US1728802A - Temperature-control system - Google Patents

Description

Sept. 17, '1929. E. B. NEWILL 1,728,802

TEIPERATURE CONTROL SYSTEI Filed Feb. 1, 1927 ITNESS s: INVENTOR Y &-{ Edward New/W 'ATA'ORNEY Patented Sept. 17, 1929 UNITED STATES- PATENT OFFICE EDWARD B. NEWILL, OF WILKINSBURG,

PENNSYLVANIA, ASSIGNOR TO WESTING- VANIA TEMIERATURE-CONTROL SYSTEM Application filed February My invention relates tocontrol systems and particularly to systems for controlling such conditions as temperature, pressure and the like.

An object of my invention is to provide a system for controlling such conditions as temperature, pressure, etc, in which arcing at the contacts of a device responsive to said conditions is avoided.

Another object of my invention is to'provide a system for controlling such conditions as temperature, pressure, etc., that shall be of simple construction, easily manufactured and eflicient in its operation.

In practicing my invention, a system for controlling conditions of temperature, pres sure, etc., is provided that comprises a magnet coil for actuating an electric switch to circuit-opening and circuit-closing positions,

and a device responsive to said conditionsfor energizing and deenergizing the coil in order to maintain said conditions in a predetermined average state.

The device that is responsive to the conditions to be controlled is of the type in which a plurality of stationary contact members and a movable contact member are embodied. The movable contact member is actuated bymeans responsive to conditions to be-controllech The contact members are so connected to the electroina gnet coil that it is energized when the movable contact member engages one of the stationary con .tact members and de-energized when the contact member engages another of the stationary contact members.

In order to avoid sparking at the contacts of the responsive device, resistor elements are so proportioned in the circuit of the magnet coil and so connected to the contact members that energization and de-energization of the magnet coilis effected by causing certain of said resistor elements to be short-circuited when the movable contact member engages any one of the stationary contactmembers.

In the single figure of the drawing, a system .forcontrolling the temperature of an electrically heated device is illustrated schematically..

1, 1927. Serial No. 165,234.

The heating unit 15 is connected to a source of supply 16 by means of switches 17 and 18 that are adapted to be actuated to circuit-opening and closing positions by means of an electromagnet coil 19.

The energization of the electromagnet coil 19 is controlled by means of a relay 21 and a temperature responsive means 22.

The relay 21 comprises switch members 24 and 25 that are actuated to their circuitopen ng and closing positions by means of an electromagnet coil 23. I

The electromagnet coil 23 is connected in series-circuit relation to resistor elements 26 and 27 and in parallel or shunt circuit relation to resistor elements 28 and29.-

When the coil 23 is in a de-energized condition, a portion of the resistor element 27 is normally short-circuited by means of a contact-bridging member 30, but, when energized, the contact-bridging member 30 is actuated to a circuit-openingposition, thereby increasing the total resistance included in series-circuit relation to the coil 23.

The resistor elements 26, 27', 28 and 29 are so proportioned that, when the switches 24 and 25 are in the circuit-opening position, the current flowing in the coil 23 is insuflicient to cause it to actuate the switches 24 and 25 to circuit-closing positions, but, when resistor element 26 is short-circuited, the current flowing in the coil 23 increases sufficient ly to cause it to actuate the switches 24 and 25 to a circuit-closing position.

Upon the energization of the coil.23, the contact-bridging member 30 is actuated to its circuit-opening position, therebyincreasing the resistance in circuit with the coil 23 and reducing the current flow through 'it. In order to de-energize the coil 23, the resistor element 29 is short-circuited, thereby reducing the current flowing in the coil 23 to such value that its magnetic pull is insufficient to maintain the switches 24 and 25 in their circuit-closing positions, and they are, therefore, caused to move into a circuit-opening position.

The short-circuiting of the elements 26 and 29 is effected by the temperature-responsive means 22 or other means responsive to the condition to be controlled. The temperatureresponsive means 22 comprises, in general, a coil 31 carried by a shaft 32 that is free to turn about its longitudinal axis. The shaft 32 is restrained from turning movementsby means of opposed springs 33 and 34. A movable contact member 35 is carried at one end of the shaft 32 and is adapted to selectively engage a pair of stationary contact members 36 and 37. v

The coil 31 is disposed between the poles of a permanent magnet 38 and is energized by means of a thermo-couple, the hot junction 39 thereof being disposed within a tubular member 41 located in the casing 14, and the cold junction 42 thereof being disposed within a casing 43 that is preferably maintained at a constant temperature.

When the switches 24 and 25 are in their circuit-opening positions and the movable con'tact member 35 is out of engagement with the stationary contact members 36 and 37, the

circuit of the magnet coil 23 comprises conductor 44 of the source ofsupply 16, conductor45, resistor element 26, conductor 46,. coil. 23, a portion of resistor element 27, contact bridging member 30 to conductor 47 of supply circuit 16. A portion ofthe current trav- .ersing the resistor element 26 is diverted through resistor elements 28 and 29, so that,

when the switches 24 and 25 are in their circuit-opening positions'and the movable contact member 35 is out of engagement with the stationary contact members 36 and 37, the magnetic pull of the coil 23 is insuflicient to actuate the switches 24 and'25 to their circuit-closing positions.

When the temperature of the container 14 I is below a predetermined value, the movable contact member 35 is actuated into engagement with the stationary contact member 36, thereby establishing an electric circuit through contact member 36, movable contact member 35, a flexible conductor 48, through resistor elements 28, 29, magnet coil 23, resistor element 27, contact-bridging member 30, to conductor 47. Since the resistor element 26 is short-circuited when the movable contact member engages the stationary contact member 36, the current flowing through the coil 23 increases to such value that its resistor or heating unit 15. With the switches 17 and 18 in their circuit-closing positions, a magnet coil 49 is energized that actuates the contact-bridging member 30 to a circuit-opening position by means of an armature 51. Thus, the entire resistor element 27 is inserted into the circuit of the magnet coil 23 and reduces the current flow therein.

' When the temperature in the container 14 has increased to a predetermined value, the movable contact member 35 engages the contact member 37, thus short-circuiting the resistor element 29. Such amount of current is, therefore, diverted from the magnet coil 23 as to cause a decrease of its magnetic pull and thus ensure actuation of the switches 24 and 25 to their circuit-opening positions, thereby de-energizing coil 19, with the result that switches 17 and 18 are actuated to their circuit-opening positions to de-energize the heating unit 15.

When the switches 17 and 18 are in their circuit-opening positions, the bridging mem-, ber 30 is actuated to its circuit-closing position, and a portion of the resistor element 27 is again short-circuited. When the temperature of the container 14 falls below a certain predetermined value, the contact member 35 engages contact member 36, and the cycle of operation, as herein set forth, again takes place.

The arrangement of the circuits, as illustrated in the drawings, is such that the movable contact member 35 never breaks an electric circuit, and carries current only for a short period after it engages either the one or the other of the contact members 36 and 37. When the contact member 35 engages the contact member 36, the switch 24 closes and carries the current which initially traversed the stationary contact 36 and the movable contact 35. Therefore, no arcing takes place between contact members 35 and 36 when they are actuated to a disengaged position because the current flowing between them, initially, is carried by switch 24.

Since a portion of the current necessary to energize coil 23 is, at all times, flowing through resistor element 26, the contact members 35 and 36, when in engagement, must carry only the remaining portion of current required to cause the coil 23 to actuate the switches 24 and 25 to a circuit-closing posi tion. Thus, wear and burning of the contact members 35 and 36 is reduced to a negligible value.

When contact member 35 engages contact member 37, the current throu h the coil 23 is reduced to such value that t e switch 24 is actuated to its circuit-opening position, thereby inserting the resistor element 26 into the circuit of the relay 21. Thus, the value of current traversing the relay circuit is still further reduced, so thatsubstantially no ourrent, for producing an arc, is traversing contact members 35 and 37 when they are actuated to a disengaged position.

Because current traverses the coil 23 at all times, the increase in current in the circuit between the conductors 44 and 47 is limited to a reasonably small value for the inductance of the coil tends to oppose any change in the value of current, which initially is flowing through it. Therefore, the current which traverses the stationary contact members and the movable contact member is relatively small, and any voltage which tends to produce arcing or sparking at the contacts is absorbed or dampened by the resistor elements 26 and 29.

If the circuit through the magnet coil 23 were to be controlled directly by means of the contact members 35, 36 and 37, the resistor elements 26, 28 and 29 being removed, the current-carrying and interrupting duties imposed on them would be greatly increased, because the current traversing the coil 23 would be reduced to zero when the switches 24 and 25 were in their circuit-openin g positions. With such an arrangement of relay circuits, the rushof current through coil 23, upon the engagement of contact members 35 and 36, may be five or six times greater than the normal value of current ordinarily required to close .switches 24; and 25. Such an initial rush of current may be attributed to the fact that the magnetic-flux densityof the coil 23 is below normal, and, until it has increased to normal value, the current traversing the coil will be of a value greater than normal. It

is also true that, when the circuit of a magnet coil is interrupted, the inductive voltage generated therein tends to cause the current flowing in the coil to continue to flow. This characteristic of the magnet coil becomes more pronounced as the rate of current change therein increases.

The efiectof the resistor elements 26, 28 and 29 is to limit the. current flowing through the coil 23 to such value that it is not suiticiently energized to close the switches 24 and 25 when the contact members 35 and 36 are out of engagement. When the resistor element 26 is short circuited, the increase in current through the coil 23 is only that necessary to cause the switches 24: and 25 to be closed. The short circuiting of the resistor element 26 is not accompanied by an abnormal rush of current because the flux density of the coil is always substantially normal.

Likewise, when contact members 35 and 37 are in engagement, resistor element 29 is short circuited, thereby diverting a suflicient amount of current irom the coil 23 to cause it to release switches 24 and 25 to their circuit-openingposit'ions. In this case, the curr'ent'is still further reduced, when switch 24 is opened, because the resistor element 6 is inserted into the relay circuit.

.It is very important, in temperature control systems, that electric arcs, which usually occur between a stationary contact memberand a slowly movable contact member, be

avoided because continued sparking will soon J for use in a system of the kind illustrated in the drawing, the distance between the movable contact member 35 and the stationary contact members 36 and 37 is sometimes as small as 0.0150 inches. Because the movable contact member 35 moves such a small distance such disturbing influences as shocks and vibration may cause it to flutter 0r chatter against the stationary contact members 36 and 37 which action, ordinarily, will destroy the contact members. By the provision of an electric circuit for the electromagnet coil, which includes the resistor elements 26 and 27 in series with the coil 23 and resistor elements 28 and 29 in parallel therewith, the resistor elements 26 and 29 being in shunt-cir-. cuit relation to the stationary contact members 36 and 37 and the movable contact member 35, sparking at the contact members is avoided.

Various modifications may be made in the device embodying my invention without departing from the spirit and scope thereof. I" desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and the appended claims.

I claim as my invention:

.1. The combination with means operable to a plurality of positions responsive to a condition to be controlled, of an electric circuit comprising a relay and resistor elements c0nnected to said means to be controlled thereby in accordance with the position of said means, one of. said resistor elements being connected in parallel with said relay and the other element connected in series therewith, said series-connected resistor element being so proportioned that when short circuited by the said means the relay is energized, and said parallel connected resistor element being so proportioned that when a portion thereof is short circuited by said means the relay is deenergized.

2. The combination with control means operable to a plurality of positions responsive to a condition to be controlled, of a relay, re-

the relay is energized and for decreasing the resistance when the relay is de-energized.

3. The combination with control means operable to a plurality of positions responsive to a condition to be controlled, of a relay, a resistor element connected in shunt with said relay, a resistor element connected in series circuit relation to the relay and the first named resistor element, and means-for connecting said relay, resistor elements and control means in an electric circuit, said resistor elements being so proportioned that the relay is energized when the second resistor element is short circuited by said control means and is deenergized when a portion of the first named resistor element is short circuited.

4. The combination with a plurality of stationary contact members, a movable contact member for selectively engaging said stationary contact members, and means responsive to a condition to be controlled for actuating said movable contact member, of an electromagnet coil, a resistor element connected in parallel therewith and a second resistor element connected in series-circuit relation to the coil and the first named resistor element, said resistor elements being so connected to the contact members that when the movable contact member engages one of the stationary contact members the second resistor element is short circuited, thereby causing said coil to be energized, and when engaging another stationary contact member a portion of the first named resistor element is short circuited, thereby causing de-energization of the coil.

5. The combination with an electromagnet coil, of means for controlling the energization of said coil comprising a resistor element electrically connected in parallel with said coil, a resistor element electrically connected in series with said coil and resistor element, and means responsive to a condition to be controlled for short-circuiting the series resistor element to cause energization of the coil when said "condition changes in one direct-ion, and for short circuiting a portion of said parallelconnected resistor when said condition changes in another direction.

6. The combination with an electromagnet coil, of means for controlling the energiza tion of said coil including a resistor element electrically connected in parallel-circuit relation to said coil, a resistor element electrically connected in series-circuit relation to said coil and the first-named resistor element to constitute therewith a series-parallel circuit and means responsive to a condition to' be controlled for reducing the resistance of the second-named resistor element to decrease the resistance of the series-parallel circuit to effect energization of the coil when said condition changes in one direction, and for reducing the resistance of said first-named resistor element to effect deenergiz'ation of said coil EDWARD B. NEWILL.

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