US2250919A - Automatic control for heating systems - Google Patents

Description

July 29, 1941 J. B. sKELLY 2,250,919

AUTOMATIC CONTROL FOR HEATING SYSTEMS Filed Feb. 1, 1940 Patented July 29, 1941 UNITED ySTATES PATENT OFFICE AUTOBIATIC CONTROL FOR IAIEATIN G SYSTEMS 1 Claim.

This invention relates to a device for controlling the operation of a mechanism such as a furnace according to any predetermined time interval of operation.

It has long been known that in the heating of f large apartment houses and other buildings of considerable size, there are many problems which make ineffective the normal automatic heating control devices of the prior art. It has been found that a thermostat in a large building is not particularly satisfactory since the conditions of temperature may vary widely from one part of the building to another. Consequently, much work has ybeen done in order to find some satisfactory means for heating these large buildings.

One of the most satisfactory solutions of these problems has been the provision of a mechanism for operating a furnace for certain predetermined time intervals. That is, the furnace may operate for live minutes and then be off for fifty-five minutes out of each hour. This type of furnace control system has been found to work very satisfactorily, since after a short period of operation, the time that a furnace may be on for any outside temperature may readily be determined by experiment.

The main diiiculty with the devices of the prior art has been that they are usually quite complicated and rather diilicult to manufacture. They are usually very expensive and are apt to get out of order and fail to perform their function.

The main object of my invention is to provide an improved device for operating an apparatus according to a predetermined, adjustable on l and off period of operation.

Another object of my invention is to provide a compact construction for such a device so that it may be as foolproof as possible, cheap to manufacture and simple to operate.

f A further object of my invention is to design a unit of this type which may be readily attached driven at a constant speed by a clock and movable over or relative to the stationary contacts.

Thus, when it is desired to run the furnace for say five minutes out of the hour, the selector switch is moved to energize the stationary contactof the clock driven switch which corresponds to a ve minute period. When the movable arm of the clock driven switch contacts the five minute contact segment of that switch, a furnace motor control relay will be actuated and the furnace will be on As the clock driven contact moves off of the ve minute period, the furnace will go off The actual operation and construction of my invention will be more readily understood by referring to the accompanying drawing, the single figure of which is a diagrammatic view of the system.

As will be seen by the drawing, there are two switches A and B. Switch A is the clock driven switch, while switch B is the selector switch. Switch A comprises a number of switch contact members A1, A2, Aa, etc. mounted on arcs of concentric circles. In the particular construction shown in the drawing, the switch segment A1 corresponds to a 2.5 minute period, that is, it covers l5 arcuate degrees. Segment A2 corresponds to 5 minutes, while segment A3 corresponds to 10 minutes. All of these segments are preferably mounted on a piece of insulating material so that they will be completely insulated from each other and may be spaced in any suitable manner. One advantage of the particular arrangement shown here is that it may be readily added to without materially increasing the size of the switch carrying member, that is, any nurnber of additional concentric arcs may be added outside of those already in position. This type of switch consequently gives a very satisfactory construction since it is extremely simple to manufacture and very compact.

As will be noted, there are two segments A5 spaced apart. This arrangement is merely typical of the latitude of variation in design and construction which may be employed in manufacturing the switch or hooking it up to the selector switch B. vThe two contacts As give an on period for the first 15 minutes and the third 15 minutes out of each hour. Of course, the switch may be so constructed or connected to the selector switch that the furnace may be on for 5 minutes, off for 10, on for l5, etc. or any other conceivable time sequence which may be found to be desirable.

I have described the switch, for the purpose of illustration, as having time segments corresponding to portions of an hour. Of course, any other suitable time base may be chosen.

The selector switch B comprises a number of contacts B1, B2, B3, etc. Each of these contacts B1, B2, B3, etc. corresponds to the segments A1, Az, Aa respectively and are connected thereto by means of wires C1, C2 and C3.

Thus, 'assuming that the Contact arm 'I of switch B is energized and is moved to contact B4 as shown on the drawing, it will be obvious that segment A4 will also be energized and the movement of the clock driven contact arm 6 will actuate the furnace operating relay for a period of l5 minutes out of each hour.

In conjunction with these two switches I have designed a circuit which, though not the only conceivable circuit, is one which I have found very satisfactory for operating my device. Power for operating the different relays and the clock motor I'I is derived from power lines I. In order to obtain low voltage for my switches, I have provided a step down transformer 2 which will provide approximately 10 volts for operating the furnace control relay 4 connected to the transformer by the line 3. The other side of the relay 4 is grounded through line 5, while the other side of transformer 2 is connected through line 6 to the switch arm 'I of the selector switch B. The rotating switch arm 8 of switch A is mounted on the shaft I6 of the clock 9 and is grounded through the frame of the clock. Thus, when the switch arm 8 is in contact with the segment A4 of the switch A and the switch arm 'I of the selector switch B is on the contact member B4, a circuit will be completed from the transformer through line 6, switch arm 1, wire C4, switch arm 8 to ground, thus energizing the solenoid 4.

Operated by the solenoid 4 is a switch arm II mounted to normally close the cir-cuitl including lines I2 and I3 and adapted to open that circuit and close the circuit comprising lines l2 yand i3 when it is actuated by solenoid 4. These lines II, I2 and I3 comprise a three line circuit control for operating either a boiler control, furnace motor control or steam valve control. In series with this circuit lare the additional automatic controls I4 and I5 which may be steam pressure or steam temperature responsive switches. Assuming that this control circuit operates the furnace motor, when `the solenoid 4 is energized it will move switch arm I0, and close the circuit between lines I3 and II thus starting the motor. When the solenoid 4 is deenergized the switch arm I will move to the right, close the circuit between lines I3 and I2 and stop the furnace motor.

By providing the `additional switches I4 and I in series with the furnace control relay 4-IQ I have been able yto obtain a very accurate control of the furnace operation. During the time that the furnace is running under the control of the switches A and B, it is usually necessary to have certain other controls on the furnace in order to prevent overheating of the steam or excessive pressures. If, while the furnace is running for one of its predetermined time periods, either the steam pressure or steam temperature rises above a desired limit, one of these switches will be operated to turn off the furnace. As soon as the pressure or temperature has dropped back to within the operating range, the circuit will again be established and the furnace will go on.

In order to tell at a glance whether or not the furnace control relay is closed, I have provided an indicating lamp in parallel therewith so that whenever the solenoid 4 is energized the lamp I3 will be lit.

At times it may be found desirable to operate the motor continuously, subject only to the control of such automatic switches as the steam pressure responsive switch and the steam temperature switch shown at I 4 and I5. In order to do this, I have provided the contact B9 on switch B which is grounded through line I9. When the switch arm 'I is moved over to contact B9, the switch A will be completely taken out of the circuit and solenoid 4 will be continuously energized.

In order to prevent any damage to the relay, transformer or motor coil, I have provided at 2B an overload fuse which may be of any suitable current capacity.

In describing my invention I have limited myself somewhat to the particular construction which I find is very apt to accomplish my purposes. It is, of course, obvious 4that many other changes may be made to this device without departing from the spirit of my invention.

It is equally obvious that the switches A `and B may be considerably modified without departing from the spirit of my invention.

Thus it is seen, from the disclosure of my invention as set forth above, that I have developed an improved apparatus for selectively controlling the on and off periods of a furnace which will not interfere with any other automatic controls which it may be found desirable to include in the furnace heating system. My device is extremely simple in operation, it is very inexpensive to manufacture and does not have any delicate parts which are liable to be damaged or get out of adjustment. It is extremely simple to operate, requiring only the setting of a single switch, `and is positive in its functioning at all times.

I claim:

For use with a control circuit, a control for varying proportions of a given period of time when said circuit is active and inactive, said controller comprising a continuously driven clockactuated shaft, Ia radial contact arm mounted to rotate with said shaft and having a plurality of spaced contact means thereonl a plurality of arcuate segmental contact members mounted concentrically around said shaft, said contact members being of varying lengths corresponding to varying increments of time, some of said contact `members being displaced radially with respect to other of said contact members, a manually operated selector switch having a movable selector arm and a plurality of stationary selector contacts adapted to be engaged by said selector arm, a single connection from one of said connecting means to a corresponding one of said selector contacts and other connections from other of said arcuate contact members to other of said selector contacts, and a switch operating solenoid in series with said selector arm, and one of said selector contacts.

JAMES B. SKELLY.

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