U.S. patent number RE43,035 [Application Number 10/991,326] was granted by the patent office on 2011-12-20 for conveyor oven having an energy management system for a modulated gas flow.
This patent grant is currently assigned to Middeby Marshall Incorporated. Invention is credited to Adrian A. Bruno, Frank Carbonara, Bruce Grau, William S. Schjerven, Sr., Gerald J. Schneeweiss, Sylvia Pauline Schneeweiss, legal representative, Mark A. Sieron.
United States Patent |
RE43,035 |
Schjerven, Sr. , et
al. |
December 20, 2011 |
Conveyor oven having an energy management system for a modulated
gas flow
Abstract
A conveyor oven has a modulating gas valve which raises and
lowers the thermal output of a burner that heats the oven. A bypass
line passes a minimum amount of gas to prevent the burner from
completely shutting down during periods while the oven remains
above a threshold demand for more heat. Electrical isolation is
provided between temperature controlling devices to prevent an
electrical feed back which might otherwise prevent a complete shut
down of the oven during hazardous conditions.
Inventors: |
Schjerven, Sr.; William S.
(Schaumburg, IL), Sieron; Mark A. (Arlington Heights,
IL), Grau; Bruce (Island Lake, IL), Bruno; Adrian A.
(Rolling Meadows, IL), Schneeweiss; Gerald J. (Romeoville,
IL), Schneeweiss, legal representative; Sylvia Pauline
(Romeoville, IL), Carbonara; Frank (Mount Juliet, TN) |
Assignee: |
Middeby Marshall Incorporated
(Elgin, IL)
|
Family
ID: |
25383337 |
Appl.
No.: |
10/991,326 |
Filed: |
November 17, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
09760194 |
Jan 12, 2001 |
6684875 |
|
|
|
60249685 |
Nov 17, 2000 |
|
|
|
Reissue of: |
09883786 |
Jun 18, 2001 |
6481433 |
Nov 19, 2002 |
|
|
Current U.S.
Class: |
126/21A; 432/121;
432/176; 99/443C; 126/21R; 126/116A |
Current CPC
Class: |
A21B
1/40 (20130101); A21B 1/245 (20130101); F24C
3/128 (20130101) |
Current International
Class: |
A21B
1/42 (20060101) |
Field of
Search: |
;126/21A,21R,19R,116A,41C,373R,52,35
;99/443R,443C,325,326,328,329R,359,360 ;219/400
;251/12,89,118,175,331,45 ;432/239,121,133,176,128 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Owner's Operating & Installation Manual for Gas Oven Models
Series PS360EWB; Middleby Marshall; Apr. 1996. cited by other .
Selectra, A200 Signal Conditioner Bulletin MS2036-01/96; Jan. 1996;
Maxitrol Company; Southfield, MI, USA. cited by other .
Selectra, AP300 Signal Conditioner Bulletin MS2036A-03/00; Mar.
2000; Maxitrol Company; Southfield, MI, USA. cited by other .
Bakers Pride Oven Company, Inc.; APC-18 Electric Conveyor Oven;
Jul. 2000. cited by other .
Bakers Pride Oven Company, Inc.; Model VHVA-1620E Electric Forced
Air Counter Top Conveyor Ovens; Mar. 2003. cited by other .
Bakers Pride Oven Company, Inc.; Model VHVA-1828E DualAir Electric
Impingement Counter Top Conveyor Ovens; Jan. 2005. cited by other
.
Bakers Pride Oven Company, Inc.; VH1620E, AHVA1620E, VH1828E &
VHVA1828E Electric Countertop Conveyor Ovens--Parts Lists &
Exploded Views; May 2005. cited by other .
7.4 Electrical Diagram, 3270-TS-D Left Hand Side, XLT-3200-TS-D
Installation & Operation Manual, p. 48. cited by other .
7.5 Electrical Diagram, 3270-TS-D- Right Hand Side, XLT-3200-TS-D
Installation & Operation Manual, p. 49. cited by other .
Owner's Operating & Installation Manual for Gas Over Models
Series PS360EWB Apr. 1996. cited by other.
|
Primary Examiner: McAllister; Steven B
Assistant Examiner: Suereth; Sarah
Attorney, Agent or Firm: Michael Best & Friedrich
LLP
Parent Case Text
This is a continuation-in-part of Ser. No. 09/760,194 filed Jan.
12, 2001 which .Iadd.now U.S. Pat. No. 6,684,875.Iaddend., in turn,
claims priority from and replaces Provisional application Serial
No. 60/249,685, filed Nov. 17, 2000.
Claims
The claimed invention is:
1. A conveyor oven control comprising an energy management system
for controlling a flowing stream of hot air through .Iadd.a cavity
of .Iaddend.an oven for baking a food product; a conveyor extending
through said cavity for conveying said food product through said
oven; a fuel gas line for conveying fuel gas from a source to a
burner in said oven; said energy management system being interposed
in said fuel gas line and between said source and said burner for
controlling a flow of fuel gas to said burner; said energy
management system comprising a controller, a signal conditioner, a
fuel gas valve, and an ignition module; a safety shut down valve
.[.associated.]. .Iadd.connected .Iaddend.with said ignition module
to prevent said ignition module from re-igniting said burner during
hazardous conditions; a pair of sensors in said oven for sensing
instantaneous oven temperatures; said controller being responsive
to said sensed temperatures for controlling said energy management
system to regulate operation of said fuel gas valve and, thereby,
the flow of fuel gas to the burner in order to maintain oven
temperature within a predetermined range, said signal conditioner
being responsive to said controller for providing signals that
control said fuel gas valve; and a pair of transformers, one
transformer being coupled to energize said signal conditioner and
.Iadd.to electrically isolate said signal conditioner from said
ignition module, and .Iaddend.the other transformer being coupled
to energize said .[.signal.]. ignition module .Iadd.and to
electrically isolate said ignition module from said signal
conditioner, the pair of transformers connected in parallel with
each other and with said controller .Iaddend.to prevent an
electrical feed back .[.which might otherwise defeat the safety
shut down valve.]. .Iadd.between said signal conditioner and said
ignition module.Iaddend..
2. The conveyor oven of claim 1 wherein said fuel gas valve
comprises a diaphragm closing a chamber having an internal pressure
controlled by fluctuations of oven temperatures, a main valve in
said fuel gas valve coupled to move with said diaphragm for
regulating an amount of fuel gas flowing from said source through
said fuel gas line to said burner in response to movement of said
diaphragm, and a tap line for applying said pressure in said
chamber acting on said diaphragm in response to said sensors
whereby the flow of said fuel gas through said main valve in said
fuel gas valve to said burner is regulated as a function of said
instantaneous oven temperature.
3. The conveyor oven of claim 2 and a by-pass line for enabling a
limited amount of fuel gas to flow around said main valve of said
fuel gas valve whereby said burner continues to burn and does not
shut down while said main valve is closed.
4. The conveyor oven of claim 1 wherein said burner heats air in a
plenum at an input end of said oven from which hot air is driven
through said cavity, said sensors being located at different places
in a plenum.
5. A conveyor oven for automatically baking a food product over a
timed period under the control of an energy management system, said
oven comprising a cavity having a burner associated therewith for
providing heated air in said cavity, a fuel gas line for delivering
fuel gas to said burner via said energy management system, said
burner heating air in a plenum, a system for delivering said stream
of heated air from said plenum through said cavity and returning at
least a portion of said stream to said plenum, a pair of sensors at
different locations in said plenum for sensing an instantaneous
temperature of said heated air in said plenum, a valve for
modulating the fuel gas delivered to said burner responsive to said
sensed instantaneous oven temperature, said delivered fuel gas
comprising at least a minimum amount of fuel gas so that said
burner .[.means.]. remains in continuous operation regardless of
said modulation of fuel gas delivered to said burner, a controller
responsive to said sensors for providing signals for regulating
said fuel gas valve, a signal conditioner, and an ignition module,
said signal conditioner converting said signals provided by said
controller into control signals for operating said fuel gas
modulating valve, and a pair of transformers, one transformer being
coupled to energize said signal conditioner and .Iadd.to
electrically isolate said signal conditioner from said ignition
module and .Iaddend.the other transformer being coupled to energize
said ignition module .Iadd.and to electrically isolate said
ignition module from said signal conditioner, wherein the pair of
transformers are connected in parallel with each other and with
said controller .Iaddend.to prevent an electrical feedback between
said signal conditioner and said ignition module.
6. The oven of claim 5 and a conveyor for delivering a food product
through said cavity over a timed period during which said burner
continuously delivers heat to said cavity, said heat baking said
product as it is conveyed through said oven, and a line for
bypassing said minimum amount of fuel gas around said fuel gas
modulating valve in order to prevent said burner .[.means.]. from
shutting down during periods while said controller is not calling
for heat.
7. An energy management system for a conveyor oven that bakes a
food product during a passage through said oven, said energy
management system delivering a flowing stream of hot air from a
burner and over said food product during said passage and
comprising a fuel gas valve, a controller for sensing and
regulating the temperature of said stream of hot air, a signal
conditioner responsive to said controller for producing signals
required to operate said fuel gas valve, an ignition module, and a
pair of transformers, one of said transformers delivering power to
.Iadd.and providing electrical isolation for .Iaddend.said signal
conditioner, and the other of said transformers delivering power to
.Iadd.and providing electrical isolation for .Iaddend.said ignition
module.Iadd., wherein the pair of transformers are coupled in
parallel with each other and with said controller .Iaddend.to
prevent an electrical feed back signal between .[.them.]. .Iadd.the
signal conditioner and the ignition module.Iaddend..
8. The system of claim 7 wherein said fuel gas valve has a pressure
chamber closed by a diaphragm which expands and contracts in
response to the pressure in said chamber, said pressure increasing
and decreasing in said chamber jointly responsive to said
controller and said signal conditioner as a function of the
temperature of said stream of hot air, a fuel gas line, and a main
valve in said fuel gas line, said main valve being connected to
said diaphragm whereby said main valve opens and closes as said
diaphragm expands and contracts in order to modulate a flow of fuel
gas in said line.
9. The system of claim 8 and a by-pass line around said main valve,
said bypass line delivering enough fuel gas to continuously
maintain said burner in at least a minimum heat condition despite
operation of said main valve responsive to said diaphragm.
10. A conveyor oven comprising a modulating fuel gas valve for
supplying heat to said oven; a controller; a signal conditioner for
converting signals from said controller into signals for operating
said fuel gas modulating valve; an on/off safety valve in said fuel
gas line to automatically shut down said oven during predetermined
conditions; an ignition module for igniting fuel gas delivered by
said safety valve; and an electrical control circuit for operating
said fuel gas modulating valve, controller, conditioner, and
ignition module, said circuit having a first section relating to
mechanical parts of the oven and a second section relating to
energy management of heat delivery in said oven, and said
electrical control circuit having electrical isolation for
preventing a feed back of electrical signals .[.which might prevent
shut down of said safety valve during said predetermined
conditions.]. .Iadd.between said signal conditioner and said
ignition module.Iaddend.; wherein said second section includes
first and second transformers coupled in parallel .Iadd.with each
other and with said controller .Iaddend.to provide said isolation
between .[.their.]. secondary windings .Iadd.of the first and
second transformers.Iaddend., one of said secondary windings
supplying power to .Iadd.and electrically isolating .Iaddend.said
signal conditioner .Iadd.and not supplying power to said ignition
module, .Iaddend.and the other of said secondary windings supplying
power to .Iadd.and electrically isolating .Iaddend.said ignition
module .Iadd.and not supplying power to said signal
conditioner.Iaddend., said safety valve being coupled to supply
fuel gas via said ignition module.
11. The oven of claim 10, and a pair of sensors for detecting heat
in said oven, said sensors being coupled to drive said controller,
said signal conditioner being coupled to operate said fuel gas
modulating valve, and a coupling from said controller to .Iadd.said
signal .Iaddend.conditioner whereby heat detected by said sensors
controls said fuel gas modulating valve.
Description
This invention relates to conveyor ovens having reduced fuel
consumption and with quieter operation, and more particularly to
such ovens having an energy management system including a modulated
gas flow with a safety feature that isolates electrical controls in
order to enhance an integrity of the safety features built into the
oven.
BACKGROUND
Prior art conveyor ovens are shown in U.S. Pat. Nos. 4,964,392 and
5,277,105 owned by the assignee of this invention and in the
references cited on the cover pages of these patents. These and
other similar patents may be consulted in order to learn details of
how conveyor ovens are constructed and operate. Often--but not
always--this type of oven is used to cook or bake pizzas, bread, or
the like.
Conveyor ovens are devices for automatically baking or cooking food
products over timed periods. Normally, they have a conveyor belt
which travels through an elongated oven cavity having open ends and
at a speed which times the exposure of the food product to the heat
of the oven. A food product, such as a pizza, for example, is
placed on one end of the conveyor at the entry to the oven cavity
and delivered from the oven at the opposite end of the cavity. The
heat in the oven and the speed of the conveyor are coordinated so
that the food product is fully and correctly cooked or baked by the
time when the conveyor delivers it at the exit end.
The conventional method of delivering controlled heat has been to
switch burners off and on in order to hold the resulting
temperature in the oven cavity within a relatively narrow range.
This process has functioned very well in the past. However,
anything can always be improved and, therefore, it is always
possible to do a better job heating and cooking or baking the food
product.
Also, the cost of the fuel (natural or propane gas) for the burners
is increasing sharply. Thus, an important goal is to reduce the
fuel consumption, which the invention has done by approximately
30%.
A conveyor oven is usually energized by gas, which always requires
a safety feature since an explosive atmosphere might be created by
leaking gas. As a result, various governmental agencies prescribe
an incorporation of safety features, such as a cut-off valve, into
the design of the oven. It is important for the oven controls to be
designed to not only enable a reliability of these safety features,
but also to provide a redundancy for the safety features. In this
invention, the safety features are enhanced by providing an
electrical isolation between control signals that might otherwise
cause a feed back that might enable the oven to continue operation
or to re-ignite after a demand for shut down.
BRIEF DESCRIPTION OF THE INVENTION
Accordingly, an object of the invention is to cook or bake a better
food product by maintaining a closer control over the uniformity of
the heat in the oven cavity. Here, an object is to maintain a
substantially smooth level of heat after the oven is switched on
and continuing throughout the oven operation. In particular, an
object is to avoid the peaks and valleys of heat swings as the
burner switches on and off as it hunts for the targeted
temperature.
Another object is to provide a quieter operation by eliminating a
blower-like noise which occurred heretofore as the burner switched
on.
Still another object is to provide a universal heat controller
which can control either a modulating valve or an on/off valve,
thereby eliminating a need for many controllers individually
dedicated to specific ovens.
A further object of the invention is to provide a control circuit
which insures the integrity of a safety feature built into the
oven. Here, an object is to provide a self-healing control which so
insures the integrity, but which docs not require a replacement of
a fuse or other element after the condition requiring a safety
valve operation subsides.
In keeping with an aspect of the invention, these and other objects
are accomplished by a use of a modulating valve which increases or
decreases the amount of the gas flow to a burner without fully
switching the burner off or on during a bake cycle. The modulating
valve is controlled responsive to temperatures sensed by
thermocouple sensors located in the oven. Furthermore, the
controller is also able to control an on/off gas valve in response
to the same type of sensor signals, so that the same controller may
be used universally for both the modern oven using the modulating
valve and the older ovens using on/off valves.
The integrity of the safety features built into the oven is
preserved by an isolation in the electrical control circuit between
the elements which control the modulating valve and a conditioner
which converts signals from sensors into signals which can enable
an operation of the modulating valve. This isolation prevents feed
back which might otherwise cause the modulating valve to behave in
a way which would defeat the shutdown of an on/off safety valve. In
order to provide a self-healing of this integrity insuring system,
it uses transformers for separating and isolating the modulation
valve control and conditioner circuits from an ignition control
module.
The advantages of the invention are many. There is an improved
reliability and a higher quality bake at a shorter bake time and at
a lower average temperature. Since the ovens operate at a lower
temperature, the components are in a cooler environment which
extends their life. The oven is quieter and the energy management
system is more efficient due to a use of the modulating gas valve
and to a two-way air return, with less turbulence, creating lower
DB noise levels. There is an increased flexibility making it easier
to rearrange the fingers for delivering heated air to the food
product. There is an ability to add a deck, as volume increases, or
to remove a deck if volume falls off. All decks are the same.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be better understood from the following
specification taken with the accompanying drawings, in which:
FIG. 1A is a perspective view which shows a plurality of ovens
stacked one upon the other in order to increase baking capacity
without increasing the oven footprint;
FIG. 1B is a perspective view of a hot air delivery finger being
removed from the oven cavity;
FIG. 1C is a perspective view of a disassembled finger;
FIG. 2 is an enlarged view of that part of FIGS. 1A 1C which is
material to the invention;
FIG. 3 is a view, partly in cross section, of an automatic safety
on/off switch and a modulating switch coupled into in a gas
line;
FIG. 4 is a schematic line drawing of the parts seen in FIG. 2,
together with labels identifying the various items shown in the
drawing;
FIG. 5 is a graph which illustrates the peaks and valleys of the
burner duty cycle of the prior conveyor ovens using on/off gas
valves;
FIG. 6 is a graph which illustrates the continuous burner operation
responsive to the inventive modulated gas flow;
FIGS. 7A and 7B are simplified cross sections showing a side
elevation and a plan view which schematically show the location of
temperature sensors in the oven;
FIG. 8 is a control circuit diagram of the oven, the control
circuit including an energy management system with a safety
integrity enhancement; and
FIG. 9 is a flow chart showing the capability of the controller for
the modulating valve.
DETAILED DESCRIPTION OF THE INVENTION
The equipment in FIGS. 1A 1C shows a conveyor for delivering a
stream of heated air through an oven cavity. More particularly,
FIGS. 1A 1C are perspective views of a conveyor oven 20 which
receives a conveyor 21 (FIG. 1A) extending from an input end 21a
through a cavity to an output end 21b of the oven. The motor for
driving the conveyor is in the housing 22.
FIG. 1A shows a plurality of the ovens 20a 20b (sometimes called
"decks") stacked one on the other to increase the baking capacity
without increasing the footprint dimensions. Each deck may be
separately programmed to bake a different food product. FIG. 1B is
a perspective view of a person removing a hot air delivery finger
from an oven by sliding it in direction A along side rail tracks.
FIG. 1C is a perspective view of the finger construction where two
perforated plates 25a, 25b direct streams of hot air downwardly and
onto the upper surface of a food product. Lower fingers 24a (FIG.
1B) direct hot air upwardly through perforated plate 25c and onto
the lower surface of a food product. The hot air recycles by
flowing from a plenum, through the fingers and returning between
the top and bottom fingers to the plenum.
The material parts 26 of the oven energy management system are
shown in greater detail in FIGS. 2 and 4. Natural or propane gas is
fed from a source to the burner via a line 28 and a modulating
valve 30 under the control of a signal conditioner 31 and a
temperature controller 32. Both the preferred modulating valve 30
and signal conditioner 31 are products of the Maxitrol Company and
are sold under the trademark "Selectra". The Maxitrol Company has a
business address at 23555 Telegraph Rd (P.O. Box 2230), Southfield,
Mich., U.S.A. 48037-2230. The temperature controller 32 is a
product of the Honeywell Company.
FIG. 3 shows gas line 28 extending from any suitable source of
natural or propane gas on the left to a burner on the right.
Interposed in the gas line between the source and the burner are
two valves 29 and 30. Valve 29 is any suitable on/off valve usually
prescribed by a governmental regulatory agency for safety purposes.
For example, a conventional valve 29 might be adapted to shut down
the gas delivery responsive to predetermined conditions such as
excessive pressure appearing in the gas supply line, excess oven
temperature, or the like.
The modulating valve 30 means is shown in cross section. A main
spring 33 biases a main valve 34 into a position either to close or
open the gas line 28 in order to prevent or enable a flow of gas to
the burner. A by-pass line 35 is provided for enabling gas to flow
around the main valve 34 and through a pressure regulator 36 even
when valve 34 is closed, thereby continuously maintaining at least
a minimum level burner operation. A manual valve 37 in the by-pass
line may cut-off or allow the by-pass gas to flow, as a safety or
shut down procedure. Midway between regulator 36 and the manual
by-pass valve 37, a tap line 38 allows the by-pass gas to flow
through modulator 39 in order to enable the gas to flow from the
source into an upper chamber 40 which is closed by a diaphragm 41.
Modulator 39 is controlled responsive to signals from thermocouple
sensors 42 in the oven. As the oven becomes colder, the diaphragm
moves down, and as it becomes hotter, the diaphragm moves up.
Hence, the diaphragm 41 moves up or down as a function of the
instantaneous oven temperatures.
As the diaphragm 41 moves down, it overcomes the bias of spring 33
and opens main valve 34 by a distance which enables a volume of gas
to flow in line 28 depending on the distance that valve 34 has
moved.
If the oven temperature sensed at 42 goes down, the modulator 39
enables more gas flow from the by-pass line 35 to increase pressure
in upper chamber 40, thereby deflecting the diaphragm 41, pushing
valve 34 against the bias of spring 33 and opening the main valve
34 by a discrete distance. If the oven temperature sensed at 42
goes up, modulator 39 restricts the flow of by-pass gas, the
pressure in upper chamber 40 reduces, the diaphragm 41 returns
somewhat from its deflected condition, and spring 33 pushes the
valve 34 to a more closed position.
Hence, it should now be clear that the amount of gas delivered to
the burner follows the instantaneous fluctuations of the oven
temperature, while maintaining a minimum flow through by-pass line
35. With a need for a low heat, there is little or no pressure on
the diaphragm 41 and gas flows only through a by-pass and at a very
low rate. In between the high and low demands for a high level of
heat and a low level of heat, the pressure in the upper chamber 40
has an intermediate effect upon the deflection of diaphragm 41 and,
therefore, on the position of main valve 34 and the amount of gas
flowing to the burner.
The temperature controller 32 (FIG. 2) is a device which receives a
signal, preferably, from a pair of thermocouple sensors located in
the baking cavity of the oven. The sensor may continuously supply
any convenient signal indicating the instantaneous oven
temperature. The signal conditioner 31 interfaces between the
temperature controller 32 and the modulating valve 30 by converting
the sensor signal into a signal which the modulating valve
uses.
The details on the arrangement of the various parts described thus
far are best seen in FIG. 4. The gas is delivered from any
convenient source through a line 44 to the various ovens via a pipe
28. As here shown, it may be assumed that pipe 28a is in oven 20a
(FIG. 1A) and pipe 28b is in oven 20b. The remainder of the ovens
20c, 20d are served in a similar manner. The top oven has a pipe
28a which is closed by a cap 46.
The manual shut-off valve 48 simply provides for a complete shut
down of the system. Usually, this valve is left in an "on"
position.
The automatic valve 29 is a conventional on/off device which meets
any local safety standards. While such safety valves tend to be
fairly uniform, various locations may have their own, non-standard
governmental requirements. Therefore, the valve 29 has special
meaning depending upon the geographical location of the oven.
Next, the modulating gas valve 30 is located to admit a regulated
amount of gas into a burner 50. While any suitable burner may be
used, a high efficiency burner is preferred. These burners are
found in many appliances from heavy duty home heating to relatively
light duty in appliances.
A blower 52 is coupled to the burner 50 via a suitable duct 54 in
order to supply combustion air to the burner. When the burner first
comes on there is a mixture of gas and forced air, which usually
produces a very noisy roar; hence, a blower which switches off and
on is noisy. The invention avoids this noise by modulating the flow
of gas which never shuts off as demand increases and decreases when
the oven temperature decreases or increases.
FIG. 5 is a graph which discloses at 56 the duty cycle of the prior
art burner as it responds to the temperature sensed in the oven and
at 58 the temperature fluctuations at various locations in the
oven. The prior art burner duty cycle 56 is shown as having peaks
60a, 60b, 60c, as the burner is generating maximum heat and valleys
62a, 60b, 60c when the burner is shut down. The peaks and valleys
depend upon sensed oven temperatures. Those temperatures vary with
ambient temperatures, drafts, frozen or thawed condition of the
food product, etc. Hence, it is not possible to predict with any
certainty as to the relationship between the appearances of the
peaks and valleys relative to the excursion of the food product on
the conveyor. As a result, the food product may have a variegated
cooking or baking depending upon the peaks and valleys.
A second point indicated in FIG. 5 is that there is a considerable
demand for fuel because the oven heats and cools depending upon the
peaks and valleys. Hence, the burner has to work harder to
repeatedly recover from a cool down when it is in the off
stage.
FIG. 6 is a graph similar to FIG. 5, but showing the operation
responsive to the inventive use of the modulating valve 30. The
flow of gas to the burner is seen in the curve 70. While the gas
flow varies almost continuously, it is never off, so that the
burner modulates its out put within a relatively narrow hand but
does not shut down. Since the burner does not come on suddenly,
there is no blow torch-like roar at the ignition. Curve 72 shows
the temperatures sensed at the front, exit and middle of the oven.
While this curve shows that the sensor does track the instantaneous
variations of the heat put out by the burner, the average
temperature in the oven is much more uniform over time.
The most important feature is that, in the prior art, the fuel
required to maintain the burner operation represented by curve 56
(FIG. 5) is 30% greater than the fuel required to maintain the
inventive burner operation represented by curve 70 (FIG. 6).
FIGS. 7A and 7B are simplified and schematic showings of the side
elevation and top plan view of the inventive oven and are provided
to show the location of two oven temperature sensors which feed the
controller 30. In greater detail, the features shown in FIGS. 7A
and 7B are the oven housing 75 that contains a rear wall
76.[.and.]..Iadd., .Iaddend.blower fan .[.compartment.].
.Iadd.compartments .Iaddend.77 .[.which together define an air
supply plenum 78 between them. This.]. .Iadd.and two air supply
plenums 78. Each .Iaddend.plenum is pressurized by hot air that is
driven into the oven via upper and lower fingers 79, 80,
respectively. A conveyor 81 passes between the lingers 79, 80,
carrying food products which are baked by the heat of the hot air
discharged from the fingers. After the hot air is emitted from the
fingers, it passes between the fingers and into an air return
plenum 82, 83 above and below the fingers.
The oven contains three thermal couples which are seen in line in
FIG. 7A so that only a high limit thermocouple sensor 84 appears.
The high limit sensor 84 causes the oven to shut down if a
predetermined threshold temperature is reached. This shut down is
well below a hazardous level. The other two of these thermocouples
which feed controller 32 are the control sensors 85, 86 seen in the
plan view of FIG. 7B.
The controls are in a compartment 87 at the front of the oven which
is cooled by fans seen in FIG. 8.
FIG. 8 is a circuit diagram showing a control section 108 relating
to the mechanical aspects and a control section 110 relating to the
energy management system of the inventive oven.
The mechanical aspects 108 include blower motors 113, 114 which are
connected to a suitable commercial power source 112 via switches
(such as 115) and circuit breakers (such as 116). The blowers
.[.76.]. .Iadd.77 .Iaddend.are in the .[.plenum 82.]. .Iadd.plenums
78 .Iaddend.to drive a stream of hot air into the oven cavity which
is recycled between the fingers and back into the plenum. The high
limit thermostat 118 does not normally provide an active function
unless the temperature in the oven exceeds some preset threshold
safety limit, beyond which the oven might go into a runaway
condition. If that limit is exceeded, the contacts 120 open to shut
down the oven while contacts 122 close to light a reset pilot lamp
124.
Next, there is a series circuit 126 of door switches which will
prevent the oven from Operating unless all doors are suitably
closed. If there are any other mechanical parts which have to be in
any particular condition for the burner to switch on, associated
switches (not shown) may also be provided in the series circuit
126.
A power transformer 128 provides power to the conveyor motor 130
which is turned on/off at switch 132. The motor has a suitable
sensing mechanism for maintaining a stable speed selected at and
under the control of a known circuit in control box 134.
The energy management system 110 controls the heat in the oven by
modulating the delivery of gas to the burners. More particularly, a
set of switches 135 either enables or disables the blower. If the
blower shuts down, the contacts 136A open and the oven cannot be
placed in operation until the manual switch 136B is closed. A coil
146 is energized when the burner blower switch 135 is closed to
provide an interlock when the blower is on. The two fans 142, 144
blow cool air over the electronic and other controls in the control
compartment 87 in order to prevent a malfunction as a result of
over heating.
The temperature controller 32 receives signals from two sensors 85,
86 located .[.at plenum.]. .Iadd.in plenums .Iaddend.78 in the
front end of a hot air stream for supplying heated air in the oven.
The controller 32 is a product of the Honeywell Company. The
switches 152 detect the presence of the various air streams in the
oven. Basically, these switches have air sails in the oven at a
location where they are moved by the air stream in order to open or
close electrical switches. These sail switches are simply on/off
switches to indicate the presence or absence of the air stream.
Switch 155 is closed in order to heat the oven.
First and second isolation transformers 156, 157 supply 24V power
for the electronic equipment coupled to their secondary windings
respectively. In particular, transformer 156 supplies an ignition
module 158 while transformer 157 supplies signal conditioner 31,
thereby isolating the two from each other. The controller 32 is
supplied from the power line 112. Signal conditioner 31 responds to
signals which it receives from the controller 32 and converts them
into signals which control the modulating valve 30. A push button
159 must be pressed to reset the modulating valve 30 after it shuts
down.
An ignition module 158 is adapted to ignite and maintain a pilot
flame that initiates the gas of burner 50 (FIG. 4). An associated
sensor 160 signals the presence of a pilot flame. The safety gas
valve shown at 29 has the characteristics prescribed by an
appropriate governmental regulation in order to shut down the oven
under predetermined hazardous conditions.
Means are provided to enhance the integrity of the safety features.
Accordingly, even though there are many safety features on the oven
so that it automatically shuts down well before any catastrophic
condition is reached, it is conceivable that there could be a feed
back condition in a loop extending between the controller 32, the
signal conditioner 31, and the ignition module 158, which might
interfere with the response of the safety valve 29.
Therefore, it is desirable to provide a safety integrity
enhancement by the electrical isolation between the controller 30,
conditioner 31 and ignition module 158, which would prevent such
feed back.
The power line voltage (here 240V) applied at 112 appears across
line conductors 162 and 164. Controller 32 is connected directly
across the line so that there will not be any feed back to it via
the lint 162, 164 from either signal conditioner 31 or the ignition
module 158. The two transformers 156 and 157 have primary windings
168 and 170 connected in parallel across the power line conductors
162, 164, so that the primaries are not affected by events after
the secondaries. The secondary winding 172 of transformer 156
supplies the 24V power to ignition module 158 and to the
governmental prescribed safety switch 29. The secondary winding 174
of transformer 174 supplies 24V to the signal conditioner 31 and
modulating valve 30.
Hence, there is no single path forming a feed back loop for causing
an interaction between the controller 32 and conditioner 31, and
ignition module 158.
A layout of a front panel control panel is shown at the top of FIG.
9. There are a display panel and eight push buttons. A list of
control panel functions are shown at the bottom of FIG. 9 to help
explain the features of controller 32. The push button "1" is a
blank which has no preselected purpose, but which is available to
control any customized feature which the owner of the oven may
request.
A four digit numeral display 200 displays either the process
variables or the setpoint during normal operation. The right-most
digit of this display shows whether the displayed value is in terms
of degrees in Fahrenheit or in Centigrade. Alternate information is
also displayed during the service depending upon the function being
carried out.
A "heat on" indicator is illuminated when the controller is
applying an output of 3% or more heat. When an on/off control is
configured, the "heat-on" indicator is illuminated when an output
heat is provided. Either the present temperature or the programmed
setpoint temperature may be displayed. A simultaneous pressing of
both the unlock and the display keys 208, 202 will display the
value of the heat output with the heat on indicator on. With the
output unlocked at key 208, the user is able to cycle through
actual temperature display indicators to reveal the actual
temperatures, setpoint temperature, and the heat on condition. When
the setpoint displays "yes", it is not possible to change the
setpoint.
A locked setpoint condition can be temporarily unlocked at key 210
for making an adjustment of the programmed oven temperature. Sixty
seconds later, the setpoint automatically returns to the locked
state if no further control operations are carried out after the
last press of the display key 202. When the 60 second time period
expires, the controller 32 is locked and the display return to the
default display.
The output display is automatically locked in a default display
when a service man or operator places the controller in the service
mode by pressing key 204 or when the hidden key 206 is pressed
while the output display is shown. A failsafe condition occurs when
any one of the various tests fail, at which time, a flashing signal
display is alternately displayed with temperature.
If the oven has not reached 200.degree. F. within fifteen (15)
minutes after an initial power-up of the oven, a message is flashed
on the display panel indicating that the controls need to be reset
(power-cycled). If a thermocouple sensor fails to operate properly,
the display will flash "open". If the polarity of the thermocouple
leads are reversed, the display will flash a signal indicating the
thermocouple leads are incorrectly connected to the instrument.
The displays also provide prompts for servicing the oven responsive
to a simultaneous pressing of the unlock key 208 and the service
tool key 204. Each additional press of the service tool key 204
advances the prompts in the order shown under "service mode" in
FIG. 9. The user can continually sequence through the service
prompts by repeatedly pressing the service tool key 204. The
service mode is exited by either pressing the display key 202 or
pressing no key for sixty seconds. Either way, the system
automatically returns to the normal mode.
Setpoint lock key 210 automatically flashes the temperature that
has been selected for an operation of the oven. The setpoint can be
changed up or down by pressing either the increment or decrement
keys 212, 214. The degrees (.degree. F. or .degree. C.) used for
the prompts is changed by pressing either the increment or
decrement keys. While at the degrees .degree. F. or .degree. C.
prompt, a selection of "F" or "C" automatically changes the units
of all the display to .degree. F. or .degree. C. While the default
display prompt is being displayed, an indicator flashes to indicate
which display is chosen as the default display, which can be
changed by pressing either the increment or decrement keys.
Those who are skilled in the art will readily perceive various
modifications that fall within the scope and spirit of the
invention. Therefore, the appended claims are to be construed to
cover all equivalents.
* * * * *