US3312398A - Humidity controller with thermal relay - Google Patents

Description

April 4, 1967 c. E. MARKHAM 3,312,398

' HUMIDITY CONTROLLER WITH THERMAL RELAY Filed June 28, 1965 atomizer.

United States Patent Ofiice 3 ,3 l2,398 Patented Apr. 4, 197

This invention concerns means for controlling the amount of moisture to be supplied to a space in accordance with the requirements to maintain some preselected moisture content of the air in the space.

The object of the invention is to provide a simple and reliable humidity controller employing a moisture sensing element of the type in which the contraction and relaxation of an organic material in response to decreasing and increasing moisture content of the ambient air provides motion to effect operation of control means and in which the work required of the sensing element in the performance of its control function is reduced to a negligible amount thereby to preclude permanent distortion of the organic material and consequent drift of the control point.

Other objects and advantages will appear from the following description when read in connection with the accompanying drawing.

The single figure of the drawing is a schematic view of a humidity controller constructed in'accorda-nce with the present invention.

Referring to the drawing, a humidifier or moisture supply means is generally indicated at and includes a normally closed solenoid valve 12 interposed in a water supply line 14 and an electric motor 16 for driving an The humidifier supplies moisture to a space in which a moisture responsive switch generally indicated at 18 is located. Switch 18 comprises a moisture sensing element consisting of a thin, flexible, formed metal strip 20 having a thin strip of organic material 22 glued thereto. The strip 22 may be wood, paper formed of wood pulp or other organic fibres, or a suitable synthetic plastic material. The construction and operation of this type of moisture responsive element is well known. It is also well known that when this type of element is constructed to such dimensions that it responds rapidly and considerably to changes in the moisture content of the ambient air it is unable to perform any appreciable amount of work in response to slight changes in the moisture content of the air. Moreover, it is well known that any appreciable stressing of elements of this type in the performance of the control function results in a distortion of the organic material and a consequent drift of the control point.

The laminated strip 20-22 is coiled at one end and fixed in a slot inthe end of rotatably adjustable stud 24. Stud 24 has an arm 26 attached thereto which sweeps an indicia plate 28 and provides means to rotatably adjust the stud. At its free end the metal strip 20 carries a contact 30 arranged to cooperate with a threadedly adjustable fixed contact 32. Metal strip 20 also carries an armature 34 adjacent its free end, and a small electromagnet 36 mounted adjacent the armature operates when energized to pull the free end of strip 20 downward. The straight portion of strip 20-22 is shown illustrated in a horizontal position; however, it may be mounted in a vertical position in order to preclude the influence of gravity.

A thermal relay is generally indicated at 38 and includes a resistance heater 40 and a bimetal switch blade 42 arranged in good heat transfer relationship with resistance heater 40. The bimetal blade 42 is anchored at one end in a support 44 and carries movable contacts 46 and 48 on opposite sides of its free end. The movable contacts 4 6 and 48 cooperate with threadedly adjustable fixed contacts 50 and 52, respectively. A snap action of relay 38 between its opposite positions of closure with fixed contacts 50 and 52 is accomplished by the provision of a pair of permanent magnets 54 and 55 arranged to attract armature pieces 56 and 57, respectively, carried by the free end of bimetal blade 42. The arrangement of the greater and lesser expanding metal strips of bimetal blade 42 is such, and the blade is so preformed, that at normal room temperatures it assumes the position shownin the drawing with contacts 46-50 closed and contacts 48-52 open, and when heated to a predetermined temperature by resistance heater 40, it warps to the left separating contacts 46-50 and closing with contacts 48-52.

The resistance heater 40 is connected across a pair of power source terminals 58 and 60 through a lead 62, the

metal strip 20, contacts 30-32, a lead 64, a lead 66, a

lead 68, contacts 50-46, bimetal blade 42, and a lead 70. The normally closed solenoid valve 12 is connected in parallel with motor 16 by leads 82 and 80, and both are connected across power source terminals 58-60 through lead 76, a lead 78, thermal relay contacts 48-50, bimetal strip 42, and lead 70. The resistance heater 40 has sufficient heat output when energized to effect the heating of bimetal strip 42 to its operating temperature at a relatively rapid rate.

In operation, when the moisture content of the air ambient to the switch 18 falls below that preselected to be maintained, the strip of organic material 22 shrinks, causing contacts 30-32 to close. This contact closing force efiected by the response of coiled strip 20-22 will be very light, but will be sufficient to at least partially energize the small electromagnet 36 which will, in turn, immediately increase the contact pressure at contacts 30- 32 so as to effect full energization of the parallel connected resistance heater 40 as well as the electromagnet. When this occurs bimetal blade 42 will be heated at a rapid rate and will, at a predetermined temperature, have built up sufficient force due to warping to pull away from the attraction of magnet 54, thereby opening contacts 46- 50 and closing contacts 48-52 with a snap action. In this position the free end of the bimetal strip is attracted by magnet 55 which provides immediate strong contact pressure between contacts 48-52 and maintains this pressure until sufficient warping of the bimetal strip in the opposite direction, upon cooling, builds up suflicien-t stress to pull away from magnet 55 and return to the position shown.

The opening of contacts 46-50 de-energizes resistance heater 40 and electromagnet 36, and the closing of contacts 48-52 completes the described circuit energizing the parallel connected motor 16 and solenoid 12, thereby supplying moisture to the air ambient to switch 18. Deenergization of electromagnet 36 releases the free end of strip 20-22 so that this sensitive element is now again entirely free to respond to an increase in the moisture content of the ambient air effected by operation of humidifier 10. De-energization of resistance heater 40 permits the bimetal strip to cool to normal room temperature, which results in its snap action return to the position shown in the drawing. Upon cooling, the permanent magnet 55 prevents movement of the free end of bimetal strip 42 until the strip has cooled considerably below the temperature to which it was heated by resistance heater 40.

Inasmuch as the resistance heater 40 has the capacity to heat the bimetal blade rapidly, the time-temperature curve upon heating rises abruptly until the operating temperature of the blade in one direction is reached. On the other hand, upon cooling when the resistance heater is de-energized and in the absence of any cooling means,

the time-temperature curve characteristically flattens out as the temperature approaches normal room temperature.

The time during which contacts 48-52 are closed is therefore considerably longer than the time required to heat the bimetal blade to its operating point. If contacts 30- 32 remain closed due to an insufliciency of moisture supplied during one operating cycle of the humidifier, it will continue its cycles of operation until sufi'icient moisture is supplied to effect opening of contacts 30-32.

The on time of the humidifier may be increased by any one of a number of expedients which slow down the cooling rate of bimetal strip 42. For example, the cooling rate of the blade 42 may be slowed down by merely increasing its thickness, or by encasing the bimetal strip 42 and heater 40 so as to retain the heat, or by providing a heat sink in proximity with and in heat transfer relationship with the heater 40 and bimetal blade 42. Preferably, the relay 38 is designed so that the time differential between heating and cooling of blade 42 is in the order of one to six so that, when the time required to heat the bimetal blade from room temperature to its operating temperature in one direction is thirty seconds, its cool-down time during which the humidifier is operating is in the order of three minutes.

In the preferred form of the invention, the electrical resistance of metal strip 20 and bimetal strip 42 is sufficiently low to preclude any significant heating.

Modifications of the illustrated embodiment within the spirit of the invention will occur to those skilled in the art, .and the use of all such modifications is contemplated. For example, an overcenter toggle action including the bimetal blade 42 as one of the toggle links may be substituted for the permanent magnets 54 and 55 and armature pieces 56 and 57 to effect a snap action. Also, any suitable arrangement of a moisture sensing element employing an organic filament or strip held in tension by spring means may be substituted for the glued and' coil metal and organic strips 2fi22 without departing from the spirit of the invention.

The foregoing description is intended to be illustrative and not limiting, the scope of the invention being set forth in the appended claims.

I claim:

1. In a humidity controller, an electrical power source, an electrically operated humidifier, a sensitive humidity responsive switch which closes its contacts in response to decreasing humidity, an electromagnet operative when energized to increase the closing force applied to said humidity responsive switch contacts when they close in response to a decrease in humidity, a double throw heat responsive switch having a normal cold position and an opposite hot position to which it moves when heated, an electrical resistance heater operative when energized to heat said double throw heat responsive switch at a rate which effects its operation from its cold to hot position in a considerably shorter time than is required for it to subsequently cool sufiiciently to effect its return to its cold position when said resistance heater is de-energized, circuit connections including in series arrangement said humidity responsive switch contacts when closed, said double throw switch in its cold position connecting said electromagnet, and said resistance heater across said power source, whereby said electromagnet and said resistance heater are de-energized when said double throw switch moves to its hot position, and circuit connections including said double throw switch in its hot position connecting said humidifier across said power source.

2. In a humidity controller, a power source, a double throw thermal relay having a normal cold position and an opposite hot position and having one pair of contacts, which are closed when in its hot position, adapted to control the operation of a humidifier and having a second pair of contacts which are closed when in its cold position, an electrical resistance heater operative when energized to heat said double throw thermal relay at a rate which effects its operation from its cold position to its hot position in a considerably shorter time than that required for it to subsequently cool sufficiently to effect its return to a cold position when said resistance heater is de-energized, a sensitive humidity responsive switch which closes its contacts in response to decreasing humidity, an electromagnet which when energized increases the pressure between the humidity responsive switch contacts when they are closed, and circuit connections including said humidity responsive switch contacts and'said secon-d pair of thermal relay contacts in series arrangement connecting said resistance heater and said electromagnet across said power source, whereby said humidity responsive switch is freed from the influence of said electromagnet when said thermal relay moves to its hot position. 1

3. In a humidity controller, a sensitive humidity responsive switch which closes its contacts in response to decreasing humidity, an electrom-agnet operative when energized to increase the pressure between said humidity responsive switch contacts when closed, a double throw,

snap action, thermal relay having a normal cold position and a hot position and including an electrical resistance heater which when energized heats said relay at a rate which effects its operation from its cold to hot position in a considerably shorter time than is required for it to cool sufiiciently to effect its return to a cool position when said resistance heater is de-energized, said double throw relay having a first pair of contacts which are closed when said relay is in its hot position and which are adapted to control the operation of moisture supply means and a second pair of contacts which are closed when said relay is in its normal cold position, and circuit connections including said humidity responsive switch contacts and said second pair of relay contacts in series arrangement for connecting said electromagnet and said electrical resistance heater across an electrical power source.

References Cited by the Examiner UNITED STATES PATENTS 435,898 9/1890 Johnson 236-78 912,815 2/1909 Cook 236-44 2,181,606 11/1939 Parks 23668 ALDEN D. STEWART, Primary Examiner.

Claims (1)

1. 3. IN A HUMIDITY CONTROLLER, A SENSITIVE HUMIDITY RESPONSIVE SWITCH WHICH CLOSES ITS CONTACTS IN RESPONSE TO DECREASING HUMIDITY, AN ELECTROMAGNET OPERATIVE WHEN ENERGIZED TO INCREASE THE PRESSURE BETWEEN SAID HUMIDITY RESPONSIVE SWITCH CONTACTS WHEN CLOSED, A DOUBLE THROW, SNAP ACTION, THERMAL RELAY HAVING A NORMAL COLD POSITION AND A HOT POSITION AND INCLUDING AN ELECTRICAL RESISTANCE HEATER WHICH WHEN ENERGIZED HEATS SAID RELAY AT A RATE WHICH EFFECTS ITS OPERATION FROM ITS COLD TO HOT POSITION IN A CONSIDERABLY SHORTER TIME THAN IS REQUIRED FOR IT TO COOL SUFFICIENTLY TO EFFECT ITS RETURN TO A COOL POSITION WHEN SAID RESISTANCE HEATER IS DE-ENERGIZED, SAID DOUBLE THROW RELAY HAVING A FIRST PAIR OF CONTACTS WHICH ARE CLOSED WHEN SAID RELAY IS IN ITS HOT POSITION AND WHICH ARE ADAPTED TO CONTROL THE OPERATION OF MOISTURE SUPPLY MEANS AND A SECOND PAIR OF CONTACTS WHICH ARE CLOSED WHEN SAID RELAY IS IN ITS NORMAL COLD POSITION, AND CIRCUIT CONNECTIONS IN-

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