WO2014021846A1

WO2014021846A1 - Indirect transducer temperature measurement

Info

Publication number: WO2014021846A1
Application number: PCT/US2012/048983
Authority: WO
Inventors: Robert Schaefer; Joseph Wuthijaroen
Original assignee: Siemens Aktiengesellschaft
Priority date: 2012-07-31
Filing date: 2012-07-31
Publication date: 2014-02-06

Abstract

The flow rate of a fluid flowing through a pipe can be measured with a clamp-on ultrasonic flowmeter, in which a pair of ultrasonic transducers are clamped onto the pipe. Each ultrasonic transducer includes an oscillator fixed to a wedge, which is fabricated from a plastic material. A parameter needed in the calculation of the flow rate is the sound velocity in the wedge. Since the sound velocity varies substantially with temperature, measurement of the temperature is needed to accurately determine the sound velocity at the operating temperature. Methods for indirectly determining the temperature of the wedge are illustrated. The ultrasonic flowmeter itself is used to determine the wedge temperature; separate temperature sensors and associated instrumentation are not required. The temperature is calculated from measurements of the transit times of acoustic signals transmitted through the pipe wall by internal reflections.

Description

INDIRECT TRANSDUCER TEMPERATURE MEASUREMENT TECHNICAL FIELD

[0001] The present invention relates generally to ultrasonic flowmeters, and more particularly to indirect measurement of the temperature of ultrasonic transducers.

BACKGROUND

[0002] In many commercial and industrial applications, fluids (liquids and gases) are transported through pipes. A key process parameter is the flow rate of the fluid through the pipe. The flow rate can be measured with an ultrasonic flowmeter. Ultrasonic flowmeters can be divided into two general categories: (a) ultrasonic flowmeters with sensors in contact with the fluid stream and (b) ultrasonic flowmeters with sensors not in contact with the fluid stream. Sensors in contact with the fluid stream have several disadvantages; for example: (a) the sensors can be attacked by the fluid, especially if the fluid is hot, corrosive, or contains abrasive particles, (b) the sensors and sensor ports can be fouled by contaminants in the fluids, and (c) maintenance or replacement of the sensors may require the fluid stream either to be turned off or to be redirected to bypass the sensors.

[0003] A widely-deployed ultrasonic flowmeter in which the sensors do not contact the fluid is a clamp-on ultrasonic flowmeter. In a clamp-on ultrasonic flowmeter, a pair of transducers is clamped onto a pipe wall. In addition to real-time monitoring of process flows, clamp-on ultrasonic flowmeters are well-suited for troubleshooting field installations, since the transducers are readily mounted and demounted. In a common configuration of a clamp-on ultrasonic flowmeter, two transducers are aligned along the pipe wall on an axis parallel to the longitudinal axis of the pipe. One transducer, consequently, is positioned downstream with respect to the other transducer: relative to the direction of fluid flow, one transducer is referenced as the upstream transducer, and the other transducer is referenced as the downstream transducer.

[0004] In the first step of the measurement process, the upstream transducer transmits an ultrasonic pulse through the near-end (adjacent) pipe wall. The near-end pipe wall is the portion of the pipe wall onto which the transducers are clamped. The ultrasonic pulse travels through the fluid, reflects off the far-end (opposite) pipe wall, travels back through the fluid, travels back through the near-end pipe wall, and is detected by the downstream transducer. The downstream transit time between the transmission and detection of the ultrasonic pulse is measured.

[0005] In the second step of the measurement process, the downstream transducer transmits an ultrasonic pulse through the near-end pipe wall. The ultrasonic pulse travels through the fluid, reflects off the far- end pipe wall, travels back through the fluid, travels back through the near- end pipe wall, and is detected by the upstream transducer. The upstream transit time between the transmission and detection of the ultrasonic pulse is measured.

[0006] Due to the flow velocity of the fluid, the downstream transit time is different from the upstream transit time. From the difference in transit times, the sound velocities in the media through which the ultrasonic pulses propagate, and the geometry of the pipe, the flow velocity can be calculated. From the flow velocity of the fluid and the geometry of the pipe, the flow rate of the fluid can be calculated.

[0007] A clamp-on transducer has two primary components: an oscillator and a wedge. The oscillator serves as both a transmitter and a detector of ultrasonic waves. The oscillator is fixed to the wedge, which is then clamped onto the pipe wall. For efficient transmission of the ultrasonic pulse from the transducer to the pipe wall, there must be tight coupling between the wedge and the pipe wall. The wedge is typically fabricated from a plastic material. In typical plastic materials used for wedges, the sound velocity has a significant variation with temperature. [0008] For accurate determination of the flow velocity, the sound velocity in the wedge must be accurately known; therefore, the temperature of the wedge must be accurately determined. From previously measured values of sound velocity as a function of temperature, the sound velocity can be determined if the wedge temperature is known. The wedge temperature can be directly measured by embedding a temperature sensor, such as a resistance temperature device (RTD), into the wedge. Embedding a temperature sensor, however, increases the manufacturing complexity and expense of the transducer. A separate set of lead wires and additional instrumentation may also be needed to process the signals from the

temperature sensor. A method and apparatus for accurately determining the temperature of the transducer without a temperature sensor would be advantageous.

BRIEF SUMMARY

[0009] In a first aspect, the temperature of the ultrasonic

transducers is determined indirectly using measurements by the ultrasonic transducers. The first ultrasonic transducer transmits a first group of acoustic pulses into the pipe wall. The second ultrasonic transducer receives a second group of acoustic pulses transmitted from the pipe wall. The second group of acoustic pulses corresponds to particular pulses in the first group of acoustic pulses that have propagated entirely within the pipe wall between the outer pipe wall surface and the inner pipe wall surface. The transit time of the second group of acoustic pulses is measured. From the transit time, the temperature of the ultrasonic transducers is calculated.

[0010] These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments will be further described in connection with the attached drawing figures. It is intended that the drawings included as a part of this specification be illustrative of the exemplary embodiments and should in no way be considered as a limitation on the scope of the invention. Indeed, the present disclosure specifically contemplates other embodiments not illustrated but intended to be included in the claims. Moreover, it is

understood that the figures are not necessarily drawn to scale.

[0011] Fig. 1 A— Fig. 1 C illustrate the geometry of a pipe;

[0012] Fig. 2 illustrates the principles of operation for a clamp-on ultrasonic flowmeter;

[0013] Fig. 3 illustrates the propagation path of pipe-wall acoustic signals;

[0014] Fig. 4 illustrates a timing diagram for acoustic signals;

[0015] Fig. 5 illustrates a high-level schematic of a measurement system for controlling an ultrasonic flowmeter and for processing data from an ultrasonic flowmeter;

[0016] Fig. 6 illustrates a high-level schematic of a signal control and processing unit implemented with a computer;

[0017] Fig. 7 illustrates a high-level flowchart for a method of indirectly determining the temperature of a transducer; and

[0018] Fig. 8 illustrates plots of the transit time of pipe-wall signals as a function of transducer temperature.

DETAILED DESCRIPTION

[0019] The exemplary embodiments provided are illustrative. The present invention is not limited to those embodiments described herein, but rather, the disclosure includes all equivalents.

[0020] A more detailed description of the embodiments will now be given with reference to Figs. 1 -8. Throughout the disclosure, like reference numerals and letters refer to like elements. The present disclosure is not limited to the embodiments illustrated; to the contrary, the present disclosure specifically contemplates other embodiments not illustrated but intended to be included in the claims.

[0021] Ultrasonic flowmeters are used to measure the flow of fluids (liquids and gases) through pipes. Herein, the term "pipe" refers to any conduit through which a fluid can flow; a duct is also an example of a pipe. Pipes can have various geometrical cross-sections, including circular, elliptical, square, rectangular, hexagonal, and irregular. For simplicity, cylindrical pipes are used in the examples below; however, embodiments of the invention can be configured for various geometrical forms.

[0022] Fig. 1 A illustrates an end view (View A), and Fig. 1 B illustrates a side view (View B), of a cylindrical pipe 100. The pipe 100 includes a pipe wall 102 with an outer pipe wall surface 104 and an inner pipe wall surface 106. The region within the inner pipe wall surface 106 is referenced as the region 108. The pipe 100 has an outer diameter D 101 , an inner diameter d 103, and a wall thickness W 105, where

w = (D - d) / 2.

[0023] Fig. 1 C illustrates a cross-sectional view (View M-M') of the pipe 100 with a fluid 120 flowing through it. The longitudinal axis of the pipe 100 is referenced as the longitudinal axis 107, which is also referred to as the

X -axis. In this cross-sectional view, the pipe wall 102 is represented by a pipe wall 102A (with an outer pipe wall surface 104A and an inner pipe wall surface 106A) and a pipe wall 102B (with an outer pipe wall surface 104B and an inner pipe wall surface 106B).

[0024] As illustrated in this example, the flow velocity of the fluid

120 is along the longitudinal axis 107 (the -axis points along the flow velocity). If the pipe is entirely filled with fluid, then the flow rate Q

(volume/time) is given by Q = { d² I )V_x,

where is the inner cross-sectional area of the pipe and V is the flow velocity. Assuming that the inner diameter d is known, the flow rate Q can be calculated from measurements of the flow velocity V .

[0025] Fig. 2 illustrates a schematic of a clamp-on ultrasonic flowmeter. The view illustrated is the cross-sectional view (View M-M'). To avoid obscuring details, the cross-hatching of the pipe wall 102A is

intentionally omitted. Two ultrasonic transducers (referred to herein also simply as transducers), referenced as the upstream transducer (transducer 202U) and the downstream transducer (transducer 202D) are coupled to the outer pipe wall surface 104A. For example, the transducers can be clamped onto the outer pipe wall surface or bonded onto the outer pipe wall surface. To simplify the figure, the coupling mechanism (for example, clamp) is not illustrated. The two transducers are aligned along a measurement axis substantially parallel to the longitudinal axis 107 of the pipe 100. The transducer 202U includes an oscillator 204U fixed to a wedge 206U.

Similarly, the transducer 202D includes an oscillator 204D fixed to a wedge 206D. The wedge 206U and the wedge 206D are typically fabricated from a plastic. Tight coupling between a wedge and the outer pipe wall surface is important for efficient transmission of acoustic energy between the transducer and the pipe wall.

[0026] Ultrasonic flowmeters typically operate over a frequency range from about 100 kHz to about 5 MHz. In keeping with common convention, waves in this frequency range are still referred to as acoustic waves. Acoustic transmission can be described by a ray-propagation model. When an incident acoustic ray strikes an interface between two different media, it is both reflected and refracted. Reflection is specular, and refraction obeys Snell's Law. A transducer can operate both as an acoustic transmitter and as an acoustic receiver. In the transmit mode, the oscillator is driven by an electronic pulse and transmits an acoustic pulse. In the receive mode, the oscillator is excited by an acoustic pulse and transmits an electronic pulse. In the example illustrated in Fig. 2, the transducer 202U acts as an acoustic transmitter, and the transducer 202D acts as an acoustic receiver. To simplify the figure, the transmitter and receiver electronics are not illustrated.

[0027] The oscillator 204U transmits an acoustic signal 201 through the wedge 206U. The acoustic signal 201 impinges upon the outer pipe wall surface 104A at the point 221 . The refracted acoustic signal 203 propagates through the pipe wall 102A and impinges upon the inner pipe wall surface 106A at the point 223. The refracted acoustic signal 205 propagates through the fluid 120 and impinges upon the inner pipe wall surface 106B at the point 225. The reflected acoustic signal 207 propagates through the fluid 120 and impinges upon the inner pipe wall surface 106A at the point 227. The refracted acoustic signal 209 propagates through the pipe wall 102A and impinges upon the outer pipe wall surface 104A at the point 229. The refracted acoustic signal 21 1 propagates through the wedge 206D and is received by the oscillator 204D.

[0028] A ray angle is referenced to a local normal axis at the point of impingement. The local normal axis is normal to the longitudinal axis 107 of the pipe 100. The incident angle 231 ( φ_λ ) is set by the geometry of the transducer 202U. The refracted angle 233 (φ₃ ), the refracted angle 235 (φ₂ ), the refracted angle 239 (φ₃ ), and the refracted angle 241 (φ_ι ) are governed by Snell's Law. The reflected angle 237 (φ₂ ) results from specular reflection.

[0029] The wedge material is referenced as medium 1 ; the fluid material is referenced as medium 2; and the pipe-wall material is referenced as medium 3. The sound velocities in medium 1 , medium 2, and medium 3 are referenced as C_x , C₂ , and C₃ , respectively. Then, according to Snell's

Law: sin(^) _ sin(^₂) _ sin(^₃)

(E2)

[0030] The downstream transit time ( T_dn ) is the time interval

between the time when an acoustic pulse is transmitted by the transducer

206U and the time that the acoustic pulse is received by the transducer 202D.

Similarly, the transducer 202D can transmit an acoustic pulse that is received by the transducer 202U. The upstream transit time ( ) is the time interval between the time when an acoustic pulse is transmitted by the transducer

206D and the time that the acoustic pulse is received by the transducer 202U.

[0031] Due to the flow velocity of the fluid 120, the downstream

transit time is different from the upstream transit time. The flow velocity V of the fluid can be calculated from the downstream transit time and the upstream transit time according to the equation:

τ fluid

where V is the transducer phase velocity, Δτ is the difference in transit times, and T ^_uid is the propagation time within the fluid. The values V , ^ 2\ and ^τ fluid are given by:

Ατ = τ ) u - τ (E5 p ( dn ' and

where T β_χβά is the fixed propagation time in the pipe wall and transducers.

From (E1 ), (E3), and (E4), the flow rate Q can be calculated as

nd AT

Q - x (E7)

Ssin^ T_FLMD

[0032] From (E7), it is apparent that the calculated value of the flow rate Q is directly dependent on the sound velocity C_X in the wedge material.

For plastic materials used for wedges, the sound velocity decreases as the temperature increases, and the temperature coefficient of sound velocity is significant. From previously measured values of C as a function of temperature, C_X can be determined if the wedge temperature is known. The wedge temperature can be directly measured by embedding a temperature sensor, such as a resistance temperature device (RTD), into the wedge.

Embedding a temperature sensor, however, increases the manufacturing

complexity and expense of the transducer. A separate set of lead wires and additional instrumentation may also be needed to process the signals from the temperature sensor.

[0033] In an embodiment of the invention, the wedge temperature is determined indirectly using measurements by the ultrasonic transducers. Temperature sensors, additional lead wires, and additional instrumentation are not needed.

[0034] Fig. 3 illustrates the principles underlying the indirect temperature measurement. The physical configuration of the transducers and the pipe is the same as that previously illustrated in Fig. 2. In this instance, the acoustic signal propagating via internal reflections within the pipe wall 102A from one transducer to the other transducer is measured. This acoustic signal, commonly referred to as the "pipe-wall signal" or "short-circuit signal", is normally considered to be an undesirable signal since it can interfere with the measurement of the primary acoustic signal propagating through the fluid. In an embodiment of the invention, however, the pipe-wall signal is

advantageously used to indirectly determine the wedge temperature.

[0035] The oscillator 204U transmits an acoustic signal 301 through the wedge 206U. The acoustic signal 301 impinges upon the outer pipe wall surface 104A at the point 321 . The refracted acoustic signal 303 propagates through the pipe wall 102A and impinges upon the inner pipe wall surface 106A at the point 323. The reflected acoustic signal 305 propagates through the pipe wall 102A and impinges upon the outer pipe wall surface 104A at the point 325. The reflected acoustic signal 307 propagates through the pipe wall 102A and impinges upon the inner pipe wall surface 106A at the point 327. The reflected acoustic signal 309 impinges upon the outer wall 104A at the point 329. The refracted acoustic signal 31 1 propagates through the wedge 206D and is received by the oscillator 204D. For illustration, three internal reflections are illustrated in Fig. 3. In general, the number of internal reflections will vary, depending on a number of parameters such as the geometry of the transducers, the geometry of the pipe, and the spacing between the transducers.

[0036] The distance 343 is the distance that the acoustic signal 301 propagates within the wedge 206U; the distance 343 is measured between the oscillator 204U and the entrance point 321 . Similarly, the distance 345 is the distance that the acoustic signal 31 1 propagates within the wedge 206D; the distance 345 is measured between the oscillator 204D and the exit point 329. In this instance, distance 343 = distance 345 = S , which is referred to herein as the propagation distance within the transducer. The spacing

(distance) between the transducer 202U and the transducer 202D is the

spacing 341 = L . The spacing L is measured along the measurement axis substantially parallel to the longitudinal axis 107 between the entrance point

321 and the exit point 329. Typical values are S = 0.5 to 6 inches, and L = 0.5 to 24 inches.

[0037] A ray angle is referenced to a local normal axis at the point of impingement. The local normal axis is normal to the longitudinal axis 107 of the pipe 100. At the transducer 202U, the incident angle 331 ( O ) is set by the geometry of the transducer 202U. The refracted angle 333 (p) is

governed by Snell's Law. At the transducer 202D, the incident angle 335 is p as a result of one or more specular reflections within the pipe wall 102A.

The refracted angle 337 is C , as governed by Snell's Law.

[0038] The pipe-wall transit time TT_pipe of an acoustic signal (the pipe-wall signal) transmitted from the oscillator 202U, transmitted through the wedge 206U, transmitted along the pipe wall 102A, transmitted through the wedge 206D, and received by the oscillator 204D can be expressed by the following equation:

L 2S

TT = + . (E8) pipe y

group wedge

In (E8), C_wedge is the compression wave sound velocity in the wedge material, and V_ormin is the group velocity (defined by the velocity of the wave packet) in the pipe wall 102A. The group velocity is given by the expression

^V group = ^Cp_ipe ^ⁿ P ' (E9) where C _{ is the shear velocity in the pipe wall 102A. Since the pipe-wall signal does not travel through the fluid 120, the pipe-wall transit time TT_pipe for an acoustic pulse transmitted by the transducer 202U and received by the transducer 202D is the same as the pipe-wall transit time TT_pipe for an acoustic pulse transmitted by the transducer 202D and received by the transducer 202U.

[0039] The wedge material is generally some formulation of thermoplastic (including, but not limited to, polyetherimide, polyether-ether- ether-ketone, or polysulfone) that has a sufficiently low compression-wave sound velocity to ensure that only the mode-converted shear-wave signal enters the pipe wall. A significant consequence of using thermoplastic wedge material is that the sound velocity of the wedge material is highly dependent on the temperature of the wedge. Pipes, however, are typically fabricated from steel or other metals. The shear velocity of steel, or other metals, is nearly constant over temperature ranges encountered in most applications of interest. Embodiments of the invention can be adapted for any pipe material in which the change of sound velocity in the pipe material is substantially less than the change in sound velocity in the wedge material over the operating temperature range of interest.

[0040] The equation below indicates a linear relationship between the sound velocity and the temperature of a wedge material:

^ wedge ^ wedge, ref ^c, wedge ^ref ) '

wedge temperature;

= reference temperature (70 deg F, in this instance) ^Cwedge ^{= souncl} velocity in the wedge material at the temperature t ; Cwedge ref ^{= reference} sound velocity in the wedge material at the reference temperature t rej _f ; and

T_{c wedge} = temperature coefficient of sound velocity in the wedge material.

The values t_ref , C_wedge^ref , and T^_wedge are known from previous measurements. A material commonly used for wedges is an amorphous thermoplastic polyetherimide (PEI) resin (such as ULTEM). For this material, the values are: t_ref = 70 deg F; cwed_ge,ref = ⁹⁷'⁰⁰⁰ 'nches/sec; and Tc,wedge = ^"34-²⁷ (inches/sec)/deg F.

[0041] This relationship can be used to infer the temperature t of the wedge by measuring TT_pipe. The temperature t of the wedge characterizes the temperature of both transducers under the following assumptions: for each transducer, the temperature of the oscillator and the temperature of the wedge is the same; for each transducer, the temperature within the transducer is uniform (no temperature gradients); and the temperature of both transducers is the same. From (E8) and (E10), the following relationship is derived:

IS

^ ^r group ^wedge,ref ^c, wedge ^ref )

[0042] The refraction angle in the pipe wall ( } ), and therefore the group velocity, is also dependent on the sound velocity in the wedge. By

Snell's Law, V_group can be written in terms of the incident angle { C ), the sound velocity in the wedge { C_wedge ), and the sound velocity in the pipe

'pipe c . sin or

γ group = c pipe . ^pipe

^C wedge (E12)

^ wedge, ref ^c, wedge ^re ^" )

[0043] Assuming that the dimensions _* and L and the sound

velocity {C _t ) in the pipe wall change negligibly with temperature compared to the change in the sound velocity in the wedge, then the TT equation can be written as: L-c wedge, ref ⁺ L-T_cwedge(t t_rr_eef_f) .

7 p„i .p.e. = +

c pip . e smcir

(E13)

IS

wedge, ref c, wedge {' -Kef)

(E13) can be rewritten as

r r wedge, ref c, wedge

pipe 2 · 2

(E14)

2S wedge, ref c, wedge

[0044] The values _* and CC are set by the geometry of the

transducer 202U and the transducer 202D. The value L is set during

installation. The values of C_wedge^ , t_ref, and T_CfWedge are known values of the wedge material. The value of C _{ is a known value of the pipe material.

Therefore, if the pipe-wall transit time TT_pipe is measured, then the wedge temperature t can be calculated by solving (E14), which can be rewritten as a quadratic equation:

A_l (At)² + A₂At + A₃=0, (E15)

where At = t— t _f. (E15) is solved for At , and t is calculated from t = t_ref + At . (E16)

From (E14), the coefficients in (E15) are given by:

(E17)

2L - c wedge, ref - T c, wedge r

(E18) c, wedge - TT pipe '

^Cp_ipe *^{m a} and

L - c²

A₃ = 2S + ^wedge'^ref - c_{wed f} · TT . (E19)

^C _pipe *^{m a}

As discussed above, the temperature t of the wedge characterizes the

temperature of both transducers under the following assumptions: for each transducer, the temperature of the oscillator and the temperature of the

wedge is the same; for each transducer, the temperature within the

transducer is uniform (no temperature gradients); and the temperature of both transducers is the same.

[0045] Fig. 4 illustrates a timing diagram for acoustic signals. The horizontal axis 401 represents time, and the vertical axis 403 represents pulse amplitude. The group of pulses 402 is the pulse train transmitted by the

oscillator 204U. The group of pulses 404, with signal envelope 406,

represents the group of pulses corresponding to the subset of the group of pulses 402 that were transmitted through the pipe wall only and received by the oscillator 204D; the group of pulses 404 correspond to the pipe-wall signal. The group of pulses 414, with signal envelope 416, represents the group of pulses corresponding to the subset of the group of pulses 402 that were transmitted both through the pipe wall and through the fluid and received by the oscillator 204D; the group of pulses 414 correspond to the fluid signal. The fluid signal has a longer transit time than the pipe-wall signal. The time interval between the transmission of the group of pulses 402 and the reception of the group of pulses 404 is the pipe-wall transit time TT_pipe 405.

The time interval between the transmission of group of pulses 402 and the reception of the group of pulses 414 is the fluid transit time TT^_uid 407, which is used to calculate the flow velocity.

[0046] Fig. 5 illustrates a high-level schematic of a measurement system used to measure the pipe-wall transit time and calculate the transducer temperature. The same measurement system is also used to measure the fluid transit time and calculate the flow rate. The measurement system 500 includes the signal control and processing unit (SCPU) 502, the transmitter 504, the receiver 506, the gain control unit 508, the analog-to- digital converter (ADC) 510, and the multiplexer switch 512.

[0047] In the transmit mode, the SCPU 502 sends a control signal 557 to the switch 512 to connect the pole 512A to the pole 512C. The SCPU 502 also sends a control signal 551 to the transmitter 504, which sends a group of electronic pulses 505 to the transducer 202U. The transducer 202U then transmits a group of acoustic pulses (ultrasonic pulses).

[0048] In the receive mode, the SCPU 502 sends a control signal 557 to the switch 512 to connect the pole 512A to the pole 512B. A group of acoustic pulses is received by the transducer 202D, which transmits a group of electronic pulses 515. The group of electronic pulses 515 is received by the receiver 506. The SCPU 502 sends a control signal 553 to the gain control unit 508. The gain control unit 508 sends a control signal 555 to the receiver 506. The control signal 555 adjusts the gain of an amplifier in the receiver 506.

[0049] The analog output signal 517 of the receiver 506 is sent to the ADC 510. The digital output signal 519 of the ADC 510 is sent to the SCPU 502 for data processing. The SCPU 502 separates the pipe-wall signals from the fluid signals, measures the pipe-wall transit time, calculates the temperature of the wedge, and calculates the sound velocity in the wedge. The pipe-wall signals can be separated from the fluid signals, for example, based on the expected range of transit times for each type of signal. The SCPU 502 also measures the fluid transit time. By suitable control of the multiplexer switch 512, both upstream and downstream transit times in the fluid can be measured. From the sound velocity in the wedge and

measurements of the upstream and downstream transit times in the fluid, the SCPU 502 calculates the flow rate of the fluid.

[0050] An embodiment of the SCPU 502 is illustrated in Fig. 6. The SCPU 502 can be configured, programmed, and operated by a user, such as a test engineer. One skilled in the art can construct the SCPU 502 from various combinations of hardware, firmware, and software. One skilled in the art can construct the SCPU 502 from various electronic components, including one or more general purpose processors (such as microprocessors), one or more digital signal processors, one or more application-specific integrated circuits (ASICs), and one or more field-programmable gate arrays (FPGAs).

[0051] The SCPU 502 includes a computer 602, which includes, but is not limited to, one or more of a processor [referred to as a central processing unit (CPU)] 604, memory 606, and a data storage device 608. The data storage device 608 includes at least one persistent, non-transitory, tangible computer readable medium, such as non-volatile semiconductor memory, a magnetic hard drive, or a compact disc read only memory.

[0052] The SCPU 502 further includes the gain control unit interface 624 for communicating with the gain control unit 508, the transmitter interface 626 for communicating with the transmitter 504, the ADC interface 628 for communicating with the ADC 510, and the multiplexer switch interface 630 for communicating with the multiplexer switch 512.

[0053] The SCPU 502 can further include a user input/output interface 620, which interfaces the computer 602 to user input/output devices 630. Examples of user input/output devices 630 include, but are not limited to, a keyboard, a mouse, a local access terminal, and a video display. Data, including computer executable code, can be transferred to and from the computer 602 via the user input/output interface 620.

[0054] The SCPU 502 can further include a communications network interface 622, which interfaces the computer 602 with the

communications network 632. The communications network 632 can be a local area network, a wide area network, or combinations of local area networks and wide area networks. A user can access the computer 602 via a remote access terminal (not illustrated) communicating with the

communications network 632. Data, including computer executable code, can be transferred to and from the computer 602 via the communications network interface 622.

[0055] Each of the interfaces described above can operate over different communications media. Examples of communications media include wires, free-space optics, and electromagnetic waves (typically in the radiofrequency range and commonly referred to as a wireless interface).

[0056] As is well known, a computer operates under control of computer software, which defines the overall operation of the computer and applications. The CPU 604 controls the overall operation of the computer and applications by executing computer program instructions that define the overall operation and applications. The computer program instructions can be stored in the data storage device 608 and loaded into the memory 606 when execution of the program instructions is desired.

[0057] Algorithms, such as one described by (E14) or one described schematically by step 704 - step 712 in the flowchart of Fig. 7 (see below), can be defined by computer program instructions stored in the memory 606 or in the data storage device 608 (or in a combination of the memory 606 and the data storage device 608) and controlled by the CPU 604 executing the computer program instructions. For example, the computer program instructions can be implemented as computer executable code programmed by one skilled in the art to perform algorithms. Accordingly, by executing the computer program instructions, the CPU 604 executes the algorithms, such as one described by (E14) or one described schematically by step 704 - step 712 in the flowchart of Fig. 7.

[0058] Fig. 7 illustrates a flowchart of a method, according to an embodiment of the invention, for indirectly determining the temperature of a pair of ultrasonic transducers in an ultrasonic flowmeter. As discussed above, the temperature of the pair of ultrasonic transducers is assumed to be the same.

[0059] In step 702, transducer 1 and transducer 2 are clamped onto the outer pipe wall surface of a pipe. Transducer 1 and transducer 2 are spaced apart along a measurement axis substantially parallel to the

longitudinal axis of the pipe. In step 704, acoustic pulses are transmitted from transducer 1 . In step 706, acoustic pulses are received by transducer 2. In 708, the received acoustic pulses corresponding to pipe-wall signals are determined. The pipe-wall signals can be distinguished from the fluid signals, for example, based on the expected range of transit times for each type of signal. In step 710, the transit time of the pipe-wall acoustic pulses are measured. In step 712, the temperature of the transducers is calculated from the transit time of the pipe-wall acoustic pulses.

[0060] Fig. 8 illustrates plots of pipe-wall transit times TT

(measured in sec ) as a function of the wedge temperature t (measured in deg F); the temperature was measured with an independent resistance temperature device embedded within the transducer wedge. Plot 802 shows the theoretical values. Plot 804 shows the measured values. There is good agreement.

[0061] The foregoing Detailed Description is to be understood as being in every respect illustrative and exemplary, but not restrictive, and the scope of the invention disclosed herein is not to be determined from the Detailed Description, but rather from the claims as interpreted according to the full breadth permitted by the patent laws. It is to be understood that the embodiments illustrated and described herein are only illustrative of the principles of the present invention and that various modifications may be implemented by those skilled in the art without departing from the scope and spirit of the invention. Those skilled in the art could implement various other feature combinations without departing from the scope and spirit of the invention. Moreover, those of skill in the art will appreciate that embodiments not expressly illustrated herein may be practiced within the scope of the present discovery, including that features described herein for different embodiments may be combined with each other and/or with currently-known or future-developed technologies while remaining within the scope of the claims presented here. Furthermore, the advantages described above are not necessarily the only advantages of the discovery, and it is not necessarily expected that all of the described advantages will be achieved with every embodiment of the discovery.

Claims

CLAIMS:

1 . A method for determining a temperature of a first ultrasonic transducer and a second ultrasonic transducer, wherein the first ultrasonic transducer and the second ultrasonic transducer are coupled to a pipe, wherein the pipe has a longitudinal axis and a pipe wall substantially parallel to the longitudinal axis, wherein the pipe wall has an outer pipe wall surface and an inner pipe wall surface, and wherein the first ultrasonic transducer and the second ultrasonic transducer are disposed on the outer pipe wall surface and spaced apart along a measurement axis substantially parallel to the longitudinal axis, the method comprising the steps of:

transmitting, at a first time, from the first ultrasonic transducer, a first plurality of acoustic pulses into the outer pipe wall surface;

receiving, at a second time, at the second ultrasonic transducer, a second plurality of acoustic pulses transmitted from the outer pipe wall surface, wherein the second plurality of acoustic pulses

corresponds to particular acoustic pulses in the first plurality of acoustic pulses that propagate entirely within the pipe wall between the outer pipe wall surface and the inner pipe wall surface;

measuring a transit time of the second plurality of acoustic pulses, wherein the transit time is a difference between the second time and the first time; and

calculating the temperature of the first ultrasonic transducer and the second ultrasonic transducer based at least in part on the transit time.

2. The method of claim 1 , wherein at least one acoustic pulse in the first plurality of acoustic pulses has a frequency from about 100 kHz to about 5 MHz.

3. The method of claim 1 , wherein the first ultrasonic transducer and the second ultrasonic transducer are clamped onto the outer pipe wall surface.

4. The method of claim 1 , wherein:

the first ultrasonic transducer comprises a first oscillator and a first wedge;

the second ultrasonic transducer comprises a second oscillator and a second wedge; and

the first wedge and the second wedge comprise a wedge material.

5. The method of claim 4, wherein the wedge material comprises a thermoplastic material.

6. The method of claim 4, wherein the step of calculating the temperature of the first ultrasonic transducer and the second ultrasonic transducer based at least in part on the transit time comprises the steps of: calculating a value At from an equation

wherein:

At t - t ref

L - T c², wedge

A 2

C pipe sm a 2L - c wedge, ref · Τ c, wedge

c, wedge •TT pipe ' c pip . e sm <

L - c

A₃ = 2S + wedge, ref

^wedge,ref TT pipe ^:

c pip . e sm a t is the temperature of the first ultrasonic transducer and the second ultrasonic transducer;

t_ref is a reference temperature;

S is a propagation distance within the first ultrasonic transducer and the second ultrasonic transducer;

L is a spacing between the first ultrasonic transducer and the second ultrasonic transducer;

^Cwedge ref ^{is 3 souncl} velocity in the wedge material at the reference temperature t_re^ ;

T _f is a temperature coefficient of sound velocity in the wedge material;

^Cpipe ^{is a souncl} velocity in the pipe wall;

C is an incident angle of the first plurality of acoustic pulses; and

TT_pipe is the transit time of the second plurality of acoustic pulses; and

calculating the temperature of the first ultrasonic transducer and the second ultrasonic transducer from the equation:

7. A computer readable medium storing computer program instructions for determining a temperature of a first ultrasonic transducer and a second ultrasonic transducer, wherein the first ultrasonic transducer and the second ultrasonic transducer are coupled to a pipe, wherein the pipe has a

longitudinal axis and a pipe wall substantially parallel to the longitudinal axis, wherein the pipe wall has an outer pipe wall surface and an inner pipe wall surface, wherein the first ultrasonic transducer and the second ultrasonic transducer are disposed on the outer pipe wall surface and spaced apart along a measurement axis substantially parallel to the longitudinal axis, and wherein the computer program instructions, when executed on a processor, cause the processor to perform a method comprising the steps of:

8. The computer readable medium of claim 7, wherein at least one acoustic pulse in the first plurality of acoustic pulses has a frequency from about 100 kHz to about 5 MHz.

9. The computer readable medium of claim 7, wherein the first ultrasonic transducer and the second ultrasonic transducer are clamped onto the outer pipe wall surface.

10. The computer readable medium of claim 7, wherein:

the first ultrasonic transducer comprises a first oscillator and a first wedge;

the first wedge and the second wedge comprise a wedge material.

1 1 . The computer readable medium of claim 10, wherein the wedge material comprises a thermoplastic material.

12. The computer readable medium of claim 10, wherein the step of calculating the temperature of the first ultrasonic transducer and the second ultrasonic transducer based at least in part on the transit time comprises the steps of:

calculating a value At from an equation

Α_λ(Αί)² + A₂At + A₃ = 0; wherein: L - T c², wedge

c p²ip. e sin a

2L - c wedge, ref - T c, wedge

c, wedge •TT pipe ' c pip . e sm a

L

2S + 'wedge, ref

^wedge,ref TT pipe

^Cpipe *^{m a} t is the temperature of the first ultrasonic transducer and the second ultrasonic transducer;

t rej _f is a reference temperature;

T _f is a temperature coefficient of sound velocity in the wedge material;

C_pipe is a sound velocity in the pipe wall;

C is an incident angle of the first plurality of acoustic pulses; and TT_pipe is the transit time of the second plurality of acoustic pulses; and

calculating the temperature of the first ultrasonic transducer and the second ultrasonic transducer from the equation: t = t_ref + At .

13. A system for determining a temperature of a first ultrasonic transducer and a second ultrasonic transducer, wherein the first ultrasonic transducer and the second ultrasonic transducer are coupled to a pipe, wherein the pipe has a longitudinal axis and a pipe wall substantially parallel to the longitudinal axis, wherein the pipe wall has an outer pipe wall surface and an inner pipe wall surface, and wherein the first ultrasonic transducer and the second ultrasonic transducer are disposed on the outer pipe wall surface and spaced apart along a measurement axis substantially parallel to the longitudinal axis, the system comprising:

a signal control and processing unit;

a transmitter;

a receiver; and

an analog-to-digital converter;

wherein:

the signal control and processing unit is configured to transmit a first control signal to the transmitter;

the transmitter is configured to:

receive the first control signal from the signal control and processing unit; and

in response to receiving the first control signal, transmit, at a first time, a first plurality of electronic pulses to the first ultrasonic transducer, wherein the first plurality of electronic pulses drives the first ultrasonic transducer to transmit a first plurality of acoustic pulses into the outer pipe wall surface;

the receiver is configured to:

receive, at a second time, a second plurality of electronic pulses from the second ultrasonic transducer, wherein the second plurality of electronic pulses is excited by a second plurality of acoustic pulses

corresponding to particular acoustic pulses in the first plurality of acoustic pulses that propagate entirely within the pipe wall between the outer pipe wall surface and the inner pipe wall surface; and

in response to receiving the second plurality of electronic pulses, transmit to the analog-to-digital converter a third plurality of electronic pulses, wherein the third plurality of electronic pulses is based at least in part on the second plurality of electronic pulses;

the analog-to-digital converter is configured to:

receive the third plurality of electronic pulses from the receiver; and

in response to receiving the third plurality of electronic pulses, transmit digital data to the signal control and processing unit, wherein the digital data is based at least in part on the third plurality of electronic pulses; and

the signal control and processing unit is further configured to:

receive the digital data from the analog-to-digital converter;

in response to receiving the digital data, determine a transit time of the second plurality of acoustic pulses, wherein the transit time is a difference between the second time and the first time; and calculate, based at least in part on the transit time, the temperature of the first ultrasonic transducer and the second ultrasonic transducer.

14. The system of claim 13, wherein at least one acoustic pulse in the first plurality of acoustic pulses has a frequency from about 100 kHz to about 5 MHz.

15. A signal control and processing unit comprising:

a processor;

memory operably coupled to the processor; and

a data storage device operably coupled to the processor and the memory;

wherein the data storage device stores computer program instructions for determining a temperature of a first ultrasonic transducer and a second ultrasonic transducer, wherein the first ultrasonic transducer and the second ultrasonic transducer are coupled to a pipe, wherein the pipe has a longitudinal axis and a pipe wall substantially parallel to the longitudinal axis, wherein the pipe wall has an outer pipe wall surface and an inner pipe wall surface, wherein the first ultrasonic transducer and the second ultrasonic transducer are disposed on the outer pipe wall surface and spaced apart along a measurement axis substantially parallel to the longitudinal axis, and wherein the computer program instructions, when executed on the processor, cause the processor to perform a method comprising the steps of:

measuring the transit time of the second plurality of acoustic pulses, wherein the transit time is a difference between the second time and the first time; and

16. The signal control and processing unit of claim 15, wherein at least one acoustic pulse in the first plurality of acoustic pulses has a frequency from about 100 kHz to about 5 MHz.

17. The signal control and processing unit of claim 15, wherein the first ultrasonic transducer and the second ultrasonic transducer are clamped onto the outer pipe wall surface.

18. The signal control and processing unit of claim 15, wherein:

the first ultrasonic transducer comprises a first oscillator and a first wedge;

the first wedge and the second wedge comprise a wedge material.

19. The signal control and processing unit of claim 18, wherein the wedge material comprises a thermoplastic material.

20. The signal control and processing unit of claim 18, wherein the step of calculating the temperature of the first ultrasonic transducer and the second ultrasonic transducer based at least in part on the transit time comprises the steps of:

calculating a value At from an equation

A_Y(At)² + A₂At + A₃ =0; wherein:

At = t-t ref

L-T c², wedge

c p²ip.e sin a

2L-c wedge, ref -T c, wedge j r i

c, wedge •TT pipe ' c pip .e sma

A _ O __| L-c w²edge,ref _

^3 ^ 2 · wedge, ref ^{' 1 1} pipe

c pip .e sm t is the temperature of the first ultrasonic transducer and the second ultrasonic transducer;

t_ref is a reference temperature;

S is a propagation distance within the first ultrasonic transducer and the second ultrasonic transducer; L is a spacing between the first ultrasonic transducer and the second ultrasonic transducer;

T is a temperature coefficient of sound velocity in the wedge material;

C_pipe is a sound velocity in the pipe wall;

C is an incident angle of the first plurality of acoustic pulses; and

TT pip■e is the transit time of the second p ^lurality ³ of acoustic pulses; and