Abstract:
The adaptive temperature controller includes an ambient temperature sensor, a device for measuring resistance, an electrically-conductive material, a power supply, and a device for controlling power. In operation, the controller determines the resistance of material at or near ambient temperature. Based on such determination so long as voltage and power are known, the resistance of the material, and therefore its instant temperature is known. Additionally, the adaptive temperature controller determines the responsiveness of the electrically-conductive material to determine the predicted increase in temperature and rate of increase in temperature relative to increases in voltage, current or power. As a result the voltage or power may be instantly varied to produce near infinite control over material temperature.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 60/767,236 entitled, “Adaptive Temperature Controller” filed on Mar. 13, 2006 in the United States Patent and Trademark Office. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Field of the Invention 
         [0004]    This invention pertains to a device for simultaneously controlling the temperature of a heating element and monitoring its temperature. In particular, the device pertains to controlling the temperature of a heating element for use in chromatographic analysis including heating of columns, detectors and other components, although it may be used in any system wherein precise heating through a range of temperatures is desired. 
         [0005]    2. Description of the Related Art 
         [0006]    An adaptive temperature controller for use with any electrically-conductive material is disclosed. It is often necessary to maintain portions of test equipment or other items above ambient temperature. This has been accomplished in the prior art with various temperature controllers. It is well known to provide a source of heat that is easily controlled. Most often heat is transferred from a conductive element. In the prior art the temperature of such conductive element was monitored by a separate device, often a Resistance Temperature Detector (RTD). However this requires multiple parts, increasing the space consumed by such equipment, the weight of such equipment, and its cost. Additionally, such systems often were unable to produce rapid temperature changes. Moreover, heating of equipment was not uniform and often was not sufficiently fast. 
         [0007]    It would therefore be a desirable improvement to have a temperature controller with fewer parts that likely would reduce weight, space and cost, would provide uniform heating, and would be capable of rapid heating and cooling. 
       SUMMARY OF THE INVENTION 
       [0008]    The adaptive temperature controller disclosed herein includes a temperature sensor, a device for measuring resistance, an electrically-conductive material, and a power supply. In operation, the controller determines the resistance of the electrically-conductive material at ambient temperature and is able to determine the corresponding resistance of the electrically-conductive material at temperatures within a temperature range and to apply the voltage or current necessary to obtain such resistance. The temperature of the electrically-conductive material may be determined by using a temperature sensor or by approximation based on ambient air temperature. As a result, the voltage or power may be instantly varied to produce near infinite control over material temperature. 
         [0009]    The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    So that the manner in which the described features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in detail, more particular description of the invention briefly summarized above may be had by reference to the embodiments thereof that are illustrated in the drawings, which drawings form a part of this specification. It is to be noted, however, that the appended drawings illustrate only typical preferred embodiments of the invention and are therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
           [0011]      FIG. 1   a  depicts a cross-sectional view of one embodiment of the prior art. 
           [0012]      FIG. 1   b  depicts a cross-sectional view of another embodiment of the prior art. 
           [0013]      FIG. 2   a  depicts direct heating of the component by the adaptive temperature controller. 
           [0014]      FIG. 2   b  depicts the component heated by direct heating controlled by the adaptive temperature controller. 
           [0015]      FIG. 3   a  depicts indirect heating of the component by the adaptive temperature controller. 
           [0016]      FIG. 3   b  depicts the component heated by indirect heating controlled by the adaptive temperature controller. 
           [0017]      FIG. 4  depicts component  101  where heating is controlled by the adaptive temperature controller via a pulse-width-modulated switching supply controlled by a microcontroller/microprocessor. 
           [0018]      FIG. 5  depicts component  101  where heating and cooling is controlled by the adaptive temperature controller. 
           [0019]      FIG. 6  depicts component  101  where heating is controlled by the adaptive temperature controller which includes a computer interface. 
           [0020]      FIG. 7  depicts a flow diagram of one embodiment of the steps for calibration of the adaptive temperature controller with an electrically conductive material. 
           [0021]      FIG. 8  depicts a flow diagram of an alternative embodiment of the steps for calibration of the adaptive temperature controller with an electrically conductive material. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    As depicted in  FIGS. 1   a  and  1   b , temperature controllers are known where a conductive element  250  and a sensor  251  were placed in proximity to or about the component  301  of a system  300  to respectively heat and monitor the temperature of element  301 . It is well known to provide a source of heat that is easily controlled. Most often heat is transferred from a conductive element  250  to be subsequently distributed to element  301 . The conductive element  250  may be placed adjacent ( FIG. 1   a ) or surrounding ( FIG. 1   b ) element  301 . In the prior art the temperature of conductive element  250  was monitored by a separate sensor  250 , often a RTD. This requires multiple parts, increasing the space consumed by such equipment, the weight of such equipment, and its cost. 
         [0023]    An electrically-conductive material  50  may be used to heat a component  101  of a system  100 , such as a detector or column in the case of chromatographic analysis, directly or indirectly. In the case of chromatographic analysis, the component  101  may be a chromatographic column  102  of chromatographic system  100 , which includes an analyte injector  103  and a detector  104 . In direct heating, depicted in  FIG. 2   a , the component  101 , a column, of the system  100  is composed, at least in part, of electrically-conductive material  50 , shown in cross-section in  FIG. 2   b . In indirect heating, depicted in  FIG. 3   a , the component  101  of the system  100  is contacted by electrically conductive material  50 , shown in cross section in  FIG. 3   b . In indirect heating, the component  101  contacted or encircled may be a detector, a column, or other device. In  FIG. 3   a , component  101  is again a column. The temperature to which the electrically-conductive material  50  heats the element, the rate of heating, and the duration of heating at any temperatures, is controlled by adaptive temperature controller  10 . In alternative embodiments, the adaptive temperature controller may be used in conjunction with any system wherein precise temperature control throughout a range is desired. 
         [0024]    As depicted in  FIGS. 2   a  and  3   a , in operation, the electrically-conductive material  50  used in conjunction with adaptive temperature controller  10  has a known electrical resistance as a function of temperature. Adaptive temperature controller  10  is in electrically conductive communication with electrically-conductive material  50 . The relationship for electrically-conductive material  50  between resistance and temperature may be obtained by adaptive temperature controller  10  by application of an equation or by interpolation from a table of such data. Since the electrical resistance of an electrically-conductive material  50  is known as a function of temperature, the temperature of the electrically-conductive material  50  can be determined by a dynamic measurement of the electrical resistance of electrically-conductive material  50 . As described below, the temperature of the electrically-conductive material  50  may be determined by contact with a temperature sensor  30  or by approximation based on the ambient air temperature determined from temperature sensor  30 . The temperature of electrically-conductive material  50  may therefore be controlled by virtue of the current (or voltage or both) applied to electrically-conductive material  50 . In the preferred embodiment, electrically-conductive material  50  is nickel. 
         [0025]    In instances when the resistance of the electrically-conductive material  50  is not immediately known, but its normalized resistance characteristic is known, such as in the case of an unknown length or diameter of nickel wire, the adaptive temperature controller  10  may be calibrated for use with electrically-conductive material  50  by measurement of the resistance of electrically-conductive material  50  while measuring the corresponding temperature of electrically-conductive material  50  by a temperature sensor  30 . The scale factor derived by dividing the measured resistance value of electrically-conductive material  50  by the normalized resistance value of the material from which electrically-conductive material  50  is composed at the reference temperature may then be applied to the normalized resistance characteristic to determine the resistance of electrically-conductive material  50  at any particular temperature. 
         [0026]    Unlike the prior art by use of adaptive temperature controller  10 , any length or size of electrically-electrically conductive material  50  may be used for heating. Providing use of any length or size of material is of significance as dimensions of heating materials may vary due to fluctuations in materials and cutting techniques. Moreover, unlike the prior art, separate temperature sensors are unnecessary as temperature may be determined at any time by measurement of the voltage and current applied. 
         [0027]    It is desirable that adaptive temperature controller  10  include a learning step to determine the responsiveness of the resistance, and therefore temperature, of electrically-conductive material  50  to change in current, voltage or power. Determination of responsiveness is important to reduce or eliminate overshoot and/or undershoot of temperature by adaptive temperature controller  110 . Having determined the resistance of electrically-conductive material  50  at ambient temperature, adaptive temperature controller  10  may then determine the rate of temperature increase relative to an increase in voltage, current or power. An electrically-conductive material  50  having a large mass will exhibit a lower rate of rise of temperature proportionate to increase in current, voltage or power. Likewise, an electrically-conductive material  50  having a small mass will exhibit a high rate of rise of temperature proportionate to an increase in current, voltage or power. In each case, the change in temperature is also related to a known thermal resistance coefficient for the material of which electrically-conductive material  50  is composed. For the range of operation the thermal resistance coefficient may be assumed to be a constant. Adaptive temperature controller  10  therefore determines the resulting change in resistance incident to a burst of current, voltage or power applied to electrically-conductive material  50 . Adaptive temperature controller  10  thereby avoids overshoot or undershoot of the desired temperature of temperature rate change by determining in advance the responsiveness of electrically-conductive material  50  to changes in current, voltage or power. In an alternative embodiment, adaptive temperature controller  10  may include a look-up table of known materials used for electrically-conductive material  50  at various temperatures and include the appropriate thermal resistance coefficient at the temperature of electrically-conductive material  50  to determine the associated increase in temperature. In a further embodiment, adaptive temperature controller  10  may record the change in resistance as a function of the change in current throughout operation, thereby mapping the function throughout. 
         [0028]    Adaptive temperature controller  10  may control or maintain one or more electrically conductive materials  50 . 
         [0029]    Further, adaptive temperature controller  10  may control an electrically-conductive material  50  to provide varying temperatures to a particular device or over a corresponding period of time, such as stepped or ramped temperature increases. 
         [0030]    In a further embodiment, adaptive temperature controller  10  may be used in conjunction with a component  101  composed of an electrically-conductive material  50  such as nickel. Once the thermal resistance coefficient of electrically-conductive material  50  is known, the temperature of component  101  may be controlled, such that the temperature may be increased at a stepped or fixed rate to provide increased separation between compounds having similar boiling points 
         [0031]    The adaptive temperature controller  10  configured to control the temperature of an electrically-conductive material  50  by determination of resistance and application of power, current or voltage provides several advantages over the prior art, particularly temperature controllers using heater cartridges. As no separate heater cartridge is required intermediate the heating element and the temperature controller, the mass of adaptive temperature controller  10  is less than that of such temperature controllers. Moreover, localized areas of increased or decreased temperature may be avoided as the heat flux is distributed over a large area, rather than emanating from a particular location associated with the heater cartridge. Further, the temperature may be more uniformly distributed since the heat is transferred from the surface rather than from one side associated with a cartridge heater. Finally temperature increases may be accomplished quite rapidly as the heat is generated within the electrically-conductive material  50  rather than transferred through a heat-conductive material from an exterior element. 
         [0032]    As depicted in  FIG. 4 , in one embodiment, wherein component  101  is comprised of electrically-conductive material  50 , power for producing heating is supplied by adaptive temperature controller  10  via a pulse-width-modulated switching supply  11  controlled by a microcontroller/microprocessor  12 , although other supply control systems known in the art may alternatively be used. The current supplied to electrically-conductive material  50  is determined by detecting the voltage drop across a current-sense resistor  60 , typically 0.1 Ohms, placed between the pulse-width modulated switching supply and electrically-conductive material  50 . Likewise the voltage across electrically-conductive material  50  is detected. Amplifiers to properly scale the detected voltages may be used before the representative signals are passed to analog-to-digital converters. The digitized signals thereby obtained, e.g. at 1000 times per second, are passed to a microcontroller wherein the relative resistance value is obtained by application of Ohm&#39;s Law, namely by dividing the converted voltage value by the converted current value. The relative resistance value may be compared against a reference resistance value for temperature control employing the conventional proportional-integral-derivative (PD) control algorithm. The temperature of electrically-conductive material  50  may also be determined for display or recording by solving the equation relating temperature to resistance well known in the art or interpolating a value from a table. 
         [0033]    In a further embodiment, depicted in  FIG. 5 , an adaptive temperature controller  10  may be configured to control the temperature of electrically-conductive material  50  and a fan  70  which may induce air flow about component  101 . For temperature ramping, the detected signal from the current-sense circuit may be used to control the rate, linear, exponential or otherwise, of temperature change by virtue of controlling for constant current within electrically-conductive material  50 . Fan  70  may be used to increase the rate of cooling of electrically-conductive material  50 . 
         [0034]    In a further embodiment, depicted in  FIG. 6 , adaptive temperature controller  10  includes a computer terminal  80 . The computer terminal  80  provides an interface for control via a keyboard  81  and monitor  82 . The computer terminal  80  may be any computer, including a conventional desktop computer or a handheld computer, such as those associated with Palm®, and electrically conductive material  50  calibration may be accomplished in the following steps, depicted in  FIG. 7 : 
         [0035]    1) Step  701 —The material of electrically-conductive material  50  is identified; 
         [0036]    2) Step  702 —The normalized resistance of electrically-conductive material  50  is accessed by adaptive temperature controller  10 ; 
         [0037]    3) Step  703 —The temperature of electrically-conductive material  50  is permitted to stabilize at a predetermined temperature, which may be ambient or an elevated temperature close to that at which the electrically-conductive material  50  will be used; 
         [0038]    4) Step  704 —Adaptive temperature controller  10  supplies at least once a voltage or a current to electrically-conductive material  50  and measures the current or voltage conducted therethrough; 
         [0039]    5) Step  705 —The temperature of electrically-conductive material  50  is measured by a temperature sensor  30 ; 
         [0040]    6) Step  706 —The temperature of electrically-conductive material  50  is received by adaptive temperature controller  10 ; 
         [0041]    7) Step  707 —Adaptive temperature controller  10  determines the resistance of electrically conductive material  50  at the temperature received; 
         [0042]    8) Step  708 —Adaptive temperature controller  10  receives an instruction from the operator or computer terminal  80  to alter the temperature of electrically-conductive material  50  to a particular temperature; 
         [0043]    9) Step  709 —Adaptive temperature controller  10  determines the voltage associated with the temperature instruction received from the operator or computer terminal  80 ; 
         [0044]    10) Step  710 —Adaptive temperature controller  10  causes the voltage, or current associated with the temperature instruction to be applied to electrically-conductive material  50 . 
         [0045]    Alternatively, as depicted in  FIG. 8 , calibration of the electrically-conductive material  50  may be accomplished in the following steps: 
         [0046]    1) Step  801 —The temperature of electrically-conductive material  50  is allowed to stabilize, either at ambient temperature or at some elevated temperature close to that at which the electrically-conductive material  50  will be used; 
         [0047]    2) Step  802 —The temperature of electrically-conductive material  50  is measured and output to the adaptive temperature controller  10 ; 
         [0048]    3) Step  803 —The measured temperature of electrically-conductive material  50  is entered as a parameter to the controller unit; 
         [0049]    4) Step  804 —The controller calculates a scale factor for the measured temperature of electrically-conductive material  50  from the relative resistance and preset normalized resistance characteristic; and 
         [0050]    5) Step  805 —The temperature setpoint(s) for the measured temperature of electrically-conductive material  50  are entered. 
         [0051]    The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof.