FILL-LEVEL MEASURING DEVICE

Abstract

A radar-based fill-level measuring device that operates, for example, according to the FMCW principle or the pulse time-of-flight principle comprises a temperature sensor. Thus, the measurement rate at which the fill level is determined can be controlled according to the measured temperature in such a way that, at least above a defined limit temperature, the measurement rate is reduced as the temperature increases further. Furthermore, the measurement can be completely stopped if the measured temperature exceeds a predefined maximum temperature, in particular 150° C. The development of heat in the fill-level measuring device is counteracted by the reduction of the measurement rate. The measurement rate is thereby adaptively adjusted with respect to the ambient temperature such that, even at elevated ambient temperatures, which can occur in the case of cleaning processes, the fill-level measuring device remains at least conditionally fit for use.

Claims

1-8. (canceled)

9. A radar-based fill-level measuring device for measuring a fill level of a filling material located in a container, comprising: a signal-generating unit designed to generate a high-frequency electrical signal according to an adjustable measurement rate; an antenna arrangement via which the high-frequency signal can be emitted as a radar signal in a direction of the filling material and can be received as a corresponding receive signal after reflection on a surface of the filling material; an evaluation unit designed to redetermine the fill level cyclically at least on the basis of the receive signal at the adjustable measurement rate; and a temperature sensor designed to measure a temperature at the signal-generating unit and/or at the evaluation unit, wherein the signal-generating unit and the evaluation unit are designed to control the measurement rate as a function of the measured temperature such that, at least above a defined limit temperature, the measurement rate is reduced as the measured temperature increases.

10. The fill-level measuring device according to claim 9, wherein the signal-generating unit and the evaluation unit are designed to control the measurement rate as a function of the measured temperature such that the measurement rate above the limit temperature is reduced linearly or stepwise as the measured temperature increases.

11. The fill-level measuring device according to claim 9, wherein the signal-generating unit and the evaluation unit are designed to stop the fill-level measurement if the measured temperature exceeds a predefined maximum temperature.

12. The fill-level measuring device according to claim 9, wherein at least the signal-generating unit is designed as a monolithic component of an application specific integrated circuit (ASIC).

13. The fill-level measuring device according to claim 12, wherein the signal-generating unit includes a transmission amplifier for amplifying the high-frequency signal, and wherein the temperature sensor is arranged on the transmission amplifier.

14. The fill-level measuring device according to claim 9, wherein the signal-generating unit is designed to generate the high-frequency electrical signal according to a pulse time-of-flight method, and wherein the evaluation unit is designed to determine the fill level according to the pulse time-of-flight method using a sampled receive signal.

15. The fill-level measuring device according to claim 9, wherein the signal-generating unit is designed to generate the high-frequency electrical signal according to a frequency modulated continuous wave (FMCW) method, and wherein the evaluation unit is designed to determine the fill level according to the FMCW method by mixing the high-frequency signal and the receive signal.

16. A method for a radar-based measurement of a fill level of a filling material located in a container, comprising: providing a radar-based fill-level measuring device, including: a signal-generating unit designed to generate a high-frequency electrical signal according to an adjustable measurement rate; an antenna arrangement via which the high-frequency signal can be emitted as a radar signal in a direction of the filling material and can be received as a corresponding receive signal after reflection on a surface of the filling material; an evaluation unit designed to redetermine the fill level cyclically at least on the basis of the receive signal at the adjustable measurement rate; and a temperature sensor designed to measure a temperature at the signal-generating unit and/or at the evaluation unit, wherein the signal-generating unit and the evaluation unit are designed to control the measurement rate as a function of the measured temperature such that, at least above a defined limit temperature, the measurement rate is reduced as the measured temperature increases; generating the high-frequency electrical signal corresponding to the variable measurement rate; emitting the high-frequency signal as the radar signal in the direction of the filling material; receiving the reflected radar signal as the electrical receive signal after reflection on the surface of the filling material; cyclically redetermining a distance on the basis of at least the receive signal at the adjustable measurement rate; measuring the temperature at the signal-generating unit and/or at the evaluation unit; and controlling the measurement rate as a function of the measured temperature such that, at least above a defined limit temperature, the measurement rate is reduced as the temperature increases.

Description

[0024] The invention is explained in more detail with reference to the following figures. The following is shown:

[0025] FIG. 1: a typical arrangement of a radar-based fill-level measuring device on a container,

[0026] FIG. 2: a circuit diagram of an FMCW radar-based fill-level measuring device,

[0027] FIG. 3: a circuit diagram of a fill-level measuring device which operates according to the pulse time-of-flight method, and

[0028] FIG. 4: a control of the measurement rate according to the invention as a function of the temperature in the fill-level measuring device.

[0029] For a basic understanding of the distance measurement according to the invention, FIG. 1 shows a typical arrangement of a freely radiating, radar-based fill-level measuring device 1 on a container 3. In the container 3 is a filling material 2, 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 3 above the maximum permissible fill level L. Depending on the field of application, the height h of the container 3 can be between only 30 cm up to 125 m.

[0030] As a rule, the fill-level measuring device 1 is connected via a bus system, such as “Ethernet,” “PROFIBUS,” “HART,” or “Wireless HART,” to a higher-level unit 4, such as a process control system or a decentralized database. On the one hand, information about the operating status of the fill-level measuring device 1 can thus be communicated. On the other hand, information about the fill level L can also be transmitted via the bus system in order to control any inflows or outflows that may be present at the container 3.

[0031] Since the fill-level measuring device 1 shown in FIG. 1 is designed as freely radiating radar measuring device, it comprises a corresponding transmitting/receiving antenna 12. As indicated, the antenna 12 can be designed as a horn antenna, for example. Regardless of the design, the transmitting/receiving antenna 12 is oriented such that a corresponding radar signal S.sub.HF is emitted in the direction of the filling material 3 according to the FMCW principle or the pulse time-of-flight principle.

[0032] The radar signal S.sub.HF is reflected at the surface of the filling material 3 and, after a corresponding signal time-of-flight, is correspondingly received as an electrical receive signal e.sub.HF by the transmitting/receiving antenna 12. The signal time-of-flight of the radar signal S.sub.HF, E.sub.HF depends on the distance d=h−L of the fill-level measuring device 1 from the filling material surface.

[0033] In contrast to the embodiment variant shown, it is also possible for two separate antennas to be used for separate transmission and reception of the radar signal S.sub.HF, E.sub.HF, instead of a single transmitting/receiving antenna 12. Another alternative consists of using an electrically conductive probe, such as a waveguide or a coaxial cable, which extends toward the container bottom. This embodiment variant is known as TDR (“time-domain reflectometry”).

[0034] The basic circuit design of a fill-level measuring device 1 operating according to the FMCW method is illustrated in FIG. 2: In order to generate the radar signal S.sub.HF, the measuring device 1 comprises a signal-generating unit 11, which generates a corresponding high-frequency electrical signal s.sub.HF and supplies it to the antenna 12. The frequency of the high-frequency signal s.sub.HF defines the frequency of the radar signal S.sub.HF in the microwave range. Therefore, the high-frequency signal-generating unit 11, 12 must be designed to generate the high-frequency electrical signal s.sub.HF with the ramp-shaped change of its frequency required in FMCW.

[0035] As shown in FIG. 2, for generating the high-frequency signal s.sub.HF, the signal-generating unit 11 comprises a high-frequency oscillator 112, which is controlled by means of a ramp-generating unit 111. The control takes place according to a phase control (known as “phase locked loop, PLL”). The frequency of the high-frequency oscillator 112 is thus stabilized on the one hand. On the other hand, the ramp-shaped frequency change of the high-frequency signal s.sub.HF is set thereby.

[0036] With the ramp-shaped frequency change according to the FMCW principle, the frequency of the high-frequency signal s.sub.HF increases in a periodically repeating manner within a predefined frequency band Δf at a constant rate of change. The periodicity of the individual frequency ramps may be within a range of a few 100 ms. The duration of the individual ramp can be within the range between 100 μs and 100 ms. The position of the frequency band Δf is to be set taking into account regulatory requirements, for which reason the frequency bands about frequencies of 6 GHz, 26 GHz, 79 GHz, or 120 GHz are preferably implemented as frequency band Δf. The bandwidth lies especially between 0.5 GHz and 10 GHz, depending on the position of the frequency band Δf.

[0037] In practice, the high-frequency signal s.sub.HF is not continuously generated in the case of FMCW. Rather, the ramp-shaped change is interrupted for a defined pause time after a defined number of successive frequency ramps. In the case of FMCW, the corresponding measurement rate r.sub.m at which the FMCW-based fill-level measuring device 1 cyclically redetermines the fill level L results from this number of successive frequency ramps, or from their respective ramp duration, and the subsequent pause time. In practice, the cycle duration in this case is between 0.3 Hz and 30 Hz.

[0038] For transmission, the high-frequency electrical signal s.sub.HF in the signal-generating unit 11 is supplied to the antenna 12 via a signal divider 116, a transmission amplifier 113, and a transmitting/receiving switch 114. The incoming radar signal E.sub.HF, which is reflected by the filling material surface, is converted back into a purely electrical receive signal e.sub.HF by the transmitting/receiving antenna 12. Subsequently, after any reception amplification (not shown in FIG. 2), the receive signal e.sub.HF is mixed in an evaluation unit 13 by means of a mixer 131 with the high-frequency signal s.sub.HF to be transmitted. For this purpose, the high-frequency signal s.sub.HF is branched from the signal divider 116 of the signal-generating unit 11. This generates an evaluation signal IF which is typical in the FMCW method and forms the basis for determining the distance d or the fill level L. In this case, the frequency of the evaluation signal IF according to the FMCW principle is proportional to the distance d from the fill level surface.

[0039] In order to determine the frequency of the evaluation signal IF, an analog/digital converter of a computing unit 134 digitizes the evaluation signal IF in the evaluation unit 13. The computing unit 134 can thus subject the digitized evaluation signal to a (fast) Fourier transformation, or FFT for short. The frequency of the global maximum of the corresponding FFT spectrum ideally corresponds to the distance d from the filling material surface.

[0040] A circuit diagram of a fill-level measuring device 1, which operates according to the pulse time-of-flight method, is shown in FIG. 3: In order to generate the pulse-shaped high-frequency signal SHF, the circuit of the fill-level measuring device 1 shown in FIG. 3 also comprises a signal-generating unit 11. In the case of the pulse time-of-flight method, the signal-generating unit 11 is designed such that it generates high-frequency electrical pulses s.sub.HF at a defined clock rate f.sub.c. For this purpose, the signal-generating unit 11 in the shown exemplary embodiment comprises a first pulse generator 111 that actuates a first high-frequency oscillator 112.

[0041] The frequency of the microwave pulses SHF, EHF is established by the oscillation frequency of the high-frequency oscillator 112. In the simplest case, the high-frequency oscillator 112 can be designed as an oscillating crystal. A VCO (“voltage-controlled oscillator”) can also be used. In this case, the high-frequency oscillator 112 is actuated by the pulse generator 111 by means of a corresponding DC voltage signal. The pulse generator 111 thereby defines the pulse duration of the individual microwave pulses SHF and the clock rate f.sub.c at which the microwave pulses SHF are emitted. As standard, a semiconductor-based digital resonant circuit is used as the high-frequency oscillator 112. The clock rate f.sub.c at which the individual microwave pulses s.sub.HF are excited is between 100 KHz and 1 MHz in practice. The high-frequency pulses s.sub.HF thereby generated by the high-frequency oscillator 112 are supplied to the antenna 12 analogously to the FMCW method via a transmission amplifier 113 and a transmitting/receiving switch 114 so that they are correspondingly emitted as microwave pulses SHF.

[0042] Since the reflected microwave pulses EHF are also received via the antenna 121, the transmitting/receiving switch 114 supplies the corresponding receive signal EHF to a mixer 131 in the evaluation unit of the fill-level measuring device 1. In contrast to the shown embodiment variant, an electrically conductive probe, such as a waveguide or a coaxial cable, which extends toward the container bottom can also be used instead of the antenna 12. In contrast to the circuit shown in FIG. 2, in the implementation of this embodiment variant known by the term TDR (“time-domain reflectometry”), the high-frequency oscillators 111, 133 are not required.

[0043] By means of the mixer 131, the undersampling of the receive signal e.sub.HF characteristic of the pulse time-of-flight method is carried out. For this purpose, the receive signal e.sub.HF is mixed with electrical sampling pulses s′.sub.HF by the mixer 131. In this case, the sampling rate f′.sub.c at which the sampling pulses s′.sub.HF are generated differs by a defined relative deviation Φ of far less than 0.1 per thousand from the clock rate f.sub.c of the generated high-frequency pulses s.sub.HF.

[0044] The sampling pulses s.sub.HF are generated in the evaluation unit 13 analogous to the signal-generating unit 13 by a second pulse generator 133 which actuates a second high-frequency oscillator 134. Thus, correspondingly to the high-frequency pulses s.sub.HF, the frequency of the sampling pulses s′.sub.HF is defined by the second high-frequency oscillator 134. In this case, the frequency of both high-frequency oscillators 112, 134 is set identically in practice. In this case, the second pulse generator 134 in turn controls the sampling rate f.sub.c at which the sampling pulses s′.sub.HF are generated.

[0045] Mixing the receive signal e.sub.HF with the electrical sampling pulses s′.sub.HF by means of the mixer 131 generates an evaluation signal IF which is typical for the pulse time-of-flight method and represents the receive signal e.sub.HF in a time-expanded manner. The time expansion factor is proportional to the deviation Φ between the clock rate f.sub.c and the sampling rate f.sub.c. Accordingly, in the case of the pulse time-of-flight method, the measurement rate r.sub.m is defined as the clock rate f.sub.c divided by the deviation Φ according to

[00001]$r_m=\frac{f_c}{\phi }$

[0046] The advantage of the time expansion is that the evaluation signal IF can be evaluated considerably more easily from a technical point of view due to the time expansion in comparison to the pure receive signal e.sub.HF: The reason for this is that the receive signal e.sub.HF has a correspondingly short time scale tin the nanosecond range due to the high speed of propagation of the microwave pulses S.sub.HF, E.sub.HF at the speed of light. The time expansion results in the evaluation signal ZF having a time scale in the millisecond range.

[0047] By means of the time-expanded evaluation signal IF, the computing unit 132, after corresponding analog/digital conversion, subsequently again determines the fill level L by determining the signal maximum corresponding to the distance d in the evaluation Signal IF.

[0048] Both the FMCW-based embodiment variant shown in FIG. 2, and the pulse time-of-flight-based variant of the fill-level measuring device 1 shown in FIG. 3 respectively comprise a transmission amplifier 113 in their signal-generating unit 11. With relation to the further components of the signal-generating unit 11 and of the evaluation unit 13, this component heats up most in practice during measuring mode. In a large number of applications, this is not critical since the fill-level measuring device 1 is often only used at outside temperature or room temperature. As a result, the heat arising in the transmission amplifier 113 can be sufficiently dissipated so that the temperature remains far below the critical junction temperature of 150° C. However, it becomes critical if the fill-level measuring device 1 is used at sites of use at which, at least temporarily, more than 100° C. prevail, such as in cleaning processes during food production.

[0049] According to the invention, the two embodiment variants of the fill-level measuring device 1, which are described in FIGS. 2 and 3, therefore comprise a temperature sensor 115 which is mounted on the transmission amplifier 113 in the signal-generating unit 11 so that the temperature there can be measured. This makes it possible to configure the signal-generating unit 11 and the evaluation unit 13 of the fill-level measuring device 1 in such a way that the measurement rate r.sub.m is adaptively adjusted to the temperature measured by the temperature sensor 115. This is illustrated by way of example with reference to FIG. 4:

[0050] According to the graph therein, the fill-level measuring device 1 measures the fill level L below a defined limit temperature T.sub.g at the temperature sensor 115 of, for example, 100° C. at a constant or undiminished measurement rate r.sub.m at which it also measures under normal conditions. However, above the limit temperature T.sub.g, the fill-level measuring device 1 reduces the measurement rate r.sub.m linearly as the temperature increases. In contrast to a linear reduction, a stepwise reduction is also conceivable in contrast to the shown illustration. This counteracts primarily the development of heat by the transmission amplifier 113. Thus, with a corresponding reduction in the measurement rate r.sub.m per ° C., despite a high ambient temperature (for example caused by a cleaning step in the container 2), the temperature in the fill-level measuring device 1 does not exceed a critical maximum temperature T.sub.max of, for example, 150° C. If the temperature sensor 115 nevertheless detects that the critical maximum temperature T.sub.max is being exceeded, the fill-level measuring device 1 can in this case be automatically shut off, for example, given a corresponding design. This ensures, on the one hand, that the fill-level measuring device 1 does not measure any faulty fill-level values L and, on the other hand, does not suffer irreparable damage.

[0051] It goes without saying that the control of the measurement rate r.sub.m according to the invention can also be used for fill-level measuring devices 1 that do not operate according to the pulse time-of-flight or FMCW method. Likewise, the method according to the invention can also be generally used in radar-based distance measurement.

LIST OF REFERENCE SIGNS

[0052] 1 Fill-level measuring device

[0053] 2 Object/filling material

[0054] 3 Container

[0055] 4 Higher-level unit

[0056] 11 Signal-generating unit

[0057] 12 Antenna arrangement

[0058] 13 Evaluation unit

[0059] 111 Ramp-generating unit or pulse generator

[0060] 112 High-frequency oscillator

[0061] 113 Amplifier

[0062] 114 Transmitting/receiving switch

[0063] 115 Temperature sensor

[0064] 116 Signal divider

[0065] 131 Mixer

[0066] 132 Microcontroller

[0067] 133 Pulse generator

[0068] 134 Second high-frequency oscillator

[0069] d Distance

[0070] E.sub.HF, e.sub.HF Received radar signal or receive signal

[0071] f.sub.c Clock rate

[0072] f′.sub.c Sampling rate

[0073] h Installation height or measuring range

[0074] IF Evaluation signal

[0075] L Fill level

[0076] r.sub.m Measurement rate

[0077] S.sub.HF, S.sub.HF Radar signal or high-frequency signal

[0078] S′.sub.HF Sampling signal

[0079] Φ Relative deviation between the clock rate and the sampling rate