FILL-LEVEL MEASUREMENT DEVICE

Abstract

A radar-based, fill-level measurement device for measuring a fill-level of a filling material in a container, the high-frequency unit of which can be checked with regard to its functionality, is designed redundantly and thus comprises two, activatable, high-frequency sources for generating the high-frequency signal and two, activatable receivers for sampling the received signal such that a time-prolonged evaluation signal is generated. As a result, a correspondingly designed diagnosis unit can switch between the active high-frequency source and/or between the active receiver, wherein before and after the switching, a defined property of the evaluation signal, such as a signal amplitude, is ascertained. If the defined property of the evaluation signal changes at least by a defined value as a result of the switching, the high-frequency unit is classified as not functional.

Claims

1-10. (canceled)

11. A radar-based, fill-level measurement device for measuring a fill-level of a filling material in a container, the fill-level measurement device comprising: a transmission unit via which high-frequency signals can be sent to the filling material and, after reflection on the filling material surface, can be received as received signals; a high-frequency unit, including: two activatable, high-frequency sources, each of which is designed for generating the high-frequency signal; and two activatable receivers via which the received signal can be time-prolonged; a control unit embodied to activate one of the high-frequency sources such that the activated high-frequency source generates the high-frequency signal, and to activate one of the receivers such that the activated receiver converts the received signal into a time-prolonged evaluation signal; an evaluation unit embodied to ascertain a defined property and a signal transit time of at least one signal maximum on the basis of the evaluation signal, and to determine the fill-level on the basis of the signal transit time of the at least one signal maximum; and a diagnosis unit embodied to control the control unit such that the high-frequency source that is active and/or the receiver that is active is/are deactivated, and vice versa, control the evaluation unit such that the defined property of the evaluation signal is at least ascertained before and after the switching, and classify the high-frequency unit as non-functional if the defined property of the evaluation signal changes at least by a defined value as a result of the switching.

12. The fill-level measurement device according to claim 11, wherein the diagnosis unit is designed to compare, as a defined property of the evaluation signal, an edge steepness, a signal amplitude, and/or a corresponding signal transit time of the at least one signal maximum.

13. The fill-level measurement device according to claim 12, wherein the transmission unit is further embodied as an electrically-conductive measuring probe which, in the installed state of the fill-level measurement device, extends perpendicularly to the container base.

14. The fill-level measurement device according to claim 13, wherein one of the two high-frequency sources is designed in an inverting manner, and/or wherein one of the two receivers is designed in an inverting manner.

15. The fill-level measurement device according to claim 14, wherein the evaluation unit is further embodied to invert a polarity of the evaluation signal if the polarity changes as a result of the switching, and ascertain the defined property on the basis of the polarity-inverted evaluation signal.

16. The fill-level measurement device according to claim 15, wherein the evaluation unit is further embodied to ascertain the polarity of the evaluation signal, and wherein the diagnosis unit is further embodied to control the evaluation unit such that, in each case before and after the switching of the active high-frequency source or of the active receiver, its polarity is ascertained as a defined property of the evaluation signal and to classify the high-frequency unit as non-functional if the polarity of the evaluation signal does not change as a result of the switching, or if the polarity of the evaluation signal changes as a result of the switching.

17. The fill-level measurement device according to claim 16, wherein the receivers are designed as samplers, and wherein the control unit is further embodied to actuate the high-frequency source that is active such that the high-frequency signal is generated in a pulsed manner, and actuate the sampler that is active such that the received signal is subsampled, in accordance with the pulse transit time method, such that the evaluation signal is time-discretized.

18. The fill-level measurement device according to claim 17, wherein the diagnosis unit is further embodied to generate an error signal if the diagnosis unit classifies the high-frequency unit as non-functional.

19. A method for checking a functionality of a fill-level measurement device, the method comprising: providing the fill-level measurement device, including: a transmission unit via which high-frequency signals can be sent to the filling material and, after reflection on the filling material surface, can be received as received signals; a high-frequency unit, including: two activatable, high-frequency sources, each of which is designed for generating the high-frequency signal; and two activatable receivers via which the received signal can be time-prolonged in each case; a control unit embodied to activate one of the high-frequency sources such that the activated high-frequency source generates the high-frequency signal, and to activate one of the receivers such that the activated receiver converts the received signal into a time-prolonged evaluation signal; an evaluation unit embodied to ascertain a defined property and a signal transit time of at least one signal maximum on the basis of the evaluation signal, and to determine the fill-level on the basis of the signal transit time of the at least one signal maximum; and a diagnosis unit embodied to control the control unit such that the high-frequency source that is active and/or the receiver that is active is/are deactivated, and vice versa, to control the evaluation unit such that the defined property of the evaluation signal is at least ascertained before and after the switching, and to classify the high-frequency unit as non-functional if the defined property of the evaluation signal changes at least by a defined value as a result of the switching; generating the high-frequency signal via the high-frequency source that is switched to be active; sending the high-frequency signal to the filling material and receiving the corresponding received signal after reflection on the filling material surface; receiving the received signal via the receiver that is switched to be active such that a time-prolonged evaluation signal is generated; determining at least one signal maximum of the evaluation signal; determining at least one defined property of the at least one signal maximum; switching the high-frequency source that is active so as to be passive, and vice versa, and/or switching the receiver that is active so as to be passive, and vice versa, and subsequently repeating the prior method steps; comparing the defined property before and after the switching; and classifying the high-frequency unit as non-functional when the defined property of the evaluation signal has changed at least by a defined value as a result of the switching.

20. The method according to claim 19, wherein the switching of the high-frequency source that is active or the receiver that is active, the comparison of the defined property before and after the switching, and the classification of the high-frequency unit with regard to its functionality are carried out cyclically.

Description

[0042] The invention is explained in more detail with reference to the following figures, in which:

[0043] FIG. 1: shows a TDR-based, fill-level measurement device according to the prior art,

[0044] FIG. 2: is a schematic representation of an evaluation signal,

[0045] FIG. 3: is a block diagram of a fill-level measurement device according to the invention, and

[0046] FIG. 4: shows possible effects of a faulty high-frequency unit on the evaluation curve.

[0047] For a basic understanding of the invention, FIG. 1 shows a block diagram of a fill-level measurement device 1′ constructed according to the prior art, which serves to measure the fill-level L of a filling material 2 located in a container 3. The fill-level measurement device 1′ shown is based upon the pulse transit time principle, wherein, in accordance with the TDR method, it comprises a measuring probe as the transmission unit 13. In order to determine the fill-level L, the measuring probe 13 accordingly extends in the container interior from the top side to just above the container base. In this case, the installation height h of the measuring probe 13 above the container base is known and stored in an evaluation unit 14 of the fill-level measurement device 1′.

[0048] According to the pulse transit time method, the measuring probe 13 accordingly conducts a high-frequency signal S.sub.HF, in a pulsed manner, in the direction of the filling material 2. Due to the jump in the dielectric value there, the high-frequency signal S.sub.HF is reflected at the level of the filling material surface 2 in the measuring probe 13 and received accordingly as the received signal E.sub.HF, after a corresponding signal transit time t, in the fill-level measurement device 1′. In this case, the signal transit time of the signal S.sub.HF, E.sub.HF depends upon the distance d=h−L of the container top from the filling material surface.

[0049] In order to generate the high-frequency signal S.sub.HF, the fill-level measurement device 1′ comprises, as a component of a high-frequency unit 12, a first high-frequency source 121. In this case, the first high-frequency source 121 can be designed according to the TDR method as, for example, a capacitor, which is discharged accordingly to generate the pulse lasting 100 ps to approximately 1 ns. In the case of freely-radiating radar according to the pulse transit time or FMCW method, the first high-frequency source 121 can be designed, for example, as a frequency-controlled, high-frequency, oscillating circuit or as a crystal oscillator. In order for the first high-frequency source 121 to generate the high-frequency signal S.sub.HF in accordance with the TDR method at the required cycle rate, the first high-frequency source 121 is actuated in a correspondingly clocked manner by a control unit 11 outside the first high-frequency unit 12. In this case, the first high-frequency source 121 guides the high-frequency signal S.sub.HF to be transmitted to the measuring probe 13 via a transceiver switch 122. In this case, the design of the transceiver switch 122 is, in principle, not strictly specified. In the case of TDR, as is the case in the variant shown in FIG. 1, the transceiver switch 122 can be designed, for example, purely as an electrical node. Particularly in the case of freely-radiating radar, the transceiver switch 122 can be implemented as, for example, a duplexer.

[0050] The received signal E.sub.HF entering the high-frequency unit 12 from the measuring probe 13 is guided via the transceiver switch 122 to a first receiver 123. According to the pulse transit time principle, the received signal E.sub.HF is subsampled in the first receiver 123, such that an evaluation signal A(t) is generated, which reproduces the received signal E.sub.HF in a manner time-prolonged by a defined factor. In this case, the time prolongation factor depends upon the sampling rate. The corresponding sampling rate must be selected in order to achieve a sufficient time prolongation, such that it differs from the clock rate of the emitted signal pulses S.sub.HF only in the permille range. Accordingly, the sampling rate at which the first receiver 123 samples the received signal E.sub.HF is again set at the first receiver 123 by the control unit 11, which also specifies the clock rate of the emitted signal pulses S.sub.HF. The time prolongation simplifies, from a circuitry perspective, the determination of the fill-level L on the basis of the received signal E.sub.HF. In contrast to the variant shown in FIG. 2, in the case of freely-radiating radar, in addition to the time prolongation, the received signal E.sub.HF is rectified in the first receiver 123, such that the evaluation signal A(t) has only one polarity—plus or minus—in relation to a fixed reference potential.

[0051] In order to determine the fill-level L, the first receiver 123 transmits the evaluation signal A(t) to an evaluation unit 14. If the first receiver 123 is a digital sampler, this already takes place in a digitized manner. In this case, the determination of the fill-level L by means of the evaluation signal A(t) by the evaluation unit 14 is illustrated in more detail with reference to FIG. 2:

[0052] FIG. 2 illustrates the temporal amplitude progression of the received signal E.sub.HF or the time-prolonged evaluation signal A(t). In this case, the distance d between the container top and the filling material surface is proportional to the time axis of the evaluation signal A(t) and proportional to the time axis of the received signal E.sub.HF. In the ideal case, i.e., without any external interference influences, the received signal E.sub.HF comprises three signal maxima M.sub.a. The temporally first signal maximum M.sub.a is to be attributed to the internal reflection of the high-frequency signal S.sub.HF at the transceiver switch 122. The temporally second signal maximum M.sub.a in the received signal E.sub.HF is brought about at the surface of the filling material 2, while the third signal maximum M.sub.a is caused by the probe end 131 of the measuring probe 13.

[0053] Using any filter method, the evaluation unit 14 is capable of ascertaining the signal transit time t.sub.M of the signal maximum M.sub.a, which is caused by the filling material surface. Based upon corresponding calibration data, the evaluation unit 14 calculates, from this signal transit time t.sub.M, the corresponding distance d, and due to the relationship L=h−d or the known installation height h, the fill-level L can again be determined on the basis of the distance d.

[0054] A central prerequisite for the evaluation unit 14 to be able to correctly determine the fill-level L with certainty is the error-free functioning of the high-frequency unit 12, since, depending upon the impairment, this does not lead to an obvious failure of the high-frequency unit 12. As shown in FIG. 4a, a non-functional high-frequency unit 12 can, e.g., with increasing time in use, lead to a creeping offset of the received signal E.sub.HF or an offset of the evaluation signal A(t). As a result, the signal transit time t.sub.M of the fill-level maximum M.sub.A may not be noted, and thus the ascertained distance value d be distorted. The result of a gradual degradation of a high-frequency amplifier of the high-frequency unit 12 is again illustrated in FIG. 4b; by such a failure mechanism, the amplitude of the evaluation signal S.sub.HF or of the underlying received signal E.sub.HF can be damped, such that, as a result, the evaluation unit 14 does not, in case of doubt, identify the signal maximum M.sub.A upon which the filling material surface is based, but rather, erroneously, uses a different signal maximum M.sub.A to ascertain the distance d or the fill-level L. Such non-functionality of the high-frequency unit 12 is also not directly recognizable from the outside. However, a sudden failure of one of the units is also conceivable, and can be identified, depending upon the situation. Thus, the fill-level measurement device 1′ cannot be used in applications where corresponding safety requirements such as “SIL” must be adhered to.

[0055] A possible embodiment of the fill-level measurement device 1 according to the invention, by means of which a possible non-functionality of the high-frequency unit 12 can be diagnosed, is therefore described in more detail in FIG. 3; in principle, the design and the mode of operation of the fill-level measurement device 1 shown in FIG. 3 correspond to the variant shown in FIG. 1. In addition, however, the high-frequency unit 12 of the fill-level measurement device 1 according to the invention comprises a second high-frequency source 121′ and a second receiver 123′. In this case, it is advantageous if the second high-frequency source 121′ is designed identically to the first high-frequency source 121—for example, again as a capacitor. The same applies for the second receiver 123′ in relation to the first receiver 123.

[0056] In the case of freely-radiating radar, i.e., contrary to the variant shown in FIG. 3, it is advantageous, with respect to the high-frequency sources 121, 121′, if they generate the high-frequency signal S.sub.HF at the same frequency, in order to ensure the same signal behavior. The control unit 11 can selectively activate one of the two high-frequency sources 121, 121′ by means of a first switch 120. By means of a second switch 124, the control unit 11 can again selectively activate one of the two receivers 123, 123′. In this context, the switches 120, 124 can be designed, for example, as transistors, the gate/base of which is actuated by the control unit 11.

[0057] In relation to the high-frequency sources 121, 121′, the term, “activate,” relates to switching on the high-frequency source 121, 121′ to be activated, as well as the connection of the high-frequency source 121, 121′ to be activated, to the measuring probe 13 or to the transceiver switch 122. Regarding the term, “switching,” this means that the high-frequency source 121, 121′ to be switched to be inactive is disconnected from the measuring probe 13 and/or that it is switched off. With regard to the two receivers 123, 123′, the term, “activate,” refers to the sampling of the received signal E.sub.HF and transmitting the corresponding evaluation signal A(t) to the evaluation unit 14. This in turn means, in connection with the term, “switching,” that the receiver 123, 123′ to be switched to be inactive no longer samples the received signal E.sub.HF and/or no longer transmits the evaluation signal A(t) to the evaluation unit 14, following activation of the other receiver 123, 123′.

[0058] In the case of the variant of the fill-level measurement device 1 according to the invention shown in FIG. 3, too, the control unit 11 in principle provides the clock rate of both high-frequency sources 121, 121′. The same applies for the two receivers 123, 123′, the sampling rates of which are predefined by the control unit 11.

[0059] By means of the redundant design of the high-frequency unit 12 having two high-frequency sources 121, 121′ and two receivers 123, 123′, it is possible for the control unit 14 to switch the first switch 120 or the second switch 124, for example, cyclically during measuring operation or during test operation of the fill-level measurement device 1. In this case, the switching of the two switches 120, 124 can take place either simultaneously or in a manner offset from one another, and, optionally, cyclically. In this case, at least one evaluation curve A(t) is recorded in each case before and after each switching, wherein the evaluation unit 14 determines from the two evaluation curves A(t) in each case a previously defined property, such as its polarity, the signal amplitude, and/or the corresponding signal transit time t.sub.M of one of the signal maxima M.sub.A.

[0060] The switching, the recording of the corresponding evaluation curves A(t), and the respective determination of the defined property before and after the switching are coordinated by means of a correspondingly designed diagnosis unit 15 outside the high-frequency unit 12. In addition, the diagnosis unit 15 compares the defined property before switching with the corresponding variable after the switching. Should the property change beyond a limit value, the diagnosis unit 15 classifies the high-frequency unit 12 as non-functional, and optionally outputs a corresponding error signal. If the defined property is the signal amplitude of one of the signal maxima M.sub.A, then a possible decrease in amplitude beyond the limit value, as a result of the switching, can be interpreted for example as a creeping deterioration of a high-frequency amplifier of the high-frequency unit 12, as shown in FIG. 4b.

[0061] In the embodiment of the fill-level measurement device 1 according to the invention shown in FIG. 3, the second high-frequency source 121′ and the second receiver 123′ are designed so as to be inverting. Since the fill-level measurement device 1 is based upon the TDR method, this offers the possibility of inverting the polarity of the received signal E.sub.HF or of the evaluation signal A(t), upon switching of the active receiver 123, 123′, without switching the active high-frequency source 121, 121′, or vice versa. This not only reduces the emissions of the fill-level measurement device 1, but it can again be used to check the functionality of the high-frequency unit 12; if the diagnosis unit 15 detects no polarity change, despite the switching of either the active high-frequency source 121, 121′ or the active receiver 123, 123′, the high-frequency unit 12 is to be classified as non-functional.

[0062] It goes without saying that the evaluation signal A(t), before and after switching, is in principle checked by the diagnosis unit 15 not only for one, but also for several properties, wherein the diagnosis unit 15 in this case already classifies the high-frequency unit 12 as non-functional if one of the defined properties of the evaluation signal A(t) has changed at least by a defined value as a result of the switching.

[0063] The embodiment of the fill-level measurement device 1 according to the invention shown in FIG. 3 is based upon the pulse transit time principle and, according to the TDR method, comprises a measuring probe 13 as a transmission unit. In this regard, it should be noted that the redundant design, according to the invention, of the high-frequency unit 12 having two high-frequency sources and two receivers, as well as the corresponding checking of the functionality, can in principle also be implemented in the case of freely-radiating radar or when implementing the FMCW principle.

LIST OF REFERENCE SIGNS

[0064] 1, 1′ Fill-level measurement device [0065] 2 Filling material [0066] 3 Container [0067] 11 Control unit [0068] 12 High-frequency unit [0069] 13 Transmission unit [0070] 14 Evaluation unit [0071] 120 First switch [0072] 121, 121′ High-frequency source [0073] 122 Transceiver switch [0074] 123, 123′ Receiver [0075] 124 Second switch [0076] A(t) Evaluation signal [0077] d Distance [0078] E.sub.HF Received signal [0079] h Installation height [0080] L Fill-level [0081] M.sub.a Signal maximum [0082] S.sub.HF High-frequency signal [0083] t Signal transit time