Patent Description:
Industrial processes are used in the manufacturing and transport of many types of materials. In such systems, it is often required to measure different parameters within the process. One such parameter is a temperature of the process medium.

Industrial process temperature transmitters typically measure the temperature of the process medium using a temperature sensor and communicate the measured temperature to a desired location, such as a control room. Such temperature transmitters typically isolate the temperature sensor from the process medium to protect the temperature sensor and associated electronics from process conditions that may damage the sensor, and/or adversely affect the temperature measurement.

Some temperature transmitters house the temperature sensor within a thermowell. The temperature sensor is installed in the thermowell through an open end. A sealed end of the thermowell is inserted into the process medium. This allows the temperature sensor to measure the temperature of the process medium through the thermowell without being directly exposed to the process medium. Thus, the temperature sensor may be inserted into the process medium while providing protection from harsh conditions that could damage the sensor.

Other temperature transmitters measure the temperature of the process medium while avoiding any intrusion on the process. Such non-intrusive temperature transmitters typically position a temperature sensor in contact with the exterior surface of a process vessel wall containing the process medium, such as the exterior surface of a pipe containing the process medium. The temperature sensor measures the temperature of the process medium through the process vessel wall.

Temperature transmitters experience a delay in the detection of a change in the temperature of the process medium that is caused, at least in part, to the need to communicate the temperature through the wall of the thermowell or the wall of the process vessel. For some applications, such as those where temperature measurement timing is critical for process management, such a delay in the temperature measurement may be unacceptable. A known process temperature transmitter and a method for measuring a temperature of a process medium (<CIT>) comprises a temperature sensor. The measured temperature values are stored in a memory and are evaluated by forming average values. Gradients of a process of the sensor signals are determined by forming a difference of two of the values or of two average values and by multiplication of the difference with a correction factor. The multiplication result is added to the currently stored measurement value to obtain a corrected measurement value. Another known process temperature transmitter and method for measuring a temperature of a process medium (<CIT>) comprises a measuring device for determining the temperature of a medium in a tube. A temperature sensor is arranged on the outside of the tube wall, measuring the process temperature. The device connects differentiators, capable of determining derivatives of the progression over time of the temperature registered by the temperature sensor with multipliers. The multipliers multiply the derivatives by factors which are values for the time constant of the heat transfer through the tube wall. An adder is contained at the output of the multipliers and output corrected temperature values. In order to obtain the factors for the multipliers, a separate measurement setup is used. Therefore, a test piece of the tube is placed in a test tank in which there is a medium. The interior of the tube does not contain the medium. In this empty interior, the temperature sensor is coupled to the inside of the wall of the tube. In order to monitor the actual temperature of the medium, an extra temperature-dependent resistor is arranged within the medium and outside the tube, close to the wall, as an additional reference temperature sensor.

Embodiments of the present disclosure relate to industrial process temperature transmitters for measuring a temperature of a process medium according to claim <NUM>, and methods for measuring a temperature of a process medium using an industrial process temperature transmitter according to claim <NUM>.

Embodiments of the present disclosure are described more fully hereinafter with reference to the accompanying drawings. Elements that are identified using the same or similar reference characters refer to the same or similar elements.

Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it is understood by those of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, circuits, systems, networks, processes, frames, supports, connectors, motors, processors, and other components may not be shown, or shown in block diagram form in order to not obscure the embodiments in unnecessary detail.

It will be understood that when an element is referred to as being "connected," "coupled," or "attached" to another element, it can be directly connected, coupled or attached to the other element, or it can be indirectly connected, coupled, or attached to the other element where intervening or intermediate elements may be present. In contrast, if an element is referred to as being "directly connected," "directly coupled" or "directly attached" to another element, there are no intervening elements present. Drawings illustrating direct connections, couplings, or attachments between elements also include embodiments, in which the elements are indirectly connected, coupled, or attached to each other.

Thus, a first element could be termed a second element without departing from the teachings of the present disclosure.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art relating to the present disclosure.

Embodiments of the present disclosure may also be described using flowchart illustrations and block diagrams. Although a flowchart may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. A process is terminated when its operations are completed, but could have additional steps not included in a figure or described herein.

Embodiments of the present disclosure are directed to compensating industrial temperature transmitter temperature measurements to improve the response time of the temperature measurements. This is generally accomplished by compensating a temperature signal produced by a temperature sensor that is a function of the temperature of a process medium for delays in the temperature measurements relating to the separation of the temperature sensor from the process medium by an isolation wall, and other factors. The improved response time of the temperature transmitter can improve the efficiency of the process, and allows the temperature transmitter to preferably be used in processes where high speed temperature measurements are desired.

<FIG> is a simplified block diagram of an industrial temperature transmitter, generally referred to as <NUM>, formed in accordance with one or more embodiments of the present disclosure, interacting with a process medium <NUM>. In some embodiments, the process medium <NUM> includes an industrial process that involves a material, such as a fluid, moving through pipes and tanks to transform less valuable materials into more valuable and useful products, such as petroleum, chemicals, paper, food, etc. For example, an oil refinery performs industrial processes that can process crude oil into gasoline, fuel oil, and other petrochemicals. Industrial process control systems use process devices, such as process transmitters, as measurement instruments for sensing and measuring process parameters, such as pressure, flow, temperature, level, and other parameters, in combination with, for example, control devices, such as valves, pumps and motors, to control the flow of materials during their processing.

In some embodiments, the temperature transmitter <NUM> includes a temperature sensing unit <NUM> that is configured to sense a temperature of the process medium <NUM> and output a measured temperature signal, generally referred to as <NUM>, that is indicative of the temperature of the process medium <NUM>. In some embodiments, the unit <NUM> includes one or more temperature sensors, generally referred to as <NUM>, that are used to measure a temperature of the process medium <NUM>. The one or more temperature sensors <NUM> may take on any suitable form. For example, the sensors <NUM> may each include a thermocouple, a resistive temperature detector, a thermistor, and/or another suitable temperature sensing device.

In some embodiments, the unit <NUM> includes at least one process temperature sensor 105A (hereinafter "temperature sensor 105A") that is separated from the process medium <NUM> by an isolation wall <NUM> that engages the process medium <NUM> and isolates the sensor 105A from the process medium <NUM>. As discussed below, the isolation wall <NUM> is a wall of a process vessel (e.g., a pipe, a tank, etc.) containing the process medium <NUM>, for example. In some examples not forming part of the invention, the isolation wall <NUM> is a sheath or wall of the temperature sensor 105A or other housing. The sensor 105A is configured to produce a temperature signal 106A that is a function of the temperature of the process medium <NUM> that is communicated through the wall <NUM>. In some examples not forming part of the invention, the temperature signal <NUM> is produced by the unit <NUM> using only the temperature signal 106A produced by the one or more process temperature sensors 105A, such as when the temperature transmitter <NUM> uses a thermowell, as discussed below.

In some embodiments, temperature sensing unit <NUM> includes one or more secondary temperature sensors 105B (hereinafter "secondary temperature sensor 105B") and a processing circuit <NUM>, which are illustrated in phantom lines. The processing circuit <NUM> may comprise analog circuitry and/or digital circuitry. In some embodiments, the processing circuit <NUM> represents one or more processors that are configured to execute instructions, which may be stored locally in memory of the processing circuit <NUM>, or in memory that is remote to the transmitter <NUM>, to perform one or more functions described herein.

The temperature sensor 105B is configured to output a temperature signal 106B that is processed along with the temperature signal 106A by the processing circuit <NUM> to estimate the temperature of the process medium <NUM>. In some examples not forming part of the invention, the temperature signal 106B may be indicative of the ambient conditions to which the isolation wall <NUM> and/or another component of the transmitter <NUM> is exposed. According to the invention, the processing circuit <NUM> processes the temperature signals 106A and 106B to produce the temperature signal <NUM> representing the temperature measured by the unit <NUM>. Typically, the secondary temperature sensor 105B and the processing circuit <NUM> are used with non-intrusive temperature transmitters <NUM>, as discussed below.

In some embodiments, the transmitter <NUM> is an analog device, in which the temperature signals <NUM>, 106A, and/or 106B (if present) are analog signals. In some embodiments, the temperature transmitter <NUM> includes one or more analog-to-digital converters (ADC) <NUM> that digitizes the analog temperature signals into a digital temperature signal (e.g., <NUM>', 106A', 106B') for processing by circuitry of the transmitter in the digital domain, as illustrated in <FIG>. In some embodiments, separate ADC's <NUM> are used, as shown in <FIG>. In some embodiments, a single ADC <NUM> may be used with the input signals (e.g., 106A and 106B) multiplexed into it.

The communication of the temperature of the process medium <NUM> through the isolation wall <NUM> delays the communication of a temperature change in the medium <NUM> to the temperature sensor 105A. As a result, a period of time must elapse before the temperature change of the medium <NUM> is measured by the sensor 105A and the measured temperature represented by the temperature signal <NUM> indicates the temperature change. This delay in the temperature measurement corresponds to a response time of the temperature measurement, which may be dependent on one or more variables, such as the material forming the isolation wall <NUM>, the thickness of the isolation wall <NUM>, the mass of the isolation wall <NUM>, the thermal conductivity of the isolation wall <NUM>, an ambient temperature to which the isolation wall <NUM> is exposed, and/or other variables.

Effects of the delay in the temperature measurement of the process medium <NUM> include a limit on the measurement bandwidth. Specifically, the delay acts as a low-pass filter whose cutoff frequency drops in response to an increase in the delay or a decrease in the response time. As a result, changes in the temperature of the process medium <NUM> occurring at a frequency that is above the cutoff frequency are rendered undetectable by the temperature sensing unit <NUM>. Embodiments of the present disclosure operate to reduce or eliminate the temperature measurement delay by reducing the "perceived" response time of the temperature measurement or by reducing the impact of the response time of the temperature measurement, thereby decreasing the cutoff frequency and the loss of potentially valuable information.

According to the invention, the temperature transmitter <NUM> includes a compensation circuit <NUM> that is configured to process the temperature signal <NUM> output by the temperature sensing unit <NUM> to compensate the temperature signal <NUM> or the temperature measurement indicated by the temperature signal <NUM> for the response time of the temperature measurement, and output a compensated temperature signal <NUM> that more accurately represents the current temperature of the process medium <NUM>. Thus, in some examples not forming part of the invention, the compensation circuit <NUM> compensates the temperature signal <NUM> that is produced based on the temperature signal 106A output from the process temperature sensor 105A. According to the invention, the compensation circuit <NUM> compensates the temperature signal <NUM> output by the processing circuit <NUM>, which is based on the temperature signal 106A output from the temperature sensor 105A and the temperature signal 106B output from the temperature sensor 105B.

<FIG> is a simplified block diagram illustrating exemplary signal processing performed by the compensation circuit <NUM>. For example, when a step temperature change to the process medium <NUM> occurs at time t<NUM>, such as an increase from temp T<NUM> to temp T<NUM>, as indicated in the chart within the box representing the process medium <NUM>, a delay occurs before the temperature change is measured by the temperature sensing unit <NUM>. This delay is indicated in the chart representing the temperature measurement indicated by the signal <NUM> that is presented in the box representing the temperature sensing unit <NUM>. The response time of the temperature measurement causing the delay between the temperature indicated by the temperature signal <NUM> and the actual temperature of the process medium <NUM> is due, at least in part, to the necessity to communicate the temperature change through the isolation wall <NUM>. Other factors may also contribute to the slow response time of the temperature measurement. The compensation circuit <NUM> compensates the signal <NUM> to substantially eliminate or reduce the response time of the temperature measurement, such that the compensated temperature signal <NUM> substantially matches the actual temperature of the process medium, as indicated in the box representing the compensated temperature signal <NUM>.

The compensation circuit <NUM> may comprise analog circuitry and/or digital circuitry. In some embodiments, the compensation circuit <NUM> represents one or more processors that are configured to execute instructions, which may be stored locally in memory of the compensation circuit <NUM>, or in memory that is remote to the transmitter <NUM>, to perform one or more functions described herein. In some embodiments, the compensated temperature signal <NUM> is a digital signal, and the temperature transmitter <NUM> includes a digital-to-analog converter (DAC) <NUM> that converts the compensated temperature signal <NUM> to an analog compensated temperature signal <NUM>'.

According to the invention, the temperature transmitter <NUM> includes an output circuit <NUM> that receives the compensated temperature signal <NUM> and produces a temperature output <NUM> as a function of the compensated temperature signal <NUM>. In some embodiments, the output circuit <NUM> produces the temperature output <NUM> in accordance with a desired data communication protocol.

<FIG> is a simplified diagram showing an exemplary industrial process control system <NUM> including the temperature transmitter <NUM> formed in accordance with one or more embodiments described herein. According to the invention, the transmitter <NUM> includes a housing <NUM> that may contain, for example, the compensation circuit <NUM>, the output circuit <NUM>, and/or other components of the transmitter described herein. In some embodiments, the output circuit <NUM> is configured to transmit the temperature output <NUM> to a suitable controller <NUM> that uses the temperature output <NUM> to control aspects of the process medium <NUM>, such as a process fluid flowing through a process vessel <NUM>, such as a pipe. In some embodiments, the controller <NUM> is located remotely from the temperature transmitter <NUM>, such as in a remote control room <NUM>, as shown in <FIG>.

In some embodiments, the output circuit <NUM> is connected to the controller <NUM> over a two-wire loop <NUM>, as illustrated in <FIG>. In some embodiments, the two-wire loop <NUM> is configured to transmit all electrical power required by the temperature transmitter <NUM> to operate. In some embodiments, the output circuit <NUM> communicates the temperature output <NUM> over the two-wire loop <NUM> to the controller <NUM> by modulating a current flow that varies between <NUM>-<NUM> milliamps. Alternatively, the output circuit <NUM> may be configured to transmit the temperature output <NUM> to the controller <NUM> wirelessly in a point-to-point configuration, a mesh network, or other suitable configuration with the temperature transmitter <NUM> having its own power source.

<FIG> is simplified cross-sectional view of a portion of a temperature sensing unit <NUM> within a thermowell <NUM> of a temperature transmitter <NUM>, which is not forming part of the invention. The thermowell <NUM> includes the isolation wall <NUM> and encloses the temperature sensor 105A. When the transmitter <NUM> is installed in the field, the thermowell <NUM> extends through a wall <NUM> of a process vessel <NUM>, such as a process pipe (shown), a tank, or other process vessel, to position the thermowell <NUM> within the process medium <NUM>. In some embodiments, the temperature sensor 105A is located at a distal end of a sensor probe <NUM>, which positions the temperature sensor 105A within a temperature sensing region <NUM> of the thermowell <NUM>. One exemplary thermowell of a temperature transmitter is disclosed in <CIT>.

The isolation wall <NUM> of the thermowell <NUM> isolates the temperature sensor <NUM> from the process medium <NUM>. In some examples not forming part of the invention, the isolation wall <NUM> is a cylindrical or conical wall that surrounds the temperature sensor 105A. In some examples, the isolation wall <NUM> is formed of a highly thermally conductive material, such as brass, steel, copper, or other suitably thermally conductive material. Such materials reduce the time required to communicate (i.e., conduct) the temperature of the medium <NUM> to the sensor 105A. The temperature signal <NUM> (<FIG>) output by the temperature sensor <NUM> may be communicated to other components of the transmitter <NUM>, such as the compensation circuit <NUM> through wires <NUM>, for example.

<FIG> is a diagrammatic view of a temperature sensing unit <NUM> of an exemplary non-intrusive temperature transmitter <NUM> that is located externally to the process vessel <NUM> (e.g., pipe, tank, etc.), in accordance with embodiments of the present disclosure. Another exemplary non-intrusive temperature transmitter is disclosed in <CIT>.

According to the invention, the wall <NUM> of the process vessel <NUM> forms the isolation wall <NUM> that separates the process medium <NUM> from the temperature sensor 105A (Tsensor), which is placed in contact with or in close proximity to the exterior surface <NUM> of the wall <NUM>, as shown in <FIG>. The process temperature sensor 105A performs a temperature measurement of the process medium <NUM> through the wall <NUM>, which is illustrated as a pipe in <FIG>, by measuring a temperature at the exterior surface <NUM>.

Heat flow is modeled in <FIG> in terms of electrical components. Specifically, the temperature of the process fluid is illustrated as node <NUM> and is coupled to the temperature sensor 105A via the thermal impedance (Rpipe) of the pipe <NUM> or wall <NUM> indicated diagrammatically as a resistor <NUM>. It should be noted that the thermal impedance of the pipe <NUM> or wall <NUM> can be known either by virtue of the material of the pipe <NUM> itself and the thickness of the pipe wall <NUM> such that a suitable impedance parameter could be entered into circuitry of the unit <NUM>, such as the compensation circuit <NUM>. For example, a user configuring the system may indicate that the pipe <NUM> is constructed from stainless steel and the wall <NUM> is <NUM> (<NUM>/<NUM> inch) thick. Then, suitable lookup data within memory can be accessed by the compensation circuit <NUM> to identify a corresponding thermal impedance that matches the selected material and wall thickness. Moreover, embodiments may be practiced where the pipe material is simply selected and the thermal impedance can be calculated based on the selected material and the selected wall thickness. Regardless, embodiments of the present disclosure generally leverage knowledge of the thermal impedance of the pipe material. Further, in embodiments where the thermal impedance of the pipe material cannot be known ahead of time, it is also possible that a calibration operation can be provided where a known process fluid temperature is provided to the non-invasive process fluid temperature calculation system and the thermal impedance is set as a calibration parameter.

As indicated in <FIG>, heat may also flow from the temperature sensor 105A out the sidewall of stem portion <NUM> to the ambient environment illustrated at reference numeral <NUM>. This is illustrated diagrammatically as thermal impedance (R2) at reference number <NUM>. The thermal impedance (R2) to the ambient environment can be increased by thermally insulating the temperature sensor 105A.

Heat also flows from the external surface <NUM> of the pipe <NUM> through the stem portion <NUM> to a housing <NUM> or other location that is spaced from the pipe <NUM> via conduction through stem portion <NUM>. The housing <NUM> encloses circuitry of the temperature sensing unit <NUM>, such as the compensation circuit <NUM> and the output circuit <NUM>, for example. The thermal impedance of the stem portion <NUM> (Rsensor) is illustrated diagrammatically at reference numeral <NUM>. In some embodiments, the temperature sensing unit <NUM> includes a temperature sensor 105B (Tterm) that is coupled to a terminal block or other location within the housing <NUM> to measure the terminal temperature. Heat may flow from the temperature sensor 105B to the ambient environment via thermal impedance <NUM> (R1).

When the process fluid temperature changes, it will affect both the reading from temperature sensor 105A and the reading from terminal temperature sensor 105B since there is a rigid mechanical interconnection between them (heat conduction through stem portion <NUM>) with relatively high thermal conductance. The same applies to the ambient temperature. When the ambient temperature changes, it will impact both of these measurements as well, but to a much lesser extent.

For slow changing conditions, the basis heat flux calculation can be simplified into:
<MAT>.

As mentioned above, embodiments of the compensation circuit <NUM> operate to compensate the corrected temperature (Tcorrected) indicated by the temperature signal <NUM> or <NUM>', for the response time of the temperature measurement, such as the time required to communicate the temperature of the process medium <NUM> through the isolation wall <NUM> in form of the wall <NUM> of the pipe <NUM>, as well as other materials, such as a sensor sheath or other material of the sensor 105A, for example. This can generally be approximated using the following first order equation, in which t is the update rate (e.g., <NUM> second or less) of the temperature measurement (Tcorrected), and τ is the time constant of the components involved in the temperature measurement.

According to the invention, the compensation circuit <NUM> applies dynamic compensation to the temperature measurement by knowing the time constant and trend information about the temperature measurement. The rate of change of the measurement can be evaluated over a number of samples to provide a percentage and direction of correction that minimizes sampling noise. The rate of change can be divided by the exponential portion of Equation <NUM> to provide the dynamic compensation to the measured temperature, as indicated in Equation <NUM>.

A compensated temperature measurement value (TempmeasCompensated), which is represented by the compensated temperature signal <NUM> (<FIG>), is calculated by adding the measured temperature value (Tempmeas) corresponding to the signal <NUM> or <NUM>' from the sensing unit <NUM> with the dynamic compensation value (TempdynamicComp), as indicated in Equation <NUM>. The time delay described above between the measured temperature (Tempmeas) and the current temperature of the medium <NUM> is removed or significantly reduced in the compensated temperature measurement (TempmeasCompensated), as indicated by the signal <NUM> in <FIG>.

<FIG> is a graph illustrating the amount of correction that should be applied to a temperature measurement in relation to the measurement rate of change for a stepped input from <NUM> to <NUM> with a <NUM>-minute time constant. As shown in <FIG>, as the trending change in the temperature measurement is smaller, so is the necessary correction (TempdynamicComp).

For non-intrusive temperature transmitters <NUM>, such as that discussed above with reference to <FIG>, parameters of the process vessel wall <NUM>, which forms the isolation wall <NUM>, must be known, such as the material forming the wall <NUM>, thickness of the wall <NUM>, and/or other parameters of the process vessel wall <NUM>. These can be set in the transmitter <NUM>. In some embodiments, such parameters of the process vessel wall <NUM> are used to determine the time constant for the specific process vessel wall <NUM>, through which the transmitter <NUM> is measuring the temperature of the process medium <NUM>. Testing has shown that the time constant for each supported pipe material can be approximated using a linear equation for any pipe wall thickness. For example, the time constant in minutes for carbon steel can be calculated using Equation <NUM> below.

Time constants for transmitters <NUM> utilizing a thermowell, such as the thermowell <NUM> described above with reference to <FIG>, can be calculated in a similar manner to determine the amount of correction (TempdynamicComp) of the measured temperature (Tempmeas) that is required.

Adjustments to calculated time constants can be made if additional information is supplied, such as the type of process medium contained within the process vessel <NUM>, the density of the process medium <NUM>, and/or other information.

It is understood that embodiments of the present disclosure may be applied to compensate for delays in the response time of other types of temperature sensors. For example, the response time of a resistance temperature detector (RTD) used for cold junction compensation of a thermocouple may be compensated for using the techniques described above, such as when the ambient temperature changes quickly. Furthermore, as RTD's have slower response times than thermocouples, embodiments of the present disclosure may be used to speed up measurements performed by an RTD having an isolation wall in the form of an exterior wall of the RTD, for example.

Claim 1:
An industrial process temperature transmitter (<NUM>) for measuring a temperature of a process medium (<NUM>) contained in a process vessel (<NUM>) comprising an isolation wall (<NUM>), the industrial process temperature transmitter (<NUM>) comprising:
a thermally conductive stem portion (<NUM>) having a first end, configured to be brought into contact with or in close proximity to the isolation wall (<NUM>), and a second end; and
a housing (<NUM>) attached to the second end of the stem portion (<NUM>);
a process temperature sensor (105A) configured to perform a temperature measurement of the process medium (<NUM>) through the isolation wall (<NUM>);
a secondary temperature sensor (105B) configured to produce a secondary temperature signal (106B) based on a sensed temperature, wherein the secondary temperature sensor (105B) is within the housing (<NUM>);
wherein the industrial process temperature transmitter (<NUM>) is configured to produce a temperature signal (<NUM>') that is indicative of the temperature of the process medium (<NUM>) in the process vessel (<NUM>), based on a process temperature signal (106A) output from the process temperature sensor (105A) and the secondary temperature signal (106B) during a temperature measurement;
a compensation circuit (<NUM>) configured to provide a dynamic compensation to the temperature signal (<NUM>') for a response time of the temperature measurement to a change in the temperature of the process medium (<NUM>) and a rate of change of the temperature measurement, and output a compensated temperature signal (<NUM>, <NUM>');
an output circuit (<NUM>) configured to produce a temperature output (<NUM>) as a function of the compensated temperature signal (<NUM>, <NUM>').