US20160187898A1 - Compensating for Sensor Thermal Lag - Google Patents
Compensating for Sensor Thermal Lag Download PDFInfo
- Publication number
- US20160187898A1 US20160187898A1 US15/064,782 US201615064782A US2016187898A1 US 20160187898 A1 US20160187898 A1 US 20160187898A1 US 201615064782 A US201615064782 A US 201615064782A US 2016187898 A1 US2016187898 A1 US 2016187898A1
- Authority
- US
- United States
- Prior art keywords
- temperature
- temperature control
- control system
- sensing device
- point
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 238000000034 method Methods 0.000 claims abstract description 61
- 238000010438 heat treatment Methods 0.000 claims description 29
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 29
- 239000000523 sample Substances 0.000 claims description 11
- 239000000463 material Substances 0.000 claims description 7
- 238000001816 cooling Methods 0.000 claims description 4
- 238000012546 transfer Methods 0.000 claims description 4
- 238000009413 insulation Methods 0.000 claims description 2
- 238000012935 Averaging Methods 0.000 claims 1
- 230000008569 process Effects 0.000 description 20
- 230000000712 assembly Effects 0.000 description 5
- 238000000429 assembly Methods 0.000 description 5
- 239000002184 metal Substances 0.000 description 5
- 229910052751 metal Inorganic materials 0.000 description 5
- 238000004364 calculation method Methods 0.000 description 2
- 230000008859 change Effects 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 239000007769 metal material Substances 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 229910052755 nonmetal Inorganic materials 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- 230000032683 aging Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000006399 behavior Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000006870 function Effects 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
Images
Classifications
-
- 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
- G05D23/1902—Control of temperature characterised by the use of electric means characterised by the use of a variable reference value
-
- 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
- G05D23/1951—Control of temperature characterised by the use of electric means with control of the working time of a temperature controlling device
-
- 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
- G01K7/42—Circuits effecting compensation of thermal inertia; Circuits for predicting the stationary value of a temperature
Definitions
- the present disclosure relates to methods and apparatus for compensating for sensor thermal lag.
- the heating of water in a tank is controlled by a processor-based control that receives and evaluates temperature information sensed by one or more thermistors immersed in the tank.
- the electrical and/or mechanical components of the thermistor are generally separated from the water by a physical barrier.
- Exemplary embodiments are disclosed of a method of compensating for thermal lag in a temperature control system.
- a method is performed by a controller of the temperature control system. The method includes receiving a first temperature obtained by a temperature sensing device at an end of a temperature control cycle. A second temperature obtained by the temperature sensing device is received at a pre-defined time after the end of the temperature control cycle. The method includes changing an operational set-point temperature of the temperature control system using a difference between the received temperatures.
- Exemplary embodiments also are disclosed of a controller for a temperature control system having at least one temperature sensing device.
- the controller includes at least one processor and memory configured to receive a temperature obtained by the temperature sensing device indicating that a control set-point temperature has been reached.
- the processor(s) and memory are also configured to receive, upon expiration of a predetermined time period after the control set-point temperature has been reached, another temperature obtained by the temperature sensing device.
- the processor(s) and memory are configured to use a difference between the received temperatures to offset the control set-point temperature.
- Exemplary embodiments also are disclosed of a temperature control system that includes a temperature sensing device and a controller having a processor and memory configured to use a difference between a first temperature obtained by the temperature sensing device indicating that an end of a temperature control cycle has been reached and a second temperature obtained by the temperature sensing device at a pre-defined time after the end of the temperature control cycle, to offset a control set-point temperature of the temperature control system.
- FIG. 1 is a perspective view of a temperature sensing device and controller according to an exemplary embodiment
- FIG. 2 is a graph of a heating cycle of a temperature control system according to an exemplary embodiment
- FIG. 3 is a flow diagram of a method of compensating for thermal lag according to an exemplary embodiment
- FIG. 4 is a graph of a heating cycle of a temperature control system according to an exemplary embodiment
- FIG. 5 is a flow diagram of a method of compensating for thermal lag according to an exemplary embodiment.
- FIG. 6 is a graph of a heating cycle of a temperature control system according to an exemplary embodiment.
- a temperature sensor is imperfectly coupled thermally to a medium in or on which temperature is to be sensed.
- the heating of water may be controlled by a microprocessor-based control that receives temperature information via a voltage input determined through a thermistor and thermistor assembly.
- the thermal mass of the thermistor assembly and the heat transfer coefficient of the materials that make up the thermistor assembly typically introduce a thermal lag between the actual temperature of the water and the temperature sensed by the thermistor.
- the inventor has developed and discloses herein exemplary embodiments of a controller-performed method for compensating for thermal lag in a temperature control system, so that the controller can more accurately regulate the temperature.
- FIG. 1 illustrates an example temperature sensing device 20 in relation to which a method may be performed by an example controller 28 according to one or more aspects of the present disclosure.
- the temperature sensing device 20 may be used, e.g., for sensing temperature in a temperature control system such as a water heater.
- the temperature sensing device 20 includes a thermistor 32 provided in a thermistor assembly 36 .
- the thermistor assembly 36 is part of a probe assembly 40 .
- the probe assembly 40 may be secured in a water heater tank wall or other water-carrying structure by a threaded region 44 such that the thermistor 32 will be immersed in the water stored in the tank.
- the probe assembly 40 is integral with the controller 28 .
- the controller 28 includes a processor 52 and memory 56 , e.g., a microprocessor and an electrically erasable programmable read-only memory (EEPROM).
- EEPROM electrically erasable programmable read-only memory
- a probe assembly may instead be remotely located from a controller and connected thereto by a wire or cable.
- Exemplary embodiments of the disclosure may also be provided in relation to temperature sensing devices other than or in addition to thermistor assemblies, e.g., resistance temperature detectors, integrated circuit (IC) temperature sensors, etc.
- the thermistor assembly 36 and probe assembly 40 may be made of metal.
- a thermistor assembly and probe assembly could be made of and/or include non-metal materials, which typically have different thermal mass and different heat transfer rates than those of metals.
- the controller 28 receives a first temperature obtained by the temperature sensing device 20 at an end of a heating or cooling cycle.
- the controller 28 also receives a second temperature obtained by the temperature sensing device 20 at a pre-defined time after the end of the heating or cooling cycle.
- the controller 28 uses a difference between the received temperatures to change an operational set-point temperature and to offset a control set-point temperature of the water heater.
- control set-point “control set-point temperature” and the like are used herein and in the claims to refer to a set-point temperature selected, e.g., by an installer and/or user of a temperature control system.
- the terms “operational set-point,” “operational set-point temperature” and the like are used herein and in the claims to refer to a set-point temperature used in operation by a controller of a temperature control system.
- FIG. 2 is a graph 100 that represents an example heating cycle 102 , e.g., in a water heater controlled by the controller 28 .
- a curve 104 indicates actual water temperature (in degrees Fahrenheit) relative to time 108 .
- a curve 116 indicates temperature (in degrees Fahrenheit) sensed by the temperature sensing device 20 relative to time 108 .
- the heating cycle 102 is started, e.g., when a user opens a hot water faucet. At an initial call for heat by the controller 28 , both the actual temperature 104 and sensed temperature 116 are at 105° F.
- the heating cycle 102 is ended when the controller 28 determines that water around the thermistor 32 has reached a selected control set-point 124 , e.g., 120° F.
- a lag 128 is evident between the temperature curves 104 and 116 , such that the sensed temperature 116 is less than the actual temperature 104 over substantially the entire heating cycle 102 .
- the thermistor 32 senses the temperature of the control set-point 124 , the actual water temperature 104 has overshot the control set-point temperature 124 .
- the controller 28 records a temperature sensed by the thermistor 32 at the end of the heating cycle, typically the selected control set-point temperature 124 , and waits for a predetermined time period 132 (e.g., for three minutes, etc.) after the end of the heating cycle 102 .
- the length of the predetermined time period can vary for different types of temperature sensors (e.g., submersed sensors, surface sensors, etc.) and for different media in or on which temperature is being sensed.
- the length of the predetermined time period was empirically determined to be three minutes, but it is influenced by the thermal masses in the system and the insulation values of the materials.
- submersed sensors would tend to shorter times (e.g., less than three minutes, etc.), where surface sensors would tend to longer saturation times (e.g., more than three minutes but less than five minutes, etc.).
- the controller 28 captures a temperature 136 sensed by the thermistor 32 upon expiration of the predetermined time period.
- the controller 28 determines a difference between the temperatures 124 and 136 .
- the controller 28 may save and use the difference as a compensation value, e.g., as further described below, to change its operational set-point for use in controlling the water heater.
- the selected control set-point remains the same.
- the controller captures another temperature.
- the another temperature captured by the controller may be a temperature sensed by the thermistor at a predetermined time after the end of a call for heat, e.g., at three (3) minutes after the end of the heating cycle.
- the controller compares the two sensed temperatures. If, e.g., the temperature captured after the three-minute period is 122° F., the controller alters its internal operational set-point from 120° F.
- Two temperatures may be captured and compared in the same or similar manner after one or more heating cycles, e.g., after substantially each heating cycle, and the difference between the two temperatures may be used to compensate for thermal lag. In some aspects of the disclosure, compensation values based on such differences may be averaged and applied to one or more subsequent heating cycles.
- An example method shall now be described in relation to a storage water heater that includes two thermistor assemblies, one near the top of the water tank and the other near the tank bottom.
- both assemblies are controlled by the same controller.
- the method shall be described with reference to one of the two thermistor assemblies, because this example embodiment may include the controller performing the method in the same or similar way for the other thermistor assembly.
- the lag should preferably be independent of the location, but dependent on the structure (e.g., submersed bottom sensors versus surface top sensors, etc.).
- a three minute lag time may be sufficient for submersed bottom and surface top sensors.
- a submersed bottom sensors may also have the same or different lag time than a surface top sensor.
- the lag time or function may also vary between gas water heater versus electric water heater as the electric water heater may have a top heating element.
- FIG. 3 illustrates a method 200 that may be performed, e.g., when a user switches on a water heater.
- the controller determines whether it is making a first pass through the method 200 , i.e., whether a first heating cycle is being performed. If so, then in process 208 the controller sets an artificially high compensation value, e.g., 3° F., for the thermistor, to prevent overshoot on the first call for heat.
- FIG. 4 illustrates an example initial heating cycle 300 in which an initial compensation value greater than that normally expected is used.
- a curve 308 represents actual water temperature (in degrees Fahrenheit).
- a curve 316 represents thermistor-sensed temperature (in degrees Fahrenheit) combined with the initial compensation value.
- the method 200 includes process 216 in which a first temperature (which in most cases would be the control set-point temperature) is captured from the thermistor at the end of the first heating cycle.
- a first temperature which in most cases would be the control set-point temperature
- process 220 it is determined whether the predetermined time period has passed, i.e., whether it is time to obtain a new compensation value for the thermistor. If it is time to obtain a new compensation value, then a second temperature is captured (in process 224 ) from the thermistor, which is to be used to obtain the new compensation value.
- process 232 it is determined whether the second temperature, i.e., temperature sensed at the end of the predetermined time period, is greater than the first temperature.
- process 236 the first temperature (typically the control set-point temperature) is subtracted from the second temperature.
- process 240 the difference is saved, (e.g., in EEPROM, etc.) as a compensation value for use in subsequent heating cycle(s).
- process 244 includes setting the compensation value to a default value, e.g., to 2° F., etc.
- a current compensation value may be checked by determining (in process 252 ) whether the compensation value exceeds a predetermined maximum, e.g., 4° F., etc.
- the compensation value is set to the predetermined maximum value.
- the maximum value is preferably limited to prevent the routine from capturing behavior other than the thermal drift that is intended to be captured.
- the default value simply provides the routine a place to start, thus making it simpler to implement than searching for the value and also providing overshot control on the first run.
- a controller may use compensation values for bottom and top thermistor assemblies to control temperature.
- FIG. 5 illustrates an exemplary embodiment of a method 400 for controlling temperature.
- the controller combines a current temperature value sensed by the bottom thermistor with a compensation value previously saved in EEPROM for the bottom thermistor.
- the controller compares the result (“bottom result”) to the control set-point.
- the controller combines a current temperature value sensed by the top thermistor with a compensation value previously saved in EEPROM for the top thermistor.
- the controller compares the result (“top result”) to the control set-point, which may be offset by a value representing a difference between temperature at the top and temperature at the bottom of the tank.
- the controller continues to call for heat based on the results of the processes 412 and 420 .
- FIG. 6 illustrates an example heating cycle 500 that may occur subsequent to the initial heating cycle shown in FIG. 4 .
- a curve 504 represents actual water temperature (in degrees Fahrenheit).
- a curve 512 represents thermistor-sensed temperature (in degrees Fahrenheit) combined with a previously determined compensation value.
- the use of compensation values results in heat being switched off at an appropriate temperature to prevent overshoot. For example, as shown in FIG. 6 , an actual final temperature 520 at the end of the heating cycle 500 more closely matches a control set point temperature 524 than in the heating cycle 102 (shown in FIG. 1 ).
- Various embodiments of the foregoing exemplary methods and controls can be highly useful in temperature control systems in which temperature sensors are substantially enclosed or encased in materials that dampen sensor response.
- various exemplary embodiments of the foregoing methods and controls can compensate for changes in material.
- a given temperature control system may employ a thermistor probe assembly made from a metal.
- the temperature control system might be provided with a probe assembly made, e.g., from a polymer or other non-metal materials having heat transfer rates lower than those of metals.
- differences between sensed and actual temperatures would be greater, e.g., for a “plastic” probe assembly than for a metal probe, exemplary embodiments of the foregoing methods can automatically compensate for such differences or changes in material.
- Embodiments of the foregoing methods and controls can be used in relation to well sensors and/or surface sensors. Embodiments also are possible in relation to cooling systems.
- the foregoing methods and systems do not require complicated mathematical steps or large calculation overhead, can be adapted to current tank conditions, and can take system aging into account.
- the foregoing exemplary methods can be used in relation to water heaters and in relation to many, if not most or all, temperature sensing systems that exhibit an over-damped measurement response.
- Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
- first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed herein could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
- Spatially relative terms such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Automation & Control Theory (AREA)
- Control Of Temperature (AREA)
- Investigating Or Analyzing Materials Using Thermal Means (AREA)
- Thermal Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
Abstract
Exemplary embodiments are disclosed of a method of compensating for thermal lag in a temperature control system. In an exemplary embodiment, a method is performed by a controller of the temperature control system. The method includes receiving a first temperature obtained by a temperature sensing device at an end of a temperature control cycle. A second temperature obtained by the temperature sensing device is received at a pre-defined time after the end of the temperature control cycle. The method includes changing an operational set-point temperature of the temperature control system using a difference between the received temperatures.
Description
- This application is a continuation of U.S. patent application Ser. No. 13/494,524 filed Jun. 12, 2012. The entire disclosure of the above application is incorporated herein by reference.
- The present disclosure relates to methods and apparatus for compensating for sensor thermal lag.
- This section provides background information related to the present disclosure which is not necessarily prior art.
- For many water heaters, the heating of water in a tank is controlled by a processor-based control that receives and evaluates temperature information sensed by one or more thermistors immersed in the tank. The electrical and/or mechanical components of the thermistor are generally separated from the water by a physical barrier.
- This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
- Exemplary embodiments are disclosed of a method of compensating for thermal lag in a temperature control system. In an exemplary embodiment, a method is performed by a controller of the temperature control system. The method includes receiving a first temperature obtained by a temperature sensing device at an end of a temperature control cycle. A second temperature obtained by the temperature sensing device is received at a pre-defined time after the end of the temperature control cycle. The method includes changing an operational set-point temperature of the temperature control system using a difference between the received temperatures.
- Exemplary embodiments also are disclosed of a controller for a temperature control system having at least one temperature sensing device. The controller includes at least one processor and memory configured to receive a temperature obtained by the temperature sensing device indicating that a control set-point temperature has been reached. The processor(s) and memory are also configured to receive, upon expiration of a predetermined time period after the control set-point temperature has been reached, another temperature obtained by the temperature sensing device. The processor(s) and memory are configured to use a difference between the received temperatures to offset the control set-point temperature.
- Exemplary embodiments also are disclosed of a temperature control system that includes a temperature sensing device and a controller having a processor and memory configured to use a difference between a first temperature obtained by the temperature sensing device indicating that an end of a temperature control cycle has been reached and a second temperature obtained by the temperature sensing device at a pre-defined time after the end of the temperature control cycle, to offset a control set-point temperature of the temperature control system.
- Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
- The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
-
FIG. 1 is a perspective view of a temperature sensing device and controller according to an exemplary embodiment; -
FIG. 2 is a graph of a heating cycle of a temperature control system according to an exemplary embodiment; -
FIG. 3 is a flow diagram of a method of compensating for thermal lag according to an exemplary embodiment; -
FIG. 4 is a graph of a heating cycle of a temperature control system according to an exemplary embodiment; -
FIG. 5 is a flow diagram of a method of compensating for thermal lag according to an exemplary embodiment; and -
FIG. 6 is a graph of a heating cycle of a temperature control system according to an exemplary embodiment. - Example embodiments will now be described more fully with reference to the accompanying drawings.
- The inventor has observed that in currently used methods for sensing temperature, a temperature sensor is imperfectly coupled thermally to a medium in or on which temperature is to be sensed. For example, in a storage-type water heater, the heating of water may be controlled by a microprocessor-based control that receives temperature information via a voltage input determined through a thermistor and thermistor assembly. The thermal mass of the thermistor assembly and the heat transfer coefficient of the materials that make up the thermistor assembly typically introduce a thermal lag between the actual temperature of the water and the temperature sensed by the thermistor. The inventor has developed and discloses herein exemplary embodiments of a controller-performed method for compensating for thermal lag in a temperature control system, so that the controller can more accurately regulate the temperature.
- With reference now to the figures,
FIG. 1 illustrates an exampletemperature sensing device 20 in relation to which a method may be performed by anexample controller 28 according to one or more aspects of the present disclosure. As shown, thetemperature sensing device 20 may be used, e.g., for sensing temperature in a temperature control system such as a water heater. Thetemperature sensing device 20 includes athermistor 32 provided in athermistor assembly 36. Thethermistor assembly 36 is part of aprobe assembly 40. Theprobe assembly 40 may be secured in a water heater tank wall or other water-carrying structure by a threadedregion 44 such that thethermistor 32 will be immersed in the water stored in the tank. - In the present example embodiment, the
probe assembly 40 is integral with thecontroller 28. Thecontroller 28 includes aprocessor 52 andmemory 56, e.g., a microprocessor and an electrically erasable programmable read-only memory (EEPROM). In various aspects of the disclosure, a probe assembly may instead be remotely located from a controller and connected thereto by a wire or cable. Exemplary embodiments of the disclosure may also be provided in relation to temperature sensing devices other than or in addition to thermistor assemblies, e.g., resistance temperature detectors, integrated circuit (IC) temperature sensors, etc. Thethermistor assembly 36 andprobe assembly 40 may be made of metal. In various other example temperature sensing devices, a thermistor assembly and probe assembly could be made of and/or include non-metal materials, which typically have different thermal mass and different heat transfer rates than those of metals. - In one or more aspects of the disclosure, the
controller 28 receives a first temperature obtained by thetemperature sensing device 20 at an end of a heating or cooling cycle. Thecontroller 28 also receives a second temperature obtained by thetemperature sensing device 20 at a pre-defined time after the end of the heating or cooling cycle. Thecontroller 28 uses a difference between the received temperatures to change an operational set-point temperature and to offset a control set-point temperature of the water heater. Unless clearly indicated otherwise, the terms “control set-point,” “control set-point temperature” and the like are used herein and in the claims to refer to a set-point temperature selected, e.g., by an installer and/or user of a temperature control system. Additionally, unless clearly indicated otherwise, the terms “operational set-point,” “operational set-point temperature” and the like are used herein and in the claims to refer to a set-point temperature used in operation by a controller of a temperature control system. -
FIG. 2 is agraph 100 that represents anexample heating cycle 102, e.g., in a water heater controlled by thecontroller 28. Acurve 104 indicates actual water temperature (in degrees Fahrenheit) relative totime 108. Acurve 116 indicates temperature (in degrees Fahrenheit) sensed by thetemperature sensing device 20 relative totime 108. Theheating cycle 102 is started, e.g., when a user opens a hot water faucet. At an initial call for heat by thecontroller 28, both theactual temperature 104 and sensedtemperature 116 are at 105° F. Theheating cycle 102 is ended when thecontroller 28 determines that water around thethermistor 32 has reached a selected control set-point 124, e.g., 120°F. A lag 128 is evident between thetemperature curves sensed temperature 116 is less than theactual temperature 104 over substantially theentire heating cycle 102. When thethermistor 32 senses the temperature of the control set-point 124, theactual water temperature 104 has overshot the control set-point temperature 124. - In one or more aspects of the disclosure, and as shown in
FIG. 2 , thecontroller 28 records a temperature sensed by thethermistor 32 at the end of the heating cycle, typically the selected control set-point temperature 124, and waits for a predetermined time period 132 (e.g., for three minutes, etc.) after the end of theheating cycle 102. The length of the predetermined time period can vary for different types of temperature sensors (e.g., submersed sensors, surface sensors, etc.) and for different media in or on which temperature is being sensed. By way of example only, the length of the predetermined time period was empirically determined to be three minutes, but it is influenced by the thermal masses in the system and the insulation values of the materials. By way of further example, submersed sensors would tend to shorter times (e.g., less than three minutes, etc.), where surface sensors would tend to longer saturation times (e.g., more than three minutes but less than five minutes, etc.). - The
controller 28 captures atemperature 136 sensed by thethermistor 32 upon expiration of the predetermined time period. Thecontroller 28 determines a difference between thetemperatures controller 28 may save and use the difference as a compensation value, e.g., as further described below, to change its operational set-point for use in controlling the water heater. In various aspects, the selected control set-point remains the same. - Thus, e.g., when the controller ends a heating cycle after determining that water in the tank is at an operational set-point of 120° F. based on a thermistor signal, the controller captures another temperature. The another temperature captured by the controller may be a temperature sensed by the thermistor at a predetermined time after the end of a call for heat, e.g., at three (3) minutes after the end of the heating cycle. The controller compares the two sensed temperatures. If, e.g., the temperature captured after the three-minute period is 122° F., the controller alters its internal operational set-point from 120° F. to 118° F., so that when the next heating cycle is complete, the actual water temperature would be at 120° F., to thereby correspond to the selected control set-point of 120° F. Two temperatures may be captured and compared in the same or similar manner after one or more heating cycles, e.g., after substantially each heating cycle, and the difference between the two temperatures may be used to compensate for thermal lag. In some aspects of the disclosure, compensation values based on such differences may be averaged and applied to one or more subsequent heating cycles.
- An example method shall now be described in relation to a storage water heater that includes two thermistor assemblies, one near the top of the water tank and the other near the tank bottom. In this example embodiment, both assemblies are controlled by the same controller. The method shall be described with reference to one of the two thermistor assemblies, because this example embodiment may include the controller performing the method in the same or similar way for the other thermistor assembly. The lag should preferably be independent of the location, but dependent on the structure (e.g., submersed bottom sensors versus surface top sensors, etc.). A three minute lag time may be sufficient for submersed bottom and surface top sensors. A submersed bottom sensors may also have the same or different lag time than a surface top sensor. The lag time or function may also vary between gas water heater versus electric water heater as the electric water heater may have a top heating element.
-
FIG. 3 illustrates amethod 200 that may be performed, e.g., when a user switches on a water heater. Inprocess 204, the controller determines whether it is making a first pass through themethod 200, i.e., whether a first heating cycle is being performed. If so, then inprocess 208 the controller sets an artificially high compensation value, e.g., 3° F., for the thermistor, to prevent overshoot on the first call for heat.FIG. 4 illustrates an exampleinitial heating cycle 300 in which an initial compensation value greater than that normally expected is used. Acurve 308 represents actual water temperature (in degrees Fahrenheit). Acurve 316 represents thermistor-sensed temperature (in degrees Fahrenheit) combined with the initial compensation value. - Referring again to
FIG. 3 , themethod 200 includesprocess 216 in which a first temperature (which in most cases would be the control set-point temperature) is captured from the thermistor at the end of the first heating cycle. Inprocess 220, it is determined whether the predetermined time period has passed, i.e., whether it is time to obtain a new compensation value for the thermistor. If it is time to obtain a new compensation value, then a second temperature is captured (in process 224) from the thermistor, which is to be used to obtain the new compensation value. Inprocess 232, it is determined whether the second temperature, i.e., temperature sensed at the end of the predetermined time period, is greater than the first temperature. If yes, then in process 236 the first temperature (typically the control set-point temperature) is subtracted from the second temperature. Inprocess 240, the difference is saved, (e.g., in EEPROM, etc.) as a compensation value for use in subsequent heating cycle(s). If inprocess 232, it is determined that the temperature sensed at the end of the predetermined time period is not greater than the control set-point temperature, then process 244 includes setting the compensation value to a default value, e.g., to 2° F., etc. When it is not time to determine a new compensation value, a current compensation value may be checked by determining (in process 252) whether the compensation value exceeds a predetermined maximum, e.g., 4° F., etc. If so, then inprocess 256 the compensation value is set to the predetermined maximum value. In this example, the maximum value is preferably limited to prevent the routine from capturing behavior other than the thermal drift that is intended to be captured. The default value simply provides the routine a place to start, thus making it simpler to implement than searching for the value and also providing overshot control on the first run. - In various aspects of the disclosure, a controller may use compensation values for bottom and top thermistor assemblies to control temperature.
FIG. 5 illustrates an exemplary embodiment of amethod 400 for controlling temperature. Inprocess 408, the controller combines a current temperature value sensed by the bottom thermistor with a compensation value previously saved in EEPROM for the bottom thermistor. Inprocess 412, the controller compares the result (“bottom result”) to the control set-point. Inprocess 416, the controller combines a current temperature value sensed by the top thermistor with a compensation value previously saved in EEPROM for the top thermistor. Inprocess 420, the controller compares the result (“top result”) to the control set-point, which may be offset by a value representing a difference between temperature at the top and temperature at the bottom of the tank. Inprocess 428, the controller continues to call for heat based on the results of theprocesses -
FIG. 6 illustrates anexample heating cycle 500 that may occur subsequent to the initial heating cycle shown inFIG. 4 . Acurve 504 represents actual water temperature (in degrees Fahrenheit). Acurve 512 represents thermistor-sensed temperature (in degrees Fahrenheit) combined with a previously determined compensation value. In various aspects, the use of compensation values results in heat being switched off at an appropriate temperature to prevent overshoot. For example, as shown inFIG. 6 , an actualfinal temperature 520 at the end of theheating cycle 500 more closely matches a control setpoint temperature 524 than in the heating cycle 102 (shown inFIG. 1 ). - Various embodiments of the foregoing exemplary methods and controls can be highly useful in temperature control systems in which temperature sensors are substantially enclosed or encased in materials that dampen sensor response. Moreover, various exemplary embodiments of the foregoing methods and controls can compensate for changes in material. For example, a given temperature control system may employ a thermistor probe assembly made from a metal. At some future time, the temperature control system might be provided with a probe assembly made, e.g., from a polymer or other non-metal materials having heat transfer rates lower than those of metals. Although differences between sensed and actual temperatures would be greater, e.g., for a “plastic” probe assembly than for a metal probe, exemplary embodiments of the foregoing methods can automatically compensate for such differences or changes in material.
- Embodiments of the foregoing methods and controls can be used in relation to well sensors and/or surface sensors. Embodiments also are possible in relation to cooling systems. The foregoing methods and systems do not require complicated mathematical steps or large calculation overhead, can be adapted to current tank conditions, and can take system aging into account. The foregoing exemplary methods can be used in relation to water heaters and in relation to many, if not most or all, temperature sensing systems that exhibit an over-damped measurement response.
- Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. In addition, advantages and improvements that may be achieved with one or more exemplary embodiments of the present disclosure are provided for purpose of illustration only and do not limit the scope of the present disclosure, as exemplary embodiments disclosed herein may provide all or none of the above mentioned advantages and improvements and still fall within the scope of the present disclosure.
- Specific dimensions, specific materials, and/or specific shapes disclosed herein are example in nature and do not limit the scope of the present disclosure. The disclosure herein of particular values and particular ranges of values for given parameters are not exclusive of other values and ranges of values that may be useful in one or more of the examples disclosed herein. Moreover, it is envisioned that any two particular values for a specific parameter stated herein may define the endpoints of a range of values that may be suitable for the given parameter (the disclosure of a first value and a second value for a given parameter can be interpreted as disclosing that any value between the first and second values could also be employed for the given parameter). Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. In addition, disclosure of ranges includes disclosure of all distinct values and further divided ranges within the entire range.
- The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
- When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. The term “about” when applied to values indicates that the calculation or the measurement allows some slight imprecision in the value (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If, for some reason, the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring or using such parameters. For example, the terms “generally”, “about”, and “substantially” may be used herein to mean within manufacturing tolerances.
- Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed herein could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
- Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
- The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
Claims (9)
1. A method of compensating for thermal lag in a temperature control system, the method comprising:
receiving a first temperature obtained by a temperature sensing device at an end of a temperature control cycle, the temperature sensing device including a thermistor and probe assembly secured in a water heater tank wall by a threaded region such that the thermistor is immersed in water stored in the tank;
receiving a second temperature obtained by the temperature sensing device at an expiration of a pre-defined time after the end of the temperature control cycle; and
changing an operational set-point temperature of the temperature control system by subtracting a difference between the received temperatures from a control set-point temperature of the temperature control system;
the method performed by a controller of the temperature control system.
2. The method of claim 1 , performed to offset a control set-point temperature of the temperature control system.
3. The method of claim 1 , further comprising:
receiving a third temperature obtained by the temperature sensing device at an end of a second temperature control cycle;
receiving a fourth temperature obtained by the temperature sensing device at the pre-defined time after the end of the second temperature control cycle;
averaging the difference between the first and second temperatures with a difference between the third and fourth temperatures to obtain an average difference; and
using the average difference to offset a control set-point temperature of the temperature control system.
4. The method of claim 1 , performable by the controller as to two temperature sensing devices having different thermal transfer rates.
5. The method of claim 1 , wherein the end of the temperature control cycle is reached when a selected control set-point is reached in the temperature control system.
6. The method of claim 1 , performed without altering a selected control set-point of the temperature control system.
7. The method of claim 1 , wherein the pre-defined time is three minutes.
8. The method of claim 1 , wherein the temperature control cycle includes a heating cycle or a cooling cycle.
9. The method of claim 1 , wherein a length of the pre-defined time is based on insulation values of the temperature sensing device materials.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US15/064,782 US20160187898A1 (en) | 2012-06-12 | 2016-03-09 | Compensating for Sensor Thermal Lag |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US13/494,524 US9303897B2 (en) | 2012-06-12 | 2012-06-12 | Compensating for sensor thermal lag |
US15/064,782 US20160187898A1 (en) | 2012-06-12 | 2016-03-09 | Compensating for Sensor Thermal Lag |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/494,524 Continuation US9303897B2 (en) | 2012-06-12 | 2012-06-12 | Compensating for sensor thermal lag |
Publications (1)
Publication Number | Publication Date |
---|---|
US20160187898A1 true US20160187898A1 (en) | 2016-06-30 |
Family
ID=49714486
Family Applications (2)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/494,524 Active 2034-11-05 US9303897B2 (en) | 2012-06-12 | 2012-06-12 | Compensating for sensor thermal lag |
US15/064,782 Abandoned US20160187898A1 (en) | 2012-06-12 | 2016-03-09 | Compensating for Sensor Thermal Lag |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US13/494,524 Active 2034-11-05 US9303897B2 (en) | 2012-06-12 | 2012-06-12 | Compensating for sensor thermal lag |
Country Status (2)
Country | Link |
---|---|
US (2) | US9303897B2 (en) |
CA (1) | CA2809846C (en) |
Families Citing this family (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP3561381B1 (en) * | 2018-04-25 | 2022-08-31 | Bleckmann GmbH & Co. KG | Method for controlling a heating system component for a simple and safe operation and a heating system component therefor |
CN108549431A (en) * | 2018-05-16 | 2018-09-18 | 浙江复华质芯生物科技有限公司 | A kind of control method for improving precision instrument system temperature drift problem |
Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5199789A (en) * | 1990-11-19 | 1993-04-06 | Mauric Stanley J | Immersion well assembly |
US6246831B1 (en) * | 1999-06-16 | 2001-06-12 | David Seitz | Fluid heating control system |
US20060013572A1 (en) * | 2004-06-30 | 2006-01-19 | Phillips Terry G | System and method for preventing overheating of water within a water heater tank |
US20100095906A1 (en) * | 2008-10-21 | 2010-04-22 | Honeywell International Inc. | Water heater with partially thermally isolated temperature sensor |
Family Cites Families (12)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3609549A (en) | 1970-06-15 | 1971-09-28 | Universal Oil Prod Co | Corrosion-measuring device |
US4106341A (en) | 1977-01-03 | 1978-08-15 | General Electric Company | Linearized thermistor temperature measuring circuit |
US5116136A (en) | 1989-06-01 | 1992-05-26 | Massachusetts Institute Of Technology | Temperature measurements using thermistor elements |
US5026971A (en) * | 1990-01-08 | 1991-06-25 | General Electric Company | Temperature control system for a heating oven using a glass-ceramic temperature sensor |
JP3372811B2 (en) | 1997-02-03 | 2003-02-04 | キヤノン株式会社 | Heat fixing device |
EP1048188B1 (en) | 1998-01-23 | 2004-05-26 | Tom Richards, Inc. | Demand anticipation control system for a high efficiency ultra-pure fluid heater |
US8176881B2 (en) * | 2005-02-07 | 2012-05-15 | Emerson Electric Co. | Systems and methods for controlling a water heater |
US7434544B2 (en) * | 2006-06-27 | 2008-10-14 | Emerson Electric Co. | Water heater with dry tank or sediment detection feature |
US8245987B2 (en) * | 2009-12-18 | 2012-08-21 | Honeywell International Inc. | Mounting bracket for use with a water heater |
US8538597B2 (en) * | 2010-07-27 | 2013-09-17 | General Electric Company | System and method for regulating temperature in a hot water heater |
US8390420B2 (en) | 2010-12-16 | 2013-03-05 | Emerson Electric Co. | Immersion well assembly |
US20130276722A1 (en) * | 2012-04-24 | 2013-10-24 | Emerson Electric Co. | Thermal Insulators for Providing a Thermal Break Between the Body and Flange Assembly of a Gas Water Heater Control |
-
2012
- 2012-06-12 US US13/494,524 patent/US9303897B2/en active Active
-
2013
- 2013-03-19 CA CA2809846A patent/CA2809846C/en not_active Expired - Fee Related
-
2016
- 2016-03-09 US US15/064,782 patent/US20160187898A1/en not_active Abandoned
Patent Citations (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5199789A (en) * | 1990-11-19 | 1993-04-06 | Mauric Stanley J | Immersion well assembly |
US6246831B1 (en) * | 1999-06-16 | 2001-06-12 | David Seitz | Fluid heating control system |
US20060013572A1 (en) * | 2004-06-30 | 2006-01-19 | Phillips Terry G | System and method for preventing overheating of water within a water heater tank |
US20100095906A1 (en) * | 2008-10-21 | 2010-04-22 | Honeywell International Inc. | Water heater with partially thermally isolated temperature sensor |
Non-Patent Citations (3)
Title |
---|
HyperPhysics, Heat Conduction, February 2009 * |
NTC Thermistors, TDK, April 2011 * |
NTC Thermistors, Vishay, March 2004 * |
Also Published As
Publication number | Publication date |
---|---|
US9303897B2 (en) | 2016-04-05 |
CA2809846C (en) | 2016-12-20 |
US20130327840A1 (en) | 2013-12-12 |
CA2809846A1 (en) | 2013-12-12 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US8770152B2 (en) | Water Heater with partially thermally isolated temperature sensor | |
US6308009B1 (en) | Electric water heater with electronic control | |
US20200268190A1 (en) | A liquid heating appliance for making a beverage and associated method, power management system and microcontroller readable medium | |
US20240183580A1 (en) | Electronic Control System for Electric Water Heater | |
CN108158411A (en) | Anti-dry control method, anti-dry control system and drinking device | |
CN108506963B (en) | Range hood, control method and system thereof, and fire-off detection method and device | |
US11071404B2 (en) | Method for adjusting the heating power of at least one heating element of a domestic appliance | |
US8407015B2 (en) | Method and apparatus for monitoring and controlling an electrical boiler | |
CN106289431A (en) | Identify method and the electricity cooking pot of meter Shui Liang in electricity cooking pot cooking process | |
CN105928210B (en) | Control method, device and the water heating apparatus of water heating apparatus | |
CN104596116A (en) | Control method and control system of water heater and water heater | |
CN108278651B (en) | Range hood, control method and system thereof, and fire detection method and device | |
US11366075B2 (en) | Method for determining an amount of deposition of scale on a heating element and household appliance comprising a heating element | |
US6137955A (en) | Electric water heater with improved heating element | |
US20160187898A1 (en) | Compensating for Sensor Thermal Lag | |
US11311142B2 (en) | Food processor with boiling point recognition | |
US20060011613A1 (en) | Temperature calibration method for a cooking appliance | |
WO2010061268A2 (en) | Method for minimising energy consumption of a storage water heater | |
CN111713957A (en) | Cooking method, cooking equipment and computer readable storage medium | |
CN111380088A (en) | Induction cooker and method and device for identifying cooking pot on induction cooker | |
US11519625B2 (en) | Managing temperature overshoot | |
CN112325556A (en) | Heating control device, refrigerator control method and refrigerator | |
TWI696054B (en) | Heating device and abnormal detection method of heating device | |
CN109259611A (en) | Cooking apparatus and its thermal-insulation control method determine method | |
US10503183B2 (en) | System and method for dry fire protection in electric water heaters |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
AS | Assignment |
Owner name: EMERSON ELECTRIC CO., MISSOURI Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:ARENSMEIER, JEFFREY N.;REEL/FRAME:037931/0213 Effective date: 20160308 |
|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |