Ultrasonic Flowmeter Calibration System and Method

Abstract

An ultrasonic flowmeter configured to measure flow within a conduit that is configured for automatic zeroing during active flow operation of the flowmeter. The flowmeter includes: a printed circuit board that includes circuitry for ultrasonic transit time flow measurement and includes a transducer switching relay; and a first transducer cable and a second transducer cable that connect a first transducer and a second transducer, respectively, to the transducer switching relay. The flowmeter further includes a programmable processor configured to generate flow measurement data based on ultrasonic flowmeter calibration performed in situ by the ultrasonic flowmeter when measuring flow through the conduit. The calibration includes: determining a zero offset value; determining a swap offset value by: measuring the transit times of flow forward and backward through the conduit between the first transducer and the second transducer, activating the transducer switching relay to physically swap the first transducer and the second transducer, and measuring the transit times of flow forward and backward through the conduit between the swapped first transducer and the second transducer; determining a flow zero value based on the zero offset and the swap offset; and generating flow velocity data based on the flow in the conduit and the flow zero offset.

Description

Technical Field

[0001] This application relates to the field of fluid measurement devices. More specifically, this application relates to ultrasonic flowmeter calibration systems and methods for determining zero offset during active flow. Background Art

[0002] Ultrasonic flowmeters utilize transducers to send and receive ultrasonic signals through a flowing stream to measure the velocity of the flow through a conduit. In cases where the transducers include an upstream transducer and a downstream transducer, the flowmeter is configured to measure the "time-of-flight" of an ultrasonic signal transmitted between two spaced-apart transducers. The ultrasonic signal travels from the first transducer along an ultrasonic signal path through the fluid and / or gas flowing through the conduit to be received by the second transducer. The elapsed time between sending the signal from the first transducer and receiving the signal by the second transducer is the time-of-flight. The signal can then be sent in the reverse direction to determine the reverse time-of-flight. The time difference between the forward and backward "time-of-flight" is referred to as ΔT, and this time difference ΔT can be used to calculate the velocity of the flow through the conduit. The velocity of the flow through the conduit can in turn be used to calculate the flow rate and / or the flow volume.

[0003] However, the "time-of-flight" for the forward pass through the conduit and the "time-of-flight" for the backward pass through the conduit may vary due to reasons other than the flow through the conduit. No flowmeter perfectly matches the theory. For example, the "time-of-flight" may vary based on transducer alignment, inconsistencies in the conduit, etc. To account for such variations, the meter can be set to have a large uncertainty value, or the meter can be calibrated based on the variations. Giving a large uncertainty value may reduce the meter accuracy and is thus impractical for some applications. When calibrating the meter, during manufacturing, the ultrasonic flowmeter is calibrated to "factory zero", in which the "time-of-flight" is the same for the forward and backward directions during zero flow. To determine such a calibration amount, ΔT is calculated with no flow through the conduit. ΔT is used to calibrate the ultrasonic flowmeter.

[0004] Even after such factory calibration, variations may be reintroduced during the installation where the flowmeter will be used. For example, one type of flowmeter is a clamp-on flowmeter, which may be affected by the alignment of the meter, the portion of the conduit on which the meter is clamped, etc. These factors can also drift over time, thus affecting the flowmeter calibration. Therefore, it is preferred to calibrate the flowmeter during installation and recalibrate as needed to calibrate to "in-situ zero", in which the "time-of-flight" is again the same for the forward and backward directions during zero flow.

[0005] However, it is often impractical to arrange for zero flow through the conduit being measured. This is especially true in cases where the flowmeter is recalibrated periodically and / or as needed to address drift. What is needed is a flowmeter and a method for recalibrating the flowmeter such that the flowmeter can be calibrated to "in-situ zero" without requiring zero flow through the associated conduit. SUMMARY OF THE INVENTION

[0006] The present invention provides an ultrasonic flowmeter that includes an ultrasonic flowmeter configured to measure flow within a conduit, the conduit being configured for auto-zeroing during active flow operation of the flowmeter. The flowmeter includes: a printed circuit board that includes circuitry for performing ultrasonic transit time flow measurements and includes a transducer switching relay; and a first transducer cable and a second transducer cable that connect a first transducer and a second transducer to the transducer switching relay, respectively. The flowmeter further includes a programmable processor configured to generate flow measurement data based on ultrasonic flowmeter calibration performed in-situ by the ultrasonic flowmeter when measuring flow through the conduit. The calibration includes: determining a zero offset value; determining a swap offset value by: measuring the transit times of forward and backward flow through the conduit between the first transducer and the second transducer, activating the transducer switching relay to physically swap the first transducer and the second transducer, and measuring the transit times of forward and backward flow through the conduit between the swapped first transducer and the second transducer; determining a flow zero value based on the zero offset and the swap offset; and generating flow velocity data based on the flow in the conduit and the flow zero offset.

[0007] In a more detailed aspect, determining the swap offset value includes generating a forward average based on a plurality of measurements taken before activating the transducer switching relay and generating a reverse average based on a plurality of measurements taken after activating the transducer switching relay.

[0008] In another embodiment of the present invention, generating the flow velocity data includes calculating an average of a standard flow velocity based on one or more measurements taken before activating the transducer switching relay and a swapped flow velocity based on one or more measurements taken after activating the transducer switching relay.

[0009] In another embodiment of the present invention, the processor is configured to initiate ultrasonic flowmeter calibration based on user input or periodically.

[0010] In another more detailed aspect, the processor is configured to monitor the flow velocity to identify a stable flow velocity before initiating ultrasonic flowmeter calibration.

[0011] In another embodiment of the present invention, a computer-implemented method for automatically zeroing an ultrasonic flowmeter, the ultrasonic flowmeter being configured to measure flow in a conduit using a processor of the flowmeter, the processor executing auto-zeroing instructions stored in a non-transitory memory. The method includes: determining a zero offset value based on measured forward and backward transit times of flow through the conduit between a first transducer and a second transducer; and determining a swap offset value by: measuring the forward and backward transit times of flow through the conduit between the first transducer and the second transducer, activating a transducer swap relay on a printed circuit board of the flowmeter, the transducer swap relay being connected to the first transducer and the second transducer via a first transducer cable and a second transducer cable respectively to physically swap the first transducer and the second transducer, and measuring the forward and backward transit times of flow through the conduit between the swapped first transducer and the second transducer. The method further includes determining a flow zero value based on the zero offset and the swap offset, and generating flow velocity data based on the flow in the conduit and the flow zero offset for the first transducer and the second transducer.

[0012] From the following description of the exemplary embodiments, other aspects of the present invention will be apparent to those of ordinary skill in the art in addition to those discussed above. In the specification, reference is made to the accompanying drawings, which form a part of the specification and illustrate examples of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a simplified illustration of an ultrasonic flowmeter assembly shown in cross section according to an exemplary embodiment;

[0014] Figure 2 is a block diagram of a flowmeter circuit system 200 and components shown according to an exemplary embodiment;

[0015] Figure 3 is a flow chart showing a swap offset determination method for starting and maintaining calibration of an ultrasonic flowmeter by swapping transducers using a relay according to an exemplary embodiment; and

[0016] Figure 4 is a flow chart showing a method for automatically zeroing an ultrasonic flowmeter without requiring zero flow according to an exemplary embodiment. DETAILED DESCRIPTION

[0017] First, referring to Figure 1 , a simplified illustration of an ultrasonic flowmeter assembly 100 according to an exemplary embodiment is shown in cross section. The ultrasonic flowmeter assembly 100 includes an ultrasonic flowmeter 110, a conduit 120, and a flow measurement computer 200. In the following, referring to Figure 2The flow measurement computer 200 is shown and further described. Although a particular configuration of the ultrasonic flowmeter assembly 100 is shown and described herein, those of ordinary skill in the art will understand that the invention described herein can be applied to any ultrasonic flowmeter assembly that can be configured to use the signal path defining elements described herein.

[0018] The ultrasonic flowmeter 110 can be a solid-state ultrasonic measurement system configured to measure and report the flow rate of fluid or gas through the conduit 120. The ultrasonic flowmeter 110 can be configured to be fully encapsulated, weatherproof, and UV resistant within the flowmeter housing. The ultrasonic flowmeter 110 can be coupled to the conduit 120 using clamps, adhesives, etc. In an alternative embodiment, the flowmeter housing of the ultrasonic flowmeter 110 is integrally formed with the conduit 120 during manufacture.

[0019] The ultrasonic flowmeter 110 includes a first transducer 112 and a second transducer 114, which are located at positions separated by a known distance along the conduit 120, respectively. The transducer 112 can be a piezoelectric transducer, a solenoid transducer, etc.

[0020] The ultrasonic measurement path 116 is depicted to represent the ultrasonic signal path between the transducer 112 and the transducer 114 through the flow 126 traveling through the conduit 120. In the example shown, the measurement path includes a single reflection point between the transducers. However, those of ordinary skill in the art will understand that the measurement path can alternatively be configured to include zero or more reflection points between the transducer 112 and the transducer 114. Although only the first transducer and the second transducer are shown, in an alternative embodiment, the flowmeter 110 can include multiple transducers and transducer assemblies.

[0021] The transducers 112 and 114 can be housed in a housing (not shown). The transducer housing can be a housing for a clamp-on ultrasonic flowmeter, which is integrated with the conduit 120, etc. The housing can generally be configured to position the transducers such that when the transducers transmit ultrasonic signals to travel along the ultrasonic signal path 116, the transmitted signals pass through the flow in the conduit 120 and are received by the opposite transducer. The flowmeter computer 200 can be housed together with the housing or connected to the housing via one or more communication cables.

[0022] The first transducer 112 is connected to the programmable processor 200 through the first transducer cable 202. The second transducer 114 is connected to the flowmeter circuitry 200 through the second transducer cable 204. The transducer cables 202 and 204 can be any type of cable configured to facilitate the transmission and reception of electronic signals between the first transducer 112 and 114 and the flowmeter circuitry 200.

[0023] When fluid and / or gas flows into conduit 120 through upstream end 122, ultrasonic signals are continuously transmitted in both the forward and reverse directions of the flow before the fluid or gas exits conduit 120 through downstream end 124. The velocity of the fluid or gas is then determined by measuring the time difference between the measurements in the forward and reverse directions.

[0024] Flowmeter 110 may also include additional sensors such as a temperature sensor, a pressure sensor, a backflow sensor, etc. Additional information such as temperature, the pipe diameter of conduit 120, etc. may then be used to calculate the total flow rate based on the measured flow velocity.

[0025] Measured and calculated values including flow values may be converted into electrical pulses, which are counted as units of consumption of the fluid or gas. These signals may then be sent by an internal radio transceiver or via a cable to an external radio transceiver or other system. A radio transceiver generally includes a radio transmitter section and a radio receiver section. The radio transmitter section converts the measurement system signals into a radio frequency signaling protocol for transmission back to a network data collector via a wireless network.

[0026] Next, referring to Figure 2 , the flowmeter computer 200 and components according to an exemplary embodiment are shown in block diagram form. Transit time circuit board 210 includes a programmable processor 220, which also receives transit time measurement results to calculate a flow signal for display 232 and other output circuits 234, and to perform other calculations and analyses of the measurement results, as will occur. Keypad 236 provides user input such as to select display parameters, set periodic auto-zeroing, etc. Memory 240 is any type of non-transitory memory configured to store data. The components of computer 200 may be interconnected to communicate via communication bus 233. Those of ordinary skill in the art will understand that the components described herein are exemplary, and different components or different arrangements of components may be used to implement the functions described herein.

[0027] Transit time circuit board 210 is a printed circuit board (PCB) and includes a programmable processor 220 and a transducer switching relay 214. Programmable processor 220 performs transit time flow measurements to calculate flow measurement results. Programmable processor 220 is connected to transducers 112, 114 via transducer switching relay 214.

[0028] The relay 214 is used to physically switch the connections between the programmable processor 220 and the transducers 112 and 114. The relay 214 can be implemented using an electromechanical relay, a solid-state relay, etc. Although the relay 214 is described herein as multiple relays, the relay 214 can be implemented using a single relay to perform the functions described herein. As described below, the programmable processor 220 controls the operation of the relay 214 to switch between operating states.

[0029] Accordingly, the physical connections of the transducers 112 and 114 to the programmable processor 220 are controlled by the operation of the relay 214. In the non-switched operating state, the transducer 112 is connected to a first transducer connection (not shown) of the programmable processor 220 and the transducer 114 is connected to a second transducer connection (not shown) of the programmable processor 220. In the switched operating state, the transducer 114 is connected to the first transducer connection of the programmable processor 220 and the transducer 112 is connected to the second transducer connection of the programmable processor 220. The programmable processor 220 can be used to control the operation of the transducers 112 and 114 as transmit-receivers or receive-receivers, regardless of the operating state of the relay 214.

[0030] When the relay 214 is in a first operating state - in this example, the non-switched operating state - the programmable processor 220 measures the non-switched transit time. Specifically, the transit time measurement is initiated by a wave 212a from the programmable processor 220, which is connected to the transmitting transducer - shown as the transducer 112 in Figure 2 - based on the operating state of the relay 214. The pulse 212a can be a modulated symbol wave, a square wave, etc., which excites the piezoelectric transducer in the transmitting transducer to generate a sinusoidal pulse train. The received signal 212b is generated by the receiving transducer - shown as the transducer 114 in Figure 2 - as an input to the programmable processor 220. After a number of pulses are transmitted downstream from the transducer 112 to the transducer 114, the same number of pulses are transmitted upstream from the transducer 114 to the transducer 112 without changing the operating state of the relay 214. The programmable processor 220 measures the non-switched travel times upstream and downstream and provides this information to the processor 220. The processor 220 uses these non-switched travel times to calculate the non-switched ΔT.

[0031] After calculating ΔT in the first operating state, relay 214 can be actuated to switch to a second operating state - in the example a switching operating state, and the programmable processor 220 measures the switching transit time. Similar to above, the transit time measurement is initiated by a pulse 212a from the programmable processor 220, which is connected to the transmitting transducer - transducer 114 based on the switching operating state of relay 214. Wave 212a excites the piezoelectric transducer in the transmitting transducer to generate a sine pulse train. The received signal 212b is input to the programmable processor 220 from the receiving transducer - transducer 112 based on the switching operating state of relay 214. After a number of pulses are transmitted downstream from transducer 114 to transducer 112, the same number of pulses are transmitted upstream from transducer 112 to transducer 114. The programmable processor 220 measures the switching travel times upstream and downstream. Processor 220 uses these switching travel times to calculate the switching ΔT.

[0032] Clock 238 provides a time signal to processor 220. The output from the programmable processor 220 is provided to a display 232 showing flow rate and total flow and / or other output circuitry 234 that may include a transmitter to a remote display, a recorder, etc. Keypad 236 can be used to select display parameters such as milliliters per minute or gallons per hour.

[0033] Advantageously, physically swapping transducers 112 and 114 enables calibration of the ultrasonic flowmeter 110 to account for variations introduced by the installation, composition, and operation of transducers 112 and 114 and transducer cables 202 and 204. For example, if the zero point of the transducer drifts from its set value during normal operation, physical swapping of the transducers will account for some of the new offset.

[0034] Now additionally referring to Figure 3 FIG. 300 is a flow chart showing a switching offset determination method for starting and maintaining calibration of an ultrasonic flowmeter using relay switching of transducers in accordance with an exemplary embodiment. The method includes determining both a zero offset and a switching offset to enable "in-situ" calibration without zero flow through the conduit.

[0035] In step 302, a swap test is initiated to set a swap offset value. Although the swap test is used to enable auto-zeroing without requiring zero flow to the catheter 120, the swap test can be performed independent of whether flow is passing through the catheter 120. Specifically, the swap test can be performed when there is zero flow through the catheter 120 during the manufacture of the ultrasonic flowmeter, and is used in combination with a traditional zero offset to generate a factory zero value, which is all stored in the memory of the newly manufactured ultrasonic flowmeter. The ultrasonic flowmeter 110 can be configured to retain these values as default values in the memory throughout the life of the ultrasonic flowmeter.

[0036] In step 304, the ultrasonic flowmeter 110 is configured to determine a set number of ΔT values in quick succession. The set number of values can be any number, but will be described herein as ten (10) ΔT values. In typical operation, the ultrasonic flowmeter 110 is capable of generating ten (10) ΔT values in an operation of approximately one (1) second. These are complete ΔT measurements, including both the upstream flight time and the downstream flight time for each point.

[0037] The ten (10) ΔT values generated in step 304 are generated when the operating state of the relay 214 is in the un-swapped operating state. Thus, the ten (10) ΔT values are un-swapped ΔT values.

[0038] In step 306, the ultrasonic flowmeter 110 - specifically, the processor 200 is programmed - is configured to actuate the relay 214 to change the operating state of the relay 214 from the un-swapped operating state to the swapped operating state. In the swapped operating state, the transducers 112 and 114 are physically swapped with respect to the operation of the programmable processor 220.

[0039] In step 308, the ultrasonic flowmeter 110 is configured to again determine ten (10) ΔT values in quick succession. The ten (10) ΔT values are generated when the operating state of the relay 214 is in the swapped operating state. Thus, the ten (10) ΔT values are swapped ΔT values.

[0040] In step 310, the programmable processor 220 is configured to generate both the swapped ΔT value and the un-swapped ΔT value based on the following formula:

[0041]

[0042]

[0043] where ΔT 1 is the un-swapped ΔT value, and ΔT 2 is the swapped ΔT value.

[0044] In addition to the averages described above, every ten (10) ΔT values can be used to generate a standard deviation for each group of ten. The standard deviation can be used to eliminate any outlier data points in the group.

[0045] In step 312, the programmable processor 220 is configured to generate a swap offset value based on the following formula:

[0046]

[0047] where ε is the offset value.

[0048] Now additionally referring to Figure 4 , a flowchart 400 is shown that illustrates a method for automatically zeroing the ultrasonic flowmeter 110 without zero flow according to an exemplary embodiment. The method can be implemented using the programmable processor 220 in cooperation with the programmable processor 220 to initially zero after installation and to zero the flowmeter 110 during operation as needed.

[0049] In step 402, the processor 220 is configured to initiate a zeroing calculation for the ultrasonic flowmeter 110 when the ultrasonic flowmeter 110 is used in the case of zero flow through the conduit 120. Step 402 will typically be performed during the manufacture and initial testing of the ultrasonic flowmeter 110.

[0050] In step 404, the swap offset is determined using the method described above with reference to Figure 3 .

[0051] In step 406, the processor 220 is configured to determine a zero offset value (εzero) based on the following formula:

[0052] Zero = ΔT 1

[0053] ε zero = Zero - ε 交换

[0054] where ΔT is the standard zero value that requires zero flow.

[0055] In step 408, the processor 220 is configured to use the swap offset value from step 404 in combination with the zero offset value calculated in step 406 to determine the factory zero for the ultrasonic flowmeter 110 generated when zero flow passes through the conduit 120. The factory zero is the zero offset minus the swap offset. The processor 220 is then configured to store the zero offset, the swap offset, and the factory zero in the memory 240 of the ultrasonic flowmeter 110 for use as default values.

[0056] In step 410, the ultrasonic flowmeter 110 is installed "in-situ" and recalibrated after its installation. For example, in the case where the ultrasonic flowmeter 110 is a clamp-on type flowmeter, the installation may include clamping the flowmeter 110 onto the conduit 120. It is desirable to recalibrate and auto-zero the flowmeter 110 again to account for any changes introduced during transportation and installation.

[0057] In step 412, the flowmeter 110 may be configured to determine whether there is flow within the conduit 120. In the case where flow is detected, in step 414, the flowmeter 110 may determine whether the flow through the conduit 120 is a stable flow that is relatively free of swirls, eddies, particles, etc. In the case where the flow is unstable, the ultrasonic flowmeter 110 may iteratively perform a waiting operation until a stable flow is detected.

[0058] In the case where a stable flow is detected, in step 116, the flowmeter 110 is configured to determine a flow zero value based on the following formula:

[0059] ΔT 校正 = ΔT 测量 - ε 总

[0060]

[0061] In the case where no flow is detected in step 412, the steps described in the above steps 404 to 408 may be used to perform zeroing to determine the in-situ zero in step 418. After determining the in-situ zero in step 416, the flowmeter 110 may be configured to calibrate using the in-situ zero and perform flow measurement. However, the flowmeter 110 is configured to retain the factory zero setting stored in the memory 240.

[0062] In step 420, the flowmeter 110 is configured to perform zeroing during normal operation of the flowmeter 110 while metering the flow through the conduit 120. Auto-zeroing may be performed periodically based on user input received at the keypad 236 and / or based on detected zeroing requirements. Periodic zeroing may be performed based on a cycle time set again by the user using the keypad 236.

[0063] Advantageously, configuring the flowmeter 110 to perform an auto-zeroing operation when there is flow within the conduit 120 enables periodic auto-zeroing. Periodic auto-zeroing is beneficial for addressing zero drift that may occur in the ultrasonic flowmeter 100.

[0064] The detected need for auto-zeroing may include the detection of poor metering data generated by the flowmeter 110. Detecting poor metering data may include recalibrating the flowmeter 110 based on the factory zero setting generated as Figure 3 described, and then asFigure 4 Perform automatic zero adjustment.

[0065] This is a description of exemplary embodiments, but it will be apparent to those of ordinary skill in the art that details of these specific embodiments may be varied without departing from the scope and spirit of the present invention, and such variations are intended to be covered by the appended claims.

Claims

1. An ultrasonic flowmeter configured to measure flow within a conduit, comprising: a first transducer and a second transducer; a printed circuit board including circuitry for ultrasonic transit time flow measurement, the printed circuit board including a transducer exchange relay; and a first transducer cable and a second transducer cable that connect the first transducer and the second transducer to the transducer exchange relay, respectively; a programmable processor included on the printed circuit board, the programmable processor configured to generate flow measurement data based on ultrasonic flowmeter calibration performed in situ by the ultrasonic flowmeter when measuring flow through the conduit, the calibration including the steps of: determining a zero offset value, determining an exchange offset value based on an unexchanged transit time difference and an exchanged transit time difference by: measuring the unexchanged transit time difference (ΔT) forward and backward through flow in the conduit between the first transducer and the second transducer, activating the transducer exchange relay to physically exchange the first transducer and the second transducer, and measuring the exchanged transit time difference forward and backward through flow in the conduit between the exchanged first transducer and the second transducer, determining a flow zero value based on the zero offset value and the exchange offset value, and generating flow velocity data based on the flow in the conduit and the flow zero value.

2. The ultrasonic flowmeter according to claim 1, wherein determining the exchange offset value includes generating a forward average based on a plurality of measurements taken before activating the transducer exchange relay and generating a reverse average based on a plurality of measurements taken after activating the transducer exchange relay.

3. The ultrasonic flowmeter according to claim 1, wherein the transducer exchange relay is an electromechanical relay.

4. The ultrasonic flowmeter according to claim 1, wherein generating the flow velocity data includes calculating an average of a standard flow velocity based on one or more measurements taken before activating the transducer exchange relay and an exchanged flow velocity based on one or more measurements taken after activating the transducer exchange relay.

5. The ultrasonic flowmeter according to claim 1, wherein the programmable processor is configured to initiate the ultrasonic flowmeter calibration based on a user input.

6. The ultrasonic flowmeter according to claim 1, wherein the programmable processor is configured to periodically initiate the ultrasonic flowmeter calibration.

7. The ultrasonic flowmeter according to claim 1, wherein the programmable processor is configured to monitor the flow velocity to identify a stable flow velocity before initiating the ultrasonic flowmeter calibration.

8. A computer-implemented method for zeroing an ultrasonic flowmeter, the ultrasonic flowmeter configured to measure flow within a conduit using a programmable processor of the ultrasonic flowmeter, the programmable processor executing zeroing instructions stored in a non-transitory memory, the steps of the method comprising: Determine a zero offset value based on the measured transit times of forward and backward flow through the conduit between the first transducer and the second transducer; Determine a swap offset value based on the unswapped transit times and the swapped transit times as follows: Measure the forward and backward unswapped transit times of the flow through the conduit between the first transducer and the second transducer, Activate a transducer swap relay on the printed circuit board of the ultrasonic flowmeter, the transducer swap relay being connected to the first transducer and the second transducer respectively through a first transducer cable and a second transducer cable, to physically swap the first transducer and the second transducer, and Measure the forward and backward swapped transit times of the flow through the conduit between the swapped first transducer and the second transducer; Determine a flow zero value based on the zero offset value and the swap offset value; and Generate flow velocity data based on the flow through the conduit and the flow zero value.

9. The method according to claim 8, wherein, Determining the swap offset value includes generating a forward average value based on a plurality of measurement results obtained before activating the transducer swap relay and generating a backward average value based on a plurality of measurement results obtained after activating the transducer swap relay.

10. The method according to claim 8, wherein, The transducer swap relay is an electromechanical relay.

11. The method according to claim 8, wherein, Generating the flow velocity data includes calculating an average value of a standard flow velocity based on one or more measurement results obtained before activating the transducer swap relay and a swapped flow velocity based on one or more measurement results obtained after activating the transducer swap relay.

12. The method according to claim 8, wherein, The programmable processor is configured to initiate ultrasonic flowmeter calibration based on user input.

13. The method according to claim 8, wherein, The programmable processor is configured to periodically initiate ultrasonic flowmeter calibration.

14. The method according to claim 8, wherein, The programmable processor is configured to monitor the flow velocity to identify a stable flow velocity before initiating ultrasonic flowmeter calibration.

15. An ultrasonic flowmeter configured to measure the flow in a conduit, comprising: A first transducer and a second transducer; A printed circuit board including circuitry for ultrasonic transit time flow measurement, the printed circuit board including a transducer swap relay; and A first transducer cable and a second transducer cable that connect the first transducer and the second transducer to the transducer swap relay respectively; A programmable processor included on the printed circuit board, the programmable processor being configured to generate flow measurement data based on ultrasonic flowmeter calibration performed by the ultrasonic flowmeter, the calibration including the following steps: Determine a zero offset value, ​ ​ ​ Determine an exchange offset value based on an unexchanged transit time and an exchanged transit time as follows: measure the unexchanged transit time of forward and backward flow in the conduit between the first transducer and the second transducer, activate the transducer exchange relay to physically exchange the first transducer and the second transducer, and measure the exchanged transit time of forward and backward flow in the conduit between the exchanged first transducer and the second transducer. Determine a flow zero value based on the zero offset value and the exchange offset value.

16. The ultrasonic flowmeter according to claim 15, wherein, Determining the exchange offset value includes generating a forward average value based on a plurality of measurement results obtained before activating the transducer exchange relay and generating a backward average value based on a plurality of measurement results obtained after activating the transducer exchange relay.

17. The ultrasonic flowmeter according to claim 15, wherein, The transducer exchange relay is an electromechanical relay.

18. The ultrasonic flowmeter according to claim 15, wherein, Generating flow velocity data includes calculating an average value ΔT of the flow velocity based on one or more measurement results obtained before activating the transducer exchange relay and the exchanged flow velocity based on one or more measurement results obtained after activating the transducer exchange relay.

19. The ultrasonic flowmeter according to claim 15, wherein, The programmable processor is configured to initiate the ultrasonic flowmeter calibration based on a user input.

20. The ultrasonic flowmeter according to claim 15, wherein, The programmable processor is configured to monitor the flow velocity to identify a stable flow velocity before initiating the ultrasonic flowmeter calibration.

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