US1748983A - Control instrument - Google Patents

Description

March 4, 1930. R. HOFSTETTER 1,748,983 I CONTROL INSTRUMENT Filed April 13. 1927 Patented Mar. 4, 1930 UNITED sTArss PATENT OFFICE ROBERT HOFSTETTER, OF IDOWNERS GROVE "ILLINOIS, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. 55., A CORPORATION OF NEW YORK CONTROL ENSTRUMENT Application filed April 13, 1927. Serial No. 183,336.

This invention relates to control systems, and more particularly to circuit controlling mechanisms for temperature control systems.

The principal object of the invention is to provide an improved, reliable and efiicient circuit controlling mechanism for control systems.

In accordance with the general features of the invention, there is provided in one embodiment thereof a system for controlling the temperature within electrically heated furnaces wherein a mechanically operated fluid contact switch controlled'by a temperature measuring or indicating instrument serves to control the supply of heating current to the furnace in response to predetermined temperature variations within the furnace. The measuring or indicating instrument is controlled by a temperature responsive device mounted within the furnace.

Other features and advantages of the invention will become apparent in the following detailed description reference being had to the accompanying drawing, wherein Fig. 1 illustrates diagrammatically a temperature control systemembodying the features of the present invention;

Fig. 2 is an elevational view of the mechanism for operating the mercury switch which controls the supply of heating current to the furnace, and

Fig. 3 is a of Fig. 2.

It is believed that the invention will be clearly understood from the following detailed description of a specific embodiment thereof. It should be understood, however, that the invention is not to be limited to the specific structure disclosed except as defined in the appended claims.

Referring now to the drawing and particularly to Fig. 1 thereof, the reference numeral 10 indicates an electrically heated furnace which may be of any desired coiistruclion. For the purpose of clearly illustrating the invention, the furnace as shown diagrammatically in the drawing may comprise a cylindrical. outer casing 11 wit which a detail section taken on line 3-3 min smaller cylindrical inner casing is concentrically supported. Encircling the inner casing 12 is an electric heating element 13. Connected in series with the heating element 13 1s a fluid contact switch 1 1 of any well known type comprising a sealed tube 15 housing a pair of electrodes or contact members 16 and 17 and a body of mercury or other suitable conducting fluid 18. lhe electrodes 16 and 17 are spaced from each other and are adapted to be bridged by the conducting fluid to close an electrical circuit which supplies heating current to the heating element 13. As shown in the drawing, the electrode 16 is connected to one end of the heating element 18 by a conductor 19 and the opposite end of the heating element is connected to a conductor 20. The electrode 17 is connected to a conductor 21 and the conductors 20 and 21 are connected through a switch 22 to any suitable source of electricalenergy (not shown).

The contact switch 14 is supported in a substantially horizontal position and is mounted so that it may be tilted in either direction to. allow the conducting fluid 18 to flowinto and out of circuit making position to start or discontinue the supply of heating current to the heating element and means is provided for mechanically tilting the contact switch in response to predetermined temperature variations within the furnace. The

tube 15'of the contact switch is supported within a spring clamp 24 (Fig. 3) secured to the face of a pinion 25 rotatably journaled in a vertical plate 26. The plate 26 is slidably mounted in parallel guides 27 and 28 secured to a vertical supporting plate 30, which latter plate is in turn supported by suitable framework, a portion of which is indicated at 31 (Figs. 1 and 2). Secured to the plate 26 are a pair of vertically disposed parallel guide members 33 and 34 within which oppositely disposed racks and 36, respectively, are slidably mounted and arranged to engage opposite sides of the pinion 25. From the construction just described, is obvious that a reciprocatory movement is imparted to the racks 35 and 36 by the reciprocation of the plate 26 and the pinion which is movable therewith.

A reciprocatory movement is imparted to the plate 26 by a continuously rotating can 38 secured to a shaft 39 which may be driven from any suitable source of power (not shown). The cam 38 engages one end of a lever 40 which is pivoted intermediate its ends upon a pin 41 carried upon the end of an arm 42 secured to the frame 31. The opposite end of the lever 40 engages an arm 44 secured to the plate 26. A block secured to the supporting plate 30 is provided on its lower edge with a rectangular slot 46 within which transverse portions 47 and 48 of the racks 35 and 36, respectively, are designed to enter upon the racks reaching the end of their upward movement. The block 45 is provided with elongated mounting slots 49-49 whereby its position with respect to the racks 35 and 36 may be readily adjusted.

The means for tilting the contact switch 14 to start or discontinue the supply of heat ing current to the heating element 13 in response to predetermined temperature variations within the furnace 10 will now be de scribed. Arranged so as to be free to travel along the lower edge of the block 45 is a pointer 50 of a measuring or indicating in strument, such as a galvanometer 51, which is connected in the usual potentiometer circuit. As shown in Fig. 1, the galvanometer 51 is connected in series with a temperature responsive device such as a thermo-couple 53 mounted within the furnace. One end of the galvanometer coil is connected to a resistance 54 by a conductor 55 and the other end of the galvanometer coil is connected to one terminal of the thermo-couple 53 by a conductor 57. The other end of the thermocouple is connected by means of a conductor 58 to a movable contact 60 which bears upon the resistance 54. The resistance 54 is connected in series with an adjustable resistance 61 and a battery or source of direct current 62.

Associated with the movable contact 60 is a pointer 64 which cooperates with a suitably calibrated scale 65 associated with the resistance 54 to indicate the temperature desired within the furnace. The resistance 61 is adjusted in the usual manner so that the galvanometer pointer is in balanced or neutral osition when the temperature indicated by t e pointer 64 upon the scale 65 is equal to the temperature within the furnace.

In the operation of the above described control system, the contact 60 is adjusted according to the temperature which it is desired to maintain within the furnace, the temperature being indicated by the pointer 64 upon the scale 65, as hereinbefore described. The switch 22 is then closed and assuming that upon starting the operation of the system the contact switch 14. is tilted in the position shown in the drawing. it is obvious that electrical current is supplied to the heating element 13 which supplies heat to the furnace Until the desired temperature as indicated by the pointer 64 is attained within the fur nace, the galvanometer pointer 50 will remain deflected to the right from its balanced position as shown in Fig. 1. lVhen in this position, the pointer 50 serves as a stop which limits the upward movement of the rack 36, whereb the contact switch is maintained tilted in tie closed position as shown. As the temperature within the furnace approaches the desired predetermined value, the pointer 50 moves toward the left (Fig. 2) to its balanced or neutral position, and when in this position, the galvanometer pointer is positioned in the space provided therefor between the adjacent ends of the transverse portions 47 and 48 of the racks 35 and 36, respectively. lVhen the temperature within the furnace increases above the desired predetermined value, the pointer 50 is deflected to the left beyond the balanced or neutral position, and during the next upward movement of the plate 26, the galvanometer pointer serves as a stop to limit the upward movement of the rack 35 while the rack 36 continues to move upwardly, thereby causing the contact switch to become tilted in the opposite direction whereby the conducting fluid 18 is disengaged from the electrodes 16 and 17, thus discontinuing the supply of heating current to the heating element 13. This condition prevails until the temperature within the furnace increases below the predetermined value, whereupon the galvanometer pointer 50 moves to the position shown in Fig. 2, thereby tilting the contact switch into its closed position in the manner hereinbefore described.

Although the invention as herein illustrated and described is particularly applicable to systems for controlling the temperature of electrically heated apparatus, it should be understood that the novel features of the invention are capable of other applications within the scope of the appended claims \Vhat is claimed is:

1. In an electrical control system, a circuit controlling mechanism comprising a reciprocable member, a fluid contact switch pivotally carried thereby, a pinion secured to said contact switch, a reciprocable rack operatively engaging the pinion, and means for reciprocating the member to cause a reciprocatory movement of the rack.

2. In an electrical control system, a circuit controlling mechanism comprising a reciprocable member, a pinion pivotally carried thereby, a fluid contact switch carried by the pinion, a reciprocable rack operatively engaging the pinion, meanstor reciprocating the member to cause a reciprocatory movement of the rack, and a movable member actuated in response to predetermined conditions of the system for limiting the movement of the rack to cause a rotary movement of the pinion.

3. In an electrical temperature control system, a circuit controlling mechanism comprising a reciprocable member, a pinion pivotally carried thereby, a fluid contact switch I carried by the pinion, a air of oppositely dis= carried by the rotatable member and rotatable therewith, and means forrotating the rotatable member to cause a rotary movement of the contact switch.

In witness whereof, I hereunto subscribe my name this 15 day of March, A. D. 1921 ROBERT HOFSTETTER,

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