U.S. patent number 3,647,196 [Application Number 05/046,332] was granted by the patent office on 1972-03-07 for dryer control system.
This patent grant is currently assigned to The Maytag Company. Invention is credited to Curran D. Cotton.
United States Patent |
3,647,196 |
Cotton |
March 7, 1972 |
DRYER CONTROL SYSTEM
Abstract
A control system for a fabric-drying apparatus comprising an
actuation circuit including an SCR operable for initiating
termination of operation of the apparatus responsive to one of a
plurality of condition-responsive trigger circuits. The SCR is
effectively responsive to a preselected dryness condition of the
fabrics, to an absence of flame at the fuel burner, or to a
malfunction of the apparatus, for example, to initiate a shutting
down of the apparatus.
Inventors: |
Cotton; Curran D. (Newton,
IA) |
Assignee: |
The Maytag Company (Newton,
IA)
|
Family
ID: |
21942895 |
Appl.
No.: |
05/046,332 |
Filed: |
June 15, 1970 |
Current U.S.
Class: |
432/37; 432/44;
34/533 |
Current CPC
Class: |
G05D
22/02 (20130101); D06F 34/08 (20200201); D06F
2105/28 (20200201); D06F 2105/62 (20200201); D06F
58/50 (20200201); D06F 2105/46 (20200201); D06F
37/42 (20130101); D06F 58/38 (20200201); D06F
2103/32 (20200201); D06F 2103/00 (20200201); D06F
2103/10 (20200201) |
Current International
Class: |
D06B
15/12 (20060101); D06C 7/00 (20060101); D06B
15/00 (20060101); D06F 58/28 (20060101); G05D
22/02 (20060101); G05D 22/00 (20060101); F27b
007/00 (); F26b 019/00 () |
Field of
Search: |
;263/33B ;34/45 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Camby; John J.
Claims
I claim:
1. A fabric-drying apparatus comprising: means operable for
effecting drying of fabrics in said apparatus; means for energizing
and controlling operation of said means for effecting drying to
achieve said drying of fabrics; means including a solid-state
switch actuatable from a first condition to a second condition for
initiating termination of operation of the means for effecting
drying; means for sensing fabric dryness and including first
trigger means responsive to a predetermined condition of fabric
dryness for actuating said solid-state switch to said second
condition; and second trigger means responsive to a secondary
condition of said fabric-drying apparatus for actuating said
solid-state switch to said second condition whereby operation of
said drying apparatus is terminated responsive to said
predetermined fabric dryness or to the presence of said secondary
condition.
2. In a fabric-drying apparatus as defined in claim 1 and further
including means for effecting a cooldown operation subsequent to
initiating termination of operation of said drying apparatus.
3. In a fabric-drying apparatus as defined in claim 2 wherein said
first and second trigger means each include a normally
nonconductive discharge device operable at a predetermined voltage
for actuating said solid-state switch from said first condition to
said second condition.
4. In a fabric-drying apparatus as defined in claim 3 wherein each
of said first and second trigger means includes an RC circuit for
effecting operation of said discharge device at said predetermined
voltage after a time delay.
5. In a fabric-drying apparatus as defined in claim 3 wherein said
solid-state switch includes a gate portion connected to each of
said discharge devices and responsive to operation of said
discharge devices for actuating from said first condition to said
second condition.
6. A fabric-drying apparatus comprising: means operable for
effecting drying of fabrics in said apparatus including a fuel
burner; means for energizing and controlling operation of said
means for effecting drying to achieve said drying of fabrics; means
including a solid-state switching device actuatable from a first
condition to a second condition for initiating termination of
operation of said means for effecting drying including shutting
down said fuel burner; means for sensing fabric dryness and
including first trigger means responsive to a predetermined
condition of fabric dryness for actuating said solid-state
switching device to said second condition; and safety trigger means
responsive to a malfunction associated with said fuel burner for
actuating said solid-state switching device to said second
condition whereby operation of said drying apparatus is terminated
responsive to said predetermined fabric dryness or to the
occurrence of said malfunction.
7. In a fabric-drying apparatus as defined in claim 6 wherein said
safety trigger means includes means for sensing the absence of
flame at said fuel burner and is operable for actuating said
solid-state switching device from said first condition to said
second condition.
8. In a fabric-drying apparatus as defined in claim 6 wherein said
safety trigger means includes flame rod means adjacent said fuel
burner for sensing the absence of flame at said fuel burner and
actuating said solid-state switching device to said second
condition after a predetermined period of absence of flame and
wherein said safety trigger means further includes circuit means
for sensing a shunting of said flame rod for actuating said
solid-state switching device to said second condition whereby
operation of said drying apparatus is terminated responsive to the
absence of flame at said fuel burner or to a condition of flame rod
shunting.
9. A fabric-drying apparatus comprising: means operable for
effecting drying of fabrics in said apparatus; means for energizing
and controlling operation of said means for effecting drying to
achieve said drying of fabrics; circuit means including a
solid-state switching device having a gate portion for actuating
said solid-state switching device from a first condition to a
second condition for initiating termination of operation of said
means for effecting drying; means for sensing fabric dryness and
including first trigger means responsive to a predetermined
condition of fabric dryness and connected to said gate portion for
actuating said solid-state switching device to said second
condition; and second trigger means responsive to a secondary
condition of said fabric-drying apparatus and connected to said
gate portion for actuating said solid-state switching device to
said second condition whereby operation of said drying apparatus is
terminated responsive to said predetermined fabric dryness or to
the presence of said secondary condition.
10. In a fabric-drying apparatus as defined in claim 9 wherein each
of said first and second trigger means include a normally
nonconductive discharge device connected to said gate portion and
operable at a predetermined voltage for actuating said solid-state
switching device from said first condition to said second
condition.
11. In a fabric-drying apparatus as defined in claim 9 wherein said
means for energizing and controlling include manually operable
preselection means operable to an off condition for terminating
operation of said fabric-drying apparatus.
12. In a fabric-drying apparatus as defined in claim 11 and further
including solenoid means operable for resetting said preselection
means to said off condition responsive to actuation of said
gate-controlled solid-state switching means to said second
condition.
13. In a fabric-drying apparatus as defined in claim 12 and further
including means operable with said preselection means in said off
condition for effecting a cooldown operation of said fabric-drying
apparatus.
14. In a fabric-drying apparatus as defined in claim 13 wherein
said gate-controlled solid-state switching device is in the form of
an SCR having a normally nonconductive anode-to-cathode path
connected to said solenoid for effecting operation of said solenoid
to reset said preselection means to said off condition for
initiating termination of the fabric-drying apparatus.
15. A fabric-drying apparatus comprising: means operable for
effecting drying of fabrics in said apparatus and including a
rotatable fabric container, heating means, and drive means for
rotating said fabric container; preselection means manually
operable for energizing said motor means and said heating means and
initiating and controlling operation of said means for effecting
drying; solenoid means operably connected to said preselection
means and selectively actuatable for effecting a resetting of said
preselection means to an off condition; means including a
solid-state switching device actuatable from a first condition to a
second condition for actuating said solenoid means; means for
sensing fabric dryness and including first trigger means responsive
to a predetermined condition of fabric dryness for actuating said
solid-state switching device to said second condition; second
trigger means responsive to a secondary condition of said
fabric-drying apparatus for actuating said solid-state switching
device to said second condition, said preselection means being
responsive to actuation of said solenoid for effecting
deenergization of said heating means; and means operable for
maintaining said motor means energized independently of said
preselection means after deenergization of said heater means for
effecting a cooldown operation.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is related to a drying apparatus and more
particularly to a control system for initiating termination of
operation of the drying apparatus responsive to one of a plurality
of predetermined normal or abnormal conditions.
2. Description of the Prior Art
Prior art has shown a moisture-sensing control system operable in a
drying apparatus for initiating termination of operation thereof
responsive to a particular dryness condition of the fabrics. Other
prior art has shown separate control systems for independently
terminating operation of the apparatus responsive to other
conditions of the drying apparatus. These separate systems have
included, however, duplication of components resulting in increased
original cost and greater complexity and chance of malfunction.
SUMMARY OF THE INVENTION
It is an object of the instant invention to provide an improved
drying apparatus control system including means responsive to a
plurality of condition-responsive trigger circuits for initiating
termination of operation of the apparatus.
It is a further object of the instant invention to provide an
improved drying apparatus control system having a single
solid-state switching device responsive to a plurality of trigger
circuit signals for initiating termination of the apparatus.
It is a further object of the instant invention to provide an
improved drying apparatus control system responsive to a
preselected dryness condition of the fabrics and to one of a
plurality of other conditions of the apparatus.
It is a still further object of the instant invention to provide an
improved drying apparatus control system for initiating termination
of operation of the apparatus and including a gate-controlled
solid-state switching device responsive to a plurality of trigger
circuits that are independently actuatable for triggering the
solid-state switch to a conductive condition.
The instant invention achieves these objects in a control system
for a fabric-drying apparatus through use of a solid-state
switching device operable for initiating termination of operation
of the apparatus responsive to a signal from one of a plurality of
condition-responsive trigger circuits.
Operation of the device and further objects and advantages thereof
will become evident as the description proceeds and from an
examination of the accompanying three sheets of drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings illustrate a preferred embodiment of the invention
with similar numerals referring to similar parts throughout the
several views, wherein:
FIG. 1 is a view of a fabric-drying apparatus partially broken away
and sectioned and incorporating the control system of the instant
invention;
FIG. 2 is an electrical schematic diagram showing an improved
control circuit for a fabric-drying apparatus and comprising a
preferred embodiment of the instant invention;
FIG. 3 is a fragmentary view showing a portion of a fuel burner
nozzle and further showing a portion of flame-sensing means
included in one embodiment of the instant invention;
FIG. 4 is a chart indicating the operation of various switches of
the circuit of FIG. 2; and
FIG. 5 is a sectional view of one of the fabric-engaging electrodes
included in the control system of the instant invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In FIG. 1 of the accompanying drawings is shown a fabric-drying
apparatus having a base 10 that serves as a support for upwardly
extending channel members 11 and 12 that join with crosspiece 14 to
support the hollow blower housing 17. The housing 17 includes a
tubular portion 21, a divider wall 20 having a rearwardly flared
inner portion defining an intake into an impeller chamber, and
radially directed longitudinal webs 22 which converge toward a
central axis and join with a cylindrical bearing retainer member
23. A plurality of segmental passageways are therefore defined by
the tubular member 21, the bearing retainer member 23, and the
supporting webs 22.
Journaled within bearing retainer 23 is a drum drive shaft 31
projecting from both ends of the housing 17. Fixed to the drum
drive shaft 31 adjacent the rear of the dryer is a large pulley 33
which is driven by motor 34 through a motor pulley 36, a speed
reduction system (not shown) driven by the main drive belt 37, and
belt 40 driven in turn by the speed reduction system.
The forward end of the shaft 31 is rigidly connected to the drum
spider member 46 which has radiating spokes 51 that support a rim
52.
A horizontally mounted fabric-tumbling drum 60 has a rear wall 61
secured to rim 52 for support and rotation of the drum 60 by shaft
31. Rear drum wall 61 is imperforate except for a central exhaust
opening defined by the circular shoulder 55 that is aligned with
the blower tubular member 21. The outer periphery of the rear wall
61 is flanged to form a supporting shoulder for the imperforate
cylindrical sidewall 65 which carries the elevating vanes or
baffles 66 for tumbling fabrics within the drum 60 during rotation
thereof. Cylindrical sidewall 65 is connected to the front drum
wall 67. The front wall 67 has a centrally located access opening
defined by the annular flange 68 and an annular perforate portion
69 located concentrically around the access opening. This perforate
portion 69, including several concentric rows of holes, serves as
the air intake to drum 60.
Cabinet 70 is fastened to the base 10 and substantially encloses
the entire drying apparatus. The cabinet 70 has an access opening
defined by the cabinet flange 71 and aligned with the drum access
opening to receive a rearwardly extending portion of the door
gasket 72. The door 73 is hinged on the cabinet 70 and forms a
substantially airtight seal with the gasket 72. Also fastened to
the cabinet 70 is a shroud or cowling member 74 generally spaced
from the annular front wall 67 of the drum 60.
Located below the cowling or shroud member 74 and mounted on the
base 10 is an air-mixing chamber 75 through which air is drawn and
in which the air is heated and then redirected into the annular
space between the front wall 67 of the drum and the shroud member
74. A heater, such as the fuel burner apparatus 84 shown in
fragmentary form in FIG. 3, is located generally in the entry
portion of the mixing chamber 75 for raising the temperature of the
air passing through the mixing chamber 75. The air is drawn into
and through the mixing chamber 75, through the space between the
drum front wall 67 and shroud member 74, and then through the
perforate portion 69 into the interior of the fabric drum 60. A
felt seal 76 bridges the space between the shroud member 74 and the
drum 60 to prevent air from being drawn inwardly through the space
and thereby bypassing the mixing chamber 75 and the heater therein.
If an electric heater is used in the dryer apparatus, the heating
element may be disposed annularly about the drum front in the space
between the drum front 67 and shroud member 74.
Airflow into drum 60 through perforate area 69 is produced by
rotation of the revoluble impeller member 77 located in the blower
housing 17. The fan pulley 78 formed on the rear end of the
impeller 77 is driven directly by the motor 34 and main drive belt
37. A felt air-sealing member 79 encircles the gap between the
front periphery of blower housing 17 and the rear periphery of
circular shoulder 55 to prevent air from being drawn in at the
junction and thus bypassing the air mixing chamber 75 and drum
60.
The blower housing 17 supports at least one thermostat 82 connected
in series with the heating means to maintain the interior drum 60
at the proper selected drying temperature. Also connected in series
with the heating means is the high-limit thermostat 83 which is
mounted on an upper part of the shroud member 74 and operable to
turn off the heater in case the temperature near the front of the
drum should rise above a predetermined selected temperature during
operation of the clothes dryer. Such a temperature rise might
accompany reduced airflow through the drum 60.
Electrodes or probes 80 and 81 are mounted within the drum 60 to
sense the electrical conductivity or resistance of the fabrics
within the drum 60 as a measure of the condition of dryness of the
fabrics. In a preferred embodiment, the electrodes are in the form
of a pair of elongated conductor members mounted on the crown of
each of the baffle members 66.
Referring to FIG. 5, the baffle 66, on which the electrodes 80 and
81 are mounted, is formed as a substantially hollow member open at
the bottom and attachable to the peripheral wall 65 of the fabric
container 60 oriented with respect to the axis of rotation of the
fabric container for broadside engagement with the fabrics to lift
them for tumbling. The baffle 66 is formed to receive a pair of
electrode members 80 and 81 separated by an intermediate ridge 85
so that the major portion of each electrode is positioned for
contact by the tumbling fabrics within the rotating container 60.
The ridge 85 between the electrodes 80 and 81 prevents simultaneous
contact of both electrodes by rigid objects such as metal buttons
or buckles. The electrodes 80 and 81 include downwardly turned end
legs 86 insertable into openings formed in the baffle 66 for
positioning and retaining the electrodes on the baffle and for
receiving terminals to connect the electrodes 80 and 81 into the
control circuit.
The baffles 66 are formed of an electrically nonconductive material
in order to insulate the electrodes 80, 81 from each other. The
electrodes, however, may be electrically shorted by the contact of
wet materials during tumbling of the fabric container. A plurality
of baffles 66 may be mounted within the drum and provided with the
electrodes similar to 80 and 81.
Referring to FIG. 1, electrical energy is supplied to electrode 80,
for example, by a lead 88 that is connected to a brush 89 that
rotates with the drum 60 and slidingly engages the stationary slip
ring 90 while the drum 60 is rotating. The slip ring 90 is mounted
on the electrically insulative band 79 and is electrically
connected by lead 91 to the control unit 92. The electrode 81 is
connected by lead 93 to the rotatable drum and in turn is
electrically connected to earth ground through the drum 60, the
spider 46, the drive shaft 31, blower housing 17, and the chassis
including the base 10. The chassis is connected to earth ground
through a conductor 94 electrically connected with the base, for
example. The automatic control unit 92 may be secured within a
control housing 95 on the cabinet structure 70. The lead 91 is
connected to the control unit to be described hereinafter.
Referring now to FIG. 2, illustrating the control circuitry for the
fabric-drying apparatus, there is shown diagrammatically a
plurality of control components including a manually operable
preselection means 100 having a plurality of switches 101 through
108 actuatable between open and closed positions, according to the
chart of FIG. 4, under control of push rods or a plurality of
manually actuatable pushbuttons 110 through 113 for selectable
cycles of operation corresponding to "Regular," "Permanent Press,"
"Damp Dry," and "Air Fluff," respectively.
The switches 101 through 108 are shown collectively with the
pushbuttons 110 through 113 in the upper right-hand corner of the
diagram and are shown schematically in the circuit for controlling
initiation and termination of the fabric-drying apparatus as will
be more fully shown hereinafter. Operation of the group of switches
101 through 108 between open and closed positions is also under the
control of a selectively energizable solenoid 115 to terminate
operation of the drying apparatus.
The control circuitry of FIG. 2 includes a pair of conductors 118
and 119 that are selectively connectable with a conventional
two-wire single-phase alternating current supply. For the
explanation of the circuitry of FIG. 2, it will be assumed that the
first conductor 118 is connected with the powerline and that the
second conductor 119 is connected to the neutral line of the
two-wire supply and grounded through resistor 120. It is also
assumed that the Regular cycle has been selected by the
operator.
As previously indicated, the chart of FIG. 4 shows the electrical
posture of the preselection switches 101-108 for the various
selectable cycles. It is noted, for example, that the preselection
switch 101 in the first conductor is closed for each of the
Regular, Permanent Press, and Damp Dry cycles. Thus in the
following explanation of the circuit of FIG. 2, with a Regular
cycle assumed, selection switches 101, 102, 104, 107 and 108 are
closed, preselection switches 105 and 106 are open, and
preselection switch 103 is momentarily closed for initially
energizing the machine.
The cycling thermostat 82 and high-limit thermostat 83 are
connected in the powerline 118 for effective clothes-drying
operation. The normally closed cycling thermostat 82 controls the
temperature to a preselected range while the high-limit thermostat
83, also normally closed, deenergizes the circuit upon reaching a
safe maximum high temperature level. In the preferred embodiment of
FIG. 2 a conventional double-solenoid fuel valve control is
connected between the two lines 118, 119 and is energizable for
opening the fuel valve 121. Electrically operable fuel ignition
means 124, such as a glow coil or spark ignition means, may be
provided between the pair of lines 118, 119.
Also connected between the lines is the motor 34 including start
windings 125, run windings 126 and centrifugal switch 128. Door
switch 129, cool-down thermostat 130 and switches 102 and 103 are
in the motor circuit.
The foregoing portion of the circuit of FIG. 2 is operable upon
initiation of a Regular cycle as follows: Operation of one of the
pushbuttons, such as 110, will close switches 101, 102, 104, 107
and 108 and momentarily close switch 103. The motor 34 will be
energized by a circuit including the closed door switch 129, the
conductor 131, and switches 102 and 103. Initially both the run and
start windings 125, 126 will be energized through contacts 135 and
136 of the centrifugal switch 128 but, upon the motor reaching a
predetermined speed, centrifugal switch 128 will operate contact
136 to contact 138 and, assuming that momentary switch 103 is open,
deenergize the start winding 125 while maintaining the run winding
126 energized through the conductor 139.
Also, upon the motor 34 reaching the predetermined speed the
centrifugal switch 140 in line 119 will be closed. The fuel valve
121 and the fuel ignition means 124 will then be energized to
initiate the drying operation.
Other major portions of the circuit of FIG. 2 are set off by broken
lines and will be referred to as the solenoid actuation circuit
144, fabric-dryness-sensing control 145, flame-sensing circuit 146,
flame rod shunt detector circuit 148, and a DC power supply circuit
149. As previously indicated, the instant invention is directed to
the triggering of the actuation means by one of a plurality of
trigger means, such as the dryness-sensing control 145,
flame-sensing circuit 146, and the flame rod shunt detector circuit
148. These major portions of the control circuit of FIG. 2 will be
described in greater detail hereinafter.
The selectively energizable solenoid 115 is mechanically linked to
the preselection means 100 and is operable upon energization for
resetting the switch members 101 through 108 to the posture
corresponding to the "off" condition of the drying apparatus and
effectively terminating operation of the apparatus.
The solenoid 115 is under control of the actuation circuit 144 that
includes a normally nonconductive gate-controlled solid-state
switch in the form of an SCR 150 having an anode 154 and a cathode
155 in series with solenoid 115. The actuation circuit 144 also
includes a series-connected resistor 156 and capacitor 157 in a
parallel circuit across the anode 154 and cathode 155 of the SCR
150. This parallel-connected snubber network is effective to
prevent erratic triggering of the SCR 150 from stray current
spikes. There is also a filter capacitor 160 connected across the
gate 161 and cathode 155 of the SCR 150 to prevent erratic
triggering due to transient current flow within the circuit. A gate
resistor 162 is also connected across the gate 161 and cathode 155
of the SCR 150.
Upon the impression of sufficient voltage and current at the gate
161 of the SCR 150, the SCR is triggered to a conductive condition
between the anode 154 and cathode 155 for energizing the solenoid
115. The energizing circuit for the solenoid 115 extends between
the powerlines 118, 119 and includes the door switch 129, the
conductor 131, switch 108, the solenoid 115, and the conductor 163
to the anode 154 of the SCR 150. The circuit continues from the
cathode 155 of the SCR 150 to the neutral powerline 119 through the
conductor 164.
This operation of the solenoid 115 resets the switches 101-108, in
a manner shown in FIG. 4, to effectively initiate termination of
operation of the apparatus. More specifically, switch 101 will be
opened for deenergizing the fuel valve 121 to interrupt the heat.
In addition, switches 102 and 107 will be operated to the open
condition for interrupting energization of the
fabric-dryness-sensing control 145. Deenergization of the motor 34
will be delayed, through the use of cool-down thermostat 130, until
the temperature within the drum 60 decreases to a predetermined
temperature; however, the interruption of the heating means and the
deenergization of the sensing control comprise a generally
irreversible shut-down sequence and may be considered as
interruption of the drying apparatus or as initiation of
termination thereof.
The first of the trigger means for actuating the SCR 150 to the
conductive condition is the fabric-dryness-sensing control 145. The
dryness-sensing control 145 for a Regular cycle is energized across
lines 118, 119 by a circuit including closed door switch 129,
conductor 131, switch 102, switch 107 and the conductor 165. A
low-current branch circuit is also completed from conductor 131
through switch 108, the coil of solenoid 115 and resistor 166 to
conductor 165. The current flow in this branch circuit is
insufficient to energize solenoid 115. The fabric-dryness-sensing
control 145 comprises an RC circuit including resistors 168, 169
and 170. Resistor 171 is also in the circuit for a Damp Dry cycle.
The sensing circuit also includes a rectifier 174, a capacitor 175,
and a neon tube discharge device 176.
The circuit of FIG. 2 shows a series connection of the rectifier
174, resistor 168, resistor 169, and capacitor 175. The series
connection is effectively connected across the powerlines 118, 119
for charging the capacitor 175; however, it is noted that a
conductor 178, switch 104, resistor 170, conductors 91, 93, and 94,
and the chassis, indicated generally by numeral 179, effectively
connect the electrodes in parallel with the capacitor 175. Thus as
long as wet fabrics are in contact with the electrodes 80, 81, the
current for charging the capacitor 175 is conducted through the
electrodes 80, 81 and the fabrics so that the capacitor 175 is
maintained discharged. As the fabrics become dry, however, less
current passes through the fabrics and the charge on the capacitor
175 builds to a point sufficient to cause the neon tube 176 to
become conductive.
The breakdown of the neon tube 176 permits the capacitor 175 to
discharge for effecting current flow through the conductor 180 and
junction 181 to the gate 161 of the SCR 150 in the actuation
circuit 144. The current is sufficient to trigger the SCR to a
conductive condition and thereby establish a current path across
the anode 154 and cathode 155 for energizing the solenoid 115.
Closure of switch 105 in the fabric-dryness-sensing control 145
upon the reset of the preselection means 100 is operable for
completely deenergizing capacitor 175 to insure consistent
fabric-dryness sensing during the next operation of the drying
apparatus.
A second trigger means, in the form of a flame-sensing circuit 146,
is responsive to a timed absence of flame at the burner 84 for
actuating the SCR 150 and thereby initiating termination of the
drying apparatus. The flame-sensing circuit 146 is connected to a
DC power supply circuit portion 149 that includes a
current-rectifying diode 184, a resistor 185, and a capacitor 186
connected in series between lines 118 and 119.
The flame-sensing circuit includes an electrode or flame rod 188
juxtaposed to the burner 84 for contact by the flame and also
includes an RC circuit portion connected to the DC power supply 149
by conductor 189. The RC circuit portion is also connected to the
flame rod 188. The RC circuit portion comprises a resistor 190 and
capacitor 191 connected in series between junction 194 and line
119. A second resistor 195 is connected to the resistor 190 and
capacitor 191 at one terminal and to the flame rod 188 at the other
terminal. A discharge device in the form of a neon tube 196 is
connected to the capacitor 191 and through the gate 161 and cathode
155 of the SCR 150 to line 119 for discharge of the capacitor 191
upon the capacitor charging to a predetermined voltage. The
discharge of the capacitor 191 is sufficient to trigger the SCR 150
to a conductive condition.
The third trigger means is in the form of a flame rod shunt
detector circuit 148. The shunt detector circuit 148 is associated
with the flame-sensing circuit 146 by connections through the
junction 194 and conductor 198 and includes a resistor 199, neon
tube 200, capacitor 201, and diode 202. The neon tube 200 is
connected to the diode 202 that is in turn connected by conductor
204 and the junction 181 to the gate 161 of the SCR 150. The
capacitor 201 is connected by conductor 198 to the flame rod 188
and resistor 195. In order to distinguish from other capacitors in
the circuit of FIG. 1, the capacitor 201 will be referred to as a
shunt capacitor 201. It does not operate as a shunt but is used in
the shunt detector circuit 148.
The components of the flame-sensing circuit 146 and the flame rod
shunt detector circuit 148 are cooperable to provide a plurality of
circuit means operable for effecting selective actuation of the SCR
150 to a conductive condition depending upon predetermined
conditions at the fuel burner 84. A first circuit means, operable
for conducting actuation current to the SCR 150 at a level below
that sufficient to effect a change in the SCR from the
nonconductive to the conductive condition, includes the actuation
capacitor 191, resistor 195, conductor 198, shunt capacitor 201,
neon tube 200, diode 202, conductor 204, junction 181, and the gate
161 and cathode 155 of the SCR 150. This circuit is initially made,
after closing of centrifugal switch 140, and indicates an absence
of a short of the flame rod 188 to the burner 84.
A second circuit means is operable for conducting a higher current
to the SCR 150 when the flame rod 188 is shunted to substantially
ground potential by being shorted across the flame gap to the
grounded burner 84. The second circuit means includes a conductive
path from the grounded burner 84 through the flame rod 188,
conductor 198, shunt capacitor 201, neon tube 200, diode 202,
conductor 204, junction 181, the gate 161 and cathode 155 of the
SCR 150 to the neutral line 119 through conductor 164 which is a
substantially ground potential. The second circuit means thus forms
a closed loop through the grounded burner 84. This circuit effects
a discharge of the shunt capacitor 201 when the flame rod 188 is
shorted to the burner 84 and thereby conducts sufficient current to
the gate 161 of the SCR 150 to actuate it to a conductive
condition. The increased current is possible since the
current-limiting resistor 195 is excluded from the circuit by
conduction across the effectively eliminated flame gap.
A third circuit means comprises the actuation capacitor 191, the
neon tube 196, junction 181, the gate 161 and cathode 155 of the
SCR 150 and is operable for conducting sufficient current to the
gate 161 of the SCR for effecting a change in the SCR from a
nonconductive to the conductive condition after a predetermined
time delay, such as 10 seconds, following the sensing of the
absence of flame at the burner 84 and the absence of a shunt of
said flame rod 188 to said burner 84. The operation of these
circuits therefore provides fail-safe operation of the fuel
burner.
Referring to FIG. 3, there is shown a preferred embodiment of the
fuel burner 84 and the flame rod 188 adjacent thereto. The flame
rod 188 is positioned for envelopment by the flame as the burning
of the fuel takes place. The end of the flame rod is within
approximately one-fourth inch to three-sixteenths inch of the
closest part of the grounded burner 84 and is formed of stainless
steel mounted in a ceramic holder 206 with a wire 207 extending
from the back end of the holder 206 and being connected to the
circuitry as shown in FIG. 2.
By way of example, and not for purposes of limitation, a specific
reduction to practice of the preferred embodiment shown in FIG. 1
included resistors and capacitors having specific values as shown
in the following table:
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Resistors (in ohms)
Figure 2 Numeral ohms
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185 220,000 190 47,000,000 162 1,000 156 10 199 3,300,000 195
680,000 120 1,000,000 166 3,300,000 171 470,000 168 30,000,000 169
100,000 170 560,000
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Capacitors (in microfarads with voltage rating)
Figure 1 Numeral Microfarads
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157 0.1 (400 volts) 175 7.0-10.9 (100 volts) 186 0.22 (150 volts)
191 0.47 (100 volts) 160 0.1 (100 volts) 201 0.1 (150 volts)
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Further circuit details and operation explanation of the
flame-sensing circuit 146 and the flame rod shunt detector circuit
148 are included in application Ser. No. 731,907 filed May 24,
1968, by C. D. Cotton et al. and assigned to the assignee of the
instant application.
It is thus clear that the instant application describes a novel
combination of electrical components and circuit portions
comprising an improved control circuit for a fabric-drying
apparatus. The circuit is one in which a single actuation means, in
the form of an SCR, is responsive to a plurality of potential
conditions within the fabric-drying apparatus for initiating
termination of operation of the fabric-drying apparatus. In a
preferred embodiment, described herein, the SCR is responsive to
either the sensing of a desired dryness condition of the fabrics,
to the absence of flame at the fuel burner, or to an inoperative
condition of the flame rod. In each of these circumstances, it is
desirable to terminate operation of the fabric-drying
apparatus.
Other conditions of the apparatus which might necessitate a
termination of operation of the machine for which sensing circuits
could be provided and connected to the gate of the SCR include:
excessive high temperature, insufficient airflow, excessive
vibration, or inoperability of dryness-sensing control.
It is sufficiently clear that this combination provides a complete
control system for a fabric-drying apparatus while achieving
elimination of a number of components. This permits a reduction in
manufacturing costs and an improvement in reliability and
serviceability of the machine.
In the foregoing drawings and specification, there has been set
forth a preferred embodiment of the invention and although specific
terms are employed, these are used in a generic and descriptive
sense only and not for purposes of limitation. Changes in form and
the proportion of parts as well as the substitution of equivalents
are contemplated as circumstances may suggest or render expedient
without departing from the spirit or scope of this invention as
defined in the following claims.
* * * * *