阅读说明：本技术 非侵入式过程流体温度计算系统 (Non-invasive process fluid temperature calculation system ) 是由 杰森·H·路德 尤里·尼古拉耶维奇·库兹涅佐夫 塞特·塞托维奇·加里波夫 阿列克斯基·亚历山大 于 2016-01-25 设计创作，主要内容包括：一种过程流体温度计算系统包括：外壳；与过程流体管道的表面直接接触的第一温度传感器,用于测量过程流体管道的外部温度；第二温度传感器,与第一温度传感器相间隔并与外壳内的端子块耦接,用于提供参考温度测量；测量电路,与第一温度传感器和第二温度传感器耦接；设置在外壳内的微处理器,用于接收参考温度测量,所述参考温度测量不同于测量到的过程流体管道的外部温度,所述微处理器与所述测量电路耦接,以从测量电路接收指示来自第一温度传感器和第二温度传感器的信号的温度信息,并利用第一温度传感器信号和第二温度传感器信号之差,使用热通量计算来计算过程流体温度输出,其中在第一温度传感器与第二温度传感器之间存在已知热阻抗。(A process fluid temperature calculation system comprising: a housing; a first temperature sensor in direct contact with a surface of the process fluid conduit for measuring an external temperature of the process fluid conduit; a second temperature sensor spaced from the first temperature sensor and coupled to the terminal block within the housing for providing a reference temperature measurement; a measurement circuit coupled with the first temperature sensor and the second temperature sensor; a microprocessor disposed within the housing for receiving a reference temperature measurement that is different than the measured external temperature of the process fluid conduit, the microprocessor coupled to the measurement circuitry to receive temperature information from the measurement circuitry indicative of signals from the first and second temperature sensors and to calculate a process fluid temperature output using a heat flux calculation using a difference between the first and second temperature sensor signals, wherein there is a known thermal impedance between the first and second temperature sensors.)

1. A process fluid temperature calculation system comprising:

a housing;

a first temperature sensor in direct contact with a surface of the process fluid conduit arranged to measure an external temperature of the process fluid conduit;

a second temperature sensor spaced from the first temperature sensor and coupled to a terminal block within the housing configured to provide a reference temperature measurement;

a measurement circuit coupled with the first temperature sensor and the second temperature sensor;

a microprocessor disposed within the housing configured to receive the reference temperature measurement, the reference temperature measurement being different than a measured external temperature of the process fluid conduit, the microprocessor coupled with the measurement circuitry to receive temperature information from the measurement circuitry indicative of signals from the first and second temperature sensors and to calculate a process fluid temperature output using a heat flux calculation using a difference between the first and second temperature sensor signals,

wherein there is a known thermal impedance between the first temperature sensor and the second temperature sensor.

2. The process fluid temperature calculation system of claim 1, further comprising: a clamp configured to attach to the process fluid conduit and maintain thermal contact between the process fluid conduit and the first temperature sensor.

3. The process fluid temperature calculation system of claim 1, further comprising: a memory containing parameters for calculating heat flux.

4. The process fluid temperature calculation system of claim 3, wherein the parameter comprises a physical characteristic of a wall of the process fluid conduit.

5. The process fluid temperature calculation system of claim 4, wherein the physical characteristic comprises a material from which the process fluid conduit is constructed.

6. The process fluid temperature calculation system of claim 4, wherein the physical characteristic is process fluid conduit wall thickness.

7. The process fluid temperature calculation system of claim 1, further comprising: a thermal insulation disposed about the process fluid conduit adjacent the first temperature sensor.

8. The process fluid temperature calculation system of claim 2, further comprising: a thermal insulation disposed around the clamp.

9. The process fluid temperature calculation system of claim 1, wherein the microprocessor is configured to: dynamically compensating the temperature output based on a rate of change of the temperature measured by the first temperature sensor.

10. The process fluid temperature calculation system of claim 1, wherein the microprocessor is configured to: dynamically compensating the temperature output based on a rate of change of the temperature measured by the second temperature sensor.

11. The process fluid temperature calculation system of claim 1, wherein the microprocessor is configured to: dynamically compensating the temperature output based on a rate of change of the temperature measured by the first temperature sensor compared to a rate of change of the temperature measured by the second temperature sensor.

12. The process fluid temperature calculation system of claim 1, further comprising: a communication interface configured to transmit the output to a remote device.

13. The process fluid temperature calculation system of claim 1, further comprising: a local operator interface coupled to the microprocessor.

14. The process fluid temperature calculation system of claim 1, wherein the measurement circuitry includes a plurality of analog-to-digital converters, a first analog-to-digital converter coupled with the first temperature sensor, and a second analog-to-digital converter coupled with the second temperature sensor.

15. A method of calculating a temperature of a process fluid within a process fluid conduit, the method comprising:

measuring a temperature of an outer surface of the process fluid conduit with a first temperature sensor;

obtaining, by a second temperature sensor, reference temperature information relative to a position of a terminal block within a housing of a process fluid temperature calculation system;

calculating a heat flux using a heat flux equation using the measured temperature from the outer surface of the process fluid conduit and the reference temperature information;

calculating a temperature of the process fluid within the process fluid conduit using the calculated heat flux in combination with a thermal impedance parameter related to heat flow between the process fluid conduit wall and a location of a terminal block within a housing of the process fluid temperature calculation system;

wherein there is a known thermal impedance between the first temperature sensor and the second temperature sensor.

16. The method of claim 15, further comprising: a process fluid having a known temperature is provided in the process fluid conduit.

17. The method of claim 15, further comprising: dynamically compensating for an estimate of process fluid temperature based on a measured rate of change of the outer surface of the process fluid conduit.

18. A process fluid temperature calculation system comprising:

a pipe clamp;

a first temperature sensor coupled to the pipe clamp and in direct contact with a surface of the process fluid pipe and configured to measure an external temperature of the process fluid pipe;

a housing coupled to the tube clamp, the housing containing a terminal block, a measurement circuit, and a microprocessor;

a second temperature sensor mounted to a terminal block within the housing configured to provide a reference temperature measurement;

wherein the measurement circuit is coupled with the microprocessor and the first and second temperature sensors;

the microprocessor is configured to: receiving the reference temperature measurement, the reference temperature measurement being different from the measured external temperature of the process fluid conduit, the microprocessor being coupled with the measurement circuitry to receive temperature information from the measurement circuitry and provide a process fluid temperature output using a heat flux calculation and information from the measurement circuitry indicative of the external temperature of the process fluid conduit and the terminal block; and

wherein there is a known thermal impedance between the first temperature sensor and the second temperature sensor.

Technical Field

The invention relates to a non-invasive process fluid temperature calculation system.

Background

The process industry employs process variable transmitters to monitor process variables associated with substances such as solids, slurries, liquids, vapors and gases in chemical, pulp, gasoline, pharmaceutical, food and other fluid process plants. Process variables include pressure, temperature, flow, level, turbidity, density, concentration, chemical composition, and other properties.

Process fluid temperature transmitters provide an output related to the temperature of the process fluid. The temperature transmitter output can be transmitted over a process control loop to a control room or the output can be transmitted to another process device so that the process can be monitored and controlled.

Traditionally, process fluid temperature transmitters have been coupled to or employed thermowells that provide a temperature sensor in thermal communication with the process fluid, otherwise protecting the temperature sensor from direct contact with the process fluid. The thermowell is located within the process fluid to ensure substantial thermal contact between the process fluid and a temperature sensor disposed within the thermowell. Thermowells are typically designed using relatively robust metal structures so that thermowells can withstand many of the challenges presented by process fluids. These challenges may include physical challenges, such as process fluid flowing through the thermowell at a relatively high rate; thermal challenges, such as particularly high temperatures; pressure challenges, such as process fluid delivery or storage at high pressure; and chemical challenges such as those presented by corrosive process fluids. In addition, thermowells can be difficult to design into a process installation. Such thermowells require process intrusion, wherein the thermowell is installed or extended into a process vessel, such as a tank or pipe. The process intrusion itself must be carefully designed and controlled so that the process fluid does not leak from the vessel at the point of intrusion.

There are a number of factors that can compromise the structural integrity of the thermowell. In some cases, not all factors are considered completely, and the thermowell sometimes buckles or even breaks, thus stalling the process installation for a long period of time. This is highly undesirable. For some applications, thermowells simply cannot be used without potential damage. In such applications, it may be beneficial to use a non-invasive process fluid temperature calculation system, or even desirable to use a non-invasive process fluid temperature calculation system. Using such a system, a pipe clamp sensor is used to couple a temperature sensor to a process vessel (e.g., a pipe). While such non-invasive process fluid temperature calculations provide the benefit of not requiring process intrusion nor subjecting the thermowell directly to the process fluid, there are tradeoffs. In particular, non-invasive temperature calculation systems are accurate in detecting process fluid temperatures through thermowells that do not extend into the process fluid and directly measure the temperature.

Providing a non-invasive process fluid temperature calculation system that can more accurately reflect process fluid temperature would reduce some of the compromises required by users of such systems, and may also provide more accurate temperature calculations and process control where the use of thermowells is undesirable or impossible.

Disclosure of Invention

A process fluid temperature calculation system comprising: a first temperature sensor arranged to measure an external temperature of the process fluid conduit. The process fluid temperature calculation system has a stem portion with a known thermal impedance. A second temperature sensor is spaced from the first temperature sensor by the stem portion. A measurement circuit is coupled to the first and second temperature sensors. A microprocessor is coupled to the measurement circuitry to receive temperature information from the measurement circuitry and provide an estimate of process fluid temperature within the process fluid conduit using heat flux calculations.

Drawings

FIG. 1 is a graph of process fluid temperature versus pipe clamp temperature showing the error associated with a non-invasive temperature calculation system.

FIG. 2 is a schematic diagram of a non-invasive temperature calculation system coupled to a process fluid vessel in accordance with one embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating heat flow through a non-invasive process fluid temperature calculation system according to an embodiment of the present invention.

FIG. 4 is a block diagram of a non-invasive process fluid temperature calculation system according to an embodiment of the present invention.

FIG. 5 is a flow chart of a method of estimating process fluid temperature in a non-invasive temperature measurement system according to an embodiment of the present invention.

Fig. 6A and 6B are graphs illustrating corrected temperature and compensation error, respectively, of a non-invasive process fluid temperature calculation system, in accordance with an embodiment of the present invention.

Detailed Description

As set forth above, selecting a non-invasive temperature calculation system typically requires a compromise in accuracy. FIG. 1 is a graph of process fluid temperature versus clamp temperature showing the error of a non-invasive temperature calculation system as a function of process fluid temperature. The left axis of the graph shows process fluid temperature and clamp temperature, while the right axis shows error, both in degrees celsius. At the initial time, the process fluid temperature and the clamp temperature were each at about 25 degrees celsius, with an error of about 0 degrees celsius. As the process fluid temperature increases, the clamp temperature also increases, but at a lower rate. Additionally, as the process fluid temperature changes, the pipe clamp also changes, but does not closely match the process fluid temperature. This produces an error that fluctuates approximately between 14 and 16 degrees celsius. This indicates that the clamp temperature is a reading of about 14 to 16 degrees below the process fluid temperature.

FIG. 2 is a schematic view of a non-invasive process fluid computing system according to an embodiment of the present invention. The system 100 is shown coupled to a process fluid vessel 102, the process fluid vessel 102 being a pipe or conduit in the example shown. As such, the system 100 includes a clamp 104, the clamp 104 being secured around the outer surface of the pipe 102. Although the embodiment shown in FIG. 2 employs threaded fasteners to secure the clamp 104 around the pipe 102, any suitable clamping mechanism may be employed. The clamp 104 includes a temperature sensor (shown in FIG. 3) placed in direct thermal contact with the outer surface of the tube 102. The temperature sensor is electrically coupled to electronics disposed within the housing 108 such that the electronics within the housing 108 can measure the temperature of the tube 102. System 100 also includes a rod portion 110 that couples clamp 104 to housing 108. Stem portion 110 conducts heat from clamp 104 to housing 108. However, the material selected for making the stem 110, the length of the stem 110, and/or the thickness of the material comprising the stem 110 may be designed to provide a particular thermal impedance of the stem 110. As set forth herein, thermal impedance is defined as the degree to which a structure, such as a rod 110, opposes heat flow. Thermal impedance may generally be considered to be the inverse of thermal conductance. Since some process fluid tube 102 may be provided at a relatively high temperature, it may be beneficial for stem 110 to have a high thermal impedance to protect the electronics within housing 108 from such elevated temperatures.

According to some embodiments of the invention, an additional temperature sensor is provided at a certain distance from the tube 102. In one embodiment, an additional temperature sensor is disposed within the housing 108. However, the following embodiments of the invention may be practiced: wherein an additional temperature sensor is provided in a fixed position within the rod 110. As set forth in more detail below, sensing the surface temperature of the tube 102 and the separation temperature from the additional temperature sensor may provide an indication of heat flow. In addition, since environmental effects such as wind chill and ambient temperature may affect the degree to which heat is carried away by the rod 110 as it flows through the rod 110, at least some embodiments of the present invention include thermal insulation as shown in the model in FIG. 2. This thermal insulation may be provided around the tube 102 and the clamp 104, as indicated by reference numeral 112. Further, in one embodiment, the heat pipe insulation may extend a minimum distance in both directions (upstream and downstream) from the pipe clamp 104. In one embodiment, the minimum distance is at least 6 inches. Additionally, as indicated by reference numeral 114, thermal insulation may be provided around the rod portion 110. For embodiments employing insulation 112 and/or 114, the insulation should be at least 1/2 inches thick, and preferably should be selected to reduce or potentially eliminate any external heat absorption. For example, the outer surface of the thermal insulation may ideally be white or reflective.

FIG. 3 is a schematic view of a non-invasive process fluid temperature calculation system in which heat flow is modeled based on electrical components, where T_ambDenotes the ambient temperature, T_termIndicating the transmitter terminal temperature, T_sensorRepresents the process pipe surface temperature, T_processRepresenting process temperature, R1 representing ambient to terminal thermal impedance, R2 representing sensor assembly thermal impedance, R_sensorRepresenting the thermal impedance, R, of the sensor assembly_pipeIndicating the thermal impedance of the tube material. Specifically, the temperature of the process fluid is shown as node 150 and the thermal impedance (R) of the pipe material via the pipe material is illustrated as resistor 154_pipe) Coupled to a temperature sensor 152. It should be noted that the thermal impedance of the tube material may also be known by means of the material of the tube itself and the wall thickness of the tube, so that appropriate impedance parameters may be entered into the circuitry within the housing 108. For example, a user of the configuration system may indicate that the pipe is constructed of stainless steel and is 1/2 inches thick. Appropriate lookup data in the memory of the non-invasive process fluid temperature calculation system then identifies a corresponding thermal impedance that matches the selected material and wall thickness. Further, the following embodiments may be practiced: wherein only the tube material is selected and the thermal impedance is calculated based on the selected material and the selected wall thickness. Regardless, embodiments of the present invention generally employ knowledge of the thermal impedance of the tube material. In addition, inIn embodiments where the thermal impedance of the tube material can be known in advance, a calibration operation can also be provided in which a known process fluid temperature is provided to a non-invasive process fluid temperature calculation system and the thermal impedance is set as a calibration parameter.

As shown in FIG. 3, heat may also flow from the temperature sensor 152 out of the side wall of the wand portion 110 to the ambient environment as shown at reference numeral 156, and this thermal impedance (R2) is indicated by reference numeral 158. As set forth above, in some embodiments, the thermal impedance from the surface temperature sensor 152 to the surroundings may be increased by providing an insulating material. Heat will flow from the outer surface of tube 102 to housing 108 through rod portion 110 via conduction along rod portion 110. The thermal impedance (R) of the wand portion 110 is shown schematically at reference numeral 160_sensor). Finally, heat may also flow from the temperature sensor 162 coupled with the terminal block within the housing 108 to the ambient via the thermal impedance 164 (R1).

When a non-invasive process fluid temperature calculation system is connected to a process fluid conduit (e.g., pipe 102) by way of pipe clamp 104, both the surface temperature of the process fluid conduit and the transmitter terminal temperature 162 can be measured and used in the heat flux calculation to accurately infer or otherwise approximate the process fluid temperature 150 within the conduit 102.

As the process fluid temperature changes, the readings of temperature sensor 152 and the readings of terminal temperature sensor 162 will be affected because there is a rigid mechanical interconnection between them (thermal conduction through stem portion 110) with relatively high thermal conduction. The same applies to the ambient temperature. Both measurements will also be affected, but to a much lesser extent, when the ambient temperature changes.

For slowly changing conditions, the base heat flux calculation can be simplified to:

T_corrected＝T_sensor+(T_sensor-T_termminal)*(R_pipe/R_sensor)。

r can be dynamically adjusted by using the rate of change of the terminal temperature versus the rate of change of the surface temperature of the pipe_sensorCoefficients to further correct non-insulated clamp assemblies or rapidly changing process/environmental conditions. If the pipe surface temperature changes rapidly, additional corrections may be applied during this time period to minimize the time constant. Similarly, if the ambient temperature changes rapidly relative to the tube surface temperature, less correction may be applied.

FIG. 4 is a schematic view of a non-invasive process fluid temperature calculation measurement in accordance with an embodiment of the present invention. As shown in fig. 4, the housing 108 contains a microprocessor 250, a first a/D converter 252, a second a/D converter 254, and a memory 256. The first and second a/D converters 252 and 254 are analog-to-digital converters. Although the example shown in fig. 4 employs two discrete analog-to-digital converters, embodiments of the invention may be implemented with a single analog-to-digital converter and suitable switching circuitry (e.g., a multiplexer) to couple the single analog-to-digital converter with multiple temperature sensors.

The microprocessor 250 is coupled to the first temperature sensor 152 via a first analog-to-digital converter 252. The first analog-to-digital converter 252 is electrically coupled to the wires of the temperature sensor 152 to convert the analog electrical signal from the temperature sensor 152 to a digital signal for the microprocessor 250. Temperature sensor 152 and/or temperature sensor 162 may be any suitable temperature sensing device or component, including a Resistance Temperature Device (RTD), a thermocouple, a thermistor, or any other suitable device having electrical characteristics that vary with temperature. A second analog-to-digital converter 254 couples the microprocessor 250 to the second temperature sensor 162. The second temperature sensor 162 may also be any suitable temperature sensing device, but in one embodiment is the same type of temperature sensor as the temperature sensor 152. The second analog-to-digital converter 254 is electrically coupled to the wires of the temperature sensor 162 and converts the analog electrical signal from the second temperature sensor 162 to a digital signal for the microprocessor 250. Also, the first and second analog-to-digital converters 252 and 254 include measurement circuitry that couples the temperature sensors to the microprocessor 250.

Memory 256 is a digital data storage device electrically coupled to microprocessor 250. The memory 256 contains data about the tube material and the stem portion as well as parameters such as thermal impedance information. The thermal impedance of the stem portion will be determined during system manufacture and may therefore be input during manufacture. The thermal impedance of the tube material may be selected during operation of the system or otherwise may be empirically determined during calibration or other suitable process. Regardless, memory 256 contains parameters that allow microprocessor 250 to estimate process fluid temperature information from signals obtained from temperature sensors 152 and 162.

The process vessel wall parameters stored in memory 256 may include physical characteristics of the process vessel wall, such as process vessel wall K_wAnd process vessel wall thickness. When the temperature measurement assembly is manufactured, the process vessel wall parameters may be stored in memory 256. However, as set forth above, these parameters may be determined during configuration or operation of the component or during a calibration process.

The heat flux through stem portion 110 should be the same as the heat flux through the wall of process vessel 102 according to the fourier conduction law. In this case, the temperature of the process vessel wall inner surface (and the process fluid temperature) can be determined from the signal obtained from temperature sensor 152 and the signal obtained from terminal temperature sensor 162.

In the embodiment shown in fig. 4, housing 108 may also include a communication interface 258. Communication interface 258 provides communication between the temperature measurement assembly and a control or monitoring system 262. So equipped, the temperature measurement system may also be referred to as a temperature measurement transmitter, and may transmit the temperature of the process fluid to the control or monitoring system 252. Communication between the temperature measurement system and the control or monitoring system 262 may be via any suitable wireless or hard-wired connection. For example, communication may be represented by an analog current on a two-wire loop in the range of 4-20 mA. Alternatively, a high speed addressable remote transducer may be usedDigital protocols over two-wire loops or using, for example, FOUNDATION^TMThe digital protocol of the fieldbus carries communications over the communications bus. Communication interface 258 may alternatively or additionally include wireless communication circuitry 264, wireless communication circuitry 264 for communicating data using a wireless HAR according to IEC 62591T, wireless transmission of the wireless process communication protocol. Further, communication with the control or monitoring system 262 may be direct or through a network of any number of intermediate devices (e.g., a wireless mesh network (not shown)).

Communication interface 258 may help manage and control communications to and from the temperature measurement system. For example, the control or monitoring system 262 may provide for configuration of the temperature measurement system, including inputting or selecting any suitable number of parameters regarding thermal impedance of the process vessel wall, etc.

The example shown in fig. 4 may also include a local operator interface 266. A local operator interface 266 may be provided for displaying the estimated temperature of the process fluid, as well as the measured temperature of the external surface provided directly by temperature sensor 152. Additionally, the local operator interface may provide an indication of the terminal temperature measured by the temperature sensor 162. In addition, ambient temperature measurements may also be provided using additional temperature sensors, and such measurements may optionally be indicated by the local operator interface 266. The local operator interface 266 may include any suitable number of buttons or keypads that allow a user to interact with the non-invasive temperature measurement system. Such interaction may include inputting or selecting a material of the process fluid conduit and a thickness of a wall of the process fluid conduit.

FIG. 5 is a flow chart of a method of inferring process fluid temperature according to an embodiment of the present invention. The method 300 begins at block 302, where the outside temperature of the process fluid conduit is measured at block 302. As set forth above, the external temperature is preferably measured using a temperature sensor disposed directly relative to the outer diameter or surface of the process fluid conduit. Next, at block 304, a terminal temperature within a housing of the non-invasive process fluid temperature calculation system is measured. Although the embodiments described herein generally refer to measurement of transmitter terminal temperatures, embodiments of the invention may be implemented by measuring the temperature of the housing itself or any other suitable structure within the housing. Next, at block 306, the measured external pipe temperature and the measured terminal temperature are provided to a processing facility (e.g., microprocessor 250 disposed within housing 108) so that the temperature of the process fluid can be inferred using basic heat flux calculations, for example, as described above. While the embodiments described thus far have generally focused on providing a processor (e.g., microprocessor 250) that calculates within housing 108, it is expressly contemplated that the embodiments described herein may also be implemented by providing raw temperature measurements from external pipe temperature sensors and terminal temperature sensors to a remote facility or processor that can estimate process fluid temperature. Regardless, the basic heat flux calculation generally provides an estimate of the process fluid temperature using values from the external pipe temperature sensor and the terminal temperature sensor. As set forth above, dynamic weighting 308 may be applied according to some embodiments of the invention so that rapidly changing conditions may be dynamically adjusted. For example, in one embodiment, rapidly changing process fluid temperature conditions may be further corrected by: the thermal impedance of the sensor assembly parameters stored in memory 256 is dynamically adjusted by the rate of change of the terminal temperature measurements versus the rate of change of the surface temperature measurements (provided by temperature sensor 152). If the surface temperature is changing rapidly, additional corrections can be applied during the time period of the rapid temperature change to minimize errors due to the time constant. Similarly, if the ambient temperature is changing rapidly relative to the surface temperature, less correction may be applied.

Next, at block 310, the inferred process fluid temperature is provided as an output of a non-intrusive process fluid temperature calculation system. The output may be provided as a local output via a local operator interface as indicated at block 312, and/or the output may be provided to a remote device as indicated at block 314. Further, as indicated at block 316, providing output to a remote device may be communicatively coupled via a wired process as indicated at block 316, and/or may be provided wirelessly as indicated at block 318.

Fig. 6A and 6B are graphs showing the results of non-invasive process fluid temperature estimation using flux calculations according to embodiments of the present invention. As shown in FIG. 6A, the tube surface temperature fluctuates to a relatively small degree during the time interval from about 12:40PM to 2:45 PM. During this same time interval, the terminal temperature fluctuates between about 27 degrees celsius and about 33 degrees celsius. The process temperature is shown at reference numeral 400 and is tracked very closely by the corrected temperature output 402. This compensation error is directly indicated in fig. 6B. As shown, embodiments of the present invention provide a non-invasive process fluid temperature calculation or estimation system that accurately reflects the temperature of process fluid flowing within a process fluid conduit (e.g., pipe) without intruding into the process fluid conduit itself. Accordingly, the heat flux based temperature calculation techniques described herein may be used to improve process control.

While the invention has been described with reference to preferred embodiments, those skilled in the art will recognize that: changes may be made in form and detail without departing from the spirit and scope of the invention.