GB1576282A - Temperature sensing apparatus - Google Patents

Temperature sensing apparatus Download PDF

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Publication number
GB1576282A
GB1576282A GB27973/77A GB2797377A GB1576282A GB 1576282 A GB1576282 A GB 1576282A GB 27973/77 A GB27973/77 A GB 27973/77A GB 2797377 A GB2797377 A GB 2797377A GB 1576282 A GB1576282 A GB 1576282A
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United Kingdom
Prior art keywords
current
transistor
silicon
probe
temperature
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Expired
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GB27973/77A
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Duracell Inc USA
Original Assignee
PR Mallory and Co Inc
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Filing date
Publication date
Application filed by PR Mallory and Co Inc filed Critical PR Mallory and Co Inc
Publication of GB1576282A publication Critical patent/GB1576282A/en
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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/6447—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors
    • H05B6/645—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors using temperature sensors
    • H05B6/6452—Method of operation or details of the microwave heating apparatus related to the use of detectors or sensors using temperature sensors the sensors being in contact with the heated product
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K1/00—Details of thermometers not specially adapted for particular types of thermometer
    • G01K1/14—Supports; Fastening devices; Arrangements for mounting thermometers in particular locations
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/01—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using semiconducting elements having PN junctions
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D23/00—Control of temperature
    • G05D23/19—Control of temperature characterised by the use of electric means
    • G05D23/20—Control of temperature characterised by the use of electric means with sensing elements having variation of electric or magnetic properties with change of temperature
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K2207/00—Application of thermometers in household appliances
    • G01K2207/02—Application of thermometers in household appliances for measuring food temperature
    • G01K2207/06—Application of thermometers in household appliances for measuring food temperature for preparation purposes

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Automation & Control Theory (AREA)
  • Measuring Temperature Or Quantity Of Heat (AREA)
  • Control Of Temperature (AREA)
  • Electric Ovens (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)

Description

(54) IMPROVEMENTS IN AND RELATING TO TEMPERATURE SENSING APPARATUS (71) We, P.R. MALLORY & CO. INC., a corporation organised and existing under the laws of the State of Delaware, United States of America of 3029 East Washington Street, Indianapolis, State of Indiana, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to temperature sensing apparatus and to apparatus for controlling the temperature of substances or objects being heated. In some circumstances it is most important that the temperature of a substance being heated should be closely sensed and the heat to the substance closely controlled.For example in the cooking of foodstuffs in microwave ovens, the cooking of the foodstuffs is so rapid that close, accurate control of heat input is required.
The present invention provides Linear temperature sensing apparatus comprising: a probe provided with a silicon PN junction device and adapted to be positioned in thermal contact with an object so as to sense the temperature of said object, a resistance means connected in series with said silicon PN junction device, and an electrical amplifier circuit connected to said silicon PN junction device via a conductive path, said resistance means being selected so as to provide a value of current along said conductive path which varies linearly in accordance with the temperature sensed by said silicon PN junction device.
The present invention further provides a method of controlling heat input to an object to be heated comprising: placing a probe into thermal contact with said object, said probe including a silicon PN junction device, applying an electircal potential to said silicon PN junction device through a resistance means connected in series thereto said resistance means being selected so as to provide a current output from said PN junction device which varies linearly in accordance with the temperature of said object; and supplying heat to said object in response to said current output whereby to control heat input to said object in accordance with the temperature thereof.
Temperature sensing apparatus in accordance with the invention can be used in microwave oven applications. where the heat is applied substantially only to the item being cooked, and enables the temperature of the food being cooked to be directly sensed.
A feature of the preferred embodiment of the invention is the provision of the heat input to the oven which can be linearly controlled in accordance with the temperature of the object.
Liner temperature sensing apparatus is provided which relies on a silicon PN junction device to provide a linear electrical change in response to temperature change; the preferred apparatus is in the form of a probe carrying a silicon PN junction device and an electrical circuit which derives a control voltage from a current through the PN junction.
Other features and advantages of the invention will become apparent from the following description of embodiments thereof given by way of example, and the accompanying draw ings wherein: Figure 1 is a diagram depicting an embodiment of the invention in use; Figure 2 is a fragmentary view partly in section, showing the top portion of a probe as shown in Figure 1; and Figures 3 and 4 are circuit diagrams showing two different forms of electrical circuits which can be used in the arrangement of Figure 1; Figures 5 and 6 are views corresponding to Figures 2,3 and 4 showing another embodiment of the invention.
Referring now to the drawings, Figure 1 shows a substance or object 10 being heated in a suitable oven, indicated diagrammatically at 12, by a heating means 14; in Figure 1, the object being heated is shown as a turkey being cooked and the oven can be a microwave oven.
The temperature of the substance 10 is sensed by means of a temperature sensing means 16 which includes a probe 18 penetrating the substance being heated and an electrical circuit 22, arranged to provide an output signal Vo in accordance with the temperature of the substance being heated. Such signal is used to control a suitable power switching means 20, such as a relay or triac, which in turn controls the power supplied to the heating means 14. The heating means can be of any suitable type, such as an electrical resistance coil or, in the case of a microwave oven, a magnetron. Electrical power is supplied to electrical circuit 22 from power source Li, L2 through a power supply circuit 19. Power supply 19 supplies operating voltages such as V+, V and VR, VB, to circuit 22 in a suitable known manner.
As more particularly shown in Figures 1 and 2, probe 18 includes a metal rod 24 attached to a handle 26 and having a pointed end 28 for ease of penetration into the substance being heated. There is cavity 30 within the rod in which at the pointed end there is carried a silicon transistor 32. Also carried in the cavity is a resistance element 34 included in the circuit to the emitter of the transistor.
Figure 3 shows the probe electrical circuit 22. The electrical circuit 22, as shown in Figure 3, includes an input section, a current to voltage converter section 38 and section 18, including transistor 32 of the probe 18; resistor 34 of the probe is shown in this Figure as included in the input section of the circuit, of which it logically forms part. The current to voltage converter 38 includes as its active element an operational amplifier 39 having an inverting input - and a non-inverting input + and an output terminal 46. An element 36, specifically a resistor 40, is connected between the source of voltage VR in the inverting input of the operational amplifier and feedback resistor 44 is connected between the output terminal 46 and the inverting input of the operational amplifier.By this means, a reference current is established at junction 42 of resistors 40 and 44, at the inverting inputof the operational amplifier. The collector C and base B of transistor 32 are connected respectively to the inverting and non-inverting inputs of the operational amplifier, the latter input being connected also to an electrical reference point such as earth. The emitter of the transistor 32 is connected through the resistor 34 to the voltage source VB.
Operational amplifiers have well known characteristics; in particular they are designed to have very high voltage gain between input and output terminals. Such amplifiers respond to a differential input, applied between so called inverting and non-inverting input terminals, and operate to amplify such a differential input of very small magnitude to a very large voltage with respect to the balance point of the differential input, usually earth. For example, with an amplifier with an open loop voltage gain of 100,000 a differential input of 100 microvolts will produce an output voltage of 10 volts. A second characteristic of an ideal operational amplifier is that the input impedance is infinitely high so that the amplifier responds to voltage difference only. and no current flows between the two inputs; in practice, a small offset input current exists.The output of the amplifier is at low, and ideally zero, impedance, so that relatively large output currents can be obtained. For instance at 10 volts output voltage a typical operational amplifier is capable of delivering up to 10 milliamperes output current.
In Figure 3, the operational amplifier 39 is connected in a negative feedback configuration, in which a porportion of the output voltage is fed back to the inverting input of the amplifier through resistor 44. the feedback ratio and hence the gain of the amplifier stage being determined by the ratio of the resistances of resistors 40 and 44 in known manner. The output voltage of amplifier 39 will rise to that value which results in the voltage at the inverting input being substantially equal to the voltage at the non-inverting input. In Figure 3 the noninverting input is at earth potential. so that the inverting input of amplifier 39 is a so-called virtual earth point.
The inverting input of the operational amplifier can be considered a summing point: by Kirchoff's second Law the sum of the currents at point 42 must be zero, so that: If = Ip - Io where Loins a constant reference current, Ip is the collector current of the probe transistor 32, and If is the feedback current through resistor 44.
With silicon transistor 32 connected in common collector configuration as shown in Figure 3, the collector current has a temperature dependence which is, at least theoretically, linear with absolute temperature of the transistor junction. To make use of this relationship, voltage VB is made equal to the band gap voltage of silicon. and. in the embodiment of the invention described, about 1.24 volts. With different transistors although linearity is retained, the magnitude of the collector current for any given transistor varies from transistor to transistor but the value of resistor 34 can be chosen for a particular transistor to achieve a desired magnitude of current with a given value of Viii.
The relationship between the collector current of a transistor and temperature, and the choice of value of emitter resistor to give a linear relationship between current and temperature with a silicon transistor, is known and is considered in an article by J.S. Brugler entitled "Silicon Transistor Biasing for Linear Collector Current Temperature Dependence" in the I.E.E.E. Journal of Solid State Circuits for June 1967 at pages 57 and 58.In a particular embodiment of the invention, with the circuit of Figure 3, the following data applied: VO at 100"C 1 Volt VO at 0 C 0 Volt Resistor 36 5.085 K.ohms Resistor 44 2.77 K.ohms Resistor 34 549 Ohms VR + 5.000 Volts VB - 1.24 Volts VBE of Transistor 32 at OOC 0.777 Volt Current at OOC 983.34 ,uA Supply V+ + 15.0 Volts Supply V- - 15.0 Volts Rate of change of Ip 3.6 CLA/OC.
By this means, when probe 18 is inserted in the substance to be heated, the output voltage Vo of the circuit of Figure 3 is linearly proportional to the temperature sensed at the tip of the probe.
The current Io through resistor 40 is constant, and is selected to be equal to the current flowing through the PN junction of transistor 32 at a specific temperature, such as 0 F. When the probe is at OOF the collector current will exactly equal the reference current reducing the feedback current through resistor 44 to zero.The output voltage VO will then be zero volts at this temperature of 0 F. As the temperature of the probe rises above 0 F, the probe current increases in proportion to the temperature increase; this increased probe current is greater than the constant reference current and thereby the feedback current is caused to increase from zero, the voltage output VO being linearly related to temperature, and a function of the resistance of resistor 44.
Figure 4 illustrates a modification of Figure 3 wherein the error due to base current of a transistor are avoided by the use of a diode connected transistor. In Figure 3 the base current of transistor 32 does not flow to junction point 42 but flows directly to the non-inverting input. In Figure 4, transistor 32' of probe 18' is connected as a diode with base B' connected to collector C'. All other connections remain the same. With this arrangement the base current flows into the inverting input of operational amplifier 39 and the error due to base current variation is eliminated.
Figures 5 and 6 are views, corresponding to Figures 2 and 4 of a modification of Figure 4 in which the diode-connected transistor 32' is replaced by a diode 50, suitably a silicon diode. As shown in Figure 5, probe 18" includes a metal rod 24 having a cavity 30 therein in which is carried a diode 50 near its pointed end 28. As shown in Figures 5 and 6, the cathode of the diode is connected to resistor 34 while the anode is connected to junction 42. This arrangement also provides the advantage of the embodiment of Figure 4, that is, with the use of the diode there is no error due to a current component of the PN device not flowing into the summing node.
The output voltage VO is thus a measure of the temperature of the probe tip and, by comparison with an appropriate reference, can be used to control the supply of power to the oven or other load, to maintain the oven at a suitable temperature or to terminate the supply of power when a desired temperature is attained. The output voltage can be used to operate a triac or the like. or a relay, to control the current to the oven.
WHAT WE CLAIM IS: l. Linear temperature sensing apparatus comprising: a probe provided with a silicon PN junction device and adapted to be positioned in thermal contact with an object so as to sense the temperature of said object, a resistance means connected in series with said silicon PN junction device, and an electrical amplifier circuit connected to said silicon PN junction device via a conductive path, said resistance means being selected so as to provide a value of current along said conductive path which varies linearly in accordance with the temperature sensed by said
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

  1. **WARNING** start of CLMS field may overlap end of DESC **.
    described, about 1.24 volts. With different transistors although linearity is retained, the magnitude of the collector current for any given transistor varies from transistor to transistor but the value of resistor 34 can be chosen for a particular transistor to achieve a desired magnitude of current with a given value of Viii.
    The relationship between the collector current of a transistor and temperature, and the choice of value of emitter resistor to give a linear relationship between current and temperature with a silicon transistor, is known and is considered in an article by J.S. Brugler entitled "Silicon Transistor Biasing for Linear Collector Current Temperature Dependence" in the I.E.E.E. Journal of Solid State Circuits for June 1967 at pages 57 and 58.In a particular embodiment of the invention, with the circuit of Figure 3, the following data applied: VO at 100"C 1 Volt VO at 0 C 0 Volt Resistor 36 5.085 K.ohms Resistor 44 2.77 K.ohms Resistor 34 549 Ohms VR + 5.000 Volts VB - 1.24 Volts VBE of Transistor 32 at OOC 0.777 Volt Current at OOC 983.34 ,uA Supply V+ + 15.0 Volts Supply V- - 15.0 Volts Rate of change of Ip 3.6 CLA/OC.
    By this means, when probe 18 is inserted in the substance to be heated, the output voltage Vo of the circuit of Figure 3 is linearly proportional to the temperature sensed at the tip of the probe.
    The current Io through resistor 40 is constant, and is selected to be equal to the current flowing through the PN junction of transistor 32 at a specific temperature, such as 0 F. When the probe is at OOF the collector current will exactly equal the reference current reducing the feedback current through resistor 44 to zero.The output voltage VO will then be zero volts at this temperature of 0 F. As the temperature of the probe rises above 0 F, the probe current increases in proportion to the temperature increase; this increased probe current is greater than the constant reference current and thereby the feedback current is caused to increase from zero, the voltage output VO being linearly related to temperature, and a function of the resistance of resistor 44.
    Figure 4 illustrates a modification of Figure 3 wherein the error due to base current of a transistor are avoided by the use of a diode connected transistor. In Figure 3 the base current of transistor 32 does not flow to junction point 42 but flows directly to the non-inverting input. In Figure 4, transistor 32' of probe 18' is connected as a diode with base B' connected to collector C'. All other connections remain the same. With this arrangement the base current flows into the inverting input of operational amplifier 39 and the error due to base current variation is eliminated.
    Figures 5 and 6 are views, corresponding to Figures 2 and 4 of a modification of Figure 4 in which the diode-connected transistor 32' is replaced by a diode 50, suitably a silicon diode. As shown in Figure 5, probe 18" includes a metal rod 24 having a cavity 30 therein in which is carried a diode 50 near its pointed end 28. As shown in Figures 5 and 6, the cathode of the diode is connected to resistor 34 while the anode is connected to junction 42. This arrangement also provides the advantage of the embodiment of Figure 4, that is, with the use of the diode there is no error due to a current component of the PN device not flowing into the summing node.
    The output voltage VO is thus a measure of the temperature of the probe tip and, by comparison with an appropriate reference, can be used to control the supply of power to the oven or other load, to maintain the oven at a suitable temperature or to terminate the supply of power when a desired temperature is attained. The output voltage can be used to operate a triac or the like. or a relay, to control the current to the oven.
    WHAT WE CLAIM IS: l. Linear temperature sensing apparatus comprising: a probe provided with a silicon PN junction device and adapted to be positioned in thermal contact with an object so as to sense the temperature of said object, a resistance means connected in series with said silicon PN junction device, and an electrical amplifier circuit connected to said silicon PN junction device via a conductive path, said resistance means being selected so as to provide a value of current along said conductive path which varies linearly in accordance with the temperature sensed by said
    silicon PN junction device.
  2. 2. Linear temperature sensing apparatus according to claim 1 wherein said silicon PN junction device is a transistor and said resistance means is connected in series to its emitter.
  3. 3. Linear temperature sensing apparatus according to claim 1 wherein said PN junction device is a diode and said resistance means is connected to its cathode.
  4. 4. Linear temperature sensing apparatus according to claim 1, 2 or 3 wherein said probe includes a metal rod having a cavity therein, said PN junction being disposed in said cavity.
  5. 5. Linear temperature sensing apparatus according to claim 4 wherein said metal rod has a pointed end and said cavity extends into said pointed end, said silicon PN junction device being disposed therein.
  6. 6. Linear temperature sensing apparatus according to any preceding claim wherein said resistance means is carried by said probe.
  7. 7. Linear temperature sensing apparatus according to any preceding claim wherein said electrical circuit further includes means for providing a reference current and a current to voltage amplifier circuit connected to said means for providing a reference current and to said PN junction devoce.
  8. 8. Linear temperature sensing apparatus according to claim 7 wherein said current to voltage converter amplifier circuit includes an operational amplifier having an input connected to a junction of said means for providing a reference current, said PN junction device, and a further resistance means connected between said junction and an output to said operational amplifier.
  9. 9. Linear temperature sensing apparatus according to claim 8 as dependent on claim 2 wherein said silicon PN junction device is a transistor, said means for providing a reference current being connected to its collector, and said operational amplifier being connected negative side to its collector, positive side to an electrical reference point, the base of said transistor also being connected to the electrical reference point.
  10. 10. Linear temperature sensing apparatus according to claim 7, 8 or 9 wherein said means for providing a reference current comprises a resistor.
  11. 11. Linear temperature sensing apparatus according to claim 8 as dependent on claim 2 wherein said silicon PN junction device is a diode connected transistor and wherein said resistance means is connected to its emitter, said means for providing a reference current is connected to its collector, and said operational amplifier is connected negative side to said collector and positive side to an electrical reference point.
  12. 12. Linear temperature sensing apparatus according to claim 8 as dependent on claim'3 wherein said means for providing a reference current is connected to the anode of said diode, and said operational amplifier is connected negative side to said anode and positive side to an electrical reference point.
  13. 13. Apparatus for heating an object including linear temperature sensing apparatus according to any preceding claim, said heating apparatus further including means responsive to the output signal from said electrical circuit to control heat input to the object.
  14. 14. Apparatus for heating an object according to claim 13 wherein said means responsive to the output signal comprises power switching means arranged to be connected to a power supply and to a source of heat to be applied to the object.
  15. 15. A method of controlling heat input to an object to be heated comprising: placing a probe into thermal contact with said object said probe including a silicon PN junction device; applying an electrical potential to said silicon PN junction device through a resistance means connected in series thereto. said resistance means being selected so as to provide a current output from said PN junction device which varies linearly in accordance with the temperature of said object; and supplying heat to said object in response to said current output whereby to control heat input to said object in accordance with the temperature thereof.
  16. 16. A method according to claim 15 wherein said silicon PN junction device is a transistor and said resistance means is connected to its emitter.
  17. 17. A method according to claim 15 wherein said silicon PN junction device is a diode and said resistance means is connected to its cathode.
  18. 18. A method according to claim 15, 16 or 17 wherein said step of supplying heat to said object comprises switching power from a power supply to a source of heat in response to said current output.
  19. 19. Linear temperature sensing apparatus substantially as hereinbefore described with reference to the accompanying drawings.
  20. 20. A method of controlling heat input to an object substantially as hereinbefore described with reference to the accompanying drawings.
GB27973/77A 1976-07-02 1977-07-04 Temperature sensing apparatus Expired GB1576282A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US70234376A 1976-07-02 1976-07-02

Publications (1)

Publication Number Publication Date
GB1576282A true GB1576282A (en) 1980-10-08

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Application Number Title Priority Date Filing Date
GB27973/77A Expired GB1576282A (en) 1976-07-02 1977-07-04 Temperature sensing apparatus

Country Status (5)

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JP (1) JPS536086A (en)
DE (1) DE2730086A1 (en)
FR (1) FR2356917A1 (en)
GB (1) GB1576282A (en)
SE (1) SE7707618L (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4458140A (en) * 1980-10-14 1984-07-03 Kidde Consumer Durables Corp. Temperature control apparatus for convection oven

Also Published As

Publication number Publication date
JPS536086A (en) 1978-01-20
FR2356917B3 (en) 1980-04-11
SE7707618L (en) 1978-01-03
FR2356917A1 (en) 1978-01-27
DE2730086A1 (en) 1978-01-19

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