Note: Descriptions are shown in the official language in which they were submitted.
3L2 ~3~i~3~L PATE~r - 9D-RG-16419 - Payne
-
BACKGROUND OF THE INVENTION
-
This invention relates generally to an improved power control
arrangement for an autornatic surface unit in a co~ing appl;ance such
as a dcmestic electric range. More specifically, this invention is an
5 improvement to the power control arrangement disclosed and claimed in
commonly assigned U.S. Patent 4,4g3,980 to Thomas R. Payne, -
~hic~ patent issued Januar~r 15, 1985.
The electronic control arrangement of the above referenced
patent provides a significant improvement in the temperature control
lC ~erform2 oe of automat c surrace units over tile coln~entional
electromechanical sensing and control devices con~ellcionally used or
such surface units. In that control arrangement the applied power
level for the surface unit is adjusted as a function of an error signal
which is directly proportional to the difference between the selected
utensil temperature range and the sensed utensil temperature range.
This error signal is large early ;n the transient heat up phase when
.
the differential is large resulting in a relatively high applied power
level and goes to zero as the differential goes to zero with the
applied power level diminishing accordingly. Consequently, the unit is
greatly overdriven initially to heat up the utensil rapidly, but only
slightly so.as the sensed temperature approaches the selected steady
state temperature range to minimize overshoot. This arrangement works
well for relatively small and average thermal loads. Ho~ever, for
relatively large thermal loads, during steady state operation, that is
operation after having initially reached the selected steady state
temperature range, the utensil temperature may drop below the desired
minimum steady state temperature, a condition referred to as
undershoot. When such conditions occur the error signal at least
;nit1ally is relatively small, and consequently the applied power level
:,
.~, '
` ~L~ 3~ L PATENT - 9D-RG-16419 - Payne
for the surface unit is such that utensil temperature may be
undesirably slow in returning to the selected ranye.
Therefore, it is an cbject of the present invention to provide
an improved power control arrangement which will retain the rapid
thermal response with minimum overshoot during the transient heat up
phase provided by the arrangement of the'980 patent , yet which will
provide a more rapid thermal response to undershoot conditions
occurring during operation in the steady state phase.
SUMMARY OF THE INYENTIO~
.
The present invention provides an improved power control
arrangelnenl for a cooking appliance -,ncorpoYatin3 an automatic ~urfare
unit for which the user may select a FRY mode for heating food loads to
one of a plurality of user selectable steady state temperature ranges.
The automatic surface unit ;ncludes temperature sensing means for
sensing the temperature of a cooking utensil being heated on the
surface unit. User operable selector means are provided, enabling the
user to select one of a plurality of different temperature settings for
the FRY mode, each setti~g in having associated with it a predetermined
steady state temperature range defined by a predetermined minimum and
maximum sensed utensil temperature. Electronic control means controls
energi~ation of the surface unit in response to inputs from the
temperature sensing means and the user input selector means. In
accordance with the improvement of the present invention, the control
means is operative in the FRY mode to generate first and second error
signals, as functions of the difference between the sensed utensil
temperature and the steady state temperature range for the selected
heat setting. The control means operates the surface unit at an
applied power level determined as a function of the first error signal
during the transient heat up phase, prior to the sensed utensil
--2-
.
~ L PATENT - 9D-RG-16419 - Payne
temperature first reaching the selected steady state ternperature range,
and operates the surface unit at an applied power level which is
determined as a function of the second error signal during operation in
the steady state phase after the sensed utensil temperature has first
reached the selected steady state utensil temperature range. The
second error signal is larger than the first error signal whereby
undershoot conditions occurring during the steady state phase such as
may result from a relatively large thermal load are corrected rapidly.
While the novel features of the invention are set forth ~ith
particularitJ in the appYnded claims, the invention, uoth ~s to
organization and oontent, will be better understood and appreciated
from the following detailed description taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DR~IINGS
15 - FIG. 1 is a front perspective view of a portion of an electric
range illustratively embodying the power control arrangement of the
.
present invention;
FIG. 2 is a greatly enlarged view of a portion of the control
panel of the range of Fig. 1 showing the details of one of the control
knobs thereof;
FIG. 3A is a sectional side view of a surface unit of the type
incorporated in the range of Fig. 1 showing the temperature sensor;
FIG. 3B is a graphic representation of the resistance Y5.
temperature characteristic for the temperature sensor of Fig. 2A;
FIG. 4 is a greatly simplified functional block diagram of the
control arrangement employed in the range of Fig. 1 incorporating the
power control arrangement of the present invention;
' FIG. 5 is a simplified schematic diagram of the control
circuit illustratively embodying the power control arrangement of the
present invention as used in the range of Fig. l;
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~ 3~L PATENT - 9D-RG-16419 - Pa~ne
FIG. 6 is a fla~ diagram cf the User Input Scan routine
incorporated in the control prograM for the microprocessor in the
circuit of Fig. 5;
FIG. 7 is a flow diagram of the Temperature Scan routine
incorporated in the control program for the microprocessor in the
circuit of Fig. 5;
FIG. 8 is a flow diagram of the Sensor Filter and Timing
routine incorporated in the control program for the microprocessor in
the circuit of Fig. 5;
lQ FIG.--~ is a ;l ~ diagram of the Fry rou~ine incorpolated in
the control program of the microprocessor in the circult of Fig. 5;
FIG. 10 is a flo~ diagram of the Warm routine incorporated in
the control program of the microprocessor in the circuit of Fig. 5;
FIGS. llA and llB depict the flow dlagram of the Power Compare
routine incorporated in the control program for the microprocessor in
the circuit of Fig. 5; and
.
FIG. 12 is a flow diagram of the Pcwer Out routine
incorporated in the control program of the microprocessor in the
circuit of Fig. ~.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODI~EN~
Fig. 1 illustrates an electric range 10 incorporating a
control arrangement illustratively embodying the present invention.
Range 10 includes four conventional electric surface units comprising
resistive heating elements 12, 14, 16 and 18 supported from a
substantially horizontal support surface 20. Each of elements 12-18
are adapted to support cooking utensils, such as frying pans, sauce
pans, tea kettles, etc., placed thereon for heating. Heating element
12 is arranged to function as an automatic surface unit, that is,
energization of element 12 is automatically controlled as a function of
.
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~6~3~3~ PATENT - 9D--RG-1~419 - Payne
the sensed temperature of the utensil being heated thereon and the user
selected heat setting. Heating elements 14, 16 and 18 may be arranged
to be duty cycle controlled in conventional manner to provide a
predetermined output power level corresponding to the user selected
heat setting. hhile, as is common practice, the range of the
illustrative embodiment is provided with only one automatic surface
unit, it will be appreciated that multiple automatic surface units
could be provided.
Mode selection switch 22 on control panel 24 enables the user
iO t~ select the Fry Mode or the general Boil Mode for heating element
12. Manually operable rotary control knobs 26~ 28, 30 and 32 are
mounted to control panel 24. Control knob 26 is illustrated in greater
detail in Fig. 2. Control knob 26 enables the user to select a
plurality of heat settings corresponding to various cooking
temperatures for the Fry Mode, and to select Warm, Simmer and Lo, Med
and~ Hi Boil Modes for the general 3Oil mode.
The utensil temperature sensing arrangement employed with the
automatic surface unit in the illustrative embodiment will now be
described with reference to Fig. 3A. Surface unit heating element 12
is supported on spider arms 33. The temperature sensor apparatus
designated generally 34 includes a housing 36 mounted on one end of an
elongated, generally L-shaped tubular arm 38.
A cylindrical shield 40 of low thermal mass meta~ forms the
central core to which the radial spider arms 33 are attached and also
serves to shield sensor housing 36 from radiated heat from heating
element 12. Arm 38 extends through a slot 4~ in shield 40, and bears
against the upper end of the slot to hold housing 36 in the proper
position slightly above the element 12 so as to cause the uppermost
surface 37 of housing 36 to resiliently contact the bottom of a cook;ng
8~L
9~-RG-16419
utensil when it is placed on heat:ing ele-ment 12. ~rhe temperature
sensitive element (not shown) of the sensor contained within housing 36 is
a conventional negative temperature coefficient thermistor having a
resistance vs. temperature characteristic as shown in Fig. 3B. ~he
structural details of this sensor arrangement do not form any part of the
subject invention and are thus described only to the extent necessary for
an understand mg of the present invention. Such devices are described in
greater detail in commonly assigned U.S. Patent No. 4,241,289.
A generalized functional block diagram of the control
arrangement for automatic surface unit 12 of range 10 is shown in Fig. 4.
Heating element 12 is energized by a standard 60 Hz AC power signal which
can be either 120 or 240 volts supplied to terminals Ll and L2. Power to
element 12 is controlled by switch -means 44. The switching device of
switch means 44 is switched into and out of conduction by control signals
generated by electronic control means 46.
Electronic control means 46 generates power control signals for
element 12 in response to inputs from the user operable input ælection
means 48 and 50 signifying mode and heat setting selections respec~ively
and inputs from temperature sensing means 52 which senses the temperature
of the utensil being heated by element 12.
In the illustrative embodiment, electronic control means 46
controls the output power level of heating element 12 by controlling the
duty cycle, i.e., the percentage of time power is applied to the heating
element. A predetermined control period comprising a fixed number of
control intervals is employed as the time base for power control. The
ratio of conductive control intervals to the total number of control
intervals Ln the control period, expresæ d as a percentage, is
hereinafter referred to as the duty cycle. Preferably each control
- 6 -
` ~2~3~i~31 PATENT - 9D-RG-16419 - Payne
interval comprises eight full cycles of the standard 60 Hz 240 volt AC
power signal corresponding to a time period of approxirnately 133
milliseconds. Each control period comprises 32 control intervals
corresponding to a time period of approximately 4 seconds. The
duration for the control interval and control period selected provide a
satisfactory range of heat settings for desired cooking performance and
can be programmed to make efficient use of microprocessor memory. It
is understood, however, that control intervals and control periods of
greater and lesser duration could be similarly employed.
iO . ' ' '
TABLE I
On Control Intervals Hex Rep
Power Level % On Time Per Control Period M(KB)
OFF O O O
l 3
2 6.5 2 2
3 9 3 3
4 12.5 4 - 4
16 5 5
6 22 7 6
7 25 ~3 7
8 31.5 10 8
9 37.5 12 9
44 14 A
ll 50 16 B
12 62.5 20 C
13 75 24 D
14 87.5 28 ` E
loo 32 F
~L~ 3~L PATENT - 9D-RG-16419 - Payne
Electronic control means 46 selectively implements one of
sixteen different duty cycle power levels, including a zero duty cycle
or OFF level. Table I shows the percentage ON time, i.e. the duty
cycle and the number of conductive control intervals per control period
for each of the available power levels.
Only the Fry mode, which is the mode implemented by the
improved control arrangement of the present invention, will be
described herein. A power control arrangement implementing the Boil
mode is described and claimed in commonly assigned hereinbefore
ïO re~erenced U.~. Patent 4,~93,980.
The Fry Mode is intended to rapidly bring the temperature of
the utensil to the selected relatively narrow operating temperature
range while avoiding extensive temperature overshoots and undershoots
which can adversely affect co~ing performance. Relatively tight
control over the steady state operating temperature of the heating
element is desired in the heating of a wide variety of food loads. To
this end, a relatively narrow steady state temperature range is
provided for each of the Fry Mode heat settings. The temperature range
associated with each heat setting for the Fry Mode ;n the illustrative
embodiment is shown in Table II.
The user selects the Fry Mode by manipulation of mode switch
22. To facilitate rapid thermal response to an increase in heat
setting, either from OFF or from a previously selected heat setting,
the heating element is operated at a transient p~ler level determined
by the electronic control means as a function of the difference between
the steady state temperature range and the sensed utensil temperature
when the sensed utensil temperature is less than the steady state
temperature range for the selected heat setting. `
~ 3~L PATE~IT - 9D-RG-16419 - Payne
The power level applied to the heating element exceeds the
stead~ state power level for the selected heat setting by a number of
power levels, which number of levels is a function of the difference
between the sensed utensil temperature and the steady state t~mperature
range for the selected heat setting. As the temperature difference
approaches zero, the applied power level approaches the steady state
level. By operating the heating element at relatively high power
levels when the difference between the desired temperature range and
the sensed utensil temperature is large, the utensil temperature
1~ ~nr~2ases rapidly. By perating the heating elemen~ at poher levels
which decredse toward the s~eady state level as the sensed temperature
increases toward the desired temperature range, the desired rapid
thermal response is achieved with minimal temperature overshoot. For
steady state operation each Fry Mode heat setting has associated with
it a steady state duty cycle or power level which is intended to
maintain typically loaded cooking utensils within the corresponding
steady state temperature range following the transient heat-up period.
I~hen the sensed utensil temperature exceeds the steady state
temperature range the heating element is de-energized.
The control arrangement described thus far is the control
arrangement of the hereinbefore referenced 4,493,980 patent. The
control arrangement provides very satisfactory transient heat up phase
performance for all types of thermal loads. Loads are brought to the
selected state temperature rapidly with minimal overshoot. However, it
will be recalled that an object of the present invention is to provide
improved temperature control when operating ;n the steady state phase
while retaining the highly satisfactory performance in the transient
phase.~ A problem particularly with large th`ermal loads such as large,
heavily loaded utensils is that the utensil temperature tends to
~ i36~3~ PATENT - 9D-RG-16419 - Payne
undershoot, that is drop below the selected steady state temperature
range, because the normal steady state power level is insufficient to
maintain the utensil temperature within the selected steady state
range. When the power level is adJusted in the same manner as during
the transient heat up phase, an undesirably slow response results.
More specifically, in the control arrangement of the 4,4g3,980
patent an error signal is established as a function of the temperature
differential. The power level is then increased as a function of this
error signal. However, the increase may not be enough to return the
10 ~ `nsil temperature to th~ desired`stead~ state-range 2S 4uickly as
desired. The improvement of the present invention contemplates
establishing a second error signal as a different function of the
temperature differential, which weighs the differential more heavily
resulting in a greater increase in the power level upon the occurrence
of an undershoot condition after the steady state temperature range has
initially been reached. This second error signal is employed in lieu
of the first in adJusting the power level during operation in the
steady state operating phase. In a preferred form of the invention the
error signal is at least a factor of two larger than the first error
signal and is preferably further increased by two power levels. An
error signal of this re~ative magnitude, if used during the transient
heat up phase, could result in an undesirably large overshoot.
However, it has been empirically determined that when this larger error
signal is employed in the steady state phase with the range of the
illustrative embodiment, the utensil t~mperature is rapidly returned to
the selected range without overshoot. The means for implementing this
arrangement in thè control of the range of the illustrative embodiment
.
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i2~;3~31 PATE~T - 9D-P.G-16419 - Payne
is hereinafter described wi~ reference to the control program flow
diagrams .
TAB LE I I
Fry Mode
Stea dy
Stea dy Sta te Sta te
HexadecimalSelected Utensil Power
Representati on Heat Temp . Level
of Setting (KB) Setting Range F. M(KB)
.
O ' OFF - O
. ~ Wm 116-140 2
2 Wm 116-140
3 150 141-165 5
4 175 166-190 6
200 ~91-215 7
6 225 216-240 8
7 250 241-265 8
8 275 266-290 9
9 300 291-315 A
A 325 316-340 B
B 350 341 - 365 B
C 375 366-390 C
D 400 391 -415 D
E 425 416-440 D
F 450 441-465 D
_ 1 1 _
~ 2 6~3Ç~3~L PATENT - 9D-P~G-16419 - Payne
.
Circuit Description
A control circuit illustratively implementing the improved
pu~er control arrangement of the pr~ enk invention is represented in
simplified schematic form in Fig. 5. Power to heating element 12 is
proYided by application of a standard 60 Hz AC power signal of either
120 or 240 volts across terminals Ll and L2. Heating element 12 is
connected across lines Ll and L2 via normally open relay contacts 78 of
ON/OFF relay 80 and power control triac 82. Coil 84 of ON/OFF relay 80
is serially connectedjbetween DC reference voltage supply YR and
~0 system ground via ON,~'OFF switch ~. Switch 86 is mechar,;call~ coupled
in conventional manner (i'iustrated schematically) to control knob 26
such that switch 86 is in its open position when control knob 26 is in
its OFF position. Movement of control knob 26 from its OFF position
places switch 86 in its closed position, energizing coil 84 which in
turn closes associated contacts 78 thereby enabling power control triac
82 to control energization of heating element 12.
Microprocessor 72 controls the switching of power control
triac 82 by trigger signals pr wided at output port R7. The trigger
signal at R7 is coupled to pin 2 of opto-isolator device 88 via
inverting buffer amplifier 90. Pin 1 of opto-isolator 88 is coupled to
DC reference voltage supply via current limiting resistor 92 and switch
86. The output return pin 4 of opto-isolator 8~ is coupled to p~ler
line L2 via current limiting resistor 94. Pin 6 is coupled to the gate
terminal 82A of power control triac 82 which is connected 1n series
with heating element 12. The trigger s;gnal at R7 is inverted by
amplifier 90 forward biasing light emitting diode 96 of opto-isolator
88 which in turn switches the bi-polar switch portion 98 of
opto-isolator 88 into conduction to apply a gate signal to pcwer
control triac 82 switching it into conduction.
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~ % ~3~i~3~L PATENT - 9~-RG-1641~ - Payne
A 60 Hz p~llse train is generated by conventional zero crossing
detector circuit 100 coupled between Ll and input port K8 of
microprocessor 72 to Facilitate synchron;zation of triac triggering and
other control system operations with zero crossings of the 60 Hz AC
power signal applied across Ll and L2.
Utensil temperature inputs are provided to microprocessor 72
via temperature sensing means 52 comprising a thermistor device 104
connected in parallel with linearizing precision resistor 106 and in
series with precision resistor 10~ forming a voltage divider network
energized bv a regulated +9 Yolt dc voltage supply. The divider
network is coupled to ground through transistor Ql. The junction of
thermistor 104 and resistor 108 is coupled to microprocessor input port
A1. The analog voltage at this point is proportional to the
temperature sensed by the thermistor. Microprocessor 72 has an
internal 8-bit A/D converter which operates bet~een voltage rails AVSS
and AVDD which are set at 9 volts DC and 4 volts DC respectively by
regulated voltage sources connected to input ports AYSS and AVDD of
microprocessor 72, to provide a 5 volt voltage swing. The internal A/D
con~erter measures the input voltage signal at Al and converts this
signal to a corresponding digital value. Table III lists
representative values of the thermistor resistance, and corresponding
temperature and analog voltage values. Also shown in Table III is the
Hexadecimal representation of the corresponding 8 bit binary code
resulting from the A/D conversion of the analog voltage values.
Transistor Q and biasing resistors 110 and 112 function as a
disabling circuit. Output port R12 of microprocessor 72 is coupled to
the base of Ql via resistor 110. Resistor 112 is connected between the
emitter and the base of transistor Ql. The function of the disabling
circuit is to only allow current flow through thermistor 10~ when
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~6~3~i~3~ PATENT - 9D-P~G-1641g - Payne
temperature measurements are being made. To this end, microprocessor
72 sets output R12 causing a positive voltage to be applied to the base
of Ql via resistor 110 switching Ql into conduction. After the
temperature input is obtained, R12 is reset rendering Ql and thermistor
104 non-conductive.
TABLE I II
TemperatureResistance Analog Yolts Hex ~ep
F ~J~)
_ _ .. . .
10 115 22,000 4.71 24
140 11,500 4,86 2C
165 7,600 5.04 35
190 5,000 5.33 44
215 3,300 5.63 53
15 240 23`100 6.02 67
265 1,500 6.41 7B
290 1,050 6.82 90
315 740 7.16 Al
340 560 7.47 Bl
20 365 410 - 7.77 C0
390 320 7.96 CA
415 250 8.14 D3
440 200 8.27 DA
465 150 8.45 E3
User inputs are provided to microprocessor 72 via Boil~Fry
Mode selection switch means 22 and heat setting selection means 50
comprising input potentiometer 102. Mode selection switch 22 is
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~2Çii;36~3~ PATENT - 9D-RG-16419 Payne
directly coupled between output port R2 and input port K4 of
microprocessor 72. The open and closed states of switch 22 signify
selection of the general Boil Mode and Fry Mode, respectively.
Microprocessor 72 determines the state of switch 22 by periodically
generating a logical high signal at R2 and monitoring the input signal
at K4.
Input potentiometer 102 is coupled between regulated g volt dc
and regulated 4 volt dc reference voltage supplies. Wiper arm 102A,
coupled to A/D input port A2 of microprocessor 72, is positioned by
user rotation of control bnob 26. The voltage between the wiper arm
and the 4 vc;t supply is an analog signal representing the selected
heat setting. The internal A/D converter of microprocessor 72
described briefly above for processing the temperature inputs also
processes analog voltages appearing at A2 representing the user input
~5 settings.
The processing of the resultant digitized temperature and
pcwer setting input signals will be described in conjunction ~ith the
following description of the control program.
The follcwing component values are believed suitable ~or use
in the circuit of Fig. 5. These values are illustrative only, and are
-l 5-
PATENT - 9D-RG-16419 - Payne
not intended to limit the scope of the claimed invention.
Fixed Resistors ~IL) Transistor Ql
92 lK 2N2222
94 220 - Integrated Circuits
106 2.21K 88 MDC 3020 Integrated Circuit
108 2.21K 90 ULN 2004A Integrated Circuit
~10 22~
112 27K
117 lOK
119 lOK
Potentiometer (Q )
102 50K
Thermistor ( Q ) Microprocessor
104 50K 72 Texas Instruments TMS 2300
Triac
82 General Electric SC 147
Surface Unit
12 General Electric WB 30 X 218
,
Control Program Description
~ croprocessor 72 is customized to perform control functions
in accordance with this invention by permanently configuring the Read
Only Memory (ROM) of microprocessor 72 to ;mplement predetermined
control instructions. Figs. 6 through 12 are flow diagrams which
illustrate the control routines incorporated in the control program of
16
~ $~3L PATENT - 9D-RG-16419 - Payne
microprocessor 72 to perform the control functions in accordance with
the present invention. From these diagrams one of ordinàry s~ill in
the programming art can prepare a set of control instructions for
permanent storage in the ROM of microprocessor 72. For the sake of
simplicity and brevity, the control routines to follow will be
described with respect to the implementation of the control algorithms
of the present invention It should be understood that in addition to
the control functions of the present control arrangement herein
described there may be other control functlons to be performed in
conjuncticn \;it" other operating c"dracterist ~s oF 'rhe app,i~nce
Instructions for carrying out the routines described in the diagrams
may be interleaved with instructions and routines for other control
functions which are not part of the present invention.
USER INPllT Routine - Fig. 6
The function of this routine is to read in the user selected
-- heat settinq input signals at input port A2 ~Fig. 5), and to determine
whether Boil or Fry has been selected for the automatic surface unit.
The state of mode select switch 22 is determined by setting
output R2 tBlock 130). Inquiry 132 then scans input port K4 to
determine whether switch 22 is open ~K4=~) or closed ~K4=1) If K4=1,
signifying selection of the Fry Mode, a Mode ~ ag is set for future
reference in a subsequent routine ~Block 134). If K4=0, signifying
selection of the Boil Mode, the Mode Flag is reset ~Block 136).
It will be recalled that there are 16 possible heat settings,
each represented by a corresponding digital signal. The internal A/D
conversion routine provided in microprocessor 72 will convert the
analog voltage at pin A2 to an eight bit digital code capable of
establishing 256 levels. Sixteen wiper arm positions corresponding to
16 power settings are evenly spaced along the potentiometer, By this
~6~36~3~ PATENT - 9D-RG-1641g - Pa~ne
arrangement the user selected input setting may conveniently be
represented by the four high order bits of the 8 bit A/D output
signal. The analog input at pin A2 i5 read in (B10ck 138) and
converted to its corresponding digital signal. The four high order
bits of this signal designated A/D HI are stored as the new input power
setting variable KBI (Block 140). Inquiry 1~2 compares the new input
KBI with input variable KB representing the previously stored power
setting read in during the previous pass through the program to detect
a change in setting. If KBI equals KB signifying no change in power
settir,g selection, the program branches ~Block 144) to the Temp Input
Routine (Fig. 7). If ~I differs from KB signifying a change in
setting, the new setting is stored as KB (Block 146) and a flag
designated the SS Flag utilized in the Fry routine is reset (Bloc~
148). By this arrangement the SS Flag is reset in response to each
change in power setting selection. The program then branches from the
User Input routine to the Temp Input routine.
.
TEMP INPUT Routine - Fig. 7
The function of this routine is to convert the analog voltage
` at pin Al representing the sensed utensil temperature to a digital
signal representative of the sensed utensil temperature. More
speci ff cally, this routine determines within which of 15 predetermined
temperature ranges the present sensed utensil temperature falls. A
hexadecimal value is assigned to the variable SENINP (and also SENOUT)
corresponding to the appropriate one of the 15 temperature ranges shown
in Table IV. The hexadecimal value for the upper temperature threshold
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~L PATENT - 9~-RG-16419 - Payne
value for each temperature range is also included in Table IV.
TABLE IV
Hex Rep Hex Code
SENINP & SENOUT Temp. Range F.Upper Threshold
O T~115 24
1 115C T '140 2C
2 140 ~ T ~165 35
3 165 ~ T '190 44
4 - 190 '.T ~ 215 ~ - 53
215 ~ T ~ 240 6/
6 240 ~ T_ 265 7B
7 265 ~ T~ 290 90
8 290 ~T~ 315 Al
9 315 ~ T~ 340 Bl
A 340 C T~ 365 CO
B 365 cT~ 390 CA
C 390< T ' 415 D3
D 415 ~T ~ 440 DA
E 440 ~T ~465 E3
F 465 ~T
Referring now to Fig. 7, R12 is set (Block 170~ to turn on
transistor Ql (Fig. 5) thereby enabling energization of thermistor
104. Next the analog voltage representing the sensed temperature is
read in and converted to its 8 bit digital representation (Block 172).
The variable TC in the f~ow diagram represents the digital value of the
analog signal. Inquiries 174-202 determine the temperature range in
_l g
.
PATE~iT - gD-RG-1641~ - Pa~ne
~L2~3~i8~
which tne sensed temperature falls and Blocks 204-234 assign the
appropriate Yalue to the temperature variable SFNINP in accor~nce with
Table Y. After establishing the appropriate value for SENI~P, R12 is
reset (Block 236) to turn off Ql, de-energizing thermistor 10~, and the
program branches (Block 237) to the Sensor Filter and Timing routine
(Fig. 8).
S~SOR FILTER and TIMING Routine - Fig. 8
This routine performs the dual function of iteratively
filtering the sensor output temperature signal SENINP and also
controlling the 'iming of the updating of tile tempera,ure si~nal w~ich
is actually used ,n the co,trol routines yet ~o be describea~ The
filter function is implemented to minimize the impact of aberrant
temperature measurement inputs from the temperature monitoring circuit;
the timing function is implemented to minimize the effect of radiant
energy from the heating element 12 impinging on thermistor 104 on the
accuracy of the temperature measurements.
The iterative filter portion of this routine attaches
relatively little weight to each individual input. Hence, isolated
erroneous inputs are averaged out so as to have little effect on the
accuracy of the cumulative average signal provided by the filter
routine. Referring to Fig. 8, the filter function is performed by
Block 238. It will be recalled that SENINP is the hexadecimal
representation of the temperature ran~e for the sensed utensil
temperature determined in the previously described TEMP INPUT routine.
One-sixteenth of the new SENINP input is added to 15/16 of the filter
output variable designated SUM 1 from the previous pass through this
routine. The resultant sum becomes the new value for the filter output
variable SUM 1.
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3~ ~ ~ PATE~iT - sD-RG-l6~lg - Pa~ne
A new temperature input signal S~INP is processed by the
filter portion o~ this routine to generate a new SUM 1, during each
pass through the control routine, i.e. once every 133 milliseconds
corresponding to 8 cycles of the 60 Hz power signal. However, to
minimize the effects of radiant energy for heating elernent 12 on sensor
50, the sensed utensil temperature signal which is input to the power
control portion of the control program is only updated during selected
portions of the 4.4 second duty cycle control period.
A counter designated the ZCM counter operates as a 32 count
ring courlter, counting from 0-31 and resetting to G5 In the duty cycle
control implemented in the Power Compare and Power Out rGutine
hereinafter described, for duty cycles less than 100~ the heating
elernent is energized during the first part of the control period when
the ZCM count is relatively low and de-energized while the Z~ count is
relatively high. Since, except when operating at the lOOg power level,
the heating element is always de-energized for count 31, radiant ener~y
effects on the sensor are minimum at ZCM count 31. Thus, radiation
effects are minimized by updating SENOUT, the temperature signal
utilized in implementation of the Power Control routine only at count
31. It is desirable, however, to have at least two updates of SENOUT
during each 4.4 second control period, to limit oscillations between
inputs. Hence, SENOUT is also updated at the midpoint of the control
period, i.e. at count 16. There is potentially more error due to
radiation effects for tnis measurement; however, the heating element is
de-energized at this point for the eleven lower power levels. Hence,
the effects of radiation even on this measurement are minimum except at
the highest 4 power levels.
~ hen the heating element is operated at 100~ duty cycle, the
radiation effects are the sarne at all counts; hence, for maximum
,
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PAT~NT - 9~-RG-16419 - Payne
~ 3~ L
accuracy SENOUT is updated during each execution of the control
program, i.e. every 133 milliseconds.
Referrin~ again to the flow diagram oF Fig. ~, Inquiries Z39
and 240 lo~ for ZCM counts of 16 and 31, respectively. Upon the
S occurrence of either count, SENOUT is updated by the then current value
of SUM 1 (Block 241). Otherwise, Inquiry 242 checks to determine if
the power level presently being implemented is the 100~ power level
~M(KB)=15). If it is, SENOUT is updated by SUM 1 (Block 241)
regardless of the count; if not, Block 241 is bypassed, and S~OUT is
not updated during this pass. In this fashion for p~wer levels l~er
than 15, SENOU~ ,s updated only on counts 16 ~}nd 31~ and when power
level 15 is being implemented SENOUT ;s updated every count. Upon
completion of this routine the program branches (Block 243) to the Fry
routine (Fig. 9).
FRY Routine - Fig. 9
The function of this routine is to implement the Fry ~ode. It
will be recalled that in accordance with the present invention, the
pcwer level applied to the surface unit in the FRY Mode is established
as a function of the selected temperature setting and a first error
signal during the transient heat-up phase and as a funct;on of the
selected power level and a second error signal during operation in the
steady state phase. The appropriate power level to be applied is
established in this routine. A flag designated the SS n ag is used in
- this routine to ind;cate whether or not the sensed utensil has first
reached the steady state temperature range for the selected
temperature. The SS Flag is set on the F;rst pass through this routine
after the selected steady state range is reached. The SS ~ ag is reset
in the prev;ously described User Input routine ;n response to changes
;n the temperature selection.
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~2~i3~;8~ PATENT - D-~G-16419 - Pa!/ne
Referring na" to the flow diagra" of Fig. 9, Inquiry 382
checks for an OfF setting (K~=0). If OFF is 5elected, M(KB), the pa~er
control variable utilized in the P~er Compare routine, is set to ~ero
(Block 384) and the program branches (Block 386) to the Pc7tler Compare
5 routine, Fig. llA. Otherwise, Inquiry 388 determines if one of the
Warm settings l~m(l ) or l~m(2) corresponding to K3 less than 3 has been
selected (KB 3). If so, the program branches (Block 390) to the llarm
routine, Fig. 12. Otherwise, Inquiry 392 co:npares the sensed utensil
temperature SENOUT with the reference value representing the steady
1(~ state temperature range for tne selected heat setting ~ich ,s defined
as (KB-l). For SENOUl greater than (KB-l), signifying that the sensed
utensil temperature exceeds the selected range, Power Level zero is
implemented (Block 384)~ and the program branches (Block 386) to the
Power Compare routine (Fig. llA).
If the sensed utensil temperature is not greater than the
desired temperature range, Inquiry 394 determines if (KB-l ) equals
.
SENOUT signifying that the sensed utensil temperature is within the
selected steady state temperature range. If so, the SS Flag is set
(Block 396). By this arrangement the SS Flag is first set when the
20 sensed temperature first reaches the selected steady state range
signifying for power control purposes, the transition from the heat up
phase to the steady state phase for surface unit 12. Once set, SS
remains set unless the selected temperature setting is changed.
Next the appropriate error signal is determined. Inquiry 398
25 checks the state of the SS Flag to determine whether the surface unit
is in the heat up phase (SS reset) or the steady state phase (SS set).
If SS is reset, a first error signal (ERR) is computed (Block 400~ as a
function`of the difference between the desired temperature range
represented by (KB-l) and the sensed utensil temperature represented by
~L~ L PATE~T - gD-P~G-16419 - Payne
SENOUT, by computing the difference between KB-l and SENOUT and
dividing this difference by two. If ERRl equals a fraction, it is
rounded off to the next laryer integer. IF the SS Flag is not set, a
second error signal (also labeled ERR) is calculated. Inquiry 401
determines if SENOUT equals KB~l, signifying that the sensed utensil
temperature is in the desired steady state range. If so, the error
signal ERR is set to zero (Block 402). Otherw;se, the second error
signal is set equal to the difference be~ween (KB-l) and SENOUT plus a
constant 2 (Block 403). By this arrangement the error signal employed
~o ~hen operatiny in the steady state phase is at least a ~actor of two
greater than the error signal employed when operating in the heat up
phase under undershoot conditions, that is, when the sensed utensil
temperature is lo~er than the selected steady state range. As will be
apparent from the following description, this results in the surface
unit being operated at a power level which is at least two levels
higher in the steady state phase than in the transient heat-up phase
during undershoot conditions except when the error signal would result
in a level higher than the maximum level of 15. Since the SS ~ ag is
reset in the User Input routine (Fig. 6) each time the user selected
setting is changed, the first error signal computed in Block 400 is
used foll~Ying each change in power setting, until the SS ~ ag is again
set as a result of the sensed utensil temperature first reaching the
steady state temperature range for the newly selected heat setting.
After computing the error signal, Inquiries 404-410 determine
the selected heat setting. A variable Y, corresponding to the steady
state power level for the selected heat setting, is introduced in
Blocks 412-420. The error signal (ERR) is summed with steady state
power`level variable Y to generate a signal representing the power
level to be applied, which ;s temporarily stored in the accumuiator
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~63~i81 PATENT - ~D-RG-1641g - Payne
(ACC) (Block 422). Inqulry 424 and Block 426 limit the maximuM value
to 15 in the event the sum of ERR-~Y is greater than 15. The value
stored in ACC is then transferred to M(KB) to implement the appropriate
power level in the Power Cornpare routine and the program branches
~Block 394) to tne Power Compare routine (Fig. llA).
To further speed the temperature response of the system in the
Fry Mode, power level 15 is implemented when the sensed utensil
temperature is less than 116 F. This is implemented by Inquiry 430
which checks the sensed utensil temperature. If the sensed utensil
temperature is less than 116 ~. (SENOUT=O)z ACC is set to 15 ~P'~ck
426), resulting in M(KB) being set to 15 (BLock 428), and the program
then branches (Block 394) to the Power Compare routine, Fig. llA.
WARM Routine - Fig. 10
This routine is entered from the Fry routine whenever KB is
less tnan 3. The function of this routine is to implement tne Warm
Mode.
For heat settings KB=l and KB=2, the maximum warm temperature
limit is 140 F corresponding to SENOUT=2. For KB=3, the maximum
warm temperature limit is 165 F corresponding to SENOUT=3. Inquiry
432 checks for KB=l representing the Wm(l) setting. For KB=l, Inquiry
433 determines ;f SENOUT is less than 2. If not, M(KB) is set to ~ero
(810ck 434) to de-energize the surface unit. If SENOUT is less than 2
signifying a sensed utensil temperature less than the maximum for K8=1,
M(KB) is set to 2 (Block 435), and the program branches (Block 436) to
the Pcwer Compare routine (Fig. llA).
Returning to Inquiry 432, if KB is not equal to one, Inquiry
437 determines if the sensed utensil temperature variable SENOUT is
less than KB=l. If SENOUT is less than KB-l, power level 6 is
implemented by setting M(KB) to 6 (Block 438). The program then
branches (Block 436) to the Power Compare routine (Fig. llA).
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~ L PATENT - 9D-RG-1641~ - Payne
-
If the sensed utensil temperature is not less than (KB-l), the
program proceeds to Inquiry 439 which checks for the upper temperature
limit for KB=2 and KB=3 which is represented by SENOUT=2, and 3
respectively.
If Inquiry 439 determines that the sensed utensil temperature
is less than the maximum warm reference temperature for the selected
heat setting (SENOUT< KB), M(KB) is set to (KB+l) (Block 440). This
implements the steady state power levels 2, 3 and 4 for heat settings
1, 2 and 3, respectively, corresponding to duty cycles of 6.5~, 9~ and
~ 12.5Z, respectively ~See Tables I and II~. If the sensed utensil
temperature is not ~ess than the maximum warm reference tempera~ure,
M(KB) is set to O ~Block 434) corresponding to the zero or OFF pcwer
level. M(KB) having been set, the program then branches (Block 436) to
the Power Compare routine (Fig. llA).
POWER COMPARE Routine - Figs. llA and llB
The function of the Power Compare routine is to determine,
based upon the power level designated by power level variable M(KB),
whether or not the power control triac should be triggered into
conduction for the next eight cycle control intervals.
It will be recalled that there are 16 possible power levels
including OFF. The % duty cycle for each power level corresponds to
the ratio of conductive control intervals to 32, the total nu~ber of
control intervals in the control period. A ZCM counter functioning as
a 32 count ring counter is incremented once for each pass through the
control program. The power control decision is made by comparing the
Z~l count with a reference count associated with the power level
represented by M(KB). The reference count for each powe. level
~represents the number of conductive control intervals per control
period corresponding to the desired duty cycle. When the ZCM count is
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~2~ 1 PATENT - 9D-RG-16419 - Pa~ne
less than the reference, a Power Out Latch (POL) is set, signifying
that power control triac 82 is to be swi tched into conducti on;
otherwise, POL is reset, signifying that the associated power control
triac is to be non-conductive.
Referring to Figs. llA and B, Inquiries 540-568 determine the
value of M(KB). The appropriate one of Inquiries 572-598 corresponding
to the identified M(KB) performs the comparison of ZCM to the
associated reference count. If ZCM ;s 1 ess than the reference, the
~er Out Latch is set by the appropriate one of Blocks 602 and 606,
siqnifying that the surface unit for which the control progr~rn is
presently executing is to be energized during the next control
interval. Otherwise, the PGwer Out Latch is reset by the appropriate
one of Blocks 604 and 608, signifying that associated surface unit is
to be de-energized during the next control interval.
Having made the power control decision, the program branches
to the P~er Out Routine, Fig. 12.
POWER OUT Routine - Fig. 12
The function of the Power Out routine is to synchronize the
firing of power control triac 82 with zero crossings of the 60 Hz AC
20 power signal applied across Ll and L2 (Fig. 5).
Referring now to Fig. 12, input port K8 receives zero crossing
pulses from zero crossing detector circuit 100 (Fig. 5). Positive
half-cycles are represented by K&l and negative half~ycles by K8=0.
Inquiry 620 determines the polarity of the present pat~er signal
25 half-cycle. If the signal is presently in a positive half~ycle,
(K8=1), Inquiry 622 waits for the beginning of the next negative
half~ycle, (K&O). Upon detection of K&l, the program proceeds to
I`nquiry 624. If the answer to Inquiry 620 is NO (K8=0), Inquiry 634
waits for the beginning of the next positive half~ycle (K8=1), then
30 proceeds to Inquiry 624.
.
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~L~ 3 3~3 PATENT 9D-RG-16419 - Payne
Inquiry 624 checks the state of the Power Out Latch (POL). If
POL is reset, signifying that surface unit lZ is not to be energized
during the next control interval, output port R7 is reset (Block 6~6);
if POL is set, signifying that the corresponding surface unit is to be
energized, R7 is set (Block 628); the program delays (el ock 630) and
then returns (Block 632) to the Start Routine (Fig. 6) to repeat the
control program for the next control interval.
In the illustrative enbodiment, execution of the control
program uses less than one-half cycle of the power signal. The
~lrat-ion of the ~ontrol inte~val is ei-ght cycles. ~nus, 31O^k ~32 -
delays the program for 15 half-cycles and then returns (Block 634) to
the User Input routine to begin execution for the next control interval.
While in accordance with the Patent Statutes, a specific
embodiment of the present invention has been illustrated and described
herein, it is realized that numerous modifications and changes will
occur to those skilled in the art. It is therefore to be understood
that the appended claims are intended to cover all such modifications
and changes as fall within the true spirit and scope of the invention.
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