect to a predetermined value whereby there is material selection with reference to a predetermined conductivity.

2. The system of claim 1 wherein said relay is of the gaseous dischargetube type.

3. The system according to claim 1 wherein said relay system includes a pair of grid controlled gas discharge tubes.

STANLEY D. EILENBERGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,926,084 Clark Sept. 12, 1933 1,995,492 Andrus et a1 Mar. 26, 1935 2,074,739 Braddon Mar. 23, 1937

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