Patent Description:
Measuring a process fluid characteristic such as pressure, flow rate, or temperature, generally requires the use of a measuring instrument that extends into the process fluid. This extension of a measuring instrument into the process fluid is an invasive measurement in that it requires the process fluid conduit to have an aperture through which the measuring instrument passes. Further, the aperture must be sealed so that the process fluid does not leak or otherwise escape. Further still, measuring instruments that are exposed to the process fluid can be worn or damaged by high velocity process fluid that, in some instance, can be very abrasive.

Patent application <CIT> discloses a pipe diagnostic system that includes a sensor capsule, measurement circuitry and a controller. The sensor capsule is configured to be coupled to an exterior surface of a pipe and has at least one temperature sensitive element disposed therein. The measurement circuitry is coupled to the sensor capsule and is configured to measure an electrical characteristic of the at least one temperature sensitive element and provide an indication of the measurement. The controller is coupled to the measurement circuitry and is configured to obtain a transmitter reference measurement and employ a heat transfer calculation with the transmitter reference measurement and the indication to generate an estimated process fluid temperature. The controller is further configured to obtain an indication of process fluid temperature and provide a pipe diagnostic indication based on a comparison of the estimated process fluid temperature and the obtained indication of process fluid temperature. An additional sensor capsule may be coupled to the exterior surface of the pipe, at a diametrically opposite location.

A process fluid flow system includes a first pipe skin sensor and a second pipe skin sensor. The first pipe skin sensor is disposed to measure an external temperature of a process fluid conduit at a first location on the process fluid conduit. The second pipe skin sensor is disposed to measure an external temperature of a process fluid conduit at a second location on the process fluid conduit. Measurement circuitry is coupled to the first and second pipe skin sensors. A controller is coupled to the measurement circuitry and is configured to identify a process fluid flow condition based on signals from the first and second pipe skin sensors and to output an indication of the process fluid flow condition. The controller is configured to obtain a reference temperature measurement having a fixed thermal relationship relative to the first and second pipe skin sensor, the reference temperature measurement being different than the measured external temperature of the process fluid conduit. The controller is configured to use the process fluid flow condition output and a heat flow calculation to provide a process fluid temperature estimation output that is adjusted based on the process fluid flow condition output.

Embodiments disclosed herein generally provide important process fluid information without requiring a measurement instrument or sensor to pass through a process fluid conduit. Thus, embodiments described herein are generally considered non-invasive in that they do not breach the process. However, based on a plurality of temperature measurements on an external surface of the process fluid conduit, important process fluid parameters can be determined and provided. Examples, include an indication of whether the process fluid is flowing in the conduit and, to some extent, the flow conditions within the process fluid conduit. Further, this process fluid flow information can be provided to a heat flow calculation or other suitable calculation in order to provide an estimate of process fluid temperature within the conduit that is adjusted or otherwise compensated for the determined process fluid flow.

It is common to place a temperature sensor within a thermowell, which is then inserted into the process fluid flow through an aperture in the conduit. However, this approach may not always be practical as described above. Additionally, thermowells generally require a threaded port or other robust mechanical mount/seal in the conduit and thus, must be designed into the process fluid flow system at a defined location. Accordingly, thermowells, while useful for providing accurate process fluid temperatures, have a number or limitations.

More recently, process fluid temperature has been estimated by measuring an external temperature of a process fluid conduit, such as a pipe, and employing a heat flow calculation. This external approach is considered non-invasive because it does not require any aperture or port to be defined in the conduit. Accordingly, such non-intrusive approaches can be deployed at virtually any location along the conduit.

As set forth above, process fluid temperatures can be estimated by measuring an external temperature of a process fluid conduit, such as a pipe, and employing a heat flow calculation. Such systems generally use the pipe skin (external surface) temperature Tskin and a reference temperature Treference and thermal impedance values (relative to the pipe wall and relative to the thermal relationship between the pipe skin location and the reference temperature measurement location) in the heat flow calculation to infer or otherwise estimate the process fluid temperature within the conduit. As the process fluid temperature changes (e.g. rises or falls), the temperature profile of the system will change. This temperature difference between the pipe skin temperature and the reference temperature is a result of heat flowing between the two locations. Coupled with knowledge of the thermal impedance (or other similar constant related to heat flow) between the two locations, the temperature on the inside surface of the process fluid conduit can be estimated. Since the inside surface of the process fluid conduit is in direct contact with the process fluid, this inside surface temperature can be used to estimate the temperature of the process fluid.

The process fluid temperature estimation described above generally relies upon the assumption that the temperature of the inside surface of the conduit is indicative of the entire process fluid cross-section flowing through the conduit. While this assumption is generally accurate for turbulent process fluid flowing through a filled conduit, there are some process fluid flow conditions where the assumption is not as accurate. For example, if the process fluid flow is laminar or partially turbulent, then the assumption is not as correct and the process fluid temperature estimation accuracy could be reduced. Further, if the process fluid conduit is not completely full, or if the process fluid is not flowing through the conduit, the temperature estimation accuracy can also be affected.

<FIG> is a diagrammatic view of a process fluid temperature estimation system not encompassed by the wording of the claims but useful for understanding the present invention. As illustrated, system <NUM> generally includes a pipe clamp portion <NUM> that is configured to clamp around conduit or pipe <NUM>. Pipe clamp <NUM> may have one or more clamp ears <NUM> in order to allow the clamp portion <NUM> to be positioned and clamped to pipe <NUM>. Pipe clamp <NUM> may replace one of clamp ears <NUM> with a hinge portion such that pipe clamp <NUM> can be opened to be positioned on a pipe and then closed and secured by clamp ear <NUM>. While the clamp illustrated with respect to <FIG> is particularly useful, any suitable mechanical arrangement for securely positioning system <NUM> about an exterior surface of a pipe can be used in accordance with embodiments described herein.

System <NUM> includes heat flow sensor capsule <NUM> or a suitable surface sensor that is urged against external diameter <NUM> of pipe <NUM> by spring <NUM>. The term "capsule" is not intended to imply any particular structure or shape and can thus be formed in a variety of shapes, sizes and configurations. While spring <NUM> is illustrated, those skilled in the art will appreciate that various techniques can be used to urge sensor capsule <NUM> into continuous contact with external diameter <NUM>. Sensor capsule <NUM> generally includes one or more temperature sensitive elements, such as resistance temperature devices (RTDs) or thermocouples. Sensors within capsule <NUM> are electrically connected to transmitter circuitry within housing <NUM>, which is configured to obtain one or more temperature measurements from sensor capsule <NUM> and calculate an estimate of the process fluid temperature based on the measurements from sensor capsule <NUM>, and a reference temperature, such as a temperature measured within housing <NUM>, or otherwise provided to circuitry within housing <NUM>.

In one example, the basic heat flow calculation can be simplified into: <MAT>.

In this equation, Tskin is the measured temperature of the external surface of the conduit. Additionally, Treference is a second temperature obtained relative to a location having a thermal impedance (Rsensor) from the temperature sensor that measures Tskin. Treference is typically sensed by a dedicated temperature sensor within housing <NUM>. However, Treference can be sensed or inferred in other ways as well. For example, a temperature sensor can be positioned external to the transmitter to replace the terminal temperature measurement in the heat transfer calculation. This external sensor would measure the temperature of the environment surrounding the transmitter. As another example, industrial electronics typically have onboard temperature measurement capabilities. This electronics temperature measurement can be used as a substitute to the terminal temperature for the heat transfer calculation. As another example, if the thermal conductivity of the system is known and the ambient temperature around the transmitter is fixed or user controlled, the fixed or user controllable temperature can be used as the reference temperature.

Rpipe is the thermal impedance of the conduit and can be obtained manually by obtaining pipe material information, pipe wall thickness information, etc. Additionally, or alternately, a parameter related to Rpipe can be determined during a calibration or calculated and stored for subsequent use. Accordingly, using a suitable heat flux calculation, such as that described above, circuitry within housing <NUM> is able to calculate an estimate for the process fluid temperature (Tcorrected) and convey an indication regarding such process fluid temperature to suitable devices and/or a control room. In the example illustrated in <FIG>, such information may be conveyed wirelessly via antenna <NUM>.

<FIG> is a block diagram of circuitry within housing <NUM> of heat flow measurement system <NUM>, with which embodiments of the present invention are particularly applicable. System <NUM> includes communication circuitry <NUM> coupled to controller <NUM>. Communication circuitry <NUM> can be any suitable circuitry that is able to convey information regarding the estimated process fluid temperature. Communication circuitry <NUM> allows heat flow measurement system <NUM> to communicate the process fluid temperature output over a process communication loop or segment. Suitable examples of process communication loop protocols include the <NUM>-<NUM> milliamp protocol, Highway Addressable Remote Transducer (HART®) protocol, FOUNDATION™ Fieldbus Protocol, and the WirelessHART protocol (IEC <NUM>).

Heat flow measurement system <NUM> also includes power supply module <NUM> that provides power to all components of system <NUM> as indicated by arrow <NUM>. In embodiments where heat flow measurement system <NUM> is coupled to a wired process communication loop, such as a HART® loop, or a FOUNDATION™ Fieldbus segment, power module <NUM> may include suitable circuitry to condition power received from the loop or segment to operate the various components of system <NUM>. Accordingly, in such wired process communication loop embodiments, power supply module <NUM> may provide suitable power conditioning to allow the entire device to be powered by the loop to which it is coupled. In other embodiments, when wireless process communication is used, power supply module <NUM> may include a source of power, such as a battery and suitable conditioning circuitry.

Controller <NUM> includes any suitable arrangement that is able to generate a heat-flow based process fluid temperature estimate using measurements from sensor(s) within capsule <NUM> and an additional reference temperature, such as a terminal temperature within housing <NUM>. In one example, controller <NUM> is a microprocessor. Controller <NUM> is communicatively coupled to communication circuitry <NUM>.

Measurement circuitry <NUM> is coupled to controller <NUM> and provides digital indications with respect to measurements obtained from one or more temperature sensors <NUM>. Measurement circuitry <NUM> can include one or more analog-to-digital converters and/or suitable multi-plexing circuitry to interface the one or more analog-to-digital converters to temperature sensors <NUM>. Additionally, measurement circuitry <NUM> can include suitable amplification and/or linearization circuitry as may be appropriate for the various types of temperature sensors employed.

Temperature sensors <NUM> illustratively include terminal temperature sensor <NUM>, electronics temperature sensor <NUM> and can include other items as well, as indicated by block <NUM>. Electronics temperature sensor <NUM> is coupled to the electronic circuitry of system <NUM> and is used to determine the temperature of the electronics. Typically, electronics temperature sensor <NUM> is used to protect the electronic circuitry from overheating. For example, when the electronics reach a certain temperature, a fan is turned on to reduce that temperature. In one embodiment, electronics temperature sensor <NUM> senses the reference temperature.

<FIG> is a diagrammatic view of a process fluid temperature estimation system in accordance with an embodiment of the present invention. System <NUM> bears some similarities to system <NUM> (shown in <FIG>) and like components are numbered similarly. In particular, system <NUM> includes a sensor capsule <NUM> that is urged into contact with an outer surface of pipe <NUM> via a spring or other suitable mechanical element <NUM>. Additionally, sensor capsule <NUM> is electrically coupled to electronics within housing <NUM> in order to generate a process fluid estimation. However, as shown in <FIG>, three additional temperature sensor capsules <NUM>, <NUM>, and <NUM>, are positioned at different radial locations about pipe <NUM>, and coupled thereto by clamp <NUM>. In the illustrated example, the four sensor capsules (<NUM>, <NUM>, <NUM>, and <NUM>), are disposed at approximately <NUM>° intervals. Accordingly, temperature sensor capsule <NUM> is positioned on a top surface of pipe <NUM> while temperature sensor capsule <NUM> is positioned at a bottom surface thereof. Similarly, sensor capsule <NUM> is positioned at one side of pipe <NUM>, while sensor capsule <NUM> is positioned substantially diametrically opposite sensor capsule <NUM>. Each sensor capsule is electrically coupled to measurement circuitry within transmitter housing <NUM> via respective connection heads, such as connection heads <NUM>, <NUM>, and <NUM> using wires (not shown) or wireless communication. As can be appreciated, each sensor capsule measures pipe skin temperature at its respective location, and, can be used to generate an estimation of the temperature of the internal surface of pipe <NUM> that corresponds with the mounting location of the respective sensor capsule. Controller <NUM> of electronics disposed within transmitter housing <NUM> is programmed, or otherwise configured, to determine process fluid flow conditions based on differences between the various estimations of internal surface temperature at the different positions. Additionally, as noted above with respect to <FIG> and <FIG>, a reference temperature indication may be provided by a reference temperature sensor disposed within transmitter housing <NUM>, or communicated thereto via process communication, such as through antenna <NUM>, or by coupling to an additional temperature sensor. In one embodiment, a temperature sensor is disposed within transmitter housing <NUM> proximate a terminal junction and is couple to a measurement circuitry <NUM>.

By placing two or more sensor capsules at different positions about pipe or conduit <NUM>, system <NUM> can determine if the process fluid is flowing properly for an accurate estimation of temperature of the process fluid to be provided. Additionally, embodiments described herein can also determine if process fluid conduit <NUM> is only partially filled, and/or whether process fluid is flowing through process fluid conduit <NUM>. These additional indications may be provided locally by system <NUM> (such as via a local display) or they may be communicated to a remote device, such as via process communication through antenna <NUM>.

In some embodiments, the mounting orientation for the various sensor capsules is important to know before determining what the sensor characteristics mean. In other words, controller <NUM>, within transmitter housing <NUM>, must know that sensor capsule <NUM> is disposed at a top of process fluid conduit <NUM>, as well as to know that sensor capsule <NUM> is disposed at a bottom side thereof. Similarly, the controller must also know that sensor capsules <NUM> and <NUM> are disposed on opposite sides of the process fluid conduit. With this information, controller <NUM> can generate indications and/or correct for varying process fluid flow conditions in order to provide a more accurate process fluid temperature estimation. The following are examples of flow conditions and the way that they can be identified by controller <NUM>.

If the gradient across the process fluid produces the highest temperature at the top sensor and the bottom temperature sensor is the lowest, and both side sensors provide substantially the same indication, controller <NUM> can determine that no process fluid is flowing through process fluid conduit <NUM>. This is because process fluid is in contact with all internal surfaces of the process fluid conduit and since the fluid is not flowing, the warmer fluid will move to the top of the process fluid conduit and the cooler fluid will remain at the bottom. When such profile occurs, controller <NUM> can provide an indication of a no flow condition relative to the process fluid. Additionally, an average of the temperature of the process fluid can be provided by averaging the top and bottom sensors and comparing that estimation with the estimation provided with the two side sensors. In this example, controller <NUM> could provide an estimation of process fluid temperature, as well as an additional indication that the process fluid is not flowing.

If the bottom and side sensors all provide nearly equal temperature, but the top sensor (sensor capsule <NUM>) is at a temperature that is between ambient and the values of the side and bottom sensor, then controller <NUM> can indicate that greater than <NUM>% of the process fluid conduit is filled. Additionally, when this condition occurs, controller <NUM> can provide an estimation of process fluid temperature based only on the side and bottom sensor capsule values, and may additionally provide an indication that the conduit is filled greater than <NUM>%, but less than <NUM>%.

If the top and side sensors are measured at a temperature that is between ambient and the temperature of the bottom sensor, but the top sensor value is closest to ambient temperature, then controller <NUM> can indicate that the process fluid conduit is filled less than <NUM>% full. Additionally, an indication of the process fluid temperature can be provided based solely on the temperature from bottom sensor capsule <NUM>, and controller <NUM> can provide an indication that conduit <NUM> is filled less than <NUM>% full.

If the top and side sensors are at substantially the same temperature, but bottom sensor capsule <NUM> registers a different value, then controller <NUM> can determine that some material is present on the bottom inside surface of the process fluid conduit. Examples of such material can include moisture, sediment, etc. In such instance, the process fluid temperature estimation can be provided based on the top and side sensors only, and the controller <NUM> can provide an additional indication that material is detected in the bottom inside surface of conduit <NUM>.

<FIG> is a chart showing temperature of different pipe wall locations over time as process fluid flow varies. The data shown in <FIG> is illustrative of a condition when process fluid is not flowing. The data shows a difference between the side mounted sensor, as illustrated at reference numeral <NUM>, and the data from the bottom-mounted sensor as indicated at reference numeral <NUM>. At time t<NUM>, a pump is engaged in order to begin generating process fluid flow. As can be seen, the sensors are exposed to a similar temperature measurement, and their values quickly converge at time t<NUM>.

While the embodiment illustrated with respect to <FIG> shows multiple sensor capsules coupled to a clamping mechanism and each coupled to respective connection heads, it is expressly contemplated that in other implementations multiple sensor points could be built directly into a clamping mechanism and the various sensor wires could be routed into transmitter housing <NUM> and coupled to measurement circuitry <NUM> directly. Additionally, while the embodiments shown with respect to <FIG> utilize a total of four sensor capsules, it is also contemplated that some process fluid variation information may be discernable by using three such sensor capsules (top, bottom, and one side sensor capsule). Additionally, it is also expressly contemplated that additional information may be discernable by using more than four sensor capsules. Further still, it is also expressly contemplated that multiple such systems <NUM> may be located at different longitudinal positions along a process fluid conduit, and that one or both of the controllers within the respective systems may be provided with additional information from the other process fluid estimation system such that variations of temperature flow along the direction of the flow may be analyzed to determine additional process fluid flow conditions and/or corrections in the process fluid estimation system. For example, such information may indicate that process fluid flow is turbulent, laminar, or transitional. Cross-sectional gradients may also be used to detect disturbances to the turbulent flow condition as well as to indicate if the flow is fully developed. Disruptions in the piping such as elbows, valves, or reducers may break up the fully developed turbulent flow. Accurate temperature measurements (as well as flow measurements) often depend on having a fully developed flow condition.

In embodiments that employ additional temperature measurements about the external surface of the process fluid conduit, the linearity of the cross-sectional temperature can be determined. This linearity indication can help detect situations such as scaling, thinning, the presence of sediment, or unwanted water in steam applications and may even provide an indication to take action. This may be important because, in some cases, lack of action may lead to an efficiency impact, pressure build up, or even permanent damage to the process fluid conduit.

Steady state temperature differences, in some cases, may be all that is required to determine actionable states, but by monitoring timing information due to temperature change, a better understanding of a level of scaling or thinning can be provided. Thus, the various process fluid estimations provided by system <NUM> may be stored by an external device, or stored internally and analyzed over time to identify trends indicative of wear or other deterioration in the system.

While embodiments described thus far have generally contemplated the use of sensor capsules having resistance temperature devices (RTDs) in the sensor capsule, any suitable temperature sensing structures or techniques can be used in accordance with embodiments of the present invention. For example, sensor methods such as fiber optics can provide a technique to provide higher density of temperature measurement points about conduit <NUM>.

<FIG> is a block diagram of a method for estimating process fluid temperature within a flow conduit for various flow conditions in accordance with an embodiment of the present invention. Method <NUM> begins at block <NUM> where the skin temperature is measured at multiple locations about the process fluid conduit. For example, the skin temperature may be measured at top, bottom, and side locations, as described above with respect to <FIG>. Next, at block <NUM>, any differences between the various temperature measurements are analyzed in order to identify particular flow conditions. Examples of flow conditions, and the differences in measured temperatures that such flow conditions generate have been described above. It is also expressly contemplated that the degree to which measurement differences (or equality) are required can be set as user-selected thresholds, or can be entered programmatically via the manufacturer during the assembly or building of the process fluid temperature estimation system. Examples of various conditions that may be identified based on the differences in the measured temperatures include a <NUM>% full, flowing process fluid conduit, as indicated at reference numeral <NUM>; a no flow condition as indicated at reference numeral <NUM>; a greater than <NUM>% filled, flowing condition, as indicated at reference numeral <NUM>; a less than <NUM>% filled, flowing condition, as indicated at reference numeral <NUM>, and the presence of material at the bottom inside surface of the process fluid conduit as indicated at reference numeral <NUM>. As can be appreciated, if additional sensor capsules are disposed about the process fluid conduit (such as spaced at <NUM>° intervals), then additional levels of process fluid conduit filling (such as <NUM>% and <NUM>%) may also be provided. Next, at block <NUM>, the process fluid flow condition is provided as an output and is used to adjust or otherwise compensate a process fluid temperature estimate. As described above, in certain instances, the process fluid temperature estimation may be based on data from less than all of the available sensors. For example, if the process conduit is filled less than <NUM>%, then the process fluid estimation will be based solely on the skin temperature as sensed by the bottom sensor capsule (<NUM> as shown in <FIG>). In contrast, if the process fluid flow condition indicates that material (such as sediment) is disposed proximate the bottom surface of process fluid conduit <NUM>, but that the process fluid conduit is otherwise full, then the process fluid temperature estimation will be based on the top and side sensor capsule measurements, and will omit the value received from the bottom sensor capsule. Accordingly, an adjusted process fluid temperature estimation is provided based on the identified process fluid flow condition. Next, at block <NUM>, the system may optionally report the identified process fluid flow condition.

Claim 1:
A process fluid flow system (<NUM>) comprising:
a first pipe skin sensor (<NUM>) disposed to measure an external temperature of a process fluid conduit (<NUM>) at a first location on the process fluid conduit;
a second pipe skin sensor (<NUM>, <NUM>, <NUM>) disposed to measure an external temperature of the process fluid conduit at a second location on the process fluid conduit;
measurement circuitry (<NUM>) coupled to the first and second pipe skin sensors; and
a controller (<NUM>) coupled to the measurement circuitry and configured to identify a process fluid flow condition based on signals from the first and
second pipe skin sensors and to output an indication of the process fluid flow condition, wherein
the controller is configured to obtain a reference temperature measurement having a fixed thermal relationship relative to the first and
second pipe skin sensor, the reference temperature measurement being different than the measured external temperature of the process fluid conduit, and wherein the controller is configured to use the process fluid flow condition output and a heat flow calculation to provide a process fluid temperature estimation output that is adjusted based on the process fluid flow condition output.