Patent Description:
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 in that the process fluid may have a very high temperature, be very corrosive, or both. 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. From prior art, methods and systems are known to measure and monitor fluid temperature of process fluids, e.g. from <CIT> or <CIT> or <CIT> or <CIT>.

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.

A process fluid temperature estimation system includes a mounting assembly configured to mount the process fluid temperature estimation system to an external surface of a process fluid conduit. A sensor capsule has at least one temperature sensitive element disposed therein. Measurement circuitry is coupled to the sensor capsule and configured to detect an electrical characteristic of the at least one temperature sensitive element that varies with temperature and provide sensor capsule temperature information. A controller is coupled to the measurement circuitry and is configured to obtain a reference temperature and employ a heat transfer calculation with the reference temperature, the sensor capsule temperature information and the known thermal conductivity of the process fluid conduit to generate an estimated process fluid temperature output. The reference temperature is obtained from a reference temperature source selected from the group consisting of: a terminal temperature sensor, process communication, an electronics temperature sensor, an external ambient temperature sensor, and an estimation based on known thermal properties.

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 in the heat flow calculation to infer or otherwise estimate the process fluid temperature within the conduit. This feature generally requires the thermal conductivity to be known from the process fluid to the transmitter terminals. Thus, such systems may require a transmitter terminal temperature sensor to generally be connected or as close as possible to the process fluid temperature transmitter terminals or the "cold end" of the pipe skin sensor. This relationship provides a better correlation between the measurement points in the system (Tskin, Treference). As the process temperature rises, typically the temperature profile will change in the system causing the cold end of the sensor to rise slightly. This change is important to understand to provide a proper inference of the process temperature. For ambient and process temperatures that change slightly or not at all, direct measurements are not necessary between the skin temperature and another temperature point in the mounted assembly for a reasonable correction of the process temperature.

<FIG> is a diagrammatic view of a heat flow measurement system with which embodiments of the present invention are particularly applicable. 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> 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). 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 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 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.

According to one embodiment, system <NUM> also includes a variety of different logic components as indicated by blocks <NUM>-<NUM>. Each logic component provides a variety of different functions, that can be performed by controller <NUM>. Backup mode logic <NUM> monitors the status of terminal temperature sensor <NUM>, and in the event of sensor failure or malfunction, turns on a backup mode. That is, a mode where the reference temperature is received from a source other than terminal temperature sensor <NUM>. This is an example of controller logic determining the occurrence of a reference temperature switchover event. This way in the event of sensor failure or malfunction the measurement point does not have to go completely off-line. In another example, controller <NUM> may receive a commend, either through local technician interaction with system <NUM> or via process communication, to switch to an alternate reference temperature source. Other suitable conditions for determining the occurrence of a reference temperature switchover event can be practiced in accordance with embodiments described herein.

During normal operation, information can be learned, by learning logic <NUM>, about the correlation between the conduit skin temperature and terminal temperature measurements. If one or the other measurement points fail (terminal temperature or skin temperature sensors), the learned correlation can be applied as an additional backup mode option.

Estimation logic <NUM> can calculate the reference temperature with the measured skin temperature changes, if the thermal conductivity of the system is known and/or the ambient temperature around the transmitter is fixed or controlled.

<FIG> is a diagrammatic view of a sensor capsule with which embodiments of the present invention are particularly applicable. Sensor capsule <NUM> generally includes a cylindrical side wall <NUM> with an endcap <NUM> coupled thereto. In one example, endcap <NUM> is formed of silver. One or more RTD elements <NUM> are disposed proximate endcap <NUM> and are provided in thermal communication with endcap <NUM> via thermal grease <NUM>. Conductors <NUM> electrically couple RTD element(s) <NUM> to measurement circuitry within housing <NUM>. In one embodiment, element <NUM> is formed in accordance with thin-film RTD technology. Thin-film RTDs are generally considered to be very rugged and generally low cost. A thin-film element is typically manufactured by coating a small ceramic chip with a very thin (such as. <NUM> inch) film of a temperature-sensitive metal (such as platinum) and then laser cutting or chemical or chemical etching a resistance path in the metal film.

<FIG> is a flow diagram of a method of estimating and providing a process fluid temperature based on heat flow in accordance with an embodiment to the present invention. Method <NUM> begins at block <NUM> where a temperature is measured from an external diameter of a process fluid conduit, such as pipe <NUM>. Next, at block <NUM>, a stored thermal conductivity of the conduit is obtained. This step can be preformed by accessing local memory of controller <NUM> of the system, or by communicating with an external device, such as a process controller, to receive information indicative of the thermal conductivity of the conduit.

Next, at optional block <NUM>, a referenced temperature is obtained. This reference temperature may be obtained in a variety of ways. For example, the reference temperature may be obtained via receiving process communication indicating the reference temperature, as indicated at block <NUM>. Alternately, at block <NUM>, the reference temperature is measured by the system. In one example, this measurement is a temperature measurement at a location within housing <NUM>, such as at a terminal block. As another example, a reference temperature can be obtained via electronics temperature sensors, as indicated by block <NUM>. However, these are only examples and the measurement can be obtained from any location having a relatively fixed thermal relationship with respect to external diameter <NUM> of process fluid conduit <NUM>. Via this fixed thermal arrangement, the flow of heat from the process fluid conduit to the reference temperature location is fixed and thus follows the heat flow calculation described above.

Additionally, the reference temperature may be obtained by an external ambient temperature sensor, as indicated at block <NUM>. For example, if the process fluid conduit is located within a climate-controlled interior of a facility, the nominal temperature of the climate (such as <NUM> degrees Fahrenheit) can be used for the reference temperature.

Further, the reference temperature, in well understood systems, may be estimated, as indicated by block <NUM>. For example, learning logic <NUM> determines a pattern between the skin temperature and another variable, indicative of a relationship to a reference temperature. Then estimation logic <NUM> uses this pattern to determine a reference temperature.

At block <NUM>, the measured temperature of the conduit skin, thermal conductivity of the conduit, and reference temperature, are applied to a heat flow calculation, such as that set forth above, to calculate an estimate of process fluid temperature. Finally, at block <NUM>, the estimated process fluid temperature is output. In one example, the output is communicated over a process communication loop in accordance with a process communication protocol, such as that set forth above.

Claim 1:
A method of estimating process fluid temperature (Tcorrected) within a conduit (<NUM>) by a process fluid temperature estimation system (<NUM>), the method comprising:
obtaining a conduit temperature (Tskin) proximate a process conduit (<NUM>) by a heat flow sensor capsule (<NUM>);
obtaining thermal conductivity information (Rpipe) relative to the process conduit (<NUM>);
obtaining a reference temperature (Treference) from a transmitter terminal temperature sensor (<NUM>); and
storing the thermal conductivity information (Rpipe) in the process fluid temperature estimation system (<NUM>) to use in a heat transfer equation for estimating process fluid temperature, (Tcorrected) based at least on the conduit temperature (Tskin), the reference temperature (Treference), and the thermal conductivity (Rpipe),
the method being characterized in that it further comprises the following steps:
determining if a reference temperature switchover event has occurred; and
based on the determination, obtaining a second reference temperature (Treference) from a second source,
wherein the reference temperature switchover event is a malfunction of the transmitter terminal temperature sensor (<NUM>).