Method for measuring fill level

Abstract

The invention relates to a method for radar-based measurement of a filling level (L) of a filling material (3) contained in a container (2). The method is characterized in that, in addition to conventional method steps using radar, the following method steps are performed in the relevant measuring cycle (m). In successive measuring cycles (n), the following steps are performed step by step: storing the relevant current evaluation curve (ZF n ); Evaluation curve (ZF based on the current measurement cycle (n) n ) and the stored evaluation curve (ZF ) of the previous measurement cycle (n‑m) n‑m ) forms the first difference curve (Diff n ); and based on the current first difference curve (Diff n ) in the maximum value (A m ) is used to determine the filling level (L). According to the invention, the filling level is thus determined according to the difference curve (Diff n ) rather than being established on the basis of an evaluation curve (ZF) referred to as an intermediate frequency signal. As a result, the filling level (L) can be determined more certainly, in particular in the case of a filling material with a corrugated surface. This means that the filling level (L) can be determined more reliably overall.

Description

Technical Field

[0001] The invention relates to a method for measuring the filling level of a filling material in a container and to a filling level measuring device for carrying out the method. Background Art

[0002] In process automation technology, field devices are often used to capture or influence process variables. To this end, the function of the field device is based in each case on a suitable measuring principle in order to capture the corresponding process variable, such as fill level, flow rate, pressure, temperature, pH value, redox potential or conductivity. Endress+Hauser manufactures and sells a wide range of such field devices.

[0003] In order to measure the filling level of the filling material in the container, radar-based measurement methods have been established because they are robust and require minimal maintenance. Within the scope of the present invention, the term "container" also refers to an unclosed container, such as a pool, a lake or a flowing body of water. A key advantage of radar-based measurement methods is their ability to more or less continuously measure the filling level. In the context of this patent application, the term "radar" refers to a microwave signal with a frequency between 0.03 GHz and 300 GHz. The typical frequency band for performing filling level measurement is 2 GHz, 6 GHz, 26 GHz or 79 GHz. The higher the selected frequency band, the narrower the beam cone of the emitted microwave signal.

[0004] In the case of radar-based fill level measurement, the pulsed time-of-flight principle is an established measuring principle. Here, a pulse-shaped microwave signal is cyclically emitted in the direction of the filling material, and the flight time until a corresponding pulse-shaped reception signal is received is measured. Based on this measuring principle, fill level measuring devices can be implemented with relatively low circuit complexity.

[0005] If more complex circuit technology is acceptable, FMCW (Frequency Modulated Continuous Wave) is a possible measuring principle for radar-based fill level measurement. This measuring principle is based on the fact that microwave signals are transmitted continuously, but with a modulated frequency. In this case, the frequency of the microwave signal lies in a defined frequency band within the range of the standard center frequency. The characteristic of FMCW is that the transmission frequency is not constant, but varies periodically within a defined frequency band. At a center frequency of 79 GHz, the frequency band is, for example, 2 GHz, i.e. from 78 to 80 GHz. With FMCW, the transmission or reception of the microwave signal is divided into successive measuring cycles.

[0006] In the case of FMCW, the frequency variation over time is by default linear and has a sawtooth or triangular shape. However, in principle, a sinusoidal variation can also be used. Unlike the pulsed time-of-flight method, when implementing the FMCW method, the distance or fill level is determined based on the instantaneous frequency difference between the currently received signal and the microwave signal that has just been transmitted.

[0007] The measuring principles of FMCW and the pulsed time-of-flight method are described, for example, in "Radar Level Detection, Peter Devine, 2000". In both measuring principles, in order to determine the filling level based on the received signal, a corresponding evaluation curve is recorded. In the case of the pulse radar-based method, due to the high pulse frequency, the evaluation curve is generated by undersampling the reflected received signal. As a result, the evaluation curve represents the actual reflected received signal in a time-expanded manner. When the FMCW method is implemented, an evaluation curve is generated by mixing the just transmitted microwave signal with the reflected received signal. Here, the evaluation curve is also expanded on its time axis by mixing. Regardless of the measuring principle, the evaluation curve again reflects the amplitude of the reflected received signal as a function of the measured distance. In FMCW and pulsed time-of-flight methods, evaluation curves with complex values ​​are created, depending on the type of signal processing circuit structure.

[0008] The filling level is determined from the evaluation curve by detecting and locally assigning corresponding local maxima. Ideally, there would be no maxima other than those generated by the surface of the filling material. However, with increasing automation of the systems, the containers for which the filling level is to be determined are becoming more and more complex. In addition to the filling material, they may contain, for example, internal components such as filling nozzles, stirrers, heating rods or cleaning devices. In addition, there is a trend towards smaller and smaller production batches and therefore smaller containers. This creates the risk that in addition to the filling level maximum in the evaluation curve, other maxima occur at the corresponding positions on the evaluation curve, which could be incorrectly interpreted by the filling level measuring device as a filling level maximum.

[0009] Therefore, for reliable fill level measurement in complex and small containers, it is crucial that the beam cone of the microwave signal can only detect the filling material and not the container wall or container internal components. Therefore, fill level measuring devices operating in the high frequency band are preferred so that the microwave signal is emitted with a high degree of beam focusing.

[0010] As a result, depending on the installation situation, the filling level measuring device can emit microwave signals in such a way that no radiation is radiated to interfering internal components or container walls. However, if the filling material surface moves due to boiling, stirring, shaking, etc., the small illumination spot on the filling material surface caused by the high beam focusing will be disadvantageous. In the case of wave-like motion or shaking, most of the reflected microwave signals will be deflected and therefore no longer return to the antenna of the filling level measuring device. Therefore, in the corresponding evaluation curve, the amplitude of the filling level maximum value sometimes drops so sharply that the filling level can no longer be determined. If this happens too frequently, any signal tracking algorithm will fail, and the filling level maximum value is also lost as the measurement cycle progresses. This usually leads to a complete failure of the filling level measurement. Summary of the invention

[0011] It is therefore an object of the present invention to provide a fill level measuring device by means of which the fill level can be determined more reliably.

[0012] The invention achieves this object by a method for radar-based measurement of the filling level of a filling material in a container. The method comprises the following method steps which are repeated in successive measurement cycles:

[0013] - emit a microwave signal in the direction of the filling material,

[0014] - receiving a received signal after reflecting the microwave signal in the container,

[0015] - generating an evaluation curve based on at least the received signal,

[0016] - gradually store the corresponding current evaluation curve,

[0017] - forming a first difference curve based on the evaluation curve of the current measurement cycle and the stored evaluation curve of the previous measurement cycle, and

[0018] - The filling level is determined based on the maximum value in the current first difference curve.

[0019] Since the filling level according to the invention is determined - if necessary - not on the basis of an evaluation curve but on the basis of a difference curve, the filling level can also be determined with a high degree of certainty in the case of a displacement of the filling material surface. In combination with the classical determination of the filling level, the filling level can thus be determined more reliably overall.

[0020] By means of the difference curve, in the case of a displacement of the filling material surface, the filling level can be determined particularly reliably if evaluation curves are created which each have complex values. In this case, the difference curve can therefore also be created with complex values, i.e. consisting of a real part and an imaginary part. The filling level can thus be determined based on the maximum of the imaginary part or the real part of the current first difference curve.

[0021] If the measuring cycles in which the filling level is newly determined in each case are repeated at a defined measuring rate, it is advantageous for the method according to the invention that a first distance from the current measuring cycle to the previous measuring cycle, according to which the evaluation curve stored is used to form the first difference curve, is in particular set inversely proportional to the measuring rate. By means of this coupling of distance and measuring rate, the time elapsed since the previous measuring cycle, according to which the evaluation curve stored is used to form the first difference curve, can remain constant even in the case of a change in the measuring rate. In this context, the term "distance" refers to the number of measuring cycles between the current measuring cycle and the previous measuring cycle, according to which the evaluation curve stored is used to form the difference curve. Alternatively, however, the first difference curve can also be formed solely on the basis of the current evaluation curve and the evaluation curve created in the previous measuring cycle.

[0022] If the measurement cycle is repeated at a defined measurement rate, the generation of a second difference curve can be additionally implemented, similar to the first difference curve. In the case of the second difference curve, a second distance from the current measurement cycle to the previous measurement cycle is set, according to which the evaluation curve stored is used to form the second difference curve. Here, the second distance is selected to be different from the first distance from the current measurement cycle to the previous measurement cycle, according to which the evaluation curve stored is used to form the first difference curve. Two difference curves are thus created, in which two stored evaluation curves are used, each curve relating to a different time in the past. How far apart the first distance and the second distance are can be selected individually depending on the respective situation in the container. This provides, in particular, the following advantage: provided that the filling level cannot be determined based on the first difference curve, the filling level can be determined based on the second difference curve, and vice versa. Alternatively, the filling level can also be determined based on a difference curve whose maximum value has a larger amplitude.

[0023] As an alternative or in addition to determining the filling level based on the difference curve, the filling level can be determined based on the current evaluation curve. This is particularly advantageous if the filling level cannot be determined based on the first difference curve and / or based on the second difference curve, ie, for example, if the filling material surface is not moving.

[0024] Analogously to the method according to the invention in one of the above-described embodiments, the object on which the invention is based is achieved by a corresponding radar-based filling level measuring device. In order to carry out the method according to at least one of the above-described embodiment variants, it accordingly comprises the following components:

[0025] a signal generating unit which is designed to emit a microwave signal in each case in the direction of the filling material in successive measuring cycles,

[0026] a receiving unit, which is designed to receive a corresponding reception signal after reflecting the microwave signal in the container,

[0027] – Evaluation unit, which is designed to:

[0028] o generating an evaluation curve per measurement cycle based on at least the received signal,

[0029] o storing the individual current evaluation curves step by step,

[0030] o forming a first difference curve by subtracting the evaluation curve of the current measurement cycle from the evaluation curve of the previous measurement cycle, and

[0031] o Determine the filling level based on the first difference curve.

[0032] With regard to the filling level measuring device, within the framework of the present invention, the term "unit" is understood in principle to mean any electronic circuit that is appropriately designed for the respective intended purpose. Depending on the requirements, it can therefore be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit, such as a microcontroller or a storage medium that operates with a program. In this case, the program is designed to perform the corresponding method steps or to apply the necessary calculation operations of the corresponding unit. In this context, in the sense of the present invention, the various electronic units of the filling level measuring device can also potentially access a common physical memory or operate by means of the same physical digital circuit.

[0033] The method according to the invention is particularly advantageous when the evaluation unit of the fill level measuring device is designed to generate an evaluation curve and a difference curve with complex values, which is the default case for FMCW. In this case, the real and imaginary parts of the evaluation curve are subtracted from one another individually. In this way, any differences between the evaluation curves can be detected more clearly. This in turn makes it easier to determine the possible maximum value and the corresponding fill level from the current difference curve. It is therefore advantageous if the signal generation unit, the receiving unit and the evaluation unit are designed to determine the fill level based on the FMCW principle.

[0034] Since the method according to the invention has advantageous effects, in particular in the case of movement of the filling material surface, the method will be particularly effective due to the narrow beam cone at high frequencies if the signal generation unit is designed to emit microwave signals in a frequency band of at least 60 GHz or if the receiving unit and the evaluation unit are designed to process the corresponding received signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention is explained in more detail with reference to the following drawings. Shown are:

[0036] Figure 1is a typical arrangement of a radar-based fill level measuring device, and

[0037] Figure 2 is a schematic diagram of the method according to the present invention. DETAILED DESCRIPTION

[0038] In order to have a basic understanding of the present invention, Figure 1 Shown is a typical arrangement of a free-radiating radar-based fill level measuring device 1 on a container 2. In the container 2 is a filling material 3, whose fill level L is to be determined by the fill level measuring device 1. For this purpose, the fill level measuring device 1 is mounted on the container 2 above the maximum permissible fill level L. Depending on the field of application, the installation height h of the fill level measuring device 1 above the container bottom can be greater than 100 meters.

[0039] Typically, the fill level measuring device 1 is connected to a superordinated unit 4, such as a process control system or a decentralized database, via a bus system, such as "Ethernet", "PROFIBUS", "HART" or "WirelessHART". On the one hand, information about the operating state of the fill level measuring device 1 can thus be transmitted. However, information about the fill level L can also be transmitted via the bus system in order to control any inflow or outflow that may be present in the container 2.

[0040] because Figure 1 The fill level measuring device 1 shown is designed as a free-radiating radar, which comprises a corresponding antenna. As indicated above, the antenna can be designed, for example, as a horn antenna. In particular, in the case of radar frequencies above 100 GHz, the antenna can also be implemented as a planar antenna. Regardless of the design, the antenna is oriented so that the corresponding microwave signal S HF The microwave signal S is emitted in the direction of the filling material 3. In this way, depending on the measuring method (pulsed time-of-flight or FMCW), a microwave signal S is generated in a corresponding signal generating unit of the filling level measuring device 1. HF .

[0041] Microwave signal S HF It is reflected on the surface of the filling material 3 and, after a corresponding signal propagation time, is received by a downstream receiving unit or antenna of the filling level measuring device 1 as a received signal E HF The filling level L can be determined according to the received signal E HF OK, because the microwave signal S HF 、E HF The signal propagation time of φ depends on the distance d=h-L from the filling level measuring device 1 to the filling material surface.

[0042] In order to determine the filling level L, the evaluation unit of the filling level measuring device 1 designed for this purpose receives the signal EHF For each measuring cycle n an evaluation curve ZF is created n-1 , ZF n In this case, the evaluation curve ZF n-1 , ZF n The amplitude A (or, in the case of complex-valued recording, also the phase) of the reflected received signal is reconstructed as a function of the measured distance d or the transmitted signal S HF / Receive signal E HF The signal propagation time changes.

[0043] When the FMCW method is implemented, the evaluation unit of the fill level measuring device 1 basically calculates the received signal E that has just been received by HF The microwave signal S HF Mix to generate the evaluation curve ZF n-1 , ZF n , where the microwave signal S HF For this purpose it is transmitted continuously with a sawtooth-shaped frequency change.

[0044] In the case of the pulsed time-of-flight method, the pulse-shaped received signal E HF Undersampling is performed to generate the evaluation curve ZF n-1 , ZF n The pulse frequency of the sampling signal deviates from the microwave signal S by 1 / 100 mil. HF Or receive signal E HF The pulse frequency.

[0045] In the case of FMCW and pulsed time-of-flight methods, the evaluation curve ZF n-1 , ZF n The received signal E HF The signal amplitude A is shown as a function of the measuring distance d. In the case of free-radiation, radar-based fill level measurement, the corresponding measuring range h extends accordingly from the antenna of the fill level measuring device 1 to the bottom of the container 2. Schematic evaluation curve ZF n-1 , ZF n exist Figure 2 Shown in.

[0046] According to the prior art, the evaluation unit of the fill level measuring device 1 is based on the evaluation curve ZF n-1 , ZF n Determine the filling level L. To do this, determine the maximum A of the filling material surface. m Position d.

[0047] Since the emitted microwave signal S HFA higher degree of focusing and a potentially higher resolution of the measured filling level L use the highest possible radar frequencies above 60 GHz, especially when implementing the FMCW method. However, it is precisely in the case of sloshing of the filling material 3 that the narrow beam cone can lead to a microwave signal S HF When reflected on the surface of the filling material, it is deflected so that the antenna of the filling level measuring device 1 does not receive the received signal E HF In this case, the evaluation curve ZF n ,like Figure 2 As shown, there is no maximum A in the corresponding measurement cycle n-1 m .

[0048] The method according to the invention therefore consists in Figure 2 In more detail, it is shown that the filling level L can also be reliably determined in this case using the method: the method is based on the stored evaluation curve ZF from the previous measurement cycle nm (in the simplest case, the previous measurement cycle n-1) n-m The evaluation curve ZF of the current measuring cycle n is subtracted from n , to create the first difference curve Diff n In the sense of the present invention, which evaluation curve ZF n-m1 , ZF n-1 The subtraction from the other curve is not of decisive importance. According to the invention, the fill level measuring device 1 is based on the first difference curve Diff n Determine the filling level L. In order to n Search for the maximum value A in m (or minimum, depending on how the difference is formed), any algorithm suitable for this can be implemented in the evaluation unit.

[0049] from Figure 2 It can be seen that the advantage of this method is that even if the evaluation curve ZF of the current measurement cycle n n Does not have maximum A m ——For example, due to the shaking of the filling material 3, the maximum A on the surface of the filling material m Also appears in the first difference curve Diff n Therefore, the benefit is the maximum Diff n The evaluation curve ZF contained in the previous measurement cycle n-1 n-1 Middle. Evaluation curve ZF n , ZF n-m The peripheral maximum value caused by the static internal components in container 3 (for clarity, Figure 2 ) are masked by the method according to the invention so that these maxima do not lead to an erroneous determination of the filling level L.

[0050] With the method according to the invention, the filling level L can be determined very reliably, in particular when the filling level measuring device 1 generates an evaluation curve ZF having complex values. n Sum difference curve Diff n hour.

[0051] Since in this case, even if complex values ​​are used for subtraction (i.e., the evaluation curve ZF n and ZF n-m The real or imaginary part of n and ZF n-m Any changes between Figure 2 In the exemplary embodiment shown, the graph shows the evaluation curve ZF n , ZF n-1- The imaginary part of the difference curve Diff is shown accordingly. n As the evaluation curve ZF n , ZF n-1 As a result of the complex value analysis, the filling level can be expressed as a minimum value, as in the current evaluation curve ZF n The situation in.

[0052] In addition to the filling level measuring device 1 having sufficient computing power and storage capacity, the difference curve Diff n For complex value recording, it is necessary that the signal generation unit and the evaluation unit are coherently clocked.

[0053] Most importantly, if during the past measurement period nm the fill level has reached a maximum value A m In the evaluation curve ZF n , ZF n-m If the filling level L cannot be calculated from the difference curve Diff n In this respect, if the fill level measuring device 1 is designed to at least in these cases be derived from the current evaluation curve ZF n It is advantageous to determine the filling level L.

[0054] In order to reliably implement the method according to the invention, in addition to the current evaluation curve ZF n In addition, it can be advantageous to use in each case not only the evaluation curve ZF of the previous measurement cycle n-1 n-1 , in order to form the difference curve Diff of the current measurement cycle n n Depending on the type of disturbances on the filling material surface or their frequency of occurrence, it may be advantageous to set a greater distance m from the current measuring period n to the measuring period nm from which the stored evaluation curve ZF is used. n-m, in order to form the corresponding current difference curve Diff n .

[0055] In this case, it is advantageous to adapt this distance m to the rate or frequency of disturbances, taking into account the measurement rate r of the filling level measuring device 1 with which the measurement cycle n is repeated. In the process, a sloshing of the filling material 3 can be caused, for example, by a stirrer operating at a defined frequency. If disturbances then occur at a frequency of approximately 1 Hz and the measurement rate r is only 10 Hz - which is customary for the filling level measuring device 1 with the aid of a limited energy supply of a 4-20 mA signal - the corresponding distance must be set to m=10 measurement cycles. Therefore, if the filling level measuring device 1 changes the measurement rate r during operation, it makes sense to adjust the distance m between the measurement cycles m, mn to be inversely proportional to the measurement rate r.

[0056] Within the scope of the invention, for redundancy purposes, the fill level measuring device 1 can be further developed such that in addition to the first difference curve Diff n In addition, it also records the second difference curve Diff2 n The basic distance l from the current measurement period n to the measurement period nl deviates from the first difference curve Diff n The corresponding first distance m is based on the evaluation curve ZF stored in the measurement cycle nl. n-l is used to form the difference curve. The deviation of the two distances l, m can here be set, for example, to a fixed value with 10 measuring cycles. In this further development of the filling level measuring device 1, for example, it is possible to form the difference curve Diff by separately n 、Diff2 n Redundancy is checked by determining the fill level L. If the two measured fill level values ​​L match, redundancy exists.

[0057] Reference numerals list

[0058] 1 Filling level measuring device

[0059] 2 Container

[0060] 3 Filling materials

[0061] 4 Parent unit

[0062] A m Maximum

[0063] d Measurement distance

[0064] Diff n First difference curve

[0065] Diff2 n Second difference curve

[0066] E HF Receiving Signals

[0067] h Installation height or measuring range

[0068] L Filling level

[0069] Second distance

[0070] n Measurement cycle

[0071] m First distance

[0072] S HF Microwave signal

[0073] ZF n Evaluation curve

Claims

1. A method for radar-based measurement of a filling level (L) of a filling material (3) in a container (2), wherein: The method comprises the following method steps which are repeated in successive measurement cycles (n): - emitting a microwave signal (S) in the direction of the filling material (3) via an antenna HF ), - reflecting the microwave signal (S) in the container (2) HF ) and then receives the received signal (E) through the antenna HF ), - based on at least the received signal (E HF ) Generate an evaluation curve (ZF n ), - In each case, the current evaluation curve (ZF n ), - based on said evaluation curve (ZFn) of the current measurement cycle (n) and the stored evaluation curves (ZFn) of the previous measurement cycles (nm) n-m ), forming the first difference curve (Diff n ), wherein by making the evaluation curve (ZF n ) and the evaluation curve (ZF) of the previous measurement cycle (nm) n-m ) are subtracted to form the first difference curve (Diff n ),as well as -Based on the current first difference curve (Diff n ) on the maximum value (A m ) determines the filling level (L), Wherein, the evaluation curve (ZF) having complex values ​​is created n , ZF n-m ), The first difference curve (Diff n ), and wherein the filling level (L) is based on the current first difference curve (Diff n ) is the maximum value of the imaginary or real part (A m ) to determine.

2. The method according to claim 1, wherein: The measuring cycle (n), in which the filling level (L) is determined anew in each case, is repeated at a defined measuring rate (r).

3. The method according to claim 2, wherein: A first distance (m) from the current measurement cycle (n) to the previous measurement cycle (nm) is set to be inversely proportional to the measurement rate (r), and an evaluation curve (ZF) stored according to the first distance (m) is calculated. n-m ) is used to form the first difference curve (Diff n ).

4. The method according to any one of claims 1 to 3, wherein: The first difference curve (Diff n ) Based on the current evaluation curve (ZF n ) and the evaluation curve (ZF) created in the previous measurement cycle (n-1) n-1 )form.

5. The method according to any one of claims 1 to 3, wherein: Similar to the first difference curve (Diff n ), create the second difference curve (Diff2 n ), and wherein a second distance (l) from the current measurement cycle (n) to the previous measurement cycle (nl) is selected, and an evaluation curve (ZF) stored according to the second distance (l) is calculated. n-l ) is used to form the second difference curve (Diff2 n ), the second distance (l) deviates from the first distance (m) from the current measurement cycle (n) to the previous measurement cycle (nm), according to the evaluation curve (ZF) stored in the first distance (m) n-m ) is used to form the first difference curve (Diff n ).

6. The method according to claim 5, wherein: The filling level (L) is based on the second difference curve (Diff2 n ) to determine.

7. The method according to claim 5, wherein: At the filling level (L), it is not possible to n ), the filling level (L) is determined based on the second difference curve (Diff2 n ) to determine.

8. The method according to claim 5, wherein: The filling level (L) is based on the maximum value (A M ) has a large difference curve (Diff n , Diff2 n )Sure.

9. The method according to claim 5, wherein: At the filling level (L), it is not possible to n ) and / or based on the second difference curve (Diff2 n ) is determined based on the current evaluation curve (ZF n ) to determine the filling level (L).

10. A radar-based filling level measuring device for carrying out the method according to any one of claims 1 to 9, comprising the following components: a signal generating unit which is designed to emit a microwave signal (S) via an antenna in each case in the direction of the filling material (3) in successive measuring cycles (n). HF ), - a receiving unit, the receiving unit being designed to reflect the microwave signal (S) inside the container (2) HF ) and then receives the corresponding reception signal (E HF ), - an evaluation unit, the evaluation unit being designed to: ○ Based on at least the received signal (E HF ), generating an evaluation curve (ZF) for each measurement cycle (n) n ), ○ gradually store each current evaluation curve (ZF), ○ By making the evaluation curve (ZF n ) and the evaluation curve (ZF) of the previous measurement cycle (nm) n-m ) to form the first difference curve (Diff n ),as well as ○ Based on the first difference curve (Diff n ) determines the filling level (L), in, The signal generation unit and the evaluation unit are designed to create an evaluation curve (ZF n ) and the difference curve (Diff n ).

11. The filling level measuring device according to claim 10, wherein: The signal generating unit, the receiving unit and the evaluation unit are designed to determine the filling level (L) based on the FMCW principle.

12. The filling level measuring device according to claim 10 or 11, wherein: The signal generating unit is designed to transmit the microwave signal (S) in a frequency band of at least 60 GHz. HF ), and wherein the receiving unit and the evaluating unit are designed to process the corresponding received signal (E HF ).

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