Dynamic Temperature Calibration of Ultrasonic Transducers

Abstract

A computer readable storage device (106) stores machine instructions that, when executed by one or more central processing unit (CPU) cores (102), cause the one or more CPU cores to use a first ultrasonic transducer (95) and a second ultrasonic transducer (98) to measure fluid flow using a current measurement frequency and to perform a temperature calibration process. The temperature calibration process includes sequentially generating a plurality of electrical signals for the first ultrasonic transducer (95), the generated electrical signals each having a different frequency. For each frequency, the temperature calibration process includes measuring the amplitude of the signal from the second ultrasonic transducer (98). Based on the measured amplitude of the signal from the second ultrasonic transducer (98), the temperature calibration process includes determining a new measurement frequency. The first and second ultrasonic transducers (95, 98) are used to measure fluid flow using the new measurement frequency.

Description

Background Art

[0001] Flow meters are used to measure the flow of fluid through a pipe. Some flow meters use ultrasonic transducers, where an ultrasonic signal is injected into the fluid flow in the downstream direction of the fluid flow between two ultrasonic transducers and the absolute time of flight (TOF) is determined in the downstream direction. Another ultrasonic signal is injected in the upstream direction, and the absolute TOF between the transducers in that direction is also determined. The difference in TOF between the upstream and downstream directions can be used to calculate the velocity of the fluid flow, and, knowing the cross-sectional area of ​​the pipe, the flow rate. Summary of the invention

[0002] A computer readable storage device stores machine instructions that, when executed by one or more central processing unit (CPU) cores, cause the one or more CPU cores to use a first ultrasonic transducer and a second ultrasonic transducer to measure a fluid flow rate using a current measurement frequency and to perform a temperature calibration process. The temperature calibration process includes sequentially generating a plurality of electrical signals for the first ultrasonic transducer, each of the generated electrical signals having a different frequency. For each frequency, the temperature calibration process includes measuring the amplitude of the signal from the second ultrasonic transducer. Based on the measured amplitude of the signal from the second ultrasonic transducer, the temperature calibration process includes determination of a new measurement frequency. The first and second ultrasonic transducers are used to measure the fluid flow rate using the new measurement frequency. BRIEF DESCRIPTION OF THE DRAWINGS

[0003] For a detailed description of various examples, reference will now be made to the accompanying drawings, in which:

[0004] Figure 1 A flow meter according to one example is described.

[0005] Figure 2 This indicates that the frequency response of an ultrasonic transducer is at least partially temperature dependent.

[0006] Figure 3 Illustrate the frequency sweep performed during the temperature-based calibration process.

[0007] Figure 4 The pulse train used during the temperature based calibration process is described.

[0008] Figure 5 An example of an ultrasonic transducer circuit that can be used to perform a temperature-based calibration process is presented.

[0009] Figure 6 An example of a method demonstrating a temperature based calibration process. DETAILED DESCRIPTION

[0010] For at least some ultrasonic transducers used in flow meters, the sensitivity of the transducer varies with frequency. For example, the maximum transducer sensitivity may be at a particular frequency. In addition, the sensitivity of the transducer may vary with temperature. That is, the frequency corresponding to the maximum sensitivity of the transducer may vary with the temperature of the fluid whose flow rate the flow meter is monitoring.

[0011] The described examples relate to a circuit (e.g., an integrated circuit (IC)) for a flow meter that performs a temperature-based calibration process. The flow meter includes a plurality of ultrasonic transducers. The temperature-based calibration process includes scanning one of the transducers over a frequency range from a lower frequency to a higher frequency (i.e., providing a range of excitation frequencies to the transducer), monitoring the amplitude of a signal from another transducer in the flow meter, and determining a frequency within the frequency range that corresponds to a maximum sensitivity. The flow meter is then configured to use as an excitation frequency the frequency determined according to a calibration process performed when measuring the flow rate of a fluid. The temperature-based calibration process may be repeated over time, whereby its excitation frequency is dynamically adjusted in response to changes in temperature. The temperature-based calibration process is thus performed dynamically, i.e., while the flow meter is being used to perform flow rate measurements of a fluid flow in a pipe.

[0012] Figure 1 An example of a flow meter 100 is shown. The example flow meter 100 includes one or more central processing unit (CPU) cores 102, an ultrasonic transducer (UST) circuit 104, a storage device 106, and a display 108. The term "CPU core" (singular) is used herein to refer to a single CPU core or multiple CPU cores. In one embodiment, the flow meter 100 includes a microcontroller unit (MCU) manufactured as an integrated circuit on a common semiconductor substrate. The flow meter 100 also includes or is coupled to ultrasonic transducers 95 and 98, which are shown to be coupled to a tube 90 in which a fluid flows in the direction of arrow 99. In this example, a pair of ultrasonic signal reflectors 92 and 93 are included in the tube 90. The UST circuit 104 can provide an electrical signal to either of the transducers 95 or 98 and monitor the resulting signal from the other transducer. For example, the transducer 95 can convert an electrical signal from the UST circuit 104 into an ultrasonic signal injected into the fluid flow in the tube 90. The ultrasonic signal is reflected from reflector 92 and then from reflector 93, as indicated by arrow 96 (in the downstream direction). The ultrasonic signal is then received by transducer 98 and converted back into an electrical signal and provided to UST circuit 104. Alternatively, UST circuit 104 may use transducer 98 as a transmitting transducer and transducer 95 as a receiving transducer, thereby causing the ultrasonic signal to pass through the fluid in the direction of arrow 97 (in the upstream direction). In some embodiments, tube 90 does include reflectors 92 and 93.

[0013] UST circuit 104 measures the time it takes for an ultrasonic signal to pass from one transducer through the fluid flow to another transducer. In the absence of fluid flow relative to transducers 95, 98, the velocity of the ultrasonic signal in the fluid varies depending on the type of fluid in tube 90. Time is distance / velocity, and therefore, the time required for an ultrasonic signal to pass in the downstream direction (i.e., from transducer 95 through the fluid and to transducer 98) is L / (c+v), where L is the combined distance from transducer 95 to reflector 92 to reflector 93 and to transducer 98 and is a known value, c is the velocity of ultrasound relative to the fluid being monitored, and v is the velocity of the fluid flow in direction 99. In the upstream direction (i.e., from transducer 98 to transducer 95), the time required for an ultrasonic signal to pass from transducer 98 to transducer 95 is L / (cv). The difference in the time values ​​is ΔT and the velocity of the fluid is:

[0014]

[0015] Where T1 is the measured time from transducer 95 to transducer 98, and T2 is the measured time from transducer 98 to transducer 95. Thus, by measuring T1 and T2 using UST circuit 104, the velocity of the fluid flow can be calculated. The cross-sectional area of ​​tube 90 is also known and the volume of the interior of the tube between transducers 95 and 98 can be calculated and is known a priori. Assuming the tube is full of fluid, the fluid flow rate can be determined based on the calculated velocity.

[0016] The storage device 106 includes volatile or non-volatile memory (non-transitory computer readable storage device) and includes firmware (machine instructions) 111. The firmware 111 can be executed by one or more CPU cores 102. After executing the firmware 111, the CPU core 102 interacts with the UST circuit 104 to (a) determine the flow rate of the fluid in the tube 90 and (b) perform a temperature calibration process to determine the excitation frequency for measuring the flow rate given the current temperature of the fluid in the tube 90. In some embodiments, the temperature calibration process is performed periodically (e.g., every 5 minutes, every 10 minutes, etc.) and between flow rate determinations (so as not to interfere with evaluating the flow rate). The display 108 can be used by the CPU core 102 to display flow rate, status, etc.

[0017] Figure 2Two example frequency response curves 202 and 204 of an ultrasonic transducer are illustrated. Each curve 202, 204 represents the amplitude of an electrical signal generated by the transducer in response to the reception of an ultrasonic signal across a frequency range. The amplitude of the ultrasonic signal received by the transducer is the same at each frequency. The transducer generates an electrical output signal based on the received ultrasonic signal. Each curve 202, 204 illustrates that the amplitude of the electrical output signal from the transducer varies with frequency. The amplitude response is maximum at frequency Fm1 for curve 202 and maximum at frequency Fm2 for curve 204, the frequency response curve 202 represents the frequency response of the ultrasonic transducer for a temperature at which the transducer operates, and the frequency response 204 represents the frequency response of the same transducer at different temperatures. As can be seen, the peak amplitude (maximum sensitivity) varies according to temperature. The temperature calibration process described herein determines the peak amplitude for a given fluid temperature and uses the corresponding frequency for flow rate determination.

[0018] Return to reference Figure 1 UST circuit 104 includes a register set 110 including one or more registers. At least some of the registers can be configured and / or read by CPU core 102. In one embodiment, CPU core 102 programs register set 110 with one or more values ​​indicating the frequency that UST circuit 104 will generate for one of transducers 95, 98. During the temperature calibration process, CPU core 102 sequences through a frequency range from a first frequency to a second frequency. The first frequency may be lower than the second frequency, or vice versa. That is, the frequency sweep may be from a lower frequency to a higher frequency, or from a higher frequency to a lower frequency. The frequency range should be wide enough to include an excitation frequency that will correspond to the maximum transducer sensitivity given the current temperature of the fluid in pipe 90. In one example, the first frequency is 160KHz and the second frequency is 260KHz.

[0019] For each frequency, the CPU core 102 configures a value into the register set 110. The UST circuit 104 uses that value to generate an electrical signal having a frequency corresponding to the value programmed by the CPU core 102. In one example, the UST circuit generates the electrical signal as a pulse train of a specific number of pulses at a specific frequency. The CPU core 102 programs into the register set 110 a value encoding the frequency and number of pulses (e.g., 10 pulses) that the UST circuit 104 will generate.

[0020] Next, the UST circuit 104 generates the desired electrical signal to one of the transducers 95, 98 - it is not important which transducer is used as the excitation transducer - to thereby generate an ultrasonic signal. The UST circuit 104 receives a signal from the other transducer and determines a value proportional to the amplitude of that signal. Next, the UST circuit 104 stores the determined amplitude in, for example, a storage device 106. Next, the CPU core 102 programs different values ​​into the register set 110 to cause the UST circuit 104 to generate an excitation electrical signal at different frequencies. The resulting transducer amplitude is stored in the storage device 106 together with a value indicating its excitation frequency. The process repeats until a second frequency is reached. The separation between adjacent frequency steps is application specific. In one example, a frequency from 160KHz to 260KHz in 1KHz steps is used during the calibration process.

[0021] Figure 3 An example of amplitude 302 determined for excitation frequencies between a first frequency F1 and a second frequency F2 for a temperature of the fluid in the tube 90 when performing a calibration procedure is shown. Frequency Fm generally specifies the frequency corresponding to a maximum amplitude 305. F1 should be set below the lowest predicted value of the frequency at the maximum amplitude, and F2 should be set above the highest predicted value of the frequency at the maximum amplitude, so that the frequency sweep will certainly include the frequency at the maximum amplitude for any fluid temperature that may be present in the tube 90.

[0022] Figure 1 The CPU core 102 in the memory device 106 reads back the amplitude values ​​from the memory device 106 (either after all amplitude values ​​have been acquired and stored or after each amplitude value has been stored) and determines the firing frequency corresponding to the peak amplitude (i.e., maximum sensitivity). In one embodiment, the CPU core 102 determines the maximum amplitude value from the amplitude values ​​stored in the memory device 106 and then selects the frequency associated with that value as the firing frequency to use in determining the forward flow rate.

[0023] In other embodiments, the CPU core 102 determines the maximum amplitude from the amplitudes 302 determined during the frequency sweep. The CPU core 102 converts each amplitude to decibels (dB), such as 10*log(amplitude) and subtracts X dB from the maximum dB value. In one example, X dB is 1 dB. Next, the CPU core 102 determines two frequencies corresponding to dB values ​​that are X less than the maximum dB value. Figure 3These frequencies are illustrated as F_lower and F_upper. Based on F_lower and F_upper, the CPU core 102 determines the firing frequency to be used for making flow rate measurements. For example, the CPU core 102 may average F_lower and F_upper. In another example, the CPU core 102 calculates the median of F_lower and F_upper as the firing frequency.

[0024] As mentioned above, the UST circuit 104 generates an electrical signal of a number of pulses at a particular frequency to be provided to the transducers 95, 98 as a train of pulses. Figure 4 An example of a pulse train 400 is shown. The pulse train 400 includes N pulses 402, where N is 1 or more. In one example, N is 10. Each cycle of the pulse train is characterized by time values ​​TU and TL, where TU is the time during which the pulse is at a higher voltage level and TL is the time during which the pulse is at a lower voltage value. The period of each cycle is TU+TL and is the inverse of the frequency. Thus, the desired frequency indicates the sum of TU and TL. TU and TL can be equal, but do not have to be equal. If TU and TL are equal, the resulting pulse train has a 50% duty cycle, but if TU is greater than TL, the duty cycle may be greater than 50%, and if TU is less than TL, the duty cycle may be less than 50%. In one example, the CPU core 102 programs the UST circuit 104 with three values ​​for defining a target pulse train. The three values ​​include TU, TL, and the number of pulses 402 of the pulse train.

[0025] Figure 5 An example implementation of a UST 104 coupled to a CPU core 102 , a storage device 106 , and ultrasound transducers 96 and 98 is shown. Figure 5The UST circuit 104 in the example of includes a programmable pulse generator (PPG) 510, a driver 510, multiplexers 530 and 535, a programmable gain amplifier (PGA) 540, an analog / digital converter (ADC) 550, an oscillator (OSC) 560, and a phase-locked loop (PLL) 570. The CPU core 102 programs the values ​​defining the desired pulse train into a register set 110, which is contained in or accessible to the PPG 510. The oscillator 560 generates a clock 565 based on a signal received from an external resonator 562. The external resonator may include a crystal resonator or a ceramic resonator. The clock 565 from the oscillator 560 is provided as a reference clock to the PLL 570, which in turn generates a clock 575 to the PPG 510. In some examples, clock 575 generated by PLL 570 is phase locked to clock 565, but has a higher frequency than clock 565. For example, the frequency of clock 565 may be 8 MHz, and the frequency of clock 575 may be in the range of 68 to 80 MHz.

[0026] The PPG 510 generates a pulse train using a clock 575. The number of pulses in the pulse train and the frequency of the pulse train are indicated by values ​​(e.g., TU, TL, and the number of pulses) written to the register set 110 by the CPU core 102. The resulting pulse train is provided to a driver 520, which conditions the pulse train for driving one of the transducers 95, 98. The conditioning performed by the driver 520 may include voltage level shifting, amplification, etc.

[0027] For the temperature calibration process described herein, one of the transducers is used to generate an ultrasonic signal, while the other transducer is used as an ultrasonic signal receiving transducer. The multiplexer 530 is configured by the control signal CTL1 to select one of the transducers 95, 98 to receive a pulse train from the driver 520. In this example, the PPG 510 generates CTL1. The PPG 510 also asserts a control signal CTL2 that configures the multiplexer 535 to provide the electrical signal generated by the receiving transducer to the PGA 540. To perform the temperature calibration process, for example, the PPG 510 asserts CTL1 to electrically couple the driver 520 to the transducer 95 to thereby generate the ultrasonic signal 502, and asserts CTL2 to electrically couple the transducer 95 to the PGA 540.

[0028] The signal from the sensing transducer is provided to the PGA 540 through the multiplexer 535, where the signal is amplified. The modified analog signal is then provided to the ADC 550, which converts the amplified analog signal into a digital representation. In one embodiment, the ADC 550 includes a ΣΔ modulator (e.g., a third-order ΣΔ modulator). The resulting digital value indicates the amplitude of the signal received by the ultrasonic transducer and is stored, for example, in the storage device 106. The CPU core 102 can then read the digital value from the storage device 106. Multiple excitation frequencies are used as described above, and the resulting digital values ​​are stored in the storage device 106. The CPU core 102 determines the excitation frequency to be used based on the resulting digital value.

[0029] To determine the flow rate using the excitation frequency generated by the previous execution of the temperature calibration process, the CPU core 102 configures the PPG 510 to generate a pulse train that is first provided to one transducer, where the signal of the other transducer will be provided to the PGA 540. The CPU core 102 can write values ​​to the register set 110 to specify which transducer is used to generate the ultrasonic signal and which is used as the ultrasonic signal receiving transducer (e.g., transducer 95 is used to generate the ultrasonic signal, and the electrical signal from transducer 98 will be provided to the PGA 540). The resulting digital value from the ADC 550 is stored in the storage device 106. Then, the CPU 102 can write values ​​to the register set 110 to reverse the roles of transducers 95 and 98 (e.g., transducer 98 is used to generate the ultrasonic signal, and the electrical signal from transducer 95 will be provided to the PGA 540). The timer derived from the PLL output can be used to drive a sequencer that controls the start time of the PPG 510 and the start of ADC sampling. The difference between these two events represents the static offset of both the upstream and downstream flight times. Using the signal digitized by ADC 550, any of a variety of different methods can be used to calculate TOF. In one example, the envelope of the signal is calculated, and the time when the envelope crosses a predefined threshold is determined. The threshold can be calculated based on the maximum amplitude of the signal. The amplitude of the signal across the threshold is used to determine the presence of the signal.

[0030] Figure 6 A method is shown describing an example of a temperature calibration process. The temperature calibration process is controlled by the CPU 102 executing firmware 111 and interacting with the USC circuit 104. The temperature calibration process includes operations 604 to 616 indicated by reference numeral 601. Operation 602 includes taking a flow measurement using a current value of an excitation frequency. The current excitation frequency may have been determined based on a previous execution of the temperature calibration process. The use of the UST circuit 104 to determine the flow velocity (and therefore the flow rate) is explained above.

[0031] At 604, the temperature calibration process includes selecting an initial frequency as part of the frequency sweep. In some embodiments, the initial frequency has a value lower than the lowest frequency expected for maximum transducer amplitude. In other embodiments, the initial frequency has a value higher than the highest frequency expected for maximum transducer amplitude. The initial frequency is selected via firmware 111 or otherwise programmed into CPU core 102.

[0032] At 606, the temperature calibration process includes generating an electrical signal at a frequency selected for one of the ultrasonic transducers 95, 98. In some cases, this operation includes the CPU core 102 determining the values ​​of T1 and T2 for the selected frequency and number of pulses and writing the corresponding values ​​to the register set 110 in the UST circuit 104. Next, the PPG 510 generates a programmable pulse train that is provided to one of the transducers (e.g., transducer 95) through the multiplexer 530 (controlled by CTL1 from the PPG 510).

[0033] At 608, the amplitude of the electrical signal generated by another transducer, such as transducer 98, is measured. This operation may be performed by amplifying the signal detected by PGA 540 and converting the amplified signal to a digital representation by ADC 550. The resulting digital value is then stored in storage device 106 (610).

[0034] The temperature calibration process implements a frequency sweep, and therefore at 612, the CPU 102 determines whether another frequency remains to be used for the frequency sweep. In one example, the frequency sweep includes frequencies between 160KHz and 260KHz in increments of 1KHz. In some examples, the frequencies are used in ascending or descending order, but in other examples, they can be used in an order other than ascending or descending order. If another frequency remains to be used, then the next frequency in the sweep is selected at 614, and the process repeats at operation 606. Once all frequencies within the range of the frequency sweep are used to generate amplitude values, then at 616, the temperature calibration process determines a new frequency for future flow rate measurements based on the digital value representation of the amplitude. An example of how to determine the excitation frequency to be used is provided above. Next, the latest determined excitation frequency is used at 620, and the next time, the CPU 102 uses the UST circuit 104 to determine the flow rate (flow rate).

[0035] In some cases, the temperature calibration process 601 is performed between each pair of consecutive flow rate measurements. In other cases, the temperature calibration process 601 is performed between several pairs of consecutive flow rate measurements, but not necessarily between each pair of consecutive flow rate measurements. For example, flow rate measurements may be performed at one minute intervals, but the temperature calibration process is performed at 5 minute or 10 minute (or other) intervals. In some cases, the temperature calibration process is performed at intervals that are at least 5 minute intervals.

[0036] In this description, the term "couple" or "couples" means an indirect or direct wired or wireless connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections. The statement "based on" means "based at least in part on." Thus, if X is based on Y, X may vary with Y and any number of other factors.

[0037] Modifications are possible in the described embodiments, and other embodiments are possible within the scope of the claims.

Claims

1. A non-transitory computer-readable storage device storing machine instructions which, when executed by one or more central processing unit (CPU) cores, cause the one or more CPU cores to: Using the first ultrasonic transducer and the second ultrasonic transducer to measure the fluid flow rate using the current excitation frequency; Perform a temperature calibration procedure that includes the following: sequentially generating a plurality of electrical signals for the first ultrasonic transducer, each generated electrical signal having a different corresponding frequency; measuring, for each respective frequency, the amplitude of the signal from the second ultrasonic transducer; based on a measured amplitude of the signal from the second ultrasonic transducer, determining a first frequency corresponding to a peak amplitude from among the measured amplitudes; determining a second frequency based on the peak amplitude, the second frequency being less than the first frequency, determining a third frequency based on the peak amplitude, the third frequency being greater than the first frequency; and determining a new excitation frequency based on the second frequency and the third frequency; and The fluid flow is measured using the first ultrasonic transducer and the second ultrasonic transducer using the new excitation frequency.

2. The non-transitory computer-readable storage device of claim 1 , wherein when executed by the one or more CPU cores, the machine instructions cause the one or more CPU cores to: determining the first frequency as another new excitation frequency; and The fluid flow is measured using the first ultrasonic transducer and the second ultrasonic transducer using the another new excitation frequency.

3. The non-transitory computer-readable storage device of claim 1 , wherein when executed by the one or more CPU cores, the machine instructions cause the one or more CPU cores to: To determine the new excitation frequency based on the second frequency and the third frequency, the new excitation frequency is determined as an average of the second frequency and the third frequency.

4. The non-transitory computer-readable storage device of claim 1 , wherein when executed by the one or more CPU cores, the machine instructions cause the one or more CPU cores to: To determine the new excitation frequency based on the second frequency and the third frequency, the new excitation frequency is determined as a median of the second frequency and the third frequency.

5. The non-transitory computer-readable storage device of claim 1 , wherein when executed by the one or more CPU cores, the machine instructions cause the one or more CPU cores to generate each of the plurality of electrical signals through configuration of one or more registers to include: a first value indicating the number of pulses that generated the electrical signal; a second value indicative of a first time period during which each pulse is to be at a first voltage level; and A third value is indicative of a second time period during which each pulse is to be at a second voltage level.

6. The non-transitory computer-readable storage device of claim 1, wherein when executed by the one or more CPU cores, the machine instructions cause the one or more CPU cores to perform the temperature calibration process every M minutes, and wherein M is at least 5.

7. The non-transitory computer-readable storage device of claim 1, wherein: When executed by the one or more CPU cores, the machine instructions cause the one or more CPU cores to perform the temperature calibration process between a pair of measurements of the fluid flow rate.

8. The non-transitory computer readable storage device of claim 7, wherein the pair of measurements of the fluid flow rate is a pair of consecutive measurements of the fluid flow rate.

9. A microcontroller unit MCU, comprising: One or more central processing unit (CPU) cores configured to: Using the first ultrasonic transducer and the second ultrasonic transducer to measure the fluid flow rate using the current excitation frequency; Perform a temperature calibration procedure that includes the following: sequentially generating a plurality of electrical signals for the first ultrasonic transducer, each generated electrical signal having a different corresponding frequency; measuring, for each respective frequency, the amplitude of the signal from the second ultrasonic transducer; based on a measured amplitude of the signal from the second ultrasonic transducer, determining a first frequency corresponding to a peak amplitude from among the measured amplitudes; determining a second frequency based on the peak amplitude, the second frequency being less than the first frequency, determining a third frequency based on the peak amplitude, the third frequency being greater than the first frequency; and determining a new excitation frequency based on the second frequency and the third frequency; and The fluid flow is measured using the first ultrasonic transducer and the second ultrasonic transducer using the new excitation frequency.

10. The MCU of claim 9, wherein the one or more CPU cores are configured to: determining another new excitation frequency based on the first frequency; and The fluid flow is measured using the first ultrasonic transducer and the second ultrasonic transducer using the another new excitation frequency.

11. The MCU of claim 9, wherein the one or more CPU cores are configured to average the second frequency and the third frequency to determine the new firing frequency.

12. The MCU of claim 9, wherein the one or more CPU cores are configured to: The new excitation frequency is determined based on a median of the second frequency and the third frequency.

13. The MCU according to claim 9, wherein the one or more CPU cores generate each of the plurality of electrical signals through configuration of one or more registers to include: a first value indicating the number of pulses that generated the electrical signal; a second value indicative of a first time period during which each pulse is to be at a first voltage level; and A third value is indicative of a second time period during which each pulse is to be at a second voltage level.

14. The MCU according to claim 9, further comprising: a programmable pulse generator programmable by the one or more CPU cores to generate the plurality of electrical signals; and An analog-to-digital converter is configured to convert the signal from the second ultrasound transducer into a digital value.

15. The MCU of claim 9, wherein the one or more CPU cores are configured to repeatedly perform the temperature calibration process between each pair of measurements of the fluid flow rate.

16. The MCU of claim 15, wherein each pair of measurements of the fluid flow rate is each pair of consecutive measurements of the fluid flow rate.

17. A method for measuring fluid flow, comprising: Using the first ultrasonic transducer and the second ultrasonic transducer to measure the fluid flow rate using the current excitation frequency; Perform a temperature calibration procedure that includes the following: sequentially generating a plurality of electrical signals for the first ultrasonic transducer, each generated electrical signal having a different corresponding frequency; measuring, for each respective frequency, the amplitude of the signal from the second ultrasonic transducer; based on the measured amplitude of the signal from the second ultrasonic transducer, determining a first frequency corresponding to a peak amplitude from among the measured amplitudes; determining a second frequency based on the peak amplitude, the second frequency being less than the first frequency, determining a third frequency based on the peak amplitude, the third frequency being greater than the first frequency; and determining a new excitation frequency based on the second frequency and the third frequency; and The fluid flow is measured using the first ultrasonic transducer and the second ultrasonic transducer using the new excitation frequency.

18. The method according to claim 17, further comprising: determining the first frequency as another new excitation frequency; as well as The fluid flow is measured using the first ultrasonic transducer and the second ultrasonic transducer using the another new excitation frequency.

19. The method of claim 17, wherein determining the new excitation frequency comprises averaging the second frequency and the third frequency.

20. The method of claim 17, wherein determining the new excitation frequency comprises calculating a median of the second frequency and the third frequency.

21. The method of claim 17, further comprising performing the temperature calibration process between a pair of measurements of the fluid flow rate.

22. The method of claim 21, wherein the pair of measurements of the fluid flow rate are a pair of consecutive measurements of the fluid flow rate.

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