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DE-102020129764-B4 - Level measuring device with adjustable timing and corresponding compensation method

DE102020129764B4DE 102020129764 B4DE102020129764 B4DE 102020129764B4DE-102020129764-B4

Abstract

FMCW-based level measuring device for measuring a compensated level value (L) of a fill material (2) in a container (3), comprising: - An antenna arrangement (10) by means of which a high-frequency signal (S HF ) can be sent to the filling material (2) and, after reflection at the surface of the filling material, can be received as a received signal (E HF ), - a signal generation unit (11) designed to generate the high-frequency signal (S HF ) according to the FMCW principle with reference to a defined clock rate clk 1 , - a receiving unit (12) designed to ◯ to downmix the received signal (E HF ) into a low-frequency base signal (IF) according to the FMCW principle, and ◯ to sample the base signal (IF) at a defined sampling rate clk 2 , - an evaluation unit (13) designed to ◯ to determine a distance value (d) to the filling material (2) based on the sampled basic signal (IF d ), ◯ to compensate the distance value (d) using a first compensation factor k 1 and/or a second compensation factor k 2 , and ◯ to determine the compensated level value (L) based on the compensated distance value (d), and - a diagnostic unit (14) designed to ◯ to determine the first compensation factor k 1 by comparing the clock rate clk 1 with the sampling rate clk 2 , according to R 2,1 = c l k 2 c l k 1 a ratio R 2,1 of the rates clk 1 , clk 2 to each other is determined, and where the first compensation factor k 1 according to k 1 = R 2,1 * c l k 1, s o l l c l k 2, s o l l is calculated, where clk 1,2soll represents the respective target values clk 1/2,soll of the clock rate clk 1 and the sampling rate clk 2 , respectively, and/or o in order to determine the second compensation factor k 2 by comparing the clock rate clk 1 and/or the sampling rate clk 2 with a reference frequency clk ref and/or the first compensation factor k 1 , according to R 1, r e f = c l k 1 c l k r e f ; R 2, r e f = c l k 2 c l k r e f The ratios R1,ref , R2 ,ref of the rates clk1 , clk2 to the reference frequency clkref are determined, where the second compensation factor k2 is calculated according to... k 2 = ( c l k 1, s o l l R 1, r e f * c l k r e f ) 2 ⋅ R 2, r e f * c l k r e f c l k 2, s o l l is calculated, and ◯ to transfer the first compensation factor k 1 or the second compensation factor k 2 to the evaluation unit (13) after determination.

Inventors

  • Markus Vogel
  • Harald Faber
  • Anton Kochetkov

Assignees

  • Endress+Hauser SE+Co. KG

Dates

Publication Date
20260513
Application Date
20201111

Claims (9)

  1. FMCW-based level measuring device for measuring a compensated level value (L) of a fill material (2) in a container (3), comprising: - An antenna arrangement (10) by means of which a high-frequency signal (S <sub>HF</sub> ) can be transmitted to the fill material (2) and received as a receive signal (E <sub>HF </sub>) after reflection at the surface of the fill material, - a signal generation unit (11) designed to generate the high-frequency signal (S <sub>HF</sub> ) according to the FMCW principle with reference to a defined clock rate clk<sub> 1 </sub>, - a receiver unit (12) designed to: ◯ down-convert the receive signal (E <sub>HF</sub> ) into a low-frequency base signal (IF) according to the FMCW principle, and ◯ sample the base signal (IF) at a defined sampling rate clk<sub> 2 </sub>, - an evaluation unit (13) which is designed to: ◯ determine a distance value (d) to the fill material (2) based on the sampled base signal (IF d ), ◯ compensate the distance value (d) using a first compensation factor k 1 and/or a second compensation factor k 2 , and ◯ determine the compensated fill level value (L) based on the compensated distance value (d), and - a diagnostic unit (14) designed to: ◯ determine the first compensation factor k 1 by comparing the clock rate clk 1 with the sampling rate clk 2 , according to R 2,1 = c l k 2 c l k 1 a ratio R 2,1 of the rates clk 1 , clk 2 to each other is determined, and where the first compensation factor k 1 according to k 1 = R 2,1 * c l k 1, s o l l c l k 2, s o l l is calculated, where clk 1,2soll are the respective target values clk 1/2,soll of the clock rate clk 1 and the sampling rate clk 2 , respectively, and/or to determine the second compensation factor k 2 by comparing the clock rate clk 1 and/or the sampling rate clk 2 with a reference frequency clk ref and/or the first compensation factor k 1 , according to R 1, r e f = c l k 1 c l k r e f ; R 2, r e f = c l k 2 c l k r e f The ratios R1,ref , R2 ,ref of the rates clk1 , clk2 to the reference frequency clkref are determined, where the second compensation factor k2 is calculated according to... k 2 = ( c l k 1, s o l l R 1, r e f * c l k r e f ) 2 ⋅ R 2, r e f * c l k r e f c l k 2, s o l l is calculated, and ◯ to transfer the first compensation factor k 1 or the second compensation factor k 2 to the evaluation unit (13) after determination.
  2. Level measuring device according to Claim 1 , wherein the level measuring device (1) can be connected via a manufacturing interface (18) for the transmission of the first compensation factor k 1 , the second compensation factor k 2 , the clock rate clk 1 , the sampling rate clk 2 and/or an external reference frequency clk ref .
  3. Level measuring device according to Claim 1 or 2 , wherein the signal generation unit (11) is implemented as a phase-controlled loop.
  4. Level measuring device according to one of the preceding claims, wherein the evaluation unit (13) is designed to determine the distance value (d) by means of a Fourier transform of the sampled basic signal (IF d ).
  5. A method for compensating a level measuring device (1) according to one of the preceding claims, comprising the following method steps: - determining the first compensation factor k1 by comparing the clock rate clk1 with the sampling rate clk2 , and/or - determining the second compensation factor k2 by comparing the clock rate clk1 and/or the sampling rate clk2 with the reference frequency clkref , wherein the clock rate clk1 and the sampling rate clk2 are compared with each other by means of R 2,1 = c l k 2 c l k 1 a ratio R 2,1 of the rates clk 1 , clk 2 to each other is determined, and where the first compensation factor k 1 according to k 1 = R 2,1 * c l k 1, s o l l c l k 2, s o l l is calculated, where clk 1,2soll is the respective setpoint values clk 1/2,soll of the clock rate clk 1 and the sampling rate clk 2 , respectively, and/or where the clock rate clk 1 and the sampling rate clk 2 are each compared with the reference frequency clk ref , by according to R 1, r e f = c l k 1 c l k r e f ; R 2, r e f = c l k 2 c l k r e f The ratios R1,ref , R2 ,ref of the rates clk1 , clk2 to the reference frequency clkref are determined, and the second compensation factor k2 is calculated according to k 2 = ( c l k 1, s o l l R 1, r e f * c l k r e f ) 2 ⋅ R 2, r e f * c l k r e f c l k 2, s o l l is calculated.
  6. Procedure according to Claim 5 , wherein the first compensation factor k 1 is determined repeatedly during continuous level measurements, and wherein the level measuring device (1) is considered to be functioning as long as the first compensation factor k 1 does not exceed a minimum change Ak 1 over the continuous level measurements.
  7. Procedure according to Claim 5 or 6 , wherein the second compensation factor k 2 is determined during the manufacture of the level measuring device (1) by comparing the clock rate clk 1 and/or the sampling rate clk 2 with the reference frequency clk ref of an external reference source.
  8. Procedure according to Claim 7 , wherein the second compensation factor k 2 is calculated by an external unit, and wherein the second compensation factor k 2 of the evaluation unit (13) is transferred via the manufacturing interface (18).
  9. Procedure according to Claim 7 , wherein the reference frequency clk ref is transferred to the analysis unit (14) via the manufacturing interface (18), and wherein the second compensation factor k 2 is calculated by the analysis unit (14).

Description

The invention relates to a level measuring device whose clocking rate is compensable. In automation technology, particularly in process automation, a multitude of different measured variables need to be determined, depending on the process. These can include, for example, fill level, flow rate, pressure, temperature, pH value, redox potential, conductivity, or dielectric constant of a medium in a process plant. Field devices specifically designed for this purpose are used to acquire the corresponding measured values. These devices are based on suitable sensors and/or measurement principles. The Endress+Hauser Group manufactures and distributes various types of field devices. Radar-based measurement methods have become established for measuring the fill level of contents in containers. In the context of this patent application, the terms "radar" and "high frequency" refer to corresponding signals with frequencies between 0.03 GHz and 300 GHz. Common frequency bands used for level measurement are 2 GHz, 26 GHz, 79 GHz, and 120 GHz. In addition to its robustness and ease of maintenance, radar-based level measurement offers the advantage over other methods of being able to measure the fill level almost continuously. In the case of radar, the FMCW principle (Frequency Modulated Continuous Wave) is the most common measurement principle for distance and level measurement. This principle is based on continuously transmitting a high-frequency signal with a modulated frequency. The frequency of the transmitted high-frequency signal lies within a defined frequency band around a standardized center frequency. The frequency change over time is typically linear in FMCW and therefore exhibits a ramp or triangular waveform. However, a sinusoidal change is also possible in principle. The high-frequency signal is usually generated within the level gauge's signal generation unit by a PLL (Phase Locked Loop). The PLL generates the sawtooth-shaped high-frequency signal with reference to a constant internal clock frequency clk1 , such as a quartz oscillator. The distance d to the contents, or the fill level, is determined using the FMCW method based on the instantaneous frequency difference f<sub>IF</sub> between the currently received and the currently transmitted high-frequency signals. This is achieved by generating a base signal through mixing the corresponding electrical high-frequency signals. The distance d can then be determined from the frequency f<sub> IF </sub> of the base signal, as this frequency changes proportionally to the distance d. Here, c is the speed of light, and k represents the ramp rate of the frequency change. The frequency f<sub>IF</sub> of the base signal can be determined, for example, by digitizing the base signal with a defined sampling rate clk<sub>2</sub> and then subjecting it to a Fast Fourier Transform. The FMCW-based measurement principle for level measurement is described in more detail, for example, in " Radar Level Detection, Peter Devine, 2000 “. Ideally, level gauges based on the FMCW method can achieve high level resolution with relatively little circuitry complexity, thus reaching the required sub-millimeter resolution depending on the application. However, in practice, the resolution is often limited by various component tolerances. In the case of FMCW, it is primarily component tolerances regarding internal clock frequencies that lead to corresponding measurement errors in level measurement. Compensating for these measurement errors, caused by deviations of the clock frequencies from the target frequencies, is difficult to implement within the gauge itself. This is because direct frequency measurement is not possible from a circuit design perspective; it can only be done indirectly by measuring the ratio of the actual frequency to a known reference frequency. However, integrating a reference source whose reference frequency exhibits virtually no component-related tolerances is not economically feasible. In the publication DE 102006058852 A1 In connection with FMCW-based level measurement, a method is described in which the non-linear VCO characteristic is corrected by adjusting the VCO output frequency to the respective ramp frequency. Also in the publication WO 001998038525 A1 A method is described to straighten nonlinear VCO characteristics by adjusting the transmission frequency to the desired ramp frequency at each point in time during the frequency ramp. The invention is based on the objective of providing a level measuring device whose Tolerances regarding internal clocking can be compensated for in order to minimize measurement errors. The invention solves this problem by means of an FMCW-based level measuring device for measuring a compensated level value of a product in a container according to the features of claim 1. Accordingly, the level measuring device comprises the following components: - An antenna arrangement by means of which a high-frequency signal can be sent tow