Patent Publication Number: US-6986602-B2

Title: Temperature measurement device

Description:
RELATED APPLICATIONS 
   This application is a continuation-in-part of U.S. patent application Ser. No. 10/400,330, entitled “Pressure Gauge Having Dual Function Movement Plate” and filed on Mar. 27, 2003. 

   TECHNICAL FIELD 
   This description relates to temperature measurement, and, in particular, to temperature measurement devices. 
   BACKGROUND 
   Temperature measurement gauges are commonly found in many commercial and industrial applications. Such devices typically may use bimetallic coils or gas-filled Bourdon tubes to sense temperature and drive a shaft connected to a pointer. The pointer is disposed opposite a dial having temperature indicia thereon. Thus, a technician may read the temperature at the gauge. 
   Furthermore, a variety of devices need temperature measurement for proper operation. For example, many volumetric gas flow meters require temperature to properly register the amount of gas passing therethrough. Such devices often use mechanical techniques to perform the temperature compensation. 
   SUMMARY 
   In one general aspect, a device for measuring temperature includes a housing, a temperature-responsive element, and an inductive assembly. The temperature-responsive element is supported relative to the housing and is operable to sense temperature and to move in response to temperature changes. A first inductive assembly component is fixed relative to the housing, and a second inductive assembly component is operatively and movably positioned relative to the first inductive assembly component. The second inductive assembly component is driven by movement of the temperature-responsive element, and the movement of the second inductive assembly component relative to the first inductive assembly component generates a change in a local eddy current pattern corresponding to the sensed temperature. In particular implementations, a current at a particular point in a sensing circuit is proportional to the temperature changes causing the temperature-responsive element to move. 
   Certain implementations may include a circuit board including the first inductive assembly component. The circuit board may include a processor responsive to generated eddy current patterns to generate a signal representative of sensed temperature. In generating the signal, the processor may determine the movement of the temperature-responsive element based on the generated eddy current patterns and associate the movement with a temperature to generate the signal. 
   In particular implementations, the temperature-responsive element includes a first portion generally fixed relative to the housing and a second portion displaceable relative to the first portion, wherein the second portion drives the second inductive assembly component. The device may also include a visual indicator movably positioned relative to the housing and driven by the second portion of the temperature-responsive element to indicate temperature. 
   In some implementations, the second inductive assembly component includes a gear with a pitch ratio larger than that of the temperature-responsive element. The gear may include a protuberance that operates as an inductive target in the inductive assembly. 
   In another general aspect, a device for measuring temperature includes a coil operable to displace in response to changes in temperature of a medium for which a temperature is to be sensed and a rotatable shaft driven by the temperature-responsive coil. The device also includes an inductive target displaceable by the rotatable shaft and an inductor positioned relative to the inductive target such that displacement of the inductive target by the rotatable shaft generates a change in a local eddy current pattern corresponding to the temperature to be sensed. The inductive target may be rotatable with the rotatable shaft and may include a plurality of radial features extending transversely relative to a longitudinal axis of the rotatable shaft. The coil may be a bimetallic coil including a proximal end driving the rotatable shaft. 
   Certain implementations may include a circuit board including an opening through which the rotatable shaft extends, wherein the circuit board includes the inductor. Additionally, the inductive target may rotate in a plane generally parallel to the circuit board. 
   Particular implementations include a pointer coupled to the rotatable shaft and an indicia plate fixed relative to the pointer such that the pointer rotates in a plane generally parallel to the indicia plate to indicate temperature. The inductive target may be positioned between the indicia plate and a circuit board. 
   Some implementations may include a microprocessor responsive to generated eddy current patterns to generate a signal representative of sensed temperature. The microprocessor may determine the movement of the shaft based on generated eddy current patterns and associate the movement with a temperature to generate the signal. 
   In certain implementations, the inductive target includes a gear with a pitch ratio larger than that of the rotatable shaft. The gear may include a protuberance that operates as the inductive target. The pitch ratio of the gear may be approximately fifteen times larger than that of the rotatable shaft. 
   In another general aspect, temperature measurement may be facilitated by a process performed at a temperature measurement device. The process may include sensing a temperature change, converting the sensed temperature change to mechanical movement, and converting the mechanical movement to an electrical signal representing the movement by induction. The process may also include detecting the electrical signal and determining the mechanical movement based on the electrical signal. 
   In particular implementations, converting the sensed temperature change to mechanical movement may include rotating a shaft in response to the sensed temperature change. 
   In some implementations, converting the mechanical movement to an electrical signal representing the movement by induction includes moving an inductive target relative to an inductor, the movement generating a change in an eddy current pattern. In certain implementations, moving an inductive target includes driving the target with a gear that has a pitch ratio less than that of the inductive target. 
   Particular implementations may include determining a temperature associated with the mechanical movement. Additionally, these implementations may include generating a signal representing the temperature. Determining a temperature associated with the mechanical movement may include determining the amount of mechanical movement. 
   In another general aspect, a device for measuring temperature includes a transducer, an inductive target, a circuit board, and a visual indicator. The transducer includes a temperature-responsive, bimetallic coil and a rotatable shaft. The coil is positioned to displace in response to changes in temperature of a medium for which a temperature is to be sensed. The rotatable shaft is coupled to a second end of the coil and is driven by the coil. The inductive target is coupled to the shaft and rotated thereby. The target includes a plurality of radial features extending transversely relative to a longitudinal axis of the rotatable shaft. The circuit board includes an opening through which the rotatable shaft extends and an inductor positioned relative to the inductive target such that rotation of the inductive target by the shaft generates a change in the local eddy current pattern representing the shaft rotation. The circuit board also includes a microprocessor responsive to generated eddy current patterns to determine the rotation of the shaft, to associate the rotation with a temperature, and to generate an electrical signal representative of sensed temperature. The visual indicator includes an indicia plate generally parallel to the circuit board and a pointer fixed to the rotatable shaft relative to the indicia plate to indicate temperature, wherein the inductive target is positioned between the indicia plate and the circuit board and the pointer rotates in a plane generally parallel to the indicia plate. 
   Details of one or more implementations are set forth in the accompanying drawings and the description below. Other features and advantages may be apparent from the description and drawings, and from the claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A-B  illustrate an example temperature measurement device. 
       FIG. 2  shows a top view an example inductive target. 
       FIG. 3  shows a perspective view of a sheath for protecting a temperature-responsive element. 
       FIG. 4  shows a perspective view of another example temperature measurement device. 
       FIGS. 5A-B  illustrate another example temperature measurement device. 
       FIG. 6  is a flow chart illustrating a process at a temperature measure device. 
   

   The drawing figures are not necessarily to scale, and, in certain views, parts may have been exaggerated for purposes of clarity. 
   DETAILED DESCRIPTION 
   Temperature measurement devices include devices operable to sense a temperature to be measured, convert the temperature to a mechanical movement, convert the mechanical movement to an electrical signal, and detect the electrical signal, where the electrical signal represents the sensed temperature. Thus, temperature measurement devices may produce electrical signals that represent temperature. Other temperature measurement devices, however, may have a variety of other features. 
     FIGS. 1A-B  illustrate an example temperature measurement device  100 . A sectioned, perspective view of device  100  is shown in  FIG. 1A , and a sectioned, side elevated view of device  100  is shown in FIG.  1 B. 
   Device  100  includes a temperature-responsive assembly  110 , a visual indicator assembly  130 , and a movement-indicative signal generator  140 . In operation, temperature-responsive assembly  110  generates mechanical movement in response to temperature changes. Based on this movement, visual indicator assembly  130  provides a visual indication of the temperature, and signal generator  140  produces an electrical signal representing the movement. Because the electrical signal represents the movement, and the movement is produced by the sensed temperature, the electrical signal corresponds to the sensed temperature. 
   In more detail, temperature-responsive assembly  110  includes an elongated housing  112  having a first end  114  and a second end  116 . At first end  114 , assembly  110  includes a stepped-down-diameter plug  118  that is coupled (e.g., by welding) to one end of a bimetallic, spiral-wound coil  120 . Plug  118  may also be sealingly engaged (e.g., by welding) with housing  112 . At its other end, coil  120  is coupled (e.g., by welding) to a rotatable shaft  122 . Coil  120  displaces in response to temperature changes near first end  114  and causes shaft  122  to rotate, a type of mechanical movement. Thus, coil  120  is a transducer that converts temperature to mechanical movement. The medium for which coil  120  is sensing temperature may be a solid, a liquid, or a gas. 
   Assembly  110  also includes a guide  124  that secures shaft  122 . As a multitude of transducer lengths are commonly seen in various applications, guide  124  may include multiple components properly spaced to minimize drag on shaft  122 . 
   Visual indicator assembly  130  includes a pointer  132  and a dial  134 . Pointer  132  is coupled to shaft  122  to rotate when the shaft rotates. Dial  134 , which is one example of an indicia plate, is positioned relative to pointer  132  such that rotation of shaft  122  positions pointer  132  opposite temperature indicating indicia on the face of dial  134 . This provides a visible indication of temperature at device  100 . 
   Movement-indicative signal generator  140  includes an inductive target  142  and a printed circuit board (PCB)  144 . Inductive target  142  is coupled to shaft  122  to rotate with the shaft. In particular implementations, target  142  is a light-weight, metallic (e.g., stainless steel or aluminum) member rigidly attached (e.g., by welding) to shaft  122 . 
   PCB  144  is fixed in position relative to shaft  122 , behind dial  134 . PCB  144  may be coupled to assembly  110  to minimize case strains, which may affect signal level. PCB  144  may be coupled to assembly  110  by press fit, adhesive, or other appropriate technique. 
   PCB  144  includes an aperture  146  through which housing  112 , and, hence, shaft  122 , pass. PCB  144  also includes inductors  148 , which may, for example, be inductive coils, positioned to electrically respond to the movement of inductive target  142 , target  142  and inductors  148  forming an inductive assembly. In particular implementations, inductors  148  may be cooperating inductive coil elements. These elements may be discrete or printed directly onto PCB  144 . Target  142  and inductors  148 , along with an impressed current from the PCB, generate a change in an eddy current pattern in response to the movement of target  142 . Eddy current patterns may be unique for every for each position corresponding to a different temperature value being sensed. PCB  144  additionally includes detecting circuitry  150  to detect the eddy current patterns and a processor  152  to track the movement of the target, and, hence, the shaft, and to determine the sensed temperature based on the movement. Suitable eddy current detecting circuitry is available from LZT Technology of San Bernadino, Calif. Processor  152  may, for example, be a microprocessor. 
   In  FIG. 1B , it can be seen that target  142  is in close proximity to PCB  144 . In this implementation, the distance between target  142  and PCB  144  is approximately 0.025 inches. In other implementations, however, target  142  does not have to be in close proximity to PCB  144 . In general, target  142  may be at any distance as long as it can inductively interact with inductors  148 . 
   As target  142  begins to rotate in response to rotation of shaft  122 , the rotation of target  142  relative to PCB  144  causes the eddy current pattern generated by a predetermined web of target  142  and a facing coil element instance to change. Processor  152  accumulates these changes, which are analogous to temperature. To accumulate the rotations, the processor may understand where the target starts relative to the target position and count notches (i.e., pulses) up and down scale. The required resolution of the output signal determines the number of web/space pairs required in the target. 
   Coupled to PCB  144  are a pair of wires  158 . Wires provide loop power to the electronic components of PCB  144 , such as processor  152 . In other implementations, PCB  144  may be externally powered. 
   The temperature measurement device illustrated by  FIG. 1  may have a variety of features. For example, the device may allow a relatively small inductive target  142  to be used for signal generator  140 . For instance, the target may have a mass moment of inertia on the order of 3.5×10 −5  in-lb, which may, for example, be achieved with a 0.800 inch diameter×0.007 inch thick aluminum disc with fifty percent gutting. Having a relatively small inductive target may be important because, in many implementations, the mechanical power generated by assembly  110  is small. Thus, the temperature may be measured without significantly interfering with the mechanical operation of assembly  110 . As another example, target  142  may allow inductive current generation across a wide angular range (e.g., three-hundred degrees). This may be important for implementations where pointer  132  has a wide angular range. As a further example, the signal generator may be used without the visual indicator assembly. Thus, blind temperature measurement devices are feasible. As an additional example, the device may be readily manufactured. 
   Temperature measurement device  100  may have a variety of uses. For example, it may be used as a temperature monitoring and reporting device. However, it may also be incorporated into other devices that require temperature measurements. For example, device  100  may be incorporated into a temperature correction device adapted to be self-contained in a conventional fluid meter of the fixed or constant displacement type. 
   In particular implementations, a temperature measurement device may have less, more, and/or a different arrangement of components than device  100 . For example, assembly  110  may include a low-friction bearing arrangement that supports rotatable shaft  122 . In this arrangement, guide  124  may secure shaft  122  in the bearing. Alternatively, a bushing could be used. As a further example, shaft  122  may be driven by a temperature responsive element other than a bimetallic coil. For instance, the shaft may be driven by a gas-filled Bourdon tube connected to a line and remote-sensing bulb assembly. As an additional example, the inductive target may be directly attached to pointer  132 . As another example, a digital indicator may be used in place of the illustrated analog indicator. In other implementations, though, a visual indicator may not be used. As a further example, shaft  122  may drive PCB  144  rather than inductive target  142 . As another example, PCB  144  may include a wireless transmitter to send temperature data to a remote station. The transmitter could send data using radio frequency (RF), infrared (IR), or any other appropriate technique. Structure may also be provided in PCB  144  to adjust offset and gain of the signal in known fashion. 
     FIG. 2  illustrates an example inductive target  200 . Target  200  has a hub  210  from which a series of webs  220  radially project. Between webs  220  are spaces  230 , such that webs  220  and spaces  230  alternate. The total number of webs  220  and spaces  230  is related to the required rotation of a driving shaft. 
   In operation, a driving shaft causes target  200  to move relative to inductors on a PCB, which causes the eddy current pattern between a web and facing coil element instance to change. Thus, each web/space pair produces a pulse under shaft rotation, assuming they are opposite a coil element. A processor accumulates these pulses and, thus, can determine the position of the driving shaft. The processor may accumulate these rotations, which are analogous to temperature. 
     FIG. 3  illustrates a sheath  300  for protecting a temperature-responsive element such as a bimetallic coil against injury and improving performance. Sheath  300  is formed in a tubular configuration for connection to a tubular connector flange of a temperature-responsive assembly, and includes a plurality of a parallel, elongated slots  310  through which fluid (i.e., liquid, gas, or a combination thereof) may flow in contact with a temperature-responsive element. In some implementations, sheath  300  is removable, which could make it useful for applications where aperture size varies. 
     FIG. 4  illustrates an example temperature measurement device  400 . Device  400  includes a temperature-responsive assembly  410 , an inductive assembly  420 , a visual indicator assembly  430 , and a sealing assembly  440 . In operation, temperature-responsive assembly  410  produces mechanical motion in response to temperature changes. The mechanical motion drives: 1) inductive assembly  420  such that it produces an electrical signal corresponding to the sensed temperate; and 2) visual indicator assembly  430  such that it produces a visual indication of the sensed temperature. Sealing assembly  440  protects visual indicator assembly  430 . 
   In more detail, temperature-responsive assembly  410  includes a stem  412 , a coil  414 , a shaft  416 , and a process connection  418 . Stem  412  interfaces with the fluid for which the temperature is to be sensed. Located inside stem  412  are coil  414 , which may, for example, be a bimetallic, spiral-wound coil, and shaft  416 . Stem  412  may or may not sealingly protect coil  414  and shaft  416 . Coil  414  is coupled to shaft  416  and rotates in response to temperature changes. The rotation of coil  414  causes shaft  416  to rotate. Shaft  416  passes through process connection  418  for interaction with other parts of device  400 . Process connection  418  provides a coupling between the fluid process to be measured (e.g., fluid in a pipe) and device  400  so that device  400  is not dislodged due to the movement and/or pressure of the fluid being measured. 
   Inductive assembly  420  includes a PCB  422  and an inductive target  426 . PCB  422  includes an aperture  423  through which shaft  416  passes and inductive coils  424  around aperture  423 . PCB  422  is fixed in position relative to the shaft. Inductive target  426 , on the other hand, is coupled to the shaft such that it rotates therewith. Thus, when shaft  416  rotates, target  426  rotates relative to PCB  422 . This rotation interrupts inductive coils  424 , which generates an electrical signal representative of the shaft movement, and, hence, corresponding to the temperature, as discussed previously. 
   Visual indicator assembly  430  includes a housing  431  to protect the movable components of the assembly. Assembly  430  also includes a bushing  432  that captures shaft  416  and a bearing  433  that couples to the end of the shaft to allow it to rotate. Assembly  430  additionally includes a gear  434  coupled to bushing  432  and a dial  435  coupled to the gear by screws  436 . Dial  435  includes a dial face  435   a  and a dial ring  435   b . Pressure demarcations may be on face  435   a  and/or ring  435   b . Coupled to bushing  433  is a pointer  437 . Pointer  437  rotates with shaft  416  to visually indicate the temperature. Assembly  430  additionally includes a pinion  438  and an adjuster  439 . Pinion interfaces with gear  434  so that dial  435  may be adjusted by the manipulation of adjuster  439 . 
   Sealing assembly  440  protects components of visual indicator assembly  430 . Sealing assembly  440  includes a gasket  442 , a window  444 , and a ring  446 . To seal assembly  430 , gasket  442  is compressed between housing  431  and window  444 . The compression is maintained by mating ring  446  with housing  431 . In particular implementations, sealing assembly  440  may hermetically seal the visual indicator assembly components inside housing  431 . 
     FIGS. 5A-B  illustrate an example temperature measurement device  500 .  FIG. 5A  shows a top view of temperature measurement device  500 , and  FIG. 5B  shows a perspective view temperature measurement device  500 . 
   Device  500  includes a temperature responsive coil  510  that drives a shaft  520 . Coupled to shaft  520  is a driving gear  530 . Driving gear  530  may be made of any suitable material (e.g., metal or plastic) and may be relatively small and lightweight. Device  500  also includes a driven gear  540 . In general, driven gear  540  has a pitch radius that is larger than that of driving gear  530 . In the illustrated implementation, for instance, the pitch radius of driven gear  540  is approximately fifteen times larger than that of driving gear  530 , resulting in a gear ratio of approximately 15:1. Driven gear  540  is supported by a pillar  550 . Pillar  550  is firmly affixed to a printed circuit board  560 , which has inductive coils  562  printed directly thereon. PCB  560  also includes an aperture  564  through which shaft  520  passes. PCB  560  may be rigidly attached to a tube such as tube  112  in FIG.  1 A and/or otherwise isolated from external case strains. 
   Driven gear  540  includes a tooth section  542  that meshes with driving gear  530 . Driven gear  540  also includes a protuberance  544  that acts as an inductive target for an inductive assembly. If driven gear  540  is made of plastic then at least one face of protuberance  544  should be overlaid with a layer of sheet metal (e.g., aluminum) to act as a target cooperatively functioning with coils  562  to control the eddy current patterns. Driven gear  540  further includes apertures  546  to reduce the gear&#39;s mass moment of inertia, which allows coil  510  to exert less torque to move shaft  520 . 
   Using driving gear  530  and driven gear  540  serves to reduce the rotation of the inductive target (i.e., protuberance  544 ) to a relatively small value. For example, in the illustrated implementation, the rotation is reduced to approximately 18 degrees when the required pointer rotation is 270 degrees. Another feature is that the motion of the target is almost linear in nature. This means that the electronic circuitry may only have to handle a single, “lengthened” pulse; thus, the circuitry may not have to count pulses. Hence, this implementation may or may not need a processor in the circuit design. 
     FIG. 6  illustrates a process  600  at a temperature measurement device. Process  600  may be implemented by a temperature measurement device similar to device  100  in FIG.  1 . 
   The process begins with waiting to sense a temperature change (decision block  604 ). Temperature may be sensed, for example, by a bimetallic coil or a gas-filled Bourdon tube. Once a temperature change is sensed, the process continues with converting the sensed temperature change to mechanical movement (function block  608 ). The temperature may, for example, be converted to mechanical movement by a spiral wound, bimetallic coil that causes a shaft to rotate. 
   The process also calls for converting the mechanical movement to a visual indication of temperature (function block  612 ). The conversion may, for example, be accomplished by a pointer coupled to a rotatable shaft and having an accompanying dial. 
   The process additionally calls for converting the movement to an electrical signal representing the movement (function block  616 ). This may, for example, be accomplished by an inductive target driven by the mechanical movement and inductive coils positioned to electrically respond to the target, where eddy current patterns change as the inductive target moves. 
   After the electrical signal has been generated, the process calls for detecting the electrical signal (function block  620 ) and determining the mechanical movement based on the electrical signal (function block  624 ). Determining the mechanical movement may include determining the direction and magnitude of the movement and may be accomplished by comparing the electrical signal to previously received electrical signals to determine a change in amplitude levels. 
   The process also calls for determining a temperature associated with the mechanical movement (function block  628 ). This may, for example, be accomplished by an using an algorithmic association of position and temperature, by consulting a table containing mechanical position and temperature associations, or by any other appropriate technique. The process additionally calls for generating a signal representing the temperature (function block  632 ). The signal may be in analog or digital format and may be transmitted using wireline or wireless techniques. If in analog form, the signal may be between 4-20 mA. The process then calls for again waiting to sense a temperature change. 
   Although  FIG. 6  illustrates a process at a temperature measurement device, other processes at a temperature measurement device may contain less, more, and/or a different arrangement of operations. For example, certain processes may not call for converting the mechanical movement to a visual indication. As another example, the conversion of mechanical movement to a visual indication and the conversion of mechanical movement to an electrical signal may be accomplished simultaneously. As a further example, the operations expressed by functions blocks  620 - 632  may be eliminated. As an additional example, some processes may have operations that depend on the determined temperature. For instance, temperature check rates and exception reporting may be adjusted based on the determined temperature. Furthermore, communication rates regarding the sensed temperature may be adjusted based on the determined temperature. For example, as determined temperature rises or falls below a threshold, communication rates regarding the determined temperature may be increased and/or decreased. 
   While particular implementations and applications have been illustrated and described, it is to be understood that the invention is not limited to the precise construction and compositions disclosed herein and that various additions, deletions, substitutions, and/or modifications will be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims.