Note: Descriptions are shown in the official language in which they were submitted.
~ 6 3~E3~1 PAT~NT - 9D-RG~167~7 - Payne
BACKGROUND OF T~IE I~VENTION
.
This invention relates generally to method and apparatus
applicable to a cooking appliance incorporating an automat;c surface
unit, and more particularly to method and apparatus for detecting a
- surface unit temperature sensor failure ;n such an appliance and
modifying the mode of operation of the automatic surface unit
accordingly.
An automatic surface unit is equipped with a temperature
sensor for sensing the temperature of the utensil being heated by the
surface unit and a controller for controlling the energization of the
surface unit as a function of the sensed utensil temperature. Such
surface units are well known in the art. Typically, such surface units
include a temperature sensing device such as a bi-metallic device or a
thermistor device mounted to be in thermal contact with the utensil.
When the sensed temperature is less than a predetermined threshold
temperature set by a user manipulation of input control knobs or
switches mechanically coupled to the sensor dev;ce, the heating element
is energized at full power. When the temperature exceeds the threshold
the heating element is de-energized. An electronic control system for
an automatic surface unit in which the electromechanical sensing and
control devices are replaced by a microprocessor based control
arrangement is described in commonly assigned United States
Patent ~umber-4,493,980-.
A problem common to both the electrcmechanical and the
electron;c temperature sensing arrangements for automatic surface units
is that a failure in the sensor circuitry typically resu1ts in either
the surface unit being operated at full power continuously or the
surface unit being totally de-energized. The user, being unaware of
the failure, may be greatly inconvenienced by either overheating or
3~ PATENT - 9~ RG-16707 - Payne
underheating a dish. Furthermore, even if aware of the fa;lure, the
user is unable to make productive use of that surface unit until the
sensor is repaired or replaced.
It would be desirable to provide an arrangement for
automatically detecting the occurrence of a failure of the sensor,
informing the user of the existence of the failure, and enabling the
user to continue to use the surface unit as a non-automatic surface
unit during the interim until the surface unit is repaired at the
user's convenience.
It is therefore an object of the present invention to provide
an improved control arrangement for a cooking appliance featuring an
automatic surface unit which automatically detects the failure of the
temperature sensor and provides a signal to the user indicative of the
occurrence of such a failure.
It is a further object of the invention to provide a control
arrangement of the aforement;oned type which enables the user to
continue to use the surface unit after the occurrence of a sensor
failure as a non-automatic or regular surface unit.
SUMMARY OF THE INVENTION
The present invention provides an improved control arrangement
for a cooking appliance of the type having at least one automatic
surface unit equipped with a temperature sensor for sensing the
temperature of a utensil being heated by the surface unit. In one form
of the invention the control arrangement is particularly applicable to
an appliance having a plurality of surface units at least one of which
is an automatic surface unit and at least one of which is a regular
surface unit. In such an appliance the user selects a heat setting for
each of the surface units. The electronic control means is operative
under normal operating conditions to control energization of each
~L2~i3~ L PATENT - 9D-~G-i6707 - Payne
regular surface unit in accordance with an open loop control strategy
as a function of the user selected heat setting, and to concrol
energization of each automatic surface unit in accordance with a closed
loop control strategy as a function of the user selected heat setting
and the sensed utensil temperature. The control means is provided with
a diagnostic means ~or detecting an abnormal operating condition of the
automatic surface unit temperature sensor circuit, and is operative in
response to the detection of an abnormal operating condition to change
the control strategy for the automatic surface unit from the closed
loop control strategy to the open loop control strategy. By this
arrangement in the event of a te~perature sensor circuit failure the
automatic surface unit is available to the user for use as a regular
surface unit.
In a pref~rred form of the invention the abnormal operating
condition is detected by comparing the sensed utensil temperature to a
first reference representing a temperature higher than the highest
.
sensed temperature likely to occur during normal operation of the
appliance and to a second reference representing a temperature lower
than the lowest sensed temperature likely to occur during normal
operation. An abnormal condition is signified upon detecting a sensed
utensil temperature outside of the range established by the first and
second references. To avoid erroneously identifying normal transient
conditions or circuit failures, a timer may be employed to monitor the
duration of the time period for which the temperature is outside of the
range. An abnormal condition is then si~nified only when the sensed
utensil temperature is outside the ran~e for more than a predetermined
time period of sufficient duration to prevent the system from
responding to normal transient condit;ons.
~3~
In accor~nce Witil a further aspect of the present invention
the control arrangement includes means for providing a user discernible
signal upon detection of the abnormal sensor operating condition to
inform the user that the sensor failure has been detected and that the
corresponding automatic surface unit is nuw operative as a regular
surface unit. In accordance with this aspect of the invention a first
user discernible signal is generated in the event the sensed utensil
temperature is greater than the maximum reference temperature
signifying an open circuit failure of the sensor circuit and a second
signal is generated in response to detection of a sensed utensil
te~perature less than the lower referenced temperature signifying a
short circuit failure of the sensor circuit. The information provided
by these signals as to the nature of the failure of the sensor system
~ay be useful to the service person seeking to correct the proolem.
While the novel features of the invention are set forth with
particularity in the appended claims, the invention, both as to
organization and content, will be better understood and appreciated
from the following detailed description taken in conjunction with the
drawings.
BRIEF DESCRIPTION OF THE DRAI~IINGS
FIG. 1 is a front perspective view of a portion of an electric
range illustratively embodying the sensor failure detection arrangement
of the present invention;
FIGS. 2A and 2B are greatly enlarged views of a portion of the
control panel of the range of Fig. 1 sh~wing the details of an
automatic surface unit control knob and a regular surface unit control
knob respectively;
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;
pArENT - 9D-RG-16707 - Payne
FIG. 3B is a graphic representation of the resistance versus
temperature characteristic for the temperature sensor of Fig. 3A;
FIG. 4 is a greatly simplified functional block diagram of the
control arrangement employed in the range of Fig. 1 e~bodying the
sensor failure detection arrangement of the present invention;
FIG. 5 is a simplified schemat;c diagram of a control circuit
for the range of Fig. l;
FIG. 6 is a flow diagram of the START routine incorporated in
the control program for the microprocessor in the circuit of Fig. 5;
FIG. 7 is a flow diagram of the USER INPUT routine
incorporated in the control program for the microprocessor in the
circuit of Fig. 5;
FIG. 8 is a flow diagram of the TEMP INPUT routine
incorporated in the control program for the microprocessor in the
circuit of Fig. 5;
FIG. 9 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;
FIG. lO is a flo~ diagram of the BOIL routine incorporated in
the control program of the microprocessor in the c;rcuit of Fig. 5;
FIG. 11 is a flow diagram of the FRY routine incorporated in
the control program for the m;croprocessor in the circuit of Fig. 5;
FIG. 12 is a flow diagram of the WARM routine incorporated in
the control program for the microprocessor in the circuit of Fig. S;
FIG. 13 is a fl~w diagram of the OPEN CHECK routine
incorporated in the control program for the microprocessor in the
circuit of Fig. 5;
FIG. 14 is a flow diagram of the SHORT CHECK routine
incorporated in the control program for the microprocessor in the
c;rcuit of Fig. 5;
~ 3~ PATENT - 9D-RG-16707 - Payne
FIG. 15 is a ~ o~ diagram of the KB-XFER routine incorporated
in the control program For the microprocessor in the c;rcu;t of Fig~ 5;
FIGS. 16A ~nd 16B are flow diagrams of the POWER COMPARE
routine incorporated in the control program for the microprocessor in
the circuit of Fig. 5; and
FIG. 17 is a flow diagram of the POWER OUT routine
incorporated in-the control program of the microprocessor in ~he
circuit of Fig. ~.
DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENT
. . . ~
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 adaptedrto support cooking utensils, such as frying pans, sauce
pans, tea kettles, etc., placed thereon for heating. Heating element
12 is arranged to function under normal operating condit;ons as an
automatic surface unit, that is, energization of element 12 is
automatically controlled in accordance with a closed loop power control
strategy as a function of the sensed temperature of the utensil being
heated thereon and the user selected heat setting. Heating elements
14, 16 and 18 are arranged to be duty cycle controlled in accordance
with an open loop control strategw to provide a predetermined output
power level corresponding to the user selected heat setting. While, as
is common pract~ce, 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
to select the Fry Mode or the general Boil Mode for heating element
~ 3~3~ PATENT - 9D-~G-16707 - Payne
12. Manually operable rotary control knobs 26, 28, 30 and 32 are
mounted to control panel 24 Control knobs 26 and 28 are illustrated
in greater detail in Figs. 2A and 2B respect;vely 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 Boil mode. In the
Boil ~ode the user may select from a plurality of heat settings within
these modes as well. Knob 28 and knobs 30 and 32 which are identical
to knob 28 enable the user to select the desired one of power levels
1-15 for heating elements 14, 16 and 18, respectively.
The utensil temperature sensing arrangement employed with the
automatic surface unit in the illustrative embodiment will now be
described with reference to ~ig. 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 metal 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 42 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 cooking
utensil when it is placed on heating element 12. The 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. The
structural details of this sensor arrangement do not form any part of
the subject invention and are thus described only to the extent
9D-~G-16707
necessary for an understanding of the presenk invention. Such devices
are described in greater detail in ccmmonly assigned U.S. Patent No.
4,241,289.
A generalized functional block diagram of the control
arrangement for heating elements 12-18 of range 10 is shown in Fig. 4.
Heating elements 12-18 are ~nergized by a standard 60 Hz AC pcwer signal
which can be either 120 or 240 volts supplied to terminals Ll and L2.
Pbwer to elements 12-18 is controlled by switch means ~4 comprising a
separate switching device for each of elements 12-18. m e switching
devices of switch means 44 are each 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
selection means ccmprising BoiV Fry mode selection means 48 and heat
setting selection means 50, signifying mode and heat setting selections
respectively and inputs from temperature sensing means 52 which senses
the temperature of the utensil being heated by element 12. Pcwer
control signals for elements 14-18 are generated in response only to the -
heat setting selections via ælection means 50.
In the illustrative element, electronic control means 46
controls the output power level of each of heating elements 12-18 by
controlling the duty cycle, i.e., the percentage of time Ex~er is
applied to each heating elen~nt. A predetermined control period
ccmprising a fLxed number of control intervals is employed as the time
base for power con rol. The ratio of conductive control intervals to
the total number of control intervals in the control period, expressed
as a percentage, is hereinafter referred to as the duty cycle.
Preferably each control interval comprises eight full cycles of the
standaLd 60 Hz 240 volt AC pcwer signal corresponding to a time period
` ~2q~ 3~ PATENT - 9D-RG-16707 - Payne
.
of approximately 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.
TABLE I
-
On Control Intervals Hex Rep
Power Level ~ On Time Per Control Period M(KB)
OFF o O O
1 3.0
2 6.5 2 2
3 9 3 3
4 12.5 4 4
16 5 5
6 22 7 6
7 25 8 7
8 31.5 10 8
9 37.5 12 9
44 14 A
11 50 16 B
25 12 62.5 20 C
13 75 24 D
14 87.5 28 E
100 32 F
g_ ~
~3~3~ PATENT - 9D-RG-16707 - Payne
As used herein, open loop control strategy refers to
controlling the output power of the surface unit simply as a function
of the user selected heat setting, without utensll temperature sensor
feedback, Closed loop control strategy refers to controlling the
output power of the surface unit as a function of both user heat
setting and sensed utensil temperature. Similarly, regular surface
unit refers to a surface unit operated in accordance with an open loop
control strategy; automatic surface unit refers to a surface unit
operated in accordance with a closed loop strategy.
In accordance with either the closed loop or the open loop,
control strategies electronic control means 46 selectively 1mplements
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 sixteen available power levels.
In the illustrative embodiment each of heating elements 14-18
is operated as a regular surface unit. The user selects the desired
power setting by manipulation of the corresponding one of control knobs
24-28. Control means 46 then switches the associated heating element
into conduction for the number of control intervals during each control
period to implement the duty cycle associated with the selected heat
setting. The duty cycle for each of the heat settings is shown in
Table I.
Element 12 is operated under normal operating conditions as an
automatic surface unit. As hereinafter described, with reference to
Table II, ~he particular closed loop strategy varies according to
selection of the Fry or Boil modes.
The Fry and Boil modes will be described herein only to the
extent necessary for an understanding of the present invention. A
-1 0--
9D-~G-16707
power control arrangement implementiny such operat:iny modes is described
and claimed in commonly assiyned U.S. Patent 4,493,980. Ihe user
selects the Fry or Boil Mode by manipulation of mode switch 32.
The Fry Mode is intended to rapidly bring the temperature of
the utensil to the selected relatively narrow operating temperature
range while avoiding ~xtensive temperature overshoots and undershoots
which can adversely af~ect cookiny performance. Relatively tiyht
control over the steady state operating temperature of the heating
element is desired in the heating of a wide variety of food loads. The
temperature range associated with eaGh heat set~ing for the Fry Mode in
the illustrative embodiment is shown in Table II.
To facilitate rapid thermal response to an increase in heat
setting, either frcm OFF or from a previously ælected heat ætting, the
heating element is operated at a transient pawer level determined by the
electronic control means as a function of the difference between the
steady state temperature range and the sen æd utensil temperature when
the sensed u~ensil tempera~ure is less than the steady state temperature
range for the selected heat ætting. As this temperature difference
approaches zero, the applied pcwer level approaches the steady state
level.
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
correspond mg steady state temperature range following the transient
heat-up period. When the sensed utensil temperature exceeds the steady
state temperature range the heating element is de-energized. If the
sensed utensil temperature decreases below the steady state temperature
range, the power level applied to the heating element is adjusted
- 11 ~
"~ ~
PATE~T - 9D-RG-16707 - Payne
~33~
upwardly as a function of the t~nperature difference just as during the
transient heat-up period.
The Fry Mode also enables the user to select a WARM levèl.
Operation in the Warm Mode is hereinafter described with reference to
the general Boil Mode.
TABLE II
Fry Mode -~oil ~-de
Steady Steady
Steady State State Steady State State
Hexadecimal Selected Utensil Power Selected Utensil Power
Representation Heat Temp. Level Heat Tenp. Level
of Setting (KB) Setting Range F. M(KB) Setting Range F. M(KB)
O OFF - O OFF - O
1 Wm 116-140 2 Wm(l) 116-140 2
2 Wm 116-140 3 Wm(2) 116-140 3
3 150 141-165 S Wm(3) 141-165 ' 4
4 175 166-190 6 Sim(l) 191-215 4
200 191-215 7 Sim(2) 191-215 5
6 225 216-240 8 Sim(3) 191-215 6
7 250 241 265 8 Lo(l) 216- 8
8 275 266-290 9 Lo(2) 216- 9
9 300 291-315 A Lo(3) 216- A
A 325 316-340 B Med(l) 216- B
B 350 341-365 B Med(2) 216- B
C 375 366-390 C Med(3) 216- C
D 400 391-415 D Hf(l) 216- D
E 425 416-440 D Hi(2) 216- E
F 450 441-465 D Hi~3) 216- E
.
-12-
~ 36~ PATENT - 9D-RG-16707 - Payne
The General ~oil Mode, when selected via mode switch 22,
enables the user to select the Warm, Simmer and actual Boil Modes, the
latter being further divided into Lo, Med and Hi Boil Modes. The
temperature ranges and power levels for each heat setting for the
generalized Boil Mode is presented in Table II.
The purpose of the Warm ~ode is to enable the user to warm
food quickly to a predetermined relatiYely low temperature
substantially less than the boiling po;nt of water. Three Warm
settings, Wm(l), Wm(2), and Wm(3) are available in the Warm mode. The
temperature limits and steady state duty cycles for these Warm heat
settings are shown in Table II. In the Warm mode heating element 12 is
operated at power level 6 corresponding to a 22~ duty cycle when the
sensed utensil tempPrature is less than the minimum threshold
temperature of 116 F. In order to bring the utensil temperature
rapidly to its desired temperature, it has been empirically determined
that for heating element 12 this is the maximum duty cycle which can be
applied w;thout risk of scorching food in the utensil. If the sensed
utensil temperature exceeds the temperature range for the selected
setting, the heating element is de-energized until the sensed
temperature cools to within the temperature range. Should the
temperature fall below the desired range, power level 6 is implemented
until the sensed temperature falls within the desired temperature
range. The three heat settings in this mode provide some ~ exibility
for the user in selecting the proper heat setting for the size of the
- food load being warmed.
The Simmer Mode enables the user to heat food rapidly to a
temperature closely approaching but not exceeding the boiling point of
water (212 F) and then to hold the temperature of the food at this
level without boiling when left unattended.
~3~ PATENT - 9D-RG-16707 - Payne
There are three heat settings for the Simmer ~lode designated
in Table II as Sim(l), Simt2) and Sim(3). The steady state temperature
range for all three settings is 198-220F. Th;s range for the
sensed utensil temperature assures that the contents of the utens;l
will be near the boiling point of water (212 F) but will not be hot
enough to actually boil. A more detailed description of the Simmer
mode may be found in the hereinbefore referenced U.S. Patent 4,493,980.
The three actual boil modes, that is the three modes for
controlling the actual boiling of water loads contained in utensils
placed on heating element 12, are designated Lo, Med, and Hi Modes.
Each of these modes has three heat settings corresponding to selection
marks 58(a)-(c), 60(a)-(c) and 62(a)-(c) for Lo, Med and Hi Boil Modes,
respectively for control knob 26 (Fig. 2A); hence, ;n the illustrative
embodiment the user can select from a total of 9 heat settings for
boiling water loads on heating element 12.
These nine heat settings enable the user to select the steady
state power level or duty cycle which will achieve the desired boiling
rate for various size water loads without employing a power level
substantially higher than necessary thereby enhancing the energy
efficiency of the appliance.
As described in greater detail in the aforementioned 4,493,980
patent, the Boil mode provides a rapid thermal response as well as
efficient steady state operation by operating the heating element at
full power until the sensed utensil temperature exceeds a predetermined
reference temperature and thereafter operating the heating element at a
steady state power level associated with the user selected heat
setting.
It will be appreciated that the temperature sensor circuit for
the automatic surface unit though generally highly reliable is
-14-
3~ PATENT - 9D-RG-16707 - Payne
vulnerable to open circuit and short circuit failures. An open circuit
failure appears to the electronic controller as a ver~ high resistance
and a short circuit failure appears as a very low resistance. In
accordance with the resistance versus temperature character;stic of the
S thermistor employed in sensor 34 shown ;n F;g. 3B, h;gh resistance
signifies low temperature and low resistance signifies high
t~mperature. Consequently, absent the diagnostic and adaptiYe control
arrangement of the present invention hereinafter described, the power
control system would respond to an open circuit failure by energizing
the surface unit at full power and to a short circuit failure by
de-energizing the surface unit. Consequently, the surface unit would
be rendered essentially useless to the user until the sensor failure is
corrected.
The control arrangement of the present invention detects the
occurrence of an abnormal operating condit;on of the sensor circuit in
the form of e;ther a short c;rcuit or an open circuit failure and
changes the power controt strategy for the surface unit from the closed
loop control strategy of the automatic surface unit to the open loop
control strategy of the regular surface units. Applying this
arrangement to the illustrative embodiment, should such a failure
occur, automatic surface unit 12 is automatically converted to a
regular surface unit operable in the same way as the three regular
surface units 14-18. Thus, even though surface unit 12 will not
function as an automatic surface unit until the sensor failure is
corrected, it remains available to the user for use as an additional
regular surface unit in the interim.
In the illustrative embodiment, to detect an abnormal
operating condition of`the temperature sensor, the utensil temperature
is periodically sampled by the controller. The temperature samples are
_15..
PATENT - 9D-RG~16707 - Payne
compared to a first reference representative of a temperature higher
than the highest ternperature measurement likely to be encountered in
normal operation to test for a short c;rcuit failure and to a second
reference representative of a temperature lo~er than the lowest
temperature likely to be encountered in normal operation to test for an
open circuit failure. The highest selectable temperature is 4~0 F.
in the Fry mode. The high reference represents a temperature somewhat
arbitrarily set at approximately 500 F. It will be appreciated that
this reference value should be sufficiently higher than the normally
occurring maximum to avoid erroneous or nuisance failure detections.
As additional protection against nuisance trips of the failure
detection arrangement, a minimum time period for the duration of the
high temperature condition is established which must be exceeded before
the control responds to the high temperature condition as a short
circuit failure.
The low reference represents a temperature also somewhat
arbitrarily chosen to be approximately 90 F. Under steady state
conditions for all automatic cooking modes the sensed utensil
temperature should be above 90 F. However, under transient
conditions as may exist for example when the unit is initially heating
up from room temperature, lower readings will occur even when operating
normally. To prevent erroneous response under such conditions, a
minimum reference time period for the duration of a low temperature
condition is set which must be exceeded before the control responds to
the lo~ temperature condition as an open circuit sensor circuit
failure. The duration of this period must be such that under normal
operation cond;tions for the lowest automatic heat setting, the sensed
temperature will always exceed the low reference temperature before the
reference time period expires. In the illustrative embodiment a time
period of one minute is employed.
- 1 6 -
PATENT - 9D-RG-16707 - Payne
User discernible signal generating means are provided to alert
the user to ~he occurrence of an abnormal operating condition in the
sensor circuit, and that the unit is operat;ng as a regular surface
unit. In the illustrative enbodiment, two signal lights are provided,
5 one to signify the occurrence of a short circuit failure and the other
to signify an open circuit failure. This diagnostic feature aids the
service person in diagnosing and correcting the condition.
Circuit Descri ption
A control circuit illustratively implementing the hereinbefore
10 described operating modes and illustratively embody;ng the sensor
circuit diaqnostic arrangement of the present invention is represented
in simplified schematic form in Fiy. 5. P~er to energize heating
elements 12-18 is provided by application of a standard 60 Hz AC power
signal of either 120 or 240 volts across terminals Ll and L2. Heating
15 elements 12-18 are arranged in electrical parallel fashion across lines
Ll and L2 via normally open relay contacts 78A-78D controlled by relay
coil s 80A-80D and power control triacs 8ZA-82D respectively. Each of
on-off relay coils 80A-80D is serially connected between DC reference
voltage supply of VR and system ground via switch contacts 84A-84D
20 respectively. Each of switch contacts 84A-84D is mechanically coupled
in conventional manner (illustrated schematically) to control knobs
26-32 respectively such that each of switch contacts 84A-84D is in its
open position when its associated control knob is in its off position.
Movement of its associated control knob from its off position places
25 the s~itch in its closed position, energizing the associated one of
coils 80A-80D which in turn closes associated contacts 78A-78D
respectively thereby enabling the corresponding one of p~er control
triacs 82A-82D to control energization of the corresponding heating
ei ement.
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PA~E~JT ~ 9D-P~G-1~707 - Payne
~ ,3~
Microprocessor 72 controls the switching of power control
triacs 82A-82D by trigger s;gnals provided at output ports R7, R6, ~5
and R~ respectively. The signals at output ports R7, R6, P~5 and R4 are
coupled to the gate terminal of the associated triacs via driver
circuits 87A-87D respectively. Referring to circuit 87A, which is
shown in greater detail, the trigger signal at R7 is coupled to pin 2
of opto-isolator device 88 by inverting buffer amplifier 90. Pin 1 of
opto-isolator 88 is coupled to DC reference voltage supply via current
limiting resistor 92. The output return pin 4 of opto-isolator 88 is
coupled to p~wer line L2 via current lim;ting resistor 94. Pin 6 is
coupled to the gate terminal 83A of power control triac 82A which is
connected in series with heating element 12. The trigger signal at R7
is inverted by amp1ifier 90 forward biasing light emitting diode 96 of
opto-isolator 88 which in turn switches the bi-polar sw;tch portion 98
of opto-isolator 88 into conduction to apply a gate signal to power
control triac 82A switching it into conduction. The output of
amplifier 90 is also coupled to the DC reference voltage supply VR
via current limiting resistor 95 and diode 97. Driver circuits 87B-87D
are similarly configured.
A 60 Hz pulse train is generated by conventional zero crossing
detector circuit 100 coupled between Ll and input port K8 of
microprocessor 72 to facilitate synchronization of triac triggering and
other control system operations with zero crossings of the 60 Hz AC
power signal applied across Ll and L2.
Sensed utensil temperature inputs are provided to
microprocessor 72 via temperature sensing means 52 comprising a
thermistor device 104 connected in parallel with lineariæing precis;on
resisto~ 106 and in series with precision resistor 108 forming a
voltage divider network energized by a regulated +9 volt dc ~oltage
-18-
,
~ a~ PATENT - 9~-RG-16707 - Payne
supply. The divider network is coupled to ground through trans;stor
Ql. The junction of thermistor 104 and resistor 108 is coupled to
microprocessor input port Al. The analog voltage at this point is
proportional to the temperature sensed by the therm;stor.
Microprocessor 72 has an internal 8-bit A/D converter ~hich operates
between voltage rails AVSS and AVDD which are set at 9 volts DC and 4
volts DC respectively, to provide a 5 volt voltage swing. The internal
A/D converter 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 together with biasing resistors 110 and 112
functions 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 104 when temperature measurements are being made. To this
end, when a temperature measurement is to be made 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
~ .
_l g_
3~ PATENT - 9D-RG-16707 - Payne
temperature input is obtained, R12 is reset rendering ~1 and thermistor
104 non-conducti ve.
TABLE III
.
Temperature Resistance Analog VoltsHex Rep Dec Rep
F (~L)
11~22,000 4.71 24 36
1 4011 ,500 4.86 2C 44
1657,600 5.04 35 53
1905,000 5.33 44 68
2153,300 5.63 53 83
2402,1 00 6.02 67 1 03
2651,500 6.41 7B 123
2901,050 6.82 90 144
315 740 7.16 Al 161
340 560 7,47 Bl 177
365 410 7.77 C0 1 2
390 320 7.96 CA 202
415 250 8.14 D3 211
440 200 8.27 DA 218
465 150 8.45 E3 227
User inputs are provided to microprocessor 72 via Boil/Fry
25 Mode selection switch means 22 and heat setting selection means 50
comprising input potentiometers 102(A)-(D) associated with heat;ng
elements 12-18 respect;vely. t~lode selection sw;tch 22 is directly
coupled between output port R3 and input port K4 of microprocessor 72,
The open and closed states of switch 22 signify selection of the
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PATENT w 91~-RG 16707 - Payne
general Boil Mode and Fry Mode, respectively. Microprocessor 72
determines the state of switch 22 by periodically generating a logical
hi gh si gnal at R3 and monitoring the input si gnal at K4.
Each of input potentiometers 102(A)-(D) is coupled between a
5 regulated 9 volt dc and a regulated 4 volt dc reference voltage
supply. Each of wiper arms 103(A)-(D) of potentiometers 102(A)-(D)
respectively is coupled to A/D input port A2 of microprocessor 72 via
multiplexing circuit 114. Each w;per arm is positioned by user
rotation of the associated one of control knobs 26-32. The voltage
10 between the wiper arm and the 4 volt 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 processes analog vol tages appearing at A2
representing the user input settings in multiplex fashion.
Multiplexing circuit 114 comprises a conventional decoding
circuit 116 configured to function as a 3 line to 4 line decoder and a
gating circuit 118 which gates the appropriate wiper arm voltage signal
to microprocessor input port A2. Multiplexing is controlled by
scanning signals generated at output ports R0, Rl, and R2, which are
20 coupled to input ports A, B, and C of decoder 116, Biasing resistors
117, 119, and 121 are connected between R0, Rl, and R2 respectively and
ground. Decoder outputs Ql-Q4 are coupled to the control ports A-D of
gating circuit 118. Input ports A D of gating circuit 118 are
connected directly to wiper arms 103(D)-(A) respectively. Output ports
25 A-D of gating circuit 118 are commonly connected to input port A2 of
microprocessor 72. The scan signals at R0, R1 and R2 sequentially
generate enabling signals at outputs Ql-Q4. These enabling signals are
coupled to the control inputs of gating circuit 118 to sequentially
couple the analog wiper arm voltage signals from input ports A-D to A2
30 of microprocessor 72.
~ PATENT - gD-RG-16707 - Payne
The processing of the resultant digitized temperature and
power setting input signals will be descrlbed in conjunction with the
following description of the control program.
User discernible signal generating means is provided in the
form of light emitting diodes ~LEDs) 120 and 122 coupled between output
ports R8 and R9 respectively and ground via current limiting resistors
124 and 126 respectively. LED 120 is energized by a signal at R8 in
response to detection of a short circuit failure. LED 122 is similarly
energized by a signal at R9 in response to detection of an open circuit
failure.
The following component values are suitable for use in the
circuit of Fig. 5. These values are illustrative only, and are not
\
\ '
,
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~ PATE~IT - gD-RG-16707 - Payne
intended to limit the scope of the claimed ;nvention.
_
Fixed Resistors (Q) Transistor ql
92 lK 124 1 OK 2N2222
94 220 126 lOK Integrated Circuits
270 88 MDC 3020 Integrated Circuit
106 2.21K 1~ precision 90 ULN 2004A Integrated Circuit
10108 2.21K 1~ precision 116 CD4028BC Integrated Circuit
110 22K 118 CD4026BC Integrated Circuit
112 . 27K
117 lOK
` 119 lOK
Potenti ometers (Q )
102A-D 50K
Thermistor (~L) Microprocessor
lû4 50K 72 Texas Instruments TMS 2300
Triac
82 General Electric SC 147
Surface Uni ts
12-18 General Electr~c WB 30 X 218
25 Control Program Descripti on
Microprocessor 72 is customized to perform control functions
in accordance with this invention by permanently configuring the Read
Only Memory (ROM) of microprocessor 72 to implement predetermined
control instructions. Figs. 6 through 17 are flow diagrams which
;' :
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PATENT - gD RG-16707 ~ Payne
illustrate the con~rol routines incorporated in the control program of
microprocessor 72 to perform the control functions in accordance with
the present invention~ From these diagrams one of ord;nary skill 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 contrql functions of the present control arrangement herein
described there may be other control functions to be performed in
conjunction with other operating characteristics of the appl;ance.
Instructions for carrying out the routines described in the diagrams
may be interleaved with instructions and routines for other control
func~ions which are not part of the present invention.
The control program consists of a sequence of routines which
act on information stored in the Random Access Memory (RAM) of
microprocessor 72. The RAM is arranged in four files, with one file
associated with each surface unit. A register designated the X
register is used to address the desired one of the four files. The
control program is executed once during each control interval for each
surface unit sequentially executing the control program on successive
RAM files.
Control routines for implementing the Fry and Boil modes are
described as illustrative examples of closed loop control strategies
for automatic surface unit control.
START Routine - Fig. 6
This routine is entered at the beginning of each control
interval. The function is to call up the appropriate RAM file for the
current pass through the control program. A counter is provided in
-2~-
~;~636~3~ PATENT - 9D-RG-167C7 - Payne
each RAM file designated the SU counter. Each SU counter functions as
a four count ring counter and used to call up the RAM files
sequentially such that each RAM fi1e is called up every fourth pass
through the Control Program.
Referring naw to Fig. 6, Block 186 increments the SU counters
in all four files, X=0, 1, 2, 3. Inquiries 188, 190 and 192 determine
the SU count and call up the appropriate one of RAM files 0, 1, 2 and 3
via Blocks 194, 196, 198 and 200 for SU equal to 1, 2, 3 and 4,
respectively. Block 202 resets all of the SU counters to zero when SU
equals 4.
After the appropriate R~l file is selected, the program
branches (Block 204) to the User Input routine of Fig. 7.
USER INPUT Routine - F;g. 7
The function of this routine is to control the multiplexing of
the user selected heat setting input signals at input port A2 via
multiplexing circuit 114 (Fig. 5), and to determine whether Boil or Fry
has been selected for the automatic surface unit.
It will be recalled that the control program ;s executed once
during each control ;nterval for each surface unit sequentially.
Inquir;es 224-228 determine for which surface unit the control program
;s being executed, that is, whiçh surface unit is the subject of the
present pass through the program. The three regular surface units
14-18 are designated SU2, SUl, and SU0 respect;vely; SU3 represents
automatic surface unit 12. Blocks 230-236 generate the appropriate
binary codes 100, 010, 110, and 001 for SU0-SU3, respectively at output
ports R0, Rl, and R2 to gate the appropriate one of wiper arms
103A-103D through gating circuit 118 to input port A2.
If SU-3, sign;fying that the program is being executed for the
automatic surface unit, the st~te of mode select switch 22 is
-25~
PATENT - 9D-RG-16707 ~ Payne
~ 163~
determined by setting outpu~ R3 (Block 236)~ Inquiry 23~ then scans
input port K4 to determine whether switch 32 is open (K4=0) or closed
(K4=1). If K4=1, signifying selection of the Fry ModeJ a Mode ~ ag is
set for future reference in a subsequent routine and R3 is reset (Block
240). If K4=0, signifying selection of the Boil Mode, the Mode Flag is
reset and R3 is reset (Block 242).
Having enabled the appropriate input at ;nput port A2, voltage
from the enabled one of potent;ometers 102A-102D ;s converted to a
dig;tal signal. 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 heat settings are evenly spaced along the
potentiometer. By this arrangement the user selected input setting may
conveniently be represented by the four h;gh order bits of the 8 bit
A~D output signal. The analog input at port A2 is read in (Block 244)
and converted to its corresponding digital signal. The four high order
bits of this signal designated A/D HI are stored as the input power
setting variable KB tBlock 246).
Inquiry 248 determines if the present pass through the control
is for the automatic surface unit SU3 ~SU~ 2). If not, the program
branches (Block 250) directly to the Power Compare routine of Figs.
16A, B to implement the open loop power control strategy. If the
program is being executed for the automatic surface unit, the program
branches (Block 252) to the Temp Input routine (Fig. 8) to read in the
sensed utensil temperature. Consequently, the routines associated
solely with the automaW c surface unit, namely the Temp Input, Filter
and Sensor Timing, Boil, Fry, Warm, Open Check, Short Check and KB-XFER
-26-
~3~ PATENT - 9D-RG-16707 Payne
routines are only entered when the control program is operating on the
RAM file associated with the automatic surface unit. When the control
program i5 operating on the RAM files for the regular surface units
14-18, the program branches from the User Input routine to the Power
Compare routine.
TEMP INPUT Routine - Fig. 8
The function of this routine is to convert the analog voltage
at port Al representing the sensed utensil temperature to a digital
signal representative of the sensed utensil temperature. More
specifically, this routine determines within which of 16 predetermined
temperature ranges the present sensed utensil temperature falls. A
hexadecimal value is assigned to the variable SENINP (and also SENOUT)
corresponding to each of the 16 temperature ranges, as shown in Table
IV. The hexadecimal value for the upper temperature threshold value
. _ ~
-27-
~ PATENT - 9D-RG-16707 - Payn¢
for each temperature range is also included in Table IV.
TABLE IV
.
Hex Rep Hex Co de
SENINP & SENOUT Temp. Range F.Upper Threshold
0 T~115 24
1 115~ T~140 2C
2 140~T~165 35
3 165 ~ T l 90 44
4 190 cT~215 53
215CT '240 67
6 240 ~T~ 265 7B
7 265 c T ~ 290 90
8 290 ~T~ 315 Al
9 315 ~T~ 340 Bl
A 340 cT~ 365 C0
B 365 ~T~ 390 CA
C 390 cT~ 415 D3
D 415 ~T ~ 440 DA
E 440 ~T '465 E3
F 465 cT
.
Referring now to Fig. 8, R12 is set (Block 270) to turn on
25 transistor Q1 (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 272).
The variable TC in the flow diagram represents the digital value of the
analog signal. Inquiries 274-302 determine the temperature range in
-28-
PATENT - 9D-RG-16707 - Payne
~hich the sensed te~perature ~alls and 810cks 304-334 ass;gn the
appropriate value to the temperature variable SENINP in accordance with
Table V. After establishing the approprlate value for SENINP, R12 ;s
reset (Block 336) to turn off ~1, de-energizing thermistor 104, and the
5 program branches (Block 338) to the Sensor Filter and Timing routine
(Fig. 9).
For exampl e, i f the sensed temperature i5 200 F, the
hexadecimal representation of the digital temperature signal will be
greater than 44 corresponding to lgO F and less than 53
corresponding to 215F. Hence, the answer to Inquires 274-280 ~ill
be Yes. The response to Inquiry 282 will be No. The value 4 will be
assigned to ~BIINP (Block 312~. Having assigned a value to SENINP, R12
is reset (Block 336) and the program branches (Block 338) to the Sensor
Filter and Timing routine (Fig. 9).
SENSOR FILTER and TIMING Routine - Fig. 9
This routine performs the dual function of iteratively
.
filtering the sensor output temperature signal SENINp and also
controlling the timing of the updating of the temperature signal which
is actually used in the control routines yet to be described. 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. ~lence, isolated
erroneous inputs are averaged out so as to have little effect on the
accuracy of the cumula`tive average signal provided by the filter
routine. Referring to Fig. 9, the filter function is performed by
-29-
~2~;3~3~ PATEN~ - 9D-RG-16707 - Payne
B10ck 350. It will be recalled that SENINP is the hexadecimal
representation of the temperature range for the sensed utensil
temperature determined in the hereinbefore described T~P 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.
A new temperature input siynal SENINP is processed by the
filter portion of 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 element 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 counter, counting from 0-31 and resetting to 0. In the duty cycle
control implemented in the POWER OUT routine hereinafter described, for
duty cycles less than 100% the heating element is energized during the
first part of the control period when the ZCM count is relatively low
and de-energized while the ZCM count is relatively high. Since, except
when operating at the 100% power level, the heating element fs always
de-energized for count 31, radiant energy effects on the sensor are
minimum at ~CM count 31. Thus, radiation effects are minimized by
updating SENOUT, the temperature signal utillzed in implementation of
the Power Control routine only at count 31. It is desirable, however,
to haYe at least two updates of SENOUT during each 4.4 second control
period, to limit oscillations between inputs. Hence, SENOUT ;s also
updated at the midpo;nt of the control period, i.e. at count 16. There
-30-
~ ~: r~ ~ ~
~;9 ~t PATENT - 9D-RG-16707 - Payne
is potentially more error due to radiation effects for this
measurement; hcwever, the heat;ng elernent is de-energized at this point
for the twelve lower powerlevels. Hence, the effects of radiation
even on this measurement are minimum except at the highest 4 power
5 1 evels.
When the heating element is operated at 100~ duty cycle, the
radia~ion effects are the same at all counts; hence, for maximum
accuracy SENOUT is updated during each execution of the control
program, i.e. every 133 milliseconds.
Referring again to the flow diagram of Fig. 9~ Inquires 352
and 354 look for ~CM counts of 16 and 31, respectively. Upon the
occurrenc~ of either count, SENOUT is updated by the then current value
of SUM 1 (Block 356). Otherwise, Inquiry 358 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 356)
regardless of the count; if not, Block 233 is bypassed, and SENOUT is
not updated during this pass. In this fashion for power levels l~er
than 15, SENOUT is updated only on counts 16 and 31, and when power
level 15 is being implemented SENOUT is updated every count. Upon
20 completion of this routine the program branches (Block 358) to the Boil
routine (Fi g. 10).
BOIL Rout;ne - Fig. 10
The function of this routine is to implement the actual Boil
Modes. In the actual Boil Modes, the water loads are brought to a boil
25 with the boil rate being determined by the heat setting selected by the
user. It will be recalled that in the actual Boil Mode the surface
unit is energized at a power level fifteen (100~ duty cycle) until the
sensed utensil temperature exceeds 215 F. When the sensed utensil
temperature is greater than 215 F., the surface unit is energized at
--31--
3L~63~ PATENT - 9D-RG-16707 - Payne
the steady state power level associated with the selected heat
setting. The associated steady state power levels for settings 7-lO
are 8-ll, respectively For heat settings ll-13 the associated steady
state power levels are 11-13 respectively. For both heat settings 1
5 and 15 the associated steady state power level is 14 (Table II).
Yariables KB, M(KB) and SENOUT are used in this routine. The
variable KB represents the heat setting selected by the user by
manipulation of control knob 22 (Fig. 2). Its value is assigned in the
User Input routine. M(KB) is a variable which represents the power
lO level at which the heating element is to be operated. When operating
in the Boil Mode, its value is establ ished in the Boil routine for use
in the Power Compare routine to make the triac triggering decisions.
SENOUT is the temperature variable representing the sensed utensil
temperature, which is assigned a value in the Filter and Sensor Timing
1 5 routine.
Referring na.Y to the flow dia~ram of Fig. lO, Inquiry 360
determines if the Mode Flag is set signifying selection of the Fry
Mode. If yes, the program branches (Block 361) to the Fry routine
(Fig. ll). If the Boil Mode Flag is not set, Inquiry 362 determines if
20 KB is less than 4. If so, the program branches (Block 363) to the llarm
mode (Fig. 12). If KB is not less than 4, Inquiry 364 determines if KB
is less than 7. If so, the program branches (Block 365) to the Simmer
mode. In the interest of brevity, a description of the control
algorithm for the Simmer mode is not described herein. However, a flow
25 diayram for a suitable S;mmer routine is described in the hereinbefore
referenced U.S. Patent Nu~ber 4,493,980.
If KB is not less than 7, Inquiry 366 determines if the sensed
utensil temperature exceeds the minimum boil reference temperature of
215 F (SENOUT~4). If not, power 1evel 15 is set by setting M(KB)
-32-
~3~ PATENT - sD-~G-16707 - Pd~ne
to 15 (Block 367) and the program branches (Block 368) to the Open
Check routine (Fig. 13). If the sensed utensil temperature is greater
than 215, Inquiry 370 detects the selection of any one of heat
settings 7-lO (KB~ ll ). For heat settings 7-lO, the appropriate one of
5 steady power levels 8-ll, respectively, is set by setting M(KB) to KB~1
~Block 372). The program then branches (Block 368) to the Open Check
routine (Fig. 13). Inquiry 374 detects the selection of any one of
heat settings 11-13. For these heat settings the appropriate one of
power levels 11-13 respectively is set by setting M(KB) to KB (Block
lO 376).
For heat settings 14-15, (KB not less than 14) M(KB) is set to
14 (Block 378) to set the steady state power level at 14 for each of
these heat settings. The program then branches (Block 368) to the Open
Check routine (Fig. 13).
FRY Routine - Fig. ll
The function of this routine is to implement the Fry Mode.
This routine is entered when the user selects the Fry Mode via mode
s el ecti on swi tch 22.
Inquiry 390 checks for an OFF setting (KB=O). If OFF is
20 selected, M(KB) is set to zero (Block 392) and the program branches
(Block 394) to the Pa~er Out routine, Fig. 13A. Otherwise, Inquiry 396
determines if the Warm setting has been selected (KB 3). If so, the
program branches (Block 398) to the Warm routine, Fig. 12. Otherwise,
Inqu;ry 400 compares the sensed utensil temperature SENOUT with the
25 maximum s~eady state reference temperature for the temperature range
for the selected heat setting, which in the Fry Mode is (KB-l ). For
SENOUT?(KB-l), signifying that the sensed utensil temperature exceeds
the desired range, P~er Level zero is implemented (Block 39Z), and the
program branches (Block 394) to the Open Check routine (Fig. 13). If
-33-
~ PATENT - 9D-RG-16707 - Pa~ne
the sensed utensil temperature ;s less than the desired temperature
range, an error signal (ERR) is computed ~Block 402) as ~ function of
the difference between the desired temperature range represented by
(KB-l) and the sensed utensil temperature represented by SENOUT, by
computing the difference between K8-1 and SENOUT and dividing the
difference by two. 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 pcwer level to be applied, which is temporarily stored in the
accumulator (ACC) (Block 422). Inquiry 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 Out routine and the program
branches (Block 394) to the Open Check routine (Fig. 13).
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 F. (SENOUT-O), ACC is set to 15 (Block
426), resul~ing in M(K3) being set to 15 (BLock 428), and the program
then branches (Block 394) to the Open Check routine, Fig. 13.
WARM Routine - Fig. 12
This routine is entered from the Boil or the Fry routine
whenever KB is less than 4 or 3 respectively. The function of this
routine is to implement the Warm Mode.
Inquiry 431 determines if KB equals zero corresponding to the
OFF power setting. If so, M(KB) is set to zero (Block 434) and the
program branches (Block 436) to the Open Check routine (Fig. 13).
-34-
~ PATE~JT - 9D-RG-16707 - Payne
For heat settings KB=1 and KB=2, the maximum warm temperature
limit is 140 F corresponding to SENOUT=2. Ft,r KB-3, the maximum
warm temperature limit is 165 F corresponding to SENOUT=3. Inguiry
432 checks for KB=l representing the Wm(l) setting. For KB=l, Inquiry
5 433 determines if SENOUT is less than 2. If not, M(KB) is set to zero
(Block 434) to de-energize the surface unit. If SENOUT is less than 2
signi~ying a sensed utensil temperature less than the maximum for Ke=l,
M(KB) is set to 2 ~Block 435), and the program branches (Block 436) to
the Open Check routine (Fig. 13).
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 Open Check routine (Fig. 13) .
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
20 is less than the maximum warm reference temperature for the selected
heat setting (SENOUTc KB), M(KB) is set to (KB+l) (Block 440). This
implements the steady state p ~ er levels 2, 3 and 4 for heat settings
1, 2 and 3, respectively, corresponding to duty cycles of 6.5%, 9% and
12.5%, respectively (See Tables I and II). If tne sensed utensil
temperature is not less than the maximum warm reference temperature,
M(KB) is set to O (Block 434) corresponding to the zero or OFF power
level. M(KB) having been set, the pro~ram then branches (Block 436) to
the Open Check routine (Fig. 13).
PATENT - 9D-RG-16707 - Payne
OPEN CHECK Routine - Fig. 13
The function o~ this routine is to determine if the
temperature sensor circuit has failed in an open circuit mode by
comparing the sensed utensil temperature reading to a predetermined
reference representative of a temperature lcwer than the lowest
normally occurring steady state sensed utensil temperature for a
non-OFF power level applied to the surface unit. If the temperature
reading is less than the reference under steady state operating
conditions, this signifies that an open circuit condition exists for
the sensor circuit. In order to avoid erroneously responding to the
low temperature condition as an open circuit failure during the
transient heat-up time periods when a heating element is heating up
from room temperature to the desired operating temperature, a timer is
employed to monitor the duration of the low temperature condition. The
reference temperature is set at approximately 90 F. This reference
Yalue of 90 F is selected somewhat arbitrarily, the essential
criterion being that the reference represents a tempçrature less than
the lowest sensed utensil temperature associated with normal steady
state operation at the lowest heat setting which can be selected by the
user. It has been empirically determined that for automatic surface
unit 12, during normal operating conditions the sensed utensil
temperature will alwRys rise above the 90 F. reference temperature
in less than one minute regardless of the power setting selected.
Thus, if a low temperature condition persists for more than one minute,
the condition is identified as an open circuit failure of the sensor
circuit.
A flag designated the OPNFLG flag and a timer designated
OPNTMR are utilized in this routine. The OPNFLG flag is set when an
open condition is detected and the OPNTMR timer is used to time the
-36-
3~ PATENT - 9D-P~G-16707 - Pa~ne
duration of the low temperature condition to prevent responding to
transient conditions.
Referring now to the flow diagram of Fig. 13, it will be
recalled that the variable TC is assigned a value representing the
sensed utensil temperature in the Temp Input routine. Inquiry 450
determines if the sensed utensil temperature TC is less than 90 F.
If the temperature reading is not less than 90 F., the OPNFLG flag
is reset (~lock 452) and the OPNTMR timer is reset (Block 454) and the
program proceeds (Block 455) to the Short Check routine (Fig. 14). If
the temperature is less than 90 F., Inquiry 456 checks M(KB) to make
sure that a non-OFF power setting has been selected. If M(KB) = O
signifying that the OFF setting has been selected for the automat;c
surface unit, OPNTMR is reset lBlock 454) and the program proceeds to
the Short Check routine. If M(KB) is greater than 0, the OPNTMR timer
is incremented (Block 458) and ~nquiry 460 determines whether the low
temperature condition has continued for more than approximately one
minute (67.2 seconds). If not, the program proceeds to the Short Check
routine, If the time exceeds one minute, the OPNFLG flag is set
signifying detection of an open circuit failùre and OPNT~lR is reset
(Block 462). The program then proceeds to the Short Check routine
(Fig. 14)-
SHORT CHECK Routine - Fig. 14
The function of this routine is to determine if a short
circuit condition of the temperature sensor circuit exists, by
comparing the digitized value of the temperature input at Al to a
reference temperature corresponding to a temperature greater than the
highest temperature which would occur during normal surface unit
operation on its highest power setting. In the illustrative embodiment
a reference temperature of 500 F. is used. This reference value of
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~L~63~a PATENT - 9D-RG-16707 Payne
500 F. is selected somewha~ arbitrarily, the essential cri~erion
being that the reference represents a temperature greater than the
maximum sensed utensil temperature wh;ch would occur under normal
steady state operating conditions. To prevent an erroneous response to
a temporary or transient over-temperature condition, a timer is used to
prevent identification of a high temperature condition 2S a short
circuit failure until the condition has continued for a predetermined
time period which in the illustrative embodiment is chosen somewhat
arbitrarily to be approximately 17 seconds. To this end, a short
circuit flag designated SHTFLG and a short circu;t timer designated
SHrrMR are used in this routine.
Referring to Fig. 14, Inquiry 470 determines ;f the
temperature variable TC from the Temperature Input routine (Fig. 8) is
less than 500 F. If the temperature is less than the maximum
threshold temperature of 500 F, the SHTFLG flag is reset and the
SHTTMR timer is reset (Block 472) and the program proceeds to the KB
Transfer routine of Fig. 15 (Block 473). If TC is greater than 500
F., the SHTTMR timer is incr~nented (Block 474) and Inquiry 476
determines if the condition has existed for more than 16.8 seconds. If
SHTTMR is not greater than 16.8 seconds, the program proceeds to the
KB-Xfer routine (Fig. 15). If SHTTMR is greater than 16.8 seconds,
SHTFLG is set to signify the detection of a short circuit failure
condition and SHTTMR is reset (Block 478) and the program branches
(Block 473) to the KB-Xfer routine (Fig. 15).
KB-XFER Routine - Fig. 1~
The function of this routine is to set the diagnostic displays
sisnifying a temperature sensor circuit failure when appropriate and in
the event of such a failure to convert the power control strategy being
implemented from the closed loop strategy normally employed for
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~L~ 3~8~ PATENT - 9D-R~-16707 - Payne
automatic surface unit 12 to the open loop strategy normally employed
with regular surface units 14~18. The latter funct;on is accomplished
in tne event of the detection of an abnormal condition by ass;gning the
KB value representing ~he particular one of the 16 positlons for the
control knob selected by the user to the power control variable M(KB)
utilized in the Power Compare routine to determine the duty cycle to be
implemented for the surface unit.
It will be recalled that when the control program is being
executed for the regular surface units 14-18, the pro~ram branches from
the User Input routine to the Power Compare routine, and the value of
M(KB) is simply KB as determined by the position of the associated
control knob. However, for the automatic surface unit M(KB) is
assigned a value in the appropriate one of the Boil, Fry and Warm
routines, which ~alue is a function of KB, and also the sensed utensil
temperature SENOUT, in accordance with the closed loop control
strategies implemented by these routines.
In this routine, if a sensor circuit failure, either open
circuit or short circuit, is detected, the variable M(KB) is assigned
the value KB, with the result that the control strateqy for surface
unit 12 will be the same open loop strategy employed for regular
surface units 14-18.
LEDs 120 and 122 (Fig. 5) which constitute the diagnostic
display to signify to the user that either an open circuit or short
circuit failure has been detected are also controlled in this routine.
If an abnormal condition is detected, the appropriate one of these LEDs
is energized by an output signal at the appropriate one of output ports
R8 and R9 of microprocessor 72. Once an output port is set in this
routine signifying the detection of an abnormal condition, it will -
remain set until power is removed from the system such as by
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~ 3~ PATENT - 9D-RG-16707 - Pa~ne
disconnecting the appliance for serv;ce. The ports are automatically
reset as part of the system power up routine (not shown). Thus, the
indicator lights will remain on once set untll pcwer ~s removed from
the control circuit. To this end, a flag designated the SIG Flag is
used in this routine. The SIG ~ ag is set upon detection of a fault.
This flag is only reset during Power Up of the circu;t.
Referring to the flow diagram of Fig. 15, Inquiry 479 checks
the state of the SIG Flag. If set, signifying that a fault has been
previously detected, the program proceeds directly to Block 490. If
not set, Inquiries 480 and 482 check the state of the OPNFLG flag and
SHTFLG flag respectively to determine if either an open or short
failure of the temperature sensor circuit has been detected. If
neither ~lag is set, the program branches (Block 483) to the Power
Compare routine and power control proceeds normally. If the OPNFLG
flag is set signifying the detection of an open circuit failure, the
open circuit failure display is set by setting output R9 of
microprocessor 72 (Fig. 5) (Block 484). Similarly, if the SHTFLG flag
is set signifying the detection of a short circuit condition in the
temperature sensor circuit, output port R8 of microprocessor 72 is set
to trigger the short circuit condition indicator light (Block 486)~ In
the event of the detection of either an open or a short circuit
condition, the SIG Flag is set (Block 488). Then the power control
variable M(KB) is set equal to the value of the variable KB
representing the power setting selected by user manipulation of control
knob 26 (Block 490). The program then branches to the Power Compare
routine~
POWER COMPARE Routine - Figs. 16A and 16B
The function of the Power Compare routine ;s to determine,
based upon the power level designated by M(KB), whether or not the
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~ PATENT - 9D-RG-16707 - Payne
power control triac should be tr;ggered 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 3Z, the total number of
control intervals in ~le control period. A ZCM counter functioning as
a 32 count ring counter is provided in each RAM file and is incremen~ed
once for each pass through the control program for that RAM file. The
power control decision is made by comparing the ZCM count with a
reference count associated with the power level represented by M(KB).
The reference count for each power level represents the number of
conductive control intervals per control period corresponding to the
desired duty cycle. ~hen the ZCM count is less than the reference, a
Power Out Latch (POL) is set, signifying that the associated one of
power control triacs 82A-D is to be switched into conduction;
otherwise, POL is reset, signifying that the associated power control
triac is to be n~-conductive.
Referring to Figs. 16A 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 ZoM to the
associated reference count. If ZCM is less than the reference, the
Power Out Latch is set by the appropriate one of Blocks 602 and 606,
signify;ng that the surface unit for which the control program is
presently ex~cuting is to be energized during the next control
interval. Otherwise, the P~er 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 Power Out Routine, Fig. 17.
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~3~i8~ PATENT - 9~-RG-16707 - Pdyne
POWER OUT Routine - Fig. 17
It will be recalled fr~n the description of the Start routine
(Fig. 6) that the control program ;s executed for each surface unit
sequentially. The variable SU is the ;ndexing variable used to control
5 the sequencing. SU=0,1,2 and 3 ident;f;es which of RAM file and
corresponding surface un;ts 18, 16, 14 and 12 respectively ;s the
subject of the current pass through the program.
The function of the Power Out routine is to synchronize the
firing of that one of power control triacs 82A-D associated with the
10 surface unit for which the control program is then executing with zero
crossings of the 60 Hz AC power signal applied across Ll and L2 (Fig.
5).
Referring now to Fig. 17, input port K8 receives zero crossing
pulses from zero crossing detector circuit 100 (F;g. 6). Pos;tive
15 half-cycles are represented by K&l and negative half~ycles by K8=0.
Inquiry 620 determines the polar;ty of the present power signal
half-cycle. If the signal is presently ;n a positive half-cycle,
(K8=1), Inquiry 622 waits for the beginning of the next negative
half-cycle, (K8=0). Upon detection of K&l, the program proceeds to
Inquiry 624. If the answer to Inquiry 620 is NO ~K8=0), Inquiry 634
waits for the beginning of the next positive half-cycle (K8=1), then
proceeds to Inquiry 624.
Inquiry 624 checks the state of the P~er Cut Latch (POL). If
POL is reset, signifying that the corresponding surface un~t is not to
25 be energized during the next control ;nterval, the appropriate output
port ident;fied by the index variable SU~4 (R(SU~4) ident;fies R4, RS,
R6 and R7 for SU=O, 1, 2 and 3 respectively) is reset (Block 626); if
POL is set, signifylng that the corresponding surface unit is to be
energized, R(SU+4~ is set (Bl ock 628).
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Inquiry 630 causes the control program to return directly to
the Start routine to repeat the prograrn for the next surface unit until
SU equals 3 signify;ng that executiorl has been completed for all four
surface units. When SU equals 3, tne program delays (Block 632) until
the beginning of the next control interval. In the illustrative
embodiment, execution of the control program uses Gne-half cycle of the
power signal for each pass. Thus, execution for all four units is
completed in the first two cycles of the power signal. The duration of
the control interval is eight cycles. Block 632 de1ays the program for
six cycles after which the program branches (810ck 63~) to Start to
begin execution for the next control interval.
h'hile in accordance with the Patent Statutes, a specific
embodiment of the present invention has been illustrated and described
herein, it is realized that numerous modi M cations 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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