Radar level meter system and verification test method thereof

Abstract

The present invention relates to a method for performing a verification test on a radar level gauge system and a radar level gauge system for determining a filling level of a product in a storage tank, wherein the radar level gauge system is arranged to determine the filling level of the product in the storage tank. The method comprises the following steps: transmitting an electromagnetic transmission signal towards the surface of the product in the storage tank; receiving an electromagnetic reflection signal generated by reflection of the transmission signal at the surface of the product; forming a measurement representation based on the transmission signal and the reflection signal, the measurement representation comprising surface echo information indicating the filling level of the product; adding verification test echo information indicating a predefined verification test level to the measurement representation, thereby generating a modified measurement representation; processing the modified measurement representation to determine the verification test level based on the modified measurement representation; and providing a signal indicating the result of the processing.

Description

Technical Field

[0001] The invention relates to a radar level gauge system, a method for performing a verification test on a radar level gauge system and a method for operating a radar level gauge system. Background Art

[0002] Radar level gauges are widely used to measure the filling level of products in storage tanks. Typically, radar level determination is performed by propagating an electromagnetic transmission signal toward the product in the tank and receiving an electromagnetic surface reflection signal generated by reflection of the transmission signal at the surface of the product.

[0003] The transmitted electromagnetic signal can be radiated towards the product in the tank, or it can be directed towards and into the product via a transmission line probe. The latter is often referred to as guided wave radar (GWR).

[0004] Based on the transmitted signal and the surface reflected signal, the distance to the surface of the product can be determined. From this distance, the fill level can be inferred.

[0005] Radar level gauges are generally classified as either pulse systems or FMCW systems. In a pulse system, a pulse is emitted toward the surface of the product, and the distance to the surface is determined based on the flight time of the pulse to the surface and back to the radar level gauge. In an FMCW system, a signal with a time-varying frequency is emitted toward the surface, and the distance is determined based on the frequency (and / or phase) difference between the emitted signal and the simultaneously received signal. There are also so-called pulsed FMCW systems.

[0006] In some cases, radar level meters are used in applications where failure of the radar level meter could result in a hazardous condition.

[0007] For example, a radar level meter with overfill prevention must be extremely reliable.

[0008] Various measures are taken to ensure the reliability of radar level meters, especially those with overfill prevention functions, thereby reducing the risk of hazardous conditions such as overfilling. For example, radar level meters and other important equipment can be designed to meet specific safety integrity levels (SILs) defined by the international standard IEC / EN 61508. According to this standard, safety-related systems can meet the requirements of different safety integrity levels from SIL1 to SIL4, where SIL4 represents the highest safety integrity level and SIL1 represents the lowest safety integrity level.

[0009] The SIL rating of a system is related to the probability of failure on demand, which in turn is a function of the failure rate and the time between proof tests. In order to maintain a certain SIL level, it is therefore necessary to perform proof tests at regular intervals specified according to the SIL level. For example, proof tests may need to be performed every year.

[0010] Proof testing is usually specified by the manufacturer of the SIL-rated system, and it is the responsibility of the user of the system to conduct the proof testing correctly.

[0011] The most realistic verification test is to fill the tank to its high level alarm limit, which will trigger the high level alarm (this is the safety instrumented function SIF) and then prove that it works. However, this process is usually very impractical and may also be associated with safety risks. Another way to verify the test is to add a reference reflector at the high level alarm limit in the tank. The radar level meter can then use the echo generated from the reference reflector as a reference and measure it to prove that if the actual product level is in the same position in the tank, the alarm will work as expected. This will produce enough verification test coverage to maintain the SIL level normally within the SIF mission time. The method is described in US 9325 077.

[0012] Performing proof tests using a reference reflector is a good solution and avoids the disadvantages of actually filling the tank to the high level alarm limit. However, in some cases it may not be desirable or easy to install a reference reflector kit as a retrofit installation. Summary of the invention

[0013] In view of the above, it is therefore desirable to provide an alternative verification test method that can be more easily implemented, especially in retrofit situations.

[0014] Therefore, according to a first aspect of the present invention, there is provided a method for performing a verification test on a radar level gauge system, the radar level gauge system being arranged to determine a filling level of a product in a tank, the method comprising the following steps: transmitting an electromagnetic transmit signal towards a surface of the product in the tank; receiving an electromagnetic reflection signal generated by reflection of the electromagnetic transmit signal at the surface of the product; forming a measurement representation based on the electromagnetic transmit signal and the electromagnetic reflection signal, the measurement representation comprising surface echo information indicating the filling level of the product; adding verification test echo information indicating a predefined verification test level to the measurement representation, thereby generating a modified measurement representation; processing the modified measurement representation to determine the verification test level based on the modified measurement representation; and providing a signal indicating a result of the processing.

[0015] The invention is based on the recognition that by adding the verification test echo information to the measurement signal formed by the radar level gauge system, a reliable verification test can be achieved, which does not require the provision of the product up to the high level alarm limit which is usually undesirable and does not require the installation of additional hardware in the tank. In other words, a synthetic verification test level representation, such as a signal, is added to the measurement chain of the radar level gauge system. Embodiments of the invention allow verification testing of all parts of the radar level gauge system, except possibly parts of the signal propagation device (antenna or probe) and the transceiver. Since the verification test echo information is added to the measurement representation instead of replacing the measurement representation, most of the functions of the signal propagation device and the transceiver can be verified based on the modified measurement representation by regularly determining the filling level of the product in the tank.

[0016] According to an embodiment, the method may further comprise the steps of: receiving a signal indicative of a result of the process; and providing a proof test alarm when the signal indicates a proof test level.

[0017] For the analog output interface in the radar level gauge system, the filling level can be transmitted as a current between 4mA and 20mA. The high level alarm limit can correspond to a current within this range. Alternatively, a high level alarm limit can be set at the radar level gauge, which can then be configured to communicate an overflow condition with an alarm current of, for example, 21.75mA (a current outside the range of 4mA to 20mA).

[0018] In many field applications, a digital communication link is provided. This will offer the possibility to communicate several indications for the current operating conditions. For example, an alarm and a determined filling level can be transmitted independently of each other.

[0019] According to a second aspect of the present invention, there is provided a radar level meter system for determining a filling level of a product in a storage tank, the radar level meter system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals; a signal propagation device, which is connected to the transceiver and is arranged to propagate the electromagnetic transmission signal from the transceiver toward the product in the storage tank and return the electromagnetic reflection signal generated by the reflection of the electromagnetic transmission signal at the surface of the product to the transceiver; and a measurement representation forming circuit, which is used to form a measurement representation based on the electromagnetic transmission signal and the electromagnetic reflection signal, the measurement representation including surface echo information indicating the filling level of the product; a verification test echo information adding circuit, which is used to add verification test echo information indicating a predefined verification test level to the measurement representation, thereby generating a modified measurement representation; and a level determination circuit, which is coupled to the transceiver and is configured to determine the verification test level based on the modified measurement representation.

[0020] A tank may be any container or vessel capable of containing a product and may be metallic or partially metallic or completely non-metallic, open, semi-open or closed.

[0021] A "transceiver" may be one functional unit capable of transmitting and receiving electromagnetic signals, or may be a system comprising separate transmitter and receiver units.

[0022] One or more of the measurement representation forming circuit, the verification test echo information adding circuit and the level determining circuit may be provided as separate devices or as a single device and may be implemented by hardware, software or a combination thereof.

[0023] The signal propagation device may be any device capable of propagating an electromagnetically transmitted signal. For example, the signal propagation device may include an antenna or a transmission line probe.

[0024] In various embodiments, the radar level gauge system may be controlled between a filling level measurement state and a verification test state. In the verification test state, the level determination circuit may be configured to: determine the verification test level based on the modified measurement representation; and provide a signal indicating the verification test level to allow a verification test result to be determined based on the verification test level.

[0025] In a filling level measurement state, the level determination circuit may be configured to: determine a filling level of a product in the tank based on the measurement representation; and provide a signal indicative of the filling level.

[0026] Furthermore, advantageously, the radar level gauge according to various embodiments of the present invention may be included in a filling level measurement system, which also includes a host system that receives a measurement signal from the radar level gauge. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] These and other aspects of the present invention will now be described in more detail with reference to the accompanying drawings showing currently preferred embodiments of the invention, in which:

[0028] Figure 1 Schematically shows a filling level measurement system including a radar level gauge system according to an embodiment of the present invention and a host system;

[0029] Figure 2 yes Figure 1 A magnified view of the radar level gauge system in Figure 1;

[0030] Figure 3A is a partial schematic block diagram of a radar level gauge system according to a first exemplary embodiment of the present invention;

[0031] Figure 3Bis a partial schematic block diagram of a radar level gauge system according to a second exemplary embodiment of the present invention;

[0032] Figure 4 is a flow chart schematically illustrating an example implementation of a method according to the present invention;

[0033] Figure 5 is a diagram showing an exemplary echo curve of a filling level measurement state of a radar level gauge system; and

[0034] Figure 6 is a diagram showing an exemplary echo curve of a verification test state of a radar level gauge system. DETAILED DESCRIPTION

[0035] In this detailed description, various embodiments of radar level gauge systems and methods according to various aspects of the present invention are mainly discussed with reference to FMCW (Frequency Modulated Continuous Wave) type radar level gauge systems with radiating antennas. It should be noted that this does not limit the scope of the invention, which is defined by the attached sets of claims and equally well includes, for example, pulsed radar level gauge systems or radar level gauge systems with other signal propagation devices, including, for example, other types of radiating antennas or various probes.

[0036] Figure 1 Schematically shown is a level measurement system 1 comprising a radar level gauge system 2 according to an exemplary embodiment of the invention and a host system 10 , shown as a control room.

[0037] A radar level gauge system 2 is installed to measure the filling level of a product 3 contained in a tank 4. The radar level gauge system 2 comprises a measuring unit 6 and a signal propagation device, here in the form of a parabolic antenna 7. Figure 1 The verification test level L is shown in PT , which may correspond to or be higher than the high level alarm limit of the level measurement system 1 .

[0038] exist Figure 1 It can also be seen that the storage tank 4 can be equipped with an additional radar level gauge system 15, which can be used to determine the filling level L of the product 3 in the storage tank 4. S If the radar level gauge system 2 comprises two separate measuring channels, a so-called 2-in-1 solution can also be used, whereby effectively two radar level gauges share the same antenna 7 .

[0039] In addition, the tank 4 is shown to include an inspection hatch 16 which allows access to the interior of the tank 4 so that, for example, a hand can be immersed to manually determine the fill level L. S.

[0040] Figure 1 The radar level gauge system 2 in the embodiment of the present invention is configured to allow an operator of the filling level measurement system 1 to perform reliable verification tests on the radar level gauge 2 itself and on the filling level measurement system 1 as a whole.

[0041] like Figure 2 As schematically shown in FIG. 2 , the measuring unit 6 of the radar level gauge system 2 comprises a transceiver 17 , a processing circuit 19 , a communication interface 21 and a communication antenna 23 .

[0042] The transceiver 17 is configured to generate, transmit and receive electromagnetic signals, and the processing circuit 19 is connected to the transceiver 17 and configured to receive the electromagnetic transmission signal S based on the electromagnetic transmission signal S. T The reflected, received electromagnetic reflection signal S at the surface 11 of the product 3 R To determine the filling level L of product 3 S , and the communication interface 21 is coupled to the processing circuit 19 and is configured to allow communication with the host system 10. Figure 2 In the example embodiment of the radar level meter 2, the communication between the host system 10 is represented as wireless communication. Alternatively, the communication can occur, for example, through an analog and / or digital wired communication channel. For example, the communication channel can be a two-wire 4-20mA loop, and the filling level can be communicated by providing a specific current corresponding to the filling level on the two-wire 4-20mA loop. The HART protocol can also be used to send digital data on such a 4-20mA loop. In addition, a purely digital communication protocol such as Modbus or Foundation Fieldbus can be used.

[0043] Figure 3A is a partial schematic block diagram of a radar level gauge system according to a first exemplary embodiment of the present invention. Figure 3A , the block diagram shows the Figure 2 The measurement channels of the transceiver 17 and the measurement processor 19 are shown in FIG.

[0044] The transceiver 17 is shown here as comprising a microwave source 25 driven by a step signal generator 27 which in turn is controlled by a timing circuit 29 comprised in the measurement processor 19. The microwave source 25 is connected to the antenna 7 via a power divider 31. The power divider 31 is arranged to connect the reflected signal from the antenna 7 to a mixer 33 which is also connected to receive the signal from the microwave source 25. The output of the mixer is connected to a low pass filter 35 and an amplifier 37.

[0045] In addition to the timing circuit 29, the measurement processor 19 here also includes a sampler 39, which is configured to receive the measurement signal S output by the mixer 33, low-pass filtered by the low-pass filter 35 and amplified by the amplifier 37. M (This measurement signal is usually called an intermediate frequency signal) and samples it. M is based on the transmitted signal S T and the reflected signal S R and includes an indication of the filling level L of the product 3 in the tank 4 S The surface echo information (the frequency difference between the transmitted signal and the reflected signal).

[0046] The sampler 39 may, for example, include a sample-and-hold circuit in combination with an A / D converter, or be implemented as a sigma-delta converter. The sampler 39 may be controlled by the timing circuit 29 to be in phase with the transmit signal S T Synchronous. Figure 3A In the illustrated embodiment, the measurement processor 19 further includes a verification test echo information adding circuit 40 , a signal processor 41 , a memory 43 and a level determiner 45 .

[0047] While the elements of the transceiver 17 are typically implemented in hardware and form part of an integrated unit often referred to as a microwave unit, at least some parts of the measurement processor 19 may typically be implemented by software modules executed by an embedded processor. The invention is not limited to this particular implementation and any implementation found to be suitable for implementing the functionality described herein is contemplated.

[0048] Reference Figure 3A The timing circuit 29 controls the microwave source 25 via the step signal generator 27 to form a transmission signal S T . Transmit signal S T It can be provided in the form of a plurality of discrete and mutually different frequency time series.

[0049] Reflected signal S R By transmitting signal S T At impedance discontinuities (including Figure 1 Due to the flight time from the radar level gauge system to the different impedance discontinuities and back, the reflected signal S R is the transmitting signal S T delayed copy, where the reflected signal S R The part reflected from different impedance discontinuities is the same as the transmitted signal S T In comparison, different phase differences will be presented. In addition, the phase difference will change step by step with the change of the discrete frequency of the emission.

[0050] By mixing the transmission signal S T With the reflected signal S R Combined to form the above measurement signal S M (or intermediate frequency signal).

[0051] If a transmission signal with a continuously varying frequency is used, the measurement signal S M There will be a continuous signal comprising one frequency component for each time of flight corresponding to a different impedance discontinuity encountered by the transmitted signal.

[0052] Since in this particular example the transmitted signal S T Instead, it is a series of discrete frequencies, so the phase difference will change step by step, which means that the measured signal S M will be piecewise constant, where the duration of the constant part is the same as the transmitted signal S T The transmission duration of different frequencies is the same.

[0053] Measuring signal S M The sampler 39 samples the sample and provides it to the signal processor 41. The verification test echo information adding circuit 40 provides the signal processor with a signal indicating the predefined verification test level L PT Verification test echo information, wherein the verification test echo information is added to the measurement representation (measurement signal S M In the example embodiment where the radar level gauge system 2 is of FMCW type, the added verification test echo information may simply represent the sampling value corresponding to the verification test level L. PT The digital value corresponding to a single frequency sine wave.

[0054] The signal processor 41 then processes the measurement representation thus modified in order to determine the echo indicative of the echo from the impedance discontinuity and the added impedance at the verification test level L. PT The modified measurement representation is transformed from the time domain to the frequency domain using, for example, an FFT (Fast Fourier Transform). After the modified measurement representation is transformed into the frequency domain, the resulting spectrum is transformed into an echo curve that can be used by the level determiner 45 to determine the verification test level L PT and the filling level L of the product 3 in the tank 4 S .

[0055] Figure 3B is a partial schematic block diagram of a radar level gauge system according to a second exemplary embodiment of the present invention.

[0056] Figure 3B The second exemplary embodiment shown in FIG. Figure 3A The first exemplary embodiment described differs mainly in that the verification test information is added earlier in the measurement chain. In particular, Figure 3B As schematically shown in FIG. 1 , the transceiver 17 includes a verification test echo information adding circuit 47 in the form of a controllable oscillator, which is controllable to add the verification test echo information signal to the measurement representation (the measurement signal S output by the mixer 33). M The verification test echo information signal may be a single frequency sine wave having a value selected to indicate a predefined verification test level L. PT It is desirable to provide a signal having a limited bandwidth including frequencies around the above selected frequency so that the synthetic echo resulting from the introduction of the verification test echo information signal looks real. The verification test echo information signal may be added to the measurement signal S in any suitable manner, for example using a microwave hybrid circuit such as a so-called balanced-unbalanced transformer (balun) or any other suitable microwave hybrid circuit known to those skilled in the art. M .

[0057] You can refer to the above Figure 3A The modified measurement representation S is performed as described M 'Subsequent processing.

[0058] Now refer to Figure 4 An exemplary embodiment of the method according to the invention is described by the flowchart in FIG.

[0059] In a first step 100, the radar level gauge system 2 receives a status signal indicating a desired status of the radar level gauge system 2. The status signal may be received, for example, from a host system / control room 10 or may be provided to the radar level gauge system 2 by operating a physical switch, for example a button, which may be provided on a measuring unit 6 of the radar level gauge system 2.

[0060] In a subsequent step 101, the status signal is evaluated and if the status signal indicates that the radar level gauge system 2 should be in its filling level measuring state, the method proceeds to step 102 in which the transceiver transmits a transmission signal S as further described above. T In step 103, the transceiver receives the reflected signal S R , and in step 104, a measurement representation S is formed M In step 105, based on the measurement representation S M , the processing circuit 19 determines the filling level L S As mentioned above Figure 3A and Figure 3B As described, the measurement representation may be processed to form an echo curve, such as Figure 5The example echo curve in the diagram 49. Figure 5 In the diagram of FIG. 7 , the signal strength of the reflected signal is shown as a function of the distance from the antenna 7. T The surface echo 51 generated by the reflection at the surface 11 of the product 3 in the tank 4 is Figure 5 Based on the recognition of the surface echo 51 and the a priori knowledge of the position of the antenna 7 relative to the bottom of the tank 4, the filling level L can be determined. S In step 106, the determined filling level L S The signal is provided to, for example, the host system 10 via the interface 21 and the antenna 23. Thereafter, the method returns to step 100.

[0061] If on the contrary it is determined in step 101 that the status signal indicates that the radar level gauge system 2 should be in its verification test state, the method proceeds to step 107 in which the transceiver transmits a transmission signal S as further described above. T In step 108, the transceiver receives the reflected signal S R , and in step 109, a measurement representation S is formed M In a subsequent step 110, a predefined verification test level L is indicated. PT Verification test echo information S PT Add to measurement representation S M , to form a modified measurement representation S M '. As mentioned above Figure 3A and Figure 3B Describes the verification test echo information S PT Add to measurement representation S M To form a modified measurement representation S M Two exemplary ways of '.

[0062] In order to make the verification test echo information S PT The resulting synthetic echo is more realistic and the proof test echo information can be slightly varied between measurement cycles to leave the surface level at the predefined proof test level L. PT This optional procedure can facilitate the subsequent identification of the verification test echo as a surface echo.

[0063] Furthermore, in step 110, the measurement representation S is added M Verification test information S PT The measurement conditions in the tank 4 may be adapted to provide a more realistic verification test. For example, the verification test information S may be determined based on previously acquired information about the product 3 in the tank 4 (such as the dielectric constant of the product 3). PTAdditionally, or alternatively, one may represent S based on a measurement M To determine the verification test information S PT For example, the amplitude and / or other characteristics of the surface echo may be used to determine an appropriate amplitude and / or other characteristics of the synthetic verification test echo.

[0064] Then, in step 111, the modified measurement representation S is processed M ', to determine the verification test level L PT As mentioned above Figure 3A and Figure 3B As described above, the modified measurement representation S can be processed M ' to form an echo curve, e.g. Figure 6 The example echo curve 53 in the diagram of FIG. Figure 6 In the diagram of FIG, a representation of the signal strength of the reflected signal is shown as a function of the distance from the antenna 7, including an exemplary synthetic verification test echo provided by the verification test echo information adding circuit. T The surface echo 55 generated by the reflection at the surface 11 of the product 3 in the tank 4 is Figure 5 The highest positive peak in , and the synthetic verification test echo 57 is the first clear positive peak counted from the top of tank 4.

[0065] It should be noted that the verification test information S can be determined PT To achieve different modified measurement representations S M '. For example, the verification test information S can be determined PT The filling level of the product 3 is indicated by the addition of the level determiner 45 and the synthetic verification test echo indicates the filling level of the product 3 and provides the indication verification test level L PT For this purpose, the verification test information S PT , to generate a synthetic verification test echo with an amplitude higher than a predetermined threshold, or to generate an echo with the highest amplitude in the echo curve 53. In addition, the verification test information S PT To achieve a slow movement of the synthetic verification test echo 57 over time, as further described above. How to determine the verification test information to increase the likelihood that the level determiner 45 determines that the synthetic verification test echo 57 indicates a filling level will generally depend on the algorithm used to select which surface echo candidate represents the actual surface echo under the filling level measurement state. Based on the description herein, a skilled person will be able to appropriately determine the verification test information S PT .

[0066] As an alternative or in addition to adjusting the synthetic proof test echo 57 as described above, in the proof test state, the radar level gauge system 2 may be temporarily configured to generate a signal at a predefined proof test level L PT Searches for surface echoes within a predefined range nearby.

[0067] According to another alternative, the criteria for selecting which surface echo candidate represents the actual surface echo may be temporarily changed. In case the radar level gauge system 2 is controlled to be in a verification test state, the surface echo identification criteria may for example be: the first positive peak value above a predefined threshold is designated as a surface echo, independently of any echo tracking or the like.

[0068] For example, the result may be provided to the host system / control room 10 in step 112 and may be provided in the form of a signal indicating the determined level, or as an alarm signal in embodiments where the radar level gauge system 2 itself identifies the measured level as being at or above the high level alarm limit. Thereafter, the method returns to step 100. If the radar level gauge system 2 can correctly detect and measure the predefined verification test level L PT If the radar level gauge system 2 detects the synthetic verification test echo 57 at the surface, the verification test is successful and the verification test can be terminated. If the radar level gauge system 2 cannot detect and / or does not correctly measure the synthetic verification test echo 57, the verification test may have failed and further action may need to be taken. For example, such further action may be, for example, to re-run the verification test and then possibly perform a complete verification test including bringing the surface to the high level alarm limit.

[0069] For illustrative purposes, Figure 6 A first exemplary noise level 59 and a second exemplary noise level 61 are indicated. For the first noise level 59, the proof test echo 57 can be detected and it can be determined that the proof test is successful. However, for the second noise level 61, the radar level gauge system 2 may not be able to detect the proof test echo 57, which means that the proof test will fail.

[0070] In order to make the proof test as realistic as possible, the surface echo 55 may be evaluated and the proof test information added to the measurement representation may be adapted to at least one characteristic of the surface echo signal. For example, the amplitude of the detected surface echo 55 may be used to determine the desired amplitude of the proof test echo 57. Once the desired amplitude of the proof test echo 57 is determined, the proof test information may be adjusted to achieve this amplitude. Alternatively or in combination, the proof test information may be adjusted based on other characteristics of the product in the tank, such as the dielectric constant of the product and / or the occurrence of (expected) disturbances, etc.

[0071] In the claims, the word "comprising" does not exclude other elements or steps and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

1. A method for performing a verification test on a radar level gauge system, the radar level gauge system being arranged to determine the fill level of a product in a tank, the method The following steps are involved: emitting an electromagnetic transmission signal toward a surface of a product in the tank; receiving an electromagnetic reflection signal generated by reflection of the electromagnetic transmission signal at a surface of the product; forming a measurement representation based on the electromagnetic emission signal and the electromagnetic reflection signal, the measurement representation comprising surface echo information indicative of a filling level of the product; adding proof test echo information indicative of a predefined proof test level corresponding to or above a high level alarm limit of the radar level gauge system to the measurement representation, thereby generating a modified measurement representation; processing the modified measurement representation to determine a verification test level based on the modified measurement representation; and A signal is provided indicative of a result of the processing.

2. The method according to claim 1, in, The method further comprises the following steps: receiving said signal indicative of a result of said processing; and When the signal indicates the proof test level, a proof test alarm is provided.

3. A method of operating a radar level gauge system, the radar level gauge system being arranged to determine a filling level of a product in a tank, the radar level gauge system being controllable between a filling level measurement state and a verification test state, in, The method comprises the following steps: receiving a status signal indicating a desired status of the radar level gauge system; In case the status signal indicates the filling level measurement status: emitting an electromagnetic transmission signal toward a surface of a product in the tank; receiving an electromagnetic reflection signal generated by reflection of the electromagnetic transmission signal at a surface of the product; forming a measurement representation based on the electromagnetic emission signal and the electromagnetic reflection signal, the measurement representation comprising surface echo information indicative of a filling level of the product; and determining the filling level based on the measurement representation; and In case the status signal indicates the verification test status, the steps of the method according to claim 1 or 2 are performed.

4. The method according to any one of claims 1 to 3, in: The step of forming the measurement representation comprises the following steps: combining the electromagnetic reflection signal with a reference signal time-correlated with the electromagnetic transmission signal to form an analog measurement signal; and performing analog-to-digital conversion on the analog measurement signal to form a measurement representation as a digital measurement representation; and The added steps include the following: A digital value indicative of the proof test level is added to the digital measurement representation to form the modified measurement representation.

5. The method according to any one of claims 1 to 3, in: The step of forming the measurement representation comprises the following steps: combining the electromagnetic reflection signal and a reference signal time-correlated with the electromagnetic transmission signal to form a measurement representation as an analog measurement signal; and The added steps include the following: A proof test level signal is added to the analog measurement signal to form the modified measurement representation as a modified analog measurement signal.

6. The method according to any one of claims 1 to 3, in, The added steps are: Proof test echo information is added to the measurement representation, the proof test echo information being indicative of a time sequence of different levels including the predefined proof test level.

7. The method according to any one of claims 1 to 3, further comprising: The following steps are involved: The proof test echo information is determined based on previously acquired information regarding measurement conditions in the tank.

8. The method according to claim 7, in, The proof test echo information is determined based on known characteristics of the product in the tank.

9. The method according to claim 7, in, The verification test echo information is determined based on previously acquired surface echo information.

10. The method according to any one of claims 1 to 3, in: The electromagnetic transmission signal is a frequency modulated signal exhibiting a time-varying frequency; and The step of forming the measurement representation comprises mixing the electromagnetic emission signal with the electromagnetic reflection signal.

11. The method according to claim 10, in, The proof test information includes a predefined frequency indicative of the predefined proof test level.

12. A radar level gauge system for determining the filling level of a product in a storage tank, the radar level gauge system include: A transceiver for generating, transmitting and receiving electromagnetic signals; a signal propagation device connected to the transceiver and arranged to propagate an electromagnetic transmission signal from the transceiver toward the product in the tank and return an electromagnetic reflection signal generated by reflection of the electromagnetic transmission signal at the surface of the product to the transceiver; and a measurement representation forming circuit for forming a measurement representation based on the electromagnetic emission signal and the electromagnetic reflection signal, the measurement representation comprising surface echo information indicative of a filling level of the product; a proof test echo information adding circuit for adding proof test echo information indicative of a predefined proof test level corresponding to or above a high level alarm limit of the radar level gauge system to the measurement representation, thereby generating a modified measurement representation; as well as A level determination circuit is coupled to the transceiver and is configured to determine a proof test level based on the modified measurement representation.

13. The radar level gauge system according to claim 12, in, The level determination circuit is further configured to provide a proof test signal indicative of the proof test level.

14. The radar level gauge system according to claim 12 or 13, in, The level determination circuit is further configured to determine a filling level in the tank based on the measurement representation.

15. The radar level gauge system according to claim 12 or 13, in, The radar level gauge system can be controlled between a filling level measurement state and a verification test state, and Wherein, in the verification test state, the level determination circuit is configured to: determining the verification test level based on the modified measurement representation; and A signal indicative of the proof test level is provided to enable a proof test result to be determined based on the proof test level.

16. The radar level gauge system according to claim 15, in, In the filling level measurement state, the level determination circuit is configured to: determining a fill level of the product in the tank based on the measurement representation; and A signal indicative of the fill level is provided.

17. The radar level gauge system according to claim 12 or 13, in: The measurement representation forming circuit is configured to: combining the electromagnetic reflection signal with a reference signal time-correlated with the electromagnetic transmission signal to form an analog measurement signal; and performing analog-to-digital conversion on the analog measurement signal to form the measurement representation as a digital measurement representation; and The verification test echo information adding circuit is configured to: A digital value indicative of the proof test level is added to the digital measurement representation to form the modified measurement representation.

18. The radar level gauge system according to claim 12 or 13, in: The measurement representation forming circuit is configured to: combining the electromagnetic reflection signal and a reference signal time-correlated with the electromagnetic transmission signal to form the measurement representation as an analog measurement signal; and The verification test echo information adding circuit is configured to: A proof test level signal is added to the analog measurement signal to form the modified measurement representation as a modified analog measurement signal.

19. The radar level gauge system according to claim 12 or 13, in: The transceiver is configured to transmit an electromagnetic transmission signal in the form of a frequency modulated signal exhibiting a time-varying frequency; as well as The measurement representation forming circuit comprises a mixer arranged and configured to mix the electromagnetic transmit signal with the electromagnetic reflect signal.

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