Timing control circuit for guided wave radar level transmitter

Abstract

In at least one illustrative embodiment, a guided wave radar (GWR) level transmitter may include: a timing circuit including a first oscillator circuit and a second oscillator circuit; a coincidence circuit configured to generate a coincidence signal indicating a phase shift created by a difference between a first frequency and a second frequency of the first oscillator circuit and the second oscillator circuit; and a microcontroller configured to (i) determine a stretch factor based on at least one of the oscillator signals and the coincidence signal, (ii) when the stretch factor is within a first range, use the stretch factor to calculate a distance to a surface of a medium, and (iii) when the stretch factor is outside a second range, adjust at least one of the first oscillator circuit and the second oscillator circuit to adjust the difference between the first frequency and the second frequency.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. Patent Application No. 16 / 371,126, filed on April 1, 2019, the entire disclosure of which is incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to guided wave radar level transmitters and, more particularly, to timing control circuits for such level transmitters. Background Art

[0004] Guided wave radar level transmitters typically use a time domain reflectometry technique based on sub-nanosecond electrical pulses that travel at the speed of light along a waveguide probe. When the pulses reach dielectric discontinuities, a portion of the energy is reflected back to the transmitter and captured at the receiver, which calculates the transit time and corresponding height or distance of the medium in the tank or other container. The level measurement is calculated based on the time between sending the transmitted signal and receiving the reflected signal. Summary of the invention

[0005] According to one aspect of the present disclosure, a guided wave radar (GWR) level transmitter may include a timing circuit including a first oscillator circuit and a second oscillator circuit. The first oscillator circuit may be configured to generate a first signal having a first frequency, the first signal to be transmitted along a waveguide probe toward a surface of a medium, and the second oscillator circuit may be configured to generate a second signal having a second frequency. The GWR level transmitter may also include a coincidence circuit configured to generate a coincidence signal indicating a phase shift created by a difference between the first frequency and the second frequency. The GWR level transmitter may also include a microcontroller configured to (i) determine a stretch factor based on at least one of the first signal and the second signal and the coincidence signal, (ii) in response to determining that the stretch factor is within a first range, use the stretch factor to calculate a distance between the surface of the medium and the near end of the waveguide probe, and (iii) in response to determining that the stretch factor is outside a second range, adjust at least one of the first oscillator circuit and the second oscillator circuit to adjust the difference between the first frequency and the second frequency.

[0006] In some embodiments, the first range may be greater than the second range.

[0007] In some embodiments, the GWR level transmitter may further include a mixing and filtering circuit configured to generate a time-converted signal by mixing the second signal with a reflected signal received from the waveguide probe in response to the first signal being transmitted along the waveguide probe. The microcontroller may be configured to calculate the distance between the medium surface and the near end of the waveguide probe by applying a stretch factor to the time-converted signal. The mixing and filtering circuit may be configured to bandpass filter the product of the mixing of the second signal with the reflected signal to generate a time-converted signal. The GWR level transmitter may further include an analog / digital converter configured to convert the time-converted signal into a digital signal for presentation to the microcontroller.

[0008] In some embodiments, determining the stretch factor may include determining a number of pulses generated by one of the first oscillator circuit and the second oscillator circuit during one period of the coincident signal.

[0009] In some embodiments, the GWR level transmitter may further include a pulse generator circuit configured to selectively transmit the first signal to the waveguide probe.

[0010] In some embodiments, the microcontroller may be further configured to adjust both the first oscillator circuit and the second oscillator circuit when adjustment of only one of the first oscillator circuit and the second oscillator circuit is insufficient to bring the stretch factor within the second range.

[0011] In some embodiments, the GWR level transmitter may further include a voltage controlled oscillator operable by the microcontroller to adjust at least one of: (i) a first oscillator circuit to change a first frequency and (ii) a second oscillator circuit to change a second frequency in response to determining that the stretch factor is outside a second range.

[0012] In some embodiments, the microcontroller may include a single integrated circuit configured to determine a stretch factor, determine whether the stretch factor is within a first range and a second range, calculate a distance between a surface of the medium and a proximal end of the waveguide probe, and adjust at least one of the first oscillator circuit and the second oscillator circuit to adjust a difference between the first frequency and the second frequency.

[0013] According to another aspect of the present disclosure, a method may include: generating a first oscillator signal having a first frequency; generating a second oscillator signal having a second frequency; comparing the first oscillator signal and the second oscillator signal to generate a coincidence signal indicating a phase shift created by a difference between the first frequency and the second frequency; transmitting the first oscillator signal along a waveguide probe toward a medium surface; receiving a reflected signal from the waveguide probe in response to the first oscillator signal being transmitted along the waveguide probe; determining a stretch factor based on at least one of the first oscillator signal and the second oscillator signal and the coincidence signal; when the stretch factor is within a first range, using the stretch factor to calculate a distance between the medium surface and a proximal end of the waveguide probe; and when the stretch factor is outside a second range, adjusting at least one of the first oscillator signal and the second oscillator signal using a processor to adjust the difference between the first frequency and the second frequency. Any or all of these steps may be performed by a processor or a microcontroller.

[0014] In some embodiments, the first range may be greater than the second range.

[0015] In some embodiments, the method may further include mixing the reflected signal with a second oscillator signal to produce a time-transformed signal. Calculating the distance between the medium surface and the proximal end of the waveguide probe may include applying a stretch factor to the time-transformed signal. The product of mixing the reflected signal with the second oscillator signal may be bandpass filtered to produce a time-transformed signal. The method may further include converting the time-transformed signal into a digital signal for presentation to the processor.

[0016] In some embodiments, determining the stretch factor may include determining a number of pulses in one of the first oscillator signal and the second oscillator signal during a period of the coincident signal.

[0017] In some embodiments, transmitting the first oscillator signal along the waveguide probe may include activating a pulse generator circuit.

[0018] In some embodiments, the method may include adjusting both the first oscillator signal and the second oscillator signal when adjustment of only one of the first oscillator signal and the second oscillator signal is insufficient to bring the stretch factor within the second range.

[0019] In some embodiments, adjusting at least one of the first oscillator signal and the second oscillator signal to adjust the difference between the first frequency and the second frequency may include adjusting the first frequency of the first oscillator signal using a voltage controlled oscillator.

[0020] In some embodiments, adjusting at least one of the first oscillator signal and the second oscillator signal to adjust the difference between the first frequency and the second frequency includes adjusting the second frequency of the second oscillator signal using a voltage controlled oscillator.

[0021] These and other features of the present disclosure will become more apparent from the following description of illustrative embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The concepts described in the present disclosure are illustrated in the accompanying drawings by way of example and not limitation. For simplicity and clarity of illustration, the elements shown in the drawings are not necessarily drawn to scale. For example, the dimensions of some elements may be exaggerated relative to other elements for clarity. In addition, where deemed appropriate, reference numerals are repeated in the drawings to indicate corresponding or similar elements. The detailed description makes specific reference to the accompanying drawings, in which:

[0023] Figure 1 is a simplified block diagram of at least one embodiment of a guided wave radar (GWR) level transmitter including a timing circuit;

[0024] Figure 2 yes Figure 1 A simplified signal flow diagram of at least one embodiment of a GWR level transmitter;

[0025] Figure 3 Yes Control Figure 1 and Figure 2 A simplified signal flow diagram of at least one embodiment of a method of a timing circuit for a GWR level transmitter; and

[0026] Figure 4 is to use Figure 1 and Figure 2 A simplified signal flow diagram of at least one embodiment of a method of performing level measurement with a GWR level transmitter. DETAILED DESCRIPTION

[0027] Although the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that there is no intention to limit the concepts of the present disclosure to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives consistent with the present disclosure and the appended claims.

[0028] References in the specification to "one embodiment," "an embodiment," "illustrative embodiment," etc. indicate that the described embodiment may include a particular feature, structure, or characteristic, but each embodiment may or may not necessarily include the particular feature, structure, or characteristic. Furthermore, such phrases are not necessarily referring to the same embodiment. Furthermore, when a particular feature, structure, or characteristic is described in conjunction with an embodiment, it is considered to be within the knowledge of those skilled in the art to implement such feature, structure, or characteristic in conjunction with other embodiments, whether or not explicitly described.

[0029] In some cases, the disclosed embodiments may be implemented in hardware, firmware, software, or any combination thereof. The disclosed embodiments may also be implemented as instructions carried by or stored on a transient or non-transient computer-readable storage medium, which may be read and executed by one or more processors. A computer-readable storage medium may be embodied as any storage device, mechanism, or other physical structure for storing or transmitting information in a form readable by a computing device (e.g., a volatile or non-volatile memory, a media disk, or other media device).

[0030] In the accompanying drawings, some structural or method features may be shown in a specific arrangement and / or order. However, it should be understood that such a specific arrangement and / or order may not be required. On the contrary, in some embodiments, these features may be arranged in a manner and / or order different from the manner and / or order shown in the illustrative drawings. In addition, the inclusion of structural or method features in a particular drawing does not mean that such features are required in all embodiments, and in some embodiments, such features may not be included or may be combined with other features.

[0031] Reference now Figure 1 and Figure 2, an exemplary guided wave radar (GWR) level transmitter 100 includes, among other components, a microcontroller unit (MCU) 110 and a timing circuit 130. In use, the GWR level transmitter 100 can generate a frequency signal using the timing circuit 130, which includes two oscillators: a transmitter oscillator 132 and a local oscillator 134. The transmitter oscillator 132 and the local oscillator 134 can use very low power or low jitter circuits with frequencies in the megahertz (MHz) range. In an illustrative embodiment, the transmitter oscillator 132 has a set frequency, while the local oscillator 134 has an adjustable frequency close to the frequency of the transmitter oscillator 132. It is contemplated that in other embodiments, the local oscillator 134 can have a set frequency, while the transmitter oscillator 132 has an adjustable frequency close to the frequency of the local oscillator 134. In other embodiments, both the transmitter oscillator 132 and the local oscillator 134 can have adjustable frequencies to allow for a wider range of frequency control. For example, in such an embodiment, if the adjustment of the local oscillator 134 reaches its limit, the transmitter oscillator 132 may be adjusted for further compensation. Therefore, while the following discussion will generally refer to the adjustment of the frequency of the local oscillator 134, it should be understood that these concepts are equally applicable to the adjustment of the frequency of the transmitter oscillator 132.

[0032] The GWR level transmitter 100 also includes an input / output (I / O) circuit 170, which may include a transmitter oscillator pulser 210 and a local oscillator pulser 212, which may each be activated (e.g., by the MCU 110) to selectively transmit signals from the transmitter oscillator 132 and the local oscillator 134, respectively, to other system components. For example, using the transmitter oscillator pulser 210, a signal from the transmitter oscillator 132 may be transmitted along the waveguide probe 180 at a predetermined pulse repetition frequency and reflected when the pulse reaches a dielectric discontinuity (e.g., the surface of the medium in the tank). The reflected signal is mixed with the signal from the local oscillator pulser 212 and bandpass filtered by the mixing and filtering circuit 160 of the GWR level transmitter 100. The resulting time-transformed signal is acquired by an analog-to-digital converter (ADC) 114 of the MCU 110 to produce a digital signal for determining the distance of the dielectric discontinuity to the proximal end of the waveguide probe 180 (i.e., the end of the waveguide probe 180 coupled to the I / O circuit 170 of the GWR level transmitter 100).

[0033] The GWR level transmitter 100 is configured to utilize a feedback control loop to allow adjustment of the local oscillator 134 (and / or in some embodiments, the transmitter oscillator 132) to maintain a stable differential frequency (Δf) range between the transmitter oscillator frequency and the local oscillator frequency for any disturbances from time changes and / or the environment (e.g., changes in temperature, vibration). In an illustrative embodiment, the GWR level transmitter 100 is configured to limit the number of adjustments to the local oscillator frequency because continuous frequency adjustments increase noise in the time transformation and affect the accuracy of the distance measurement. To this end, the output signals of the two oscillators 132, 134 are transmitted to a coincidence circuit 140 (e.g., a trigger circuit) to generate a coincidence signal. In an illustrative embodiment, the coincidence signal switches whenever the two oscillators are equal or opposite in phase, where the phase shift is generated by the frequency difference (Δf) between the transmitter oscillator frequency and the local oscillator frequency. It should be understood that in the present disclosure, this frequency difference is sometimes also referred to as a "differential frequency". Therefore, the frequency of the coincidence signal is equal to the difference frequency between the transmitter oscillator frequency and the local oscillator frequency (Δf = f TX -f LO ). It will be appreciated that this differential frequency (Δf) will sometimes be positive and sometimes negative.

[0034] The MCU 110 measures the number of pulses of the transmitter oscillator frequency during one cycle of the coincidence signal to determine the stretch factor. In the illustrative embodiment, the transmitter oscillator frequency is divided by the differential frequency (f TO / Δf) is used as the stretch factor. In other embodiments, the local oscillator frequency is divided by the differential frequency (f LO / Δf) can be used as a stretch factor. Instead of adjusting the local oscillator frequency to achieve and maintain a specific set point for time measurement compensation (time shift), the GWR level transmitter 100 of the illustrative embodiment adjusts the local oscillator frequency (and / or in some embodiments, the transmitter oscillator 132) only if the measured stretch factor exceeds a predetermined operating range. By allowing a wider drift of the local oscillator frequency, the number of frequency adjustments is reduced, which reduces noise in the time shift introduced during frequency adjustments. It should be appreciated that by using a measured stretch factor rather than a constant stretch factor, the accuracy of the time measurement compensation can be increased, thereby improving the accuracy of the distance measurement.

[0035] In the illustrative embodiment, the MCU 110 is communicatively coupled to the other components of the GWR level transmitter 100 via an I / O subsystem 120, which may be embodied as circuit devices and / or components for facilitating input / output operations with the MCU 110, the timing circuit 130, the coincidence circuit 140, the voltage controlled oscillator (VCO) 150, the mixing / filtering circuit 160, and other components of the GWR level transmitter 100. For example, the I / O subsystem 120 may be embodied as or otherwise include a memory controller hub, an input / output control hub, an integrated sensor hub, a firmware device, a communication link (e.g., a point-to-point link, a bus link, a wire, a cable, an optical guide, a printed circuit board trace, etc.), and / or other components and subsystems to facilitate input / output operations. In some embodiments, the I / O subsystem 120 may form part of a system on a chip (SoC) and be incorporated into the MCU 110 along with the processor 112, the memory 116, and other components.

[0036] like Figure 1 As shown, MCU 110 includes a processor 112, an analog-to-digital converter (ADC) 114, a memory 116, and / or a counter 118. Processor 112 may be embodied as any type of processor capable of performing the functions described herein. For example, processor 112 may be embodied as a multi-core processor, a microcontroller, or other processor or processing / control circuit. In some embodiments, processor 112 may be embodied as, include, or be coupled to a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), reconfigurable hardware or hardware circuit devices, or other dedicated hardware that facilitates the execution of the functions described herein. Advantageously, the functions of the present disclosure, including frequency adjustment and signal acquisition and processing, may be controlled and executed by a single MCU 110.

[0037] Analog-to-digital converter (ADC) 114 may be embodied as any circuit, device, or collection thereof capable of converting an analog signal received from mixing / filtering circuit 160 into a digital signal.

[0038] The memory 116 may be embodied as any type of volatile (e.g., dynamic random access memory (DRAM), etc.) or non-volatile memory or data storage device capable of performing the functions described herein. Volatile memory may be a storage medium that requires power to maintain the state of data stored by the medium. Non-limiting examples of volatile memory may include various types of random access memory (RAM), such as dynamic random access memory (DRAM) or static random access memory (SRAM).

[0039] The counter 118 may be embodied as any circuit, device, or collection thereof capable of measuring the number of pulses of the transmitter oscillator 132 during one cycle of the coincidence signal to determine the stretch factor. It should be understood that in some embodiments, the counter 118 may measure the number of pulses of the local oscillator 134 during one cycle of the coincidence signal to determine the stretch factor.

[0040] The timing circuit 130 may be embodied as any circuit, device, or collection thereof capable of generating a frequency signal. As described above, the timing circuit 130 includes two oscillators: a transmitter oscillator 132 and a local oscillator 134. In an illustrative embodiment, the timing circuit 130 is configured to set the transmitter oscillator 132 at a predetermined frequency and adjust the frequency of the local oscillator 134 to remain within the operating range of the transmitter oscillator frequency. The timing circuit 130 is configured to be controlled by the MCU 110 to adjust the local oscillator frequency. However, in other embodiments, the timing circuit 130 may alternatively or additionally be configured to adjust the frequency of the transmitter oscillator 132. In such an embodiment, the timing circuit 130 is configured to be controlled by the MCU 110 to adjust the transmitter oscillator frequency.

[0041] The coincidence circuit 140 may be embodied as any circuit, device, or collection thereof that is capable of generating a coincidence signal when the coincidence circuit 140 receives signals from the transmitter oscillator 132 and the local oscillator 134 within a time window. In an illustrative embodiment, the coincidence circuit 140 is configured to switch the coincidence signal whenever the transmitter oscillator 132 and the local oscillator 134 are equal in phase or opposite in phase. In other words, the frequency of the coincidence signal is equal to the differential frequency between the transmitter oscillator frequency and the local oscillator frequency. For example, the coincidence circuit 140 may be embodied as a flip-flop circuit that switches a coincidence cycle when the two oscillators 132, 134 are equal in phase or opposite in phase. As discussed further below, the coincidence cycle is used to determine the stretch factor.

[0042] Voltage controlled oscillator (VCO) 150 may be embodied as any circuit, device, or collection thereof capable of controlling the frequency of local oscillator 134 to adjust the local oscillator frequency. In embodiments where the frequency of transmitter oscillator 132 is adjustable, the VCO may additionally or alternatively control the adjustment of the transmitter oscillator frequency (e.g., Figure 21 . The VCO 150 may be configured to be close to the transmitter oscillator frequency. In some embodiments, the VCO 150 may be configured to be close to the transmitter oscillator frequency. In some embodiments, the MCU 100 may be configured to be close to the transmitter oscillator frequency. In some embodiments, the MCU 100 may be configured to be close to the transmitter oscillator frequency. In some embodiments, the VCO 15 ...

[0043] Mixing / filtering circuit 160 may be embodied as any circuit, device, or collection thereof capable of mixing a signal from local oscillator 134 with a reflected signal from waveguide probe 180 to produce a time-transformed (lower frequency) version of the reflected signal to be digitized by ADC 114 and processed by MCU 110 .

[0044] Reference now Figure 2 , a simplified signal flow diagram of the GWR level transmitter 100 is shown. In the illustrative embodiment, the differential frequency (Δf) between the two different oscillators is controlled by adjusting the local oscillator frequency by a feedback control loop. (As mentioned above, in other embodiments, the transmitter oscillator frequency can be alternatively or additionally adjusted by a feedback control loop.) The GWR level transmitter 100 utilizes an equivalent time sampling (ETS) method for level measurement. Pulses from the transmitter oscillator 132 are transmitted along the waveguide probe 180 via the transmitter oscillator pulser 210 using a frequency in the MHz range, and the reflected signal is mixed with the pulse from the local oscillator 134 via the local oscillator pulser 212, having the same or slightly different frequency as the pulse from the transmitter oscillator 132. A bandpass filter is used at the output of the mixing / filtering circuit 160 to produce a time-transformed version of the reflected signal and provide it to the ADC 114 of the MCU 110. The ETS method allows the time scale to be stretched by a stretch factor. In the illustrative embodiment, the stretch factor reflects the transmitter oscillator frequency / differential frequency (f TO / Δf). However, in other embodiments, the stretch factor may reflect the local oscillator frequency / differential frequency (f LO / Δf). It will be appreciated that the ETS method allows for the capture of sub-ns pulse signals and the reconstruction of the signal at a much lower time base, which is easier for the ADC 114 to digitize at a lower sampling rate.

[0045] In addition, the coincidence circuit 140 receives the transmitter oscillator signal (from 132) and the local oscillator signal (from 134) to generate a coincidence signal. As described above, the coincidence signal switches whenever the two oscillators are equal in phase or opposite in phase. The coincidence signal is transmitted to the MCU 110, where it is read as a digital signal.

[0046] As discussed above, the counter 118 is configured to count the number of pulses from the transmitter oscillator 132 (or in some embodiments, from the local oscillator 134) during one period of the coincidence signal. The counter is started with the rising edge of the coincidence signal, and at the same time, the output signal of the mixing / filtering circuit 160 is acquired by the ADC 114. At the next rising edge of the coincidence signal, the value of the pulse accumulation in the counter is stored in a register and represents the stretch factor of the last acquisition. The measured stretch factor value is used to determine the time shift of the last signal acquisition and optimize the time measurement. It is contemplated that in various embodiments, the value of the stretch factor can be obtained before acquisition, after acquisition, or by averaging the values ​​before and after acquisition.

[0047] The MCU 110 periodically checks the stretch factor to determine whether it is within one or more operating ranges. Specifically, the MCU 110 will determine whether the stretch factor is within a range that will provide acceptable measurement accuracy. If so, the MCU 110 will use the stretch factor to compensate the acquired measurement and calculate the distance of the medium surface along the waveguide proof 180. If not (i.e., when the stretch factor is too large or too small), the acquired measurement value will be discarded and will not be used for liquid level determination. In addition, the MCU 110 will determine whether the stretch factor is outside the range indicating that the differential frequency (Δf) between the oscillators 132 and 134 needs to be adjusted. If so, the MCU 110 will adjust one or both of the oscillators 132 and 134 to adjust (reduce or increase) the differential frequency (Δf) so that it is within the operating range. If not (i.e., when the stretch factor indicates an acceptable difference in the oscillator frequency), the adjustment will not be performed.

[0048] The ranges used by the MCU 110 when evaluating the stretch factor for measurement and for oscillator control may be the same or different. In an illustrative embodiment, when determining whether the stretch factor can be used for measurement, the MCU 110 utilizes an operating range that is larger than the operating range used by the MCU 110 to determine whether a frequency adjustment is needed. In other words, in an illustrative embodiment, the MCU 110 can achieve three results from this evaluation: (1) in the case where the stretch factor is within the two operating ranges, the MCU 110 applies it to the measurement and does not adjust the oscillators 132, 134, (2) in the case where the stretch factor is within the measurement operating range but not within the control operating range, the MCU 110 applies it to the measurement and implements an adjustment to the frequency of one or both of the oscillators 132, 134 to adjust the differential frequency (Δf), and (3) in the case where the stretch factor is outside the two operating ranges, the MCU 110 will discard the affected measurement and implement an adjustment to the frequency of one or both of the oscillators 132, 134 to adjust the differential frequency (Δf). These operations are discussed further below.

[0049] It should be appreciated that allowing the differential frequency (Δf) to float within the operating range serves to reduce the amount of feedback intervention and improve the stability of the system. The drift of the frequency of the oscillators 132, 134 is typically very slow and constantly changing, and may not require adjustment if the measured stretch factor is within the operating range. Therefore, instead of targeting a specific stretch factor and a tight feedback control loop, the operating range allows for slower drift changes in the differential frequency (Δf), and the measured stretch factor is used to compensate the time-transformed measurement signal.

[0050] When the stretch factor is outside the control operating range, the MCU 110 controls the VCO 150 to adjust the frequency of the local oscillator 134 (and / or the transmitter oscillator 132) to adjust the differential frequency (Δf). Depending on the situation (e.g., whether the differential frequency is below or above the control operating range), the adjustment can be an increase or decrease in the differential frequency (Δf). The adjustment of the differential frequency (Δf) is made during the second cycle of the coincident signal, and no acquisition of the measurement signal is made during this cycle. This allows the change in the frequency of the local oscillator 134 caused by the adjustment to stabilize before the next signal acquisition. Therefore, the illustrative GWR level transmitter 100 provides better accuracy of distance measurement by using the actual measured stretch factor associated with a particular measurement, and limiting the number of frequency adjustments to reduce noise on the frequency shift.

[0051] Reference now Figure 3In use, the GWR level transmitter 100 may perform a method 300 for controlling the local oscillator 134 (and / or in some embodiments, the transmission oscillator 132) to maintain the differential frequency (Δf) within an operating range. It should be appreciated that Figure 3 The simplified flowchart of is illustrative in nature, and the GWR level transmitter 100 may perform other methods similar to, but different from, the method 300 for maintaining the differential frequency (Δf) within the operating range. For example, in some embodiments, the method 300 may be rearranged. Figure 3 The order of the steps shown in the drawings may vary, and / or the method may include additional or different steps than those shown.

[0052] The method 300 begins at block 302, where the transmission oscillator 132 generates a transmission oscillator signal and the local oscillator 134 generates a local oscillator signal. As discussed above, one of the transmission oscillator signal and the local oscillator signal may have a set frequency and the other may have an adjustable frequency, or both the transmission oscillator signal and the local oscillator signal may have adjustable frequencies controlled by the MCU 110 (e.g., via the VCO 150). In the illustrative embodiment, the transmission oscillator signal has a set frequency and the local oscillator signal has an adjustable frequency. Block 302 is performed continuously during operation of the GWR level transmitter 100 (i.e., the transmission oscillator 132 continuously generates the transmission oscillator signal and the local oscillator 134 continuously generates the local oscillator signal during operation).

[0053] In block 304, the transmission oscillator signal and the local oscillator signal are compared by the coincidence circuit 140 to generate a coincidence signal indicating a phase shift generated by the difference between the frequencies of the transmission and local oscillator signals. For example, in block 304, the flip-flop circuit 140 may switch whenever the two oscillators 132, 134 are equal or opposite in phase, wherein the phase shift is generated by the frequency difference (Δf) between the transmitter oscillator frequency and the local oscillator frequency. Similar to block 302, block 304 is continuously performed during operation of the GWR level transmitter 100 (i.e., the coincidence circuit 140 continuously generates the coincidence signal during operation).

[0054] In block 306, the MCU 110 determines a stretch factor based on at least one of the coincidence signal generated in block 304 and the oscillator signal generated in block 302. Block 306 may be performed periodically during operation of the GWR level transmitter 100 (e.g., once during each cycle of the coincidence signal). As described above, in some embodiments, block 306 may involve counting the number of pulses received from the transmitter oscillator 132 during one cycle of the coincidence signal. Alternatively, block 306 may involve counting the number of pulses received from the local oscillator 134 during one cycle of the coincidence signal.

[0055] The method 300 then proceeds to block 308, where the MCU 110 evaluates whether the stretch factor determined in block 306 is within (or outside) an operating range suitable for level measurement. If the MCU 110 determines in block 308 that the stretch factor is outside the measurement operating range, no level measurement is made, and the method 300 proceeds directly to block 312, where one or both of the oscillators 132, 134 are adjusted (discussed further below). Conversely, if the MCU 110 determines in block 308 that the stretch factor is within the measurement operating range, a level measurement may be taken (see Figure 4 ), and the method 300 proceeds to block 310. As an illustrative example, where the expected value of the stretch factor is 200,000, block 308 may involve the MCU 110 checking whether the actual value of the stretch factor determined in block 306 is between 195,000 and 205,000. Of course, it should be understood that these numbers are merely an example, and many other values ​​may be used.

[0056] When the method 300 proceeds to block 310, the MCU then evaluates whether the stretch factor determined in block 306 is outside (or within) the operating range for the timing circuit control. If the MCU 110 determines in block 310 that the stretch factor is outside the control operating range, a level measurement may be made (see Figure 4 ), and the method 300 proceeds to block 312, where one or both of the oscillators 132, 134 are adjusted (discussed further below). Conversely, if the MCU 110 determines in block 310 that the stretch factor is within the control operating range, a level measurement may be made (see Figure 4 ), but no oscillator adjustment is performed, and the method 300 returns to block 306. As an illustrative example, where the expected value of the stretch factor is 200,000, block 310 may involve the MCU 110 checking whether the actual value of the stretch factor determined in block 306 is between 199,000 and 201,000. Of course, it should be understood that these numbers are merely an example, and many other values ​​may be used.

[0057] Based on the determination in block 308 and / or block 310, if the method 300 proceeds to block 312, the MCU 110 will adjust the frequency of one or both of the oscillators 132, 134 to adjust the differential frequency of the system. In block 312, the MCU 110 may cause the VCO 150 to provide a control signal to the local oscillator 134 (and / or the transmitter oscillator 134 in some embodiments) to adjust the frequency of the oscillator signal so as to maintain the differential frequency within the control operating range. After this adjustment in block 312 (or after block 310, if it is determined that no adjustment is needed), the method 300 returns to block 306, where the next stretch factor is determined.

[0058] Reference now Figure 4 In use, the GWR level transmitter 100 may also perform the method 400 for performing level measurement. It should be understood that Figure 4 The simplified flowchart of is illustrative in nature, and the GWR level transmitter 100 may perform other methods similar to, but different from, the method 400 for maintaining and performing level measurements. For example, in some embodiments, the Figure 4 The order of the steps shown in the drawings may vary, and / or the method may include additional or different steps than those shown.

[0059] The method 400 begins at block 402, which is similar to (or even overlaps with) block 308 of the method 300. In block 402, the MCU 110 evaluates whether the stretch factor determined in block 306 is within (or outside) an operating range suitable for level measurement. If the MCU 110 determines in block 402 that the stretch factor is outside the measurement operating range, no level measurement is taken, and the method 400 waits for the next stretch factor to be determined (and then evaluated in block 402). Conversely, if the MCU 110 determines in block 402 that the stretch factor is within the measurement operating range, the method 400 proceeds to block 404.

[0060] In block 404, the MCU 110 activates the transmission oscillator pulser 210, which causes the transmission oscillator signal from the transmission oscillator 132 to be transmitted along the waveguide probe 180. In other embodiments, the transmission oscillator pulser 210 may remain active during operation of the GWR level transmitter 100, and block 404 may be omitted from the method 400. As described above, when the transmission oscillator signal encounters a dielectric discontinuity (e.g., the surface of a medium in contact with the waveguide probe 180), a reflection signal will be generated in response.

[0061] The method 400 then proceeds to block 406 where the GWR level transmitter 100 receives the reflected signal (via the I / O circuit 170) from the waveguide probe 180. Once the reflected signal has been received, the MCU 110 may deactivate the transmission oscillator pulser 210 in block 408 to remove the transmission oscillator signal from the waveguide probe 180. In other embodiments, the transmission oscillator pulser 210 may remain active during operation of the GWR level transmitter 100, and block 408 may be omitted from the method 400.

[0062] The method 400 next proceeds to block 410, where the reflected signal received in block 406 is mixed with a local oscillator signal from the local oscillator 134 to produce a time-transformed signal. Block 410 may involve filtering the mixing product using a bandpass filter to produce the time-transformed signal.

[0063] The method 400 ends with block 412, where the MCU 110 calculates the distance between the medium surface in contact with the waveguide probe 180 and the proximal end (i.e., the end coupled to the GWR level transmitter 100) of the waveguide probe 180. Block 412 involves the MCU 110 applying a stretch factor to compensate the time-transformed signal. The stretch factor used for such compensation may be a stretch factor obtained before acquisition (i.e., the stretch factor evaluated in block 402), a stretch factor obtained after acquisition, an average of the stretch factors obtained before and after acquisition, or other values.

[0064] Although the present disclosure has been shown and described in detail in the drawings and foregoing description, such illustration and description should be considered illustrative rather than restrictive, and it should be understood that only illustrative embodiments have been shown and described and that all changes and modifications that fall within the spirit of the present disclosure are desired to be protected.

[0065] There are a number of advantages of the present invention resulting from the various features of the methods, devices, and systems described herein. It should be noted that alternative embodiments of the methods, devices, and systems of the present disclosure may not include all of the features described, while still benefiting from at least some of the advantages of these features. Those of ordinary skill in the art can readily design their own implementations of the methods, devices, and systems that incorporate one or more features of the present invention and fall within the spirit and scope of the present disclosure as defined by the appended claims.

Claims

1. A guided wave radar GWR liquid level transmitter, comprising: a timing circuit comprising a first oscillator circuit and a second oscillator circuit, wherein the first oscillator circuit is configured to generate a first signal having a first frequency, the first signal to be transmitted along the waveguide probe toward the medium surface, and wherein the second oscillator circuit is configured to generate a second signal having a second frequency; a coincidence circuit configured to generate a coincidence signal indicative of a phase shift created by a difference between the first frequency and the second frequency; as well as Microcontroller, configured as: determining a stretch factor based on at least one of the first signal and the second signal and the coincidence signal; responsive to determining that the stretch factor is within a first range, calculating a distance between the medium surface and the proximal end of the waveguide probe using the stretch factor, the first range indicating a range that provides acceptable measurement accuracy; as well as In response to determining that the stretch factor is outside of a second range, at least one of the first oscillator circuit and the second oscillator circuit is adjusted to adjust the difference between the first frequency and the second frequency, the second range indicating a range in which the differential frequency between the first oscillator circuit and the second oscillator circuit needs to be adjusted. 2 . The guided wave radar (GWR) level transmitter of claim 1 , wherein the first range is greater than the second range.

3. The guided wave radar (GWR) liquid level transmitter according to claim 1 or 2 further includes a mixing and filtering circuit, wherein the mixing and filtering circuit is configured to generate a time-transformed signal by mixing the second signal with a reflected signal received from the waveguide probe in response to the first signal being transmitted along the waveguide probe, wherein the microcontroller is configured to calculate the distance between the medium surface and the near end of the waveguide probe by applying the stretch factor to the time-transformed signal.

4. The guided wave radar (GWR) level transmitter of claim 3, wherein the mixing and filtering circuit is configured to bandpass filter a product of mixing the second signal with the reflected signal to generate the time-transformed signal.

5. The guided wave radar (GWR) level transmitter of claim 3, further comprising an analog-to-digital converter configured to convert the time-transformed signal into a digital signal for presentation to the microcontroller.

6. The guided wave radar (GWR) liquid level transmitter according to any one of claims 1, 2, 4 and 5, wherein determining the stretch factor comprises: A number of pulses generated by one of the first oscillator circuit and the second oscillator circuit during one period of the coincidence signal is determined.

7. The guided wave radar (GWR) liquid level transmitter according to any one of claims 1, 2, 4, and 5, further comprising a pulse generator circuit configured to selectively transmit the first signal to the waveguide probe.

8. The guided wave radar (GWR) liquid level transmitter according to any one of claims 1, 2, 4, and 5, wherein the microcontroller is configured to adjust both the first oscillator circuit and the second oscillator circuit when adjustment of only one of the first oscillator circuit and the second oscillator circuit is insufficient to bring the stretch factor within the second range.

9. The guided wave radar (GWR) level transmitter according to any one of claims 1, 2, 4, and 5, further comprising a voltage-controlled oscillator, which can be operated by the microcontroller to adjust at least one of the following items in response to determining that the stretch factor is outside the second range: (i) the first oscillator circuit to change the first frequency, and (ii) the second oscillator circuit to change the second frequency.

10. The guided wave radar (GWR) liquid level transmitter according to any one of claims 1, 2, 4, and 5, wherein the microcontroller includes a single integrated circuit, and the single integrated circuit is configured to determine the stretch factor, determine whether the stretch factor is within the first range and the second range, calculate the distance between the medium surface and the proximal end of the waveguide probe, and adjust at least one of the first oscillator circuit and the second oscillator circuit to adjust the difference between the first frequency and the second frequency.

11. A method for measuring using a waveguide probe, comprising: generating a first oscillator signal having a first frequency; generating a second oscillator signal having a second frequency; comparing the first oscillator signal and the second oscillator signal to produce a coincidence signal indicative of a phase shift produced by a difference between the first frequency and the second frequency; transmitting the first oscillator signal along the waveguide probe toward the medium surface; receiving a reflected signal from the waveguide probe in response to the first oscillator signal being transmitted along the waveguide probe; determining, with a processor, a stretch factor based on at least one of the first oscillator signal and the second oscillator signal and the coincidence signal; calculating, with the processor, a distance between the medium surface and the proximal end of the waveguide probe using the stretch factor when the stretch factor is within a first range, the first range indicating a range that provides acceptable measurement accuracy; as well as When the stretch factor is outside a second range, adjusting at least one of the first oscillator signal and the second oscillator signal to adjust a difference between the first frequency and the second frequency using the processor, the second range indicating a range in which a differential frequency between the first oscillator circuit and the second oscillator circuit needs to be adjusted. The method of claim 11 , wherein the first range is greater than the second range.

13. The method according to claim 11 or 12, further comprising: The reflected signal is mixed with the second oscillator signal to produce a time-transformed signal, wherein calculating the distance between the medium surface and the proximal end of the waveguide probe includes applying the stretch factor to the time-transformed signal.

14. The method of claim 13, wherein a product of mixing the reflected signal with the second oscillator signal is bandpass filtered to produce the time-transformed signal.

15. The method according to claim 13, further comprising: The time transformed signal is converted into a digital signal for presentation to the processor.

16. The method of any one of claims 11, 12, 14, and 15, wherein determining the stretch factor comprises: A number of pulses in one of the first oscillator signal and the second oscillator signal is determined during a period of the coincidence signal.

17. The method of any one of claims 11, 12, 14, and 15, wherein transmitting the first oscillator signal along the waveguide probe comprises: Activate the pulse generator circuit.

18. The method according to any one of claims 11, 12, 14, 15, comprising: When adjustment of only one of the first oscillator signal and the second oscillator signal is insufficient to bring the stretch factor within the second range, both the first oscillator signal and the second oscillator signal are adjusted.

19. The method of any one of claims 11, 12, 14, and 15, wherein adjusting at least one of the first oscillator signal and the second oscillator signal to adjust the difference between the first frequency and the second frequency comprises: The first frequency of the first oscillator signal is adjusted using a voltage controlled oscillator.

20. The method of any one of claims 11, 12, 14, and 15, wherein adjusting at least one of the first oscillator signal and the second oscillator signal to adjust the difference between the first frequency and the second frequency comprises: The second frequency of the second oscillator signal is adjusted using a voltage controlled oscillator.

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