US2283467A - Stoker alarm system - Google Patents

Description

May 19, 1942 E. K J scoGGlN 2,283,467

STOKER ALARM SYS TEM Filed May 5., 1940 Y INVENTOR Elmer K.. Scogg im ATTORN EY Patented Magie, 1.942l

UNITED STATES `ATi-INT OFFICE STOKER SYSTEM Elmer K; Scoggin, Minneapolis, Minn., assigner to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application May 3, 1940, Serial No. 333,147

10 Claims.

My invention relates to an improved control 'and alarm system for automatic stokers employf jammed or otherwise obstructed so that its normal operation is prevented.

. The object of my invention is to provide animproved arrangement for immediately stopping the stoker motor in the event it becomes overloaded and for providing a signal to indicate that the stoker has stopped.

Another object is to provide'an alarm device for thermostatically controlled stokers employing a shear pin or the like wherein the alarm circuit includes part of the thermostat circuit and is effectivel when the shear pin fails.

Another object is to control the alarm circuit from the thermostat.

Other objects and advantages of the invention will become apparent from the following detailed description and annexed drawing, Figure l of which represents diagrammatically an automatic Stoker4 system embodying my invention, and Figure 2 of which is a plan view of a detail portion of the control mechanism.

Referring tothe drawing, numeral I0 desig-l nates generally a stoker which may be of a well known type, the stoker being driven by an electric motor having a terminal box I I. The stoker feed mechanism comprises a screw conveyor I2 having a shaft I3. The stoker motor drives the shaft I3 by means of a drive collar I4 which is connected to the shaft I3 in a manner which will be pointed out more in detail presently.

The stoker is controlled primarily from a thermostat I1 disposed in a space being heated by means of a furnace or the like-to which fuel is fed by the Stoker. The thermostat I1'comprises a bimetal element I8 to which are attached va pair of resilient blades I9 and 20 cooperating with fixed electrical contacts 2| and 22, respectively. The thermostat I1 is oi a known type Numeral 24 designates an incandescent lampl nected tomovable switch blades 29'and30, the

blades 29 and 3|! moving into engagement with xed electrical contacts 3i and 32, respectively, when the winding 28 is energized.

The relay 21 which controls the Stoker motor may also be controlled by a timing mechanism generally designated at 35. The timing mechanism is driven by an electric timing motor having an armature 36 and a winding 31. The motor drives e. pair of spaced cams 38 and 39 concentrically mounted on a shaft which is driven at a relatively low speedv through a gear train 60. The cams 3d and 39 are frictionally mounted on their shaft so that they may be rotated on the shaft and relatively to each other. The cam 38 is generally circular, having two diametrically opposed abrupt drop offs 4I and 42, there being a cam portion adjacent each of the drop offs of slightly smaller radius than the remaining portions of the cam. The cam 39 has a very similar shape, being generally circular but having diametrically opposed abrupt drop offs 43 and 44, these drop offs having an intermediate shoulder so as to form two small closely spaced drop offs. Adjacent the drop offs 43 and 44 of cam as the cam has portions of slightly smaller radius than the remaining portions of the cam, the shape of the cam being generally similar as mentioned above to the cam 38. The cam 38 has an arcuate slot 45, and an adjustable screw 46 extends through this slot and engages with the cam 39, the screw acting to rmly hold the cams in their relative positions when it is tightened. The cam 38 has asecond arcuate 'slot t1 having graduapositions of the cams.

Numerals 50 and 5I (see Figure 2) designate a pair of cam followers for the cams 38 and 39, respectively, the cam followers being mounted on a shaft or arbor 52 which may be carried by a panel member 53. The cam followers are made of suitable composition material, each having an end suitably formed to engage its respective cam as shown. The ycam follower '5I` is spaced from the panel 53 by a collar 54 and carries a pin 55 extending through an opening in the panel 58, the pin 55 being connected to a fixed pin l58 on the panel 58 by a coil spring 51, the coil spring 51 urgingthe cam follower in a counter-clockwise direction about the arbor 52 against the cam 88. Fastened to the cam follower 8| is a metal contact strip 88 atl tached to the cam follower by means of a screw 5|. The contact strip 88 carries contacts 82 and 68 at its opposite ends. .Attached to the cam follower 58 are contact brackets 85 and 88, the bracket -85 being attached -by a screw 81 and the bracket 88 being attached by a screw 88. The bracket 85 carries a contact 88 at its end and it is so shaped that this contact is adjacent to and engageable with the contact 82. The bracket 81 carries a contact 18 at its end and it is so shaped that the contact 18 is adja` cent to and engageable with the contact 88. Encircling the arbor 52 between the cam followers 58 and 5| is a coil spring 1| one end of which engages the cam follower 58 urging it in a counter-clockwise direction about the arbor 82. When both the cam followers are engaging the portions of their respective cams of larger diameter they are in their relative positions as shown in Figure 1. In this position as shown, the contacts 88 and 18 are in engagement andthe contacts 82 and 88 are separated. As will be apparent from Figures 1 and 2 if the cam follower 88 were rotated in a counter-clockwise direction relativel to the cam follower 8| the contacts 88 and 18 would be separated and the contacts 82 and 89 could be brought into engagement. The operation of the contacting mechanism will be described more in detail hereinafter.

Power for operation of the relay is supplied by a transformer generally designated at 14, the transformer comprising a primary winding to which power is supplied from any suitable source by wires 18 and 11. The.transformer also includes a secondary winding 18 having a fewer.

number of turns than the primary winding.

Numeral 88 designates the mechanism enclosed within the broken lines, this mechanism re resenting the details of the mechanical connection betweenl the stoker driving motor and the shaft I8 previously referred to. As will now be described this connection embodies a shear pin and a switch device operable in response to failure of the shear pin. It will be noted that the engagement therewith and the cap 8| drives the shaft I8 through the shear pin 82. The shear pin 82 is of such size and is made of a material having such a strength that when the shaft |`8 meets a given resistance 'to rotation the shear pin 82 will shear so as to disconnect the drive collar |4 from the shaft I8 in order to prevent an undue load from being imposed Aupon the driving motor. compression spring disposed within the cap 8|, one end of the spring bearing on the shaft I8 so that the spring tends to urge the cap 8| away from lthe end of the shaft I8. On the left end of the cap 8| is a finger or prong 84 which bears against a plate 85 on a resilient snap acting switch arm 88. The switch arm 88 has one end Numeral 88 designates a coiledsecured to an electrical terminal 81 and at its o'ther end carries a contact member 88 movable with a snap action between two electrical contacts 88 and 88 carried on suitable electrical terminals. Normally when the shear pin has not sheared the parts are in the position as shown with the contact 88 in engagement with the contact 88. The various terminals of the switching mechanism just described are mounted on a suitable panel 8| and this panel has a pair of adjacent terminal members 82 and 88 which may be bridged by a screw 84 insertible between the terminal members 82 and 88.

From the foregoing description of the mechanism 88 it will be understood that when the shear pin 82 shears, for example as a result of a rock or the like getting into the stoker` feeding mechanism and obstructing the rotation of the screw I2, the coil spring 88 will urge the cap 8| to the left whereby the finger 84 acting against the switch blade 88 Will cause it to bow to the left moving contact member 88 away from con.

tact 88 and into engagement with contact 88 with a snap action. When the shear pin shears there is of coursel no further rotation of the shaft I8.

In normal operation of the system the relay 21 is energized in response to the thermostat 4'I1 when the temperature has fallen to a predetermined value causing 'the blades I8 and 28 to engage their respective contacts. The circuit so formed for the relay winding 28 is as follows: from secondary 18 of the transformer 14 through a wire |88, terminal 81, switch blade 88, contact 88, contact 88, wire I8|, relay winding 28, wire |82, screw 8|, contact strip 88, contact'88, contact 10, contact bracket' 88, screw 88, wire |88, wire I`84, contact 22, blade 28 of the thermostat, blade I8, contact 2|, wire |85, lamp 24, wire |88, and wire |81 back to the secondary 18, (it will be understood at this time the timing mechanism 85 is in a position as shown in Figure 1). Upon energization of the relay 21 the blades 28 and 88 are moved into engagement with their respective contacts, engagement of blade 28 -with contact 8| completing a maintaining circuit for the relay winding 28 which is independent of the contact 22 as follows: from secondary 18 through wire |88, terminal 81, switch blade 88. contact 88, contact 88, wire |8I, winding 28, wire |82, screw 8|, contact strip v88, contact 88, contact 18, contact bracket 88, screw 88, wire |88, wire |88, wire |88, contact 8|, switch blade 28, wire ||8, heating element 28, wire thermostatic element i8, blade I8, contact2I, wire |85, the lamp 24, wire |88 and wire |81 back to the secondary 18. As is apparent both of thecircuits described above include the lamp 24 and the relay winding 28 in series. 'I'he current which these circuits carry is sufficient to energize the relay 21 but is only suiiicient to make the lamp 24 glow very dimly. As long as the blade 28 engages the contact 22 there is nocircuit is completed for the stoker motor as follows: from wire ||2 to contact 82, blade 88, wire II8, 'terminal box to wire ||4, the wires I|2 and ||4 being connected to any suitable source acecho? of power. When the stoker motor has been enersized as VJust described, operation of thestoking mechanism commences and it continues as long as the relay 21 is energized or until the shear pin of the shear pin mechanism fails. When the temperature in the space being heated rises to a high enough value-to move blade -26 away from the contact 22 the current for maintaining the relay 21 energized passes through the maintaining circuit as above described whereby the heating element 23 is energized and it then emits a small amount of heat to ailect the thermostat |1. This small amount of heat raises the tempurpose of this sequence of operation of the contacts is to prevent the relay 21 being maintained energized by the maintaining circuit previously blade I8 of the thermostat may engage the contact 2| and when the relay is to be deenergized perature surrounding the thermostat |1 slightly so that theblade i9 separates from the contact 2| slightly sooner than it wouldif the thermostat I1 were subjected only to roomor space temperature. Whenever the blade i9 disengages from contact 2| the maintaining circuit is interrupted and the relay 21 is deenergized to stop the stoken The cams 36 and 39 are rotated in a clockwise direction so as to complete one revolution Per hour, for example, and the relay 21 may be energizedin response to the timing mechanism at periodic intervals, for example, half-hourly intervals, for purposes of operating the stoker to maintain the fire alive. With the parts of the timing mechanism in the position shown `the cam follower is .just about to drop oi! the drop off 4 oi cam 38. When the drop oil' 4| permits the left end of cam follower 50 to drop and thereby vmove in a counter-clockwise direction the contacts 63 and 10 are immediately separated and the contacts 62 and 69 are brought into engagement, the cam follower 5| remaining in the same angular position. When the contacts 62 and S9 are brought into engagement a circuit for the relay winding v28 is completed as follows: from secondary 18 through wire |09, terminal 81, switch blade 96, contact-88, contact 90, wire lili, [winding 28, wire |02, screw 6|, contactstrip 60, contact 62, contact 69, contact bracket 65, screw 61, wire H5, and wire |01 back to secondary 18. Upon energizatlon' of the relay I 94 is not in place. It the shear pin 82 should now 21 the stoker will be operated for a short interval of a few minutes, for example 5 or 6 minutes depending upon the angular spacing of drop offs 4| and 43 upon the cams 38 andv 99, the angular spacing of the drop ons corresponding to the number of minutes indicated by the pointer adjacent the graduations on cam 36. When the cams have rotated until the cam4 follower 6| drops on to the intermediate drop oil' 43, the

cam follower El' will be rotated slightly in a counter-clockwise direction so that contacts 82 and l68 will be separated but contacts I2 and 1|I will not be brought into engagement inasmuch as the cam followers, as is apparent from Figure l.,` must be in engagement with portions of their respective cams of .the same radius in order for contacts 63 and 10 to be in engagement. When the contacts 62 and 69 are separated as Just described the circuit for the winding of relay 21 is interrupted and operation of the stoker is stopped. After a further slight rotation of the cams the cam follower 6| drops oi the second portion of the drop olli 43 whereby it rotates slightly in a counter-clockwise direction so as to bring the contacts 69 and 10 into engagement.

From the foregoing it will be understood that for a brief interval when the cam follower 5| has dropped on to the intermediate shoulder ofdrop off 43, both pairs of contacts actuated by the timing mechanism are separated. The

by the timing mechanism if the contacts 63 and relay 21 'will remain energized through the maintaining circuit as above'described. The purpose of separating the contacts 63 and 10 is to interrupt the maintaining circuit at the end. of each nring intervalcontrolled by the timed mechanism.

With the parts in the position shown the screw shear during operation of the stoker the contact 88 will b'e moved away from contact 90 and into engagement with contact 89. Movement of contact 89 away from contact v9|) will interrupt the above described relay circuits causing the relay to be deenergized stopping the stoker motor. The stoker itself will of course stop as soon as the shear pin shears. Engagement ci contact 88 with contact 89 will complete a circuit conneoting the thermostat I1 directly across the secondary 18 of the transformer through the iamp 24, this circuit being as follows: from secondary 15, through wire. |95, terminal ill, switch blade 88, contact 8, contact 89, wire H5, wire tot, wire |84, contact 22, thermostat blades 2li and i9, contact 2|, wire B05, lamp 2li, wire EES, and wire |61 back to secondary 18. This circuit obviously does not include the relay winding and therefore due to the reduced, amount oi resistance in it, it carries a greater amount of current and the lamp 24 will now glow brightly and will act as a signal indicating that the shear pin has sheared and that the stoker has stopped. The lamp 24 is located relatively close to the thermostat i1 and when the last mentioned circuit is completed causing the lamp to glow brightly, the lamp will give off a considerable amount vof heat causing the thermostatic blades to be moved away from their respective contacts. As soon as blade 20 moves away from contact 22 the last described lamp circuit will be interrupted deenergizing the lamp. The thermostat will then have an opportunity to cool again causing the blade 20 to reengage the contact 22 and in this manner the lamp 24 will be intermittently energized 'so as to glow brightly at intervals or in other words, provide a nasher type of signal indicating that the stoker has been vstopped due to shear pin failure.

If desired, the lamp 24 may be connected in wire |04 leading to the contact 22.

Under some circumstances it may not be necessary to completely interrupt the circuit of the relay winding when itis desired to stop the stoker motor in the event of shear pin failure. That is, the relay winding 28 may be merely shunted so as' to reduce the amount of current flowing therethrough to such a low value that it will not be energized. In order to shunt the relay winding in this manner a single pole single throw switch actuated by the shear pin may be used thus eliminating the use of contact 90. To produce such an arrangement the screw 94 may be inserted in place bridging the terminal members 92 and 93 so that the above described circuits for the relay which pass through the switch member 88 and contact 90 would by-pass the switch through the wire H8, terminal member 92, screw4 94, terminal 93 and wire Il! towire IM.

, Thus upon movement of the switch blade to the left .bringing contact 88 into engagement with contact 89, the relay circuit through relay winding 28 would not be interrupted but the winding 2l would be shunted by the above described circuit for the lamp 2|,

From the foregoing those skilled in the art will appreciate that I have provided a very elcient and economical arrangement for stopping a stoker in the event of the stoker mechanism v placing an overload upon the driving motor, and Ifor providing a signal to indicate that the stoker has been stopped. The signal which I employ is located near the thermostat where it will be visible to the occupants of the space being heated and inasmuch as it is lconnected in the control wiring of the thermostat no kadditional wiring is required for the signal. By reason of my particular arrangement the signal is of the in-v combination, an automatic stoker having fuel` feed mechanism and motor driving means ,therefor, a thermostat for controlling the stolzery having a control circuit connected thereto, a signal device included in said circuit, said circuit normally carrying insufficient current to properly operate the signal device, means responsive to excessive load on the motor driving means for stopping the fuel feed mechanism, said last means including a switch actuatable thereby for connecting said circuit directly to a power source whereby said signal device carries suillcient current to properly operate it.

2. In apparatus of the character described, in combination,`an automatic stoker having fuel feed mechanism and motor driving means therefor, a thermostat for controlling the stoker having a control circuit connected thereto, a relay controlled by said circuit controlling said motor driving means, a signal device included in said circuit, said device being in series with thejwinding of said relay when the circuit is completed, said circuit normally carrying insufficient current to properly operate the signal device, means responsive to excessive -load on the motor driving means for stopping the fuel feed mechanism, said last means including a switch actuatable thereby for shorting said relay winding wheresaid circuit normally carrying insufii'cient current to properly operate the signal device, means responsive to excessive load on the motor driving means for stopping the fuel feed mechanism, said last means including mechanism actuatable thereby for interrupting the passage of currenty through the relay winding and icy-passing the winding whereby the circuit through said signal device carries suilicient current lto operate it.

4. In apparatus of the character described, in combination, an automatic stoker having fuel feed mechanism and motor driving means therefor, control means forr the stoker comprising a thermostat located remotely from the stoker and having a control circuitconnected thereto, a normally closed switch in said circuit, and a signal device included in said circuit, said circuit normally carrying insumcient current to properly operate said signal device, means responsive to excessive load on the motor driving means for opening said switch to stop the stoker, and a normally open switch operable to closed position by said load responsive means, means forming a circuit controlled by said normally open switch connecting said signal device directly across a power source whereby said signal device carries suicient current to properly operate it.

, 5. In apparatus of the character described, in comtination, an automatic stoker having'fuel feed mechanism `and motor driving means therefor, a thermostat for controlling the driving means having control wires connected thereto, a signal device adjacent the thermostat, means responsive to excessive load on the driving means for stopping the fuel feed mechanism, and a Aswitch operable by said load responsive means by said signal device carries sufiicient current for completing a circuit to said signal device,

said circuit including a portion of at least one of said control wires connected to the thermostat and extending through the thermostat, and said device being arranged to influence the thermostat to open said circuit to deenergize the device, the thermostat then acting normally to reclose the circuit whereby the device is intermittently energized and deenergized.

6. In apparatus of the character described, in combination, an automatic stoker having fuel feed mechanism and motor driving means therefor, a thermostat having switch contacts for controlling the driving means, said thermostat having control wiring connected thereto, a signal device adjacent the thermostat, means responsive to excessive load on the driving means for stopping the fuel feed mechanism, and a switch operable by said load responsive means lfor completing a circuit to said signal device,

said circuit including portions of said wiring and said switch contacts, said signal device emitting heat when energized for iniiuencing the thermostat to open said contacts to deenergize the device, said thermostat then acting normally to reclose the contacts whereby the device is intermittently energized and deenergized.

7. In apparatus of the character described, in combination, an automatic stoker having fuel feed mechanism and motor driving means therefor, controll means for the stoker comprising a thermostat for controlling the driving means having control wiring connected thereto, a relay controlled by the thermostat, a signal device adjacent the thermostat, means responsive to excessive load on the motor driving means for stopping the stoker comprising a normally closed switch in the circuit of the winding of said relay, and a normally open switch operable to closed position by said load responsive means for completing a circuit to said signal device, said circuit including portions of4 said control wiring connected `to the thermostat and extending through the thermostat, said device-being arranged to influence the thermostat when-energized to open the circuit to deenergize thedevice, the thermostat 'then acting normally to reclose the circuit whereby 'the deviceis intermittently energized and deenergized.

8. In apparatus of the character described, in combination, an automatic stoker having fuel feed mechanism and motor driving means therefor, a thermostat for controllingthe stoker having a control circuit connected thereto, a signal device included in said circuit near the thermokstat, said circuit normally carrying insufficient current to properly operate the signal device, means responsive to excessive load on the motor driving means for stopping the fuel feed mechanism, said last meansincluding a switch nctuatable thereby for connecting said circuit directly to a power source whereby said signal device carries suiiicient current to properly operate it, said device emitting heat influencing the thermostat to open the circuit through the device whereby the thermostat then acts normally to reclose the circuit and thereby intermittently energizing and deenergizing the device.

9. In apparatus of the character described, in

combination, an automatic stcker having fuel feed mechanism and motor driving means therefor, a thermostat for controlling the Stoker having control wires connected thereto, a relay controlled by said wires controllingl'said motor driving means, said thermostat embodying an electric signal device, the circuit arrangements comprising means whereby two circuits may be formed, the first of which operatively energizes said relay and the second of which operatively energizes said signal device, one of said circuits including said signal device and the winding of A vopen switch controlling said second circuit and arranged to operatively energize said signal device upon excessive load.

10. In apparatus of the character described, in combination, an automatic stoker having fuel feed mechanism and motor driving means therefor, control means for the Stoker including a thermostat and a relay device controlled by the thermostat, an electric signal device at the thermostat, circuit means whereby the winding of the relay device and signal device may be connected to form a series circuit, means forming a shunt circuit associated with said series circuit for shunting one of said devices, whereby opening and closing of the shunt circuit varies the energization of the winding of the relay device and the signal device, and switch means responsive to excessive load on the motor driving means controlling the shunt circuit whereby upon excessive load the relay is rendered ineffective to start the stoker and the signal de- ELMER K. SCOGGIN.

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