Measuring device

The invention relates to a measuring device comprising a signal unit (20) for emitting a measuring signal (22.1, 22.2) in a measuring frequency range (60, 62, 68, 70) adapted for measurement and an evaluation unit (36) for the spectral evaluation of an evaluation signal (34.1, 34.2) induced by the measuring signal (22.1, 22.2) to a measuring result. According to the invention, the measuring device comprises a signal processing unit (30) adapted to displace a generation signal (26) for generating a measuring signal (22.1, 22.2) in a generation frequency range (48) from the generation frequency range (48) to the measuring frequency range (60, 62, 68, 70).

The invention described and claimed hereinbelow is also described in PCT/EP2007/050322, filed Jan. 15, 2007 and DE 10 2006 002 666.7, filed Jan. 19, 2006. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119 (a)-(d).

BACKGROUND OF THE INVENTION

The present invention is directed to a measuring device with a signal unit.

Measuring devices are known that transmit a measurement signal in a certain frequency range in order to perform a measurement, the measurement signal being received and evaluated as an evaluation signal after it interacts with an object to be investigated. In the evaluation, the desired measurement result is ascertained based on a spectral analysis of the measurement signal.

SUMMARY OF THE INVENTION

The present invention is directed to a measuring device with a signal unit for transmitting a measurement signal in a measurement-frequency range that is adapted for a particular measurement, and to an evaluation unit for performing a spectral evaluation of an evaluation signal that was induced by the measurement signal in order to obtain a measurement result.

It is provided that the measuring device includes a signal-processing unit, which is provided to shift a generate signal—which generates the measurement signal and is located in a generation-frequency range—from the generation-frequency range to the measurement-frequency range. As a result, the flexibility of use of the measuring device may be increased in a simple manner. It is possible, in particular, to expand the measurement functionality of existing measuring devices with minimal outlay and in a cost-favorable manner. Existing, cost-favorable signal-generation means may be used to produce the generate signal without their needing to be tailored especially to the measurement-frequency range. A signal located in a frequency range preferably has a signal-to-noise ratio in its frequency spectrum that is greater than one, for each frequency value in the frequency range. This may take place simultaneously for all frequency values in the frequency range, e.g., by generating a pulse. As an alternative, the frequency values in the frequency range may be sampled within a certain time interval, e.g., via frequency modulation of a peak-frequency signal within the frequency range. When the generate signal is shifted, its frequency spectrum may be shifted by a frequency in the frequency scale, with the measurement-frequency range and the generation-frequency range having the same width As an alternative, the generate signal may be shifted to a measurement-frequency range that has a different width, which is broader, in particular. The expression “a measurement-frequency range (of a measurement signal) adapted for a particular measurement” refers, in particular, to a frequency range in which interactions of the measurement signal with the material may be evaluated in order to ascertain a characteristic value that is relevant to the measurement. In addition, a “spectral evaluation” of a signal refers, in particular, to a signal evaluation with which an evaluation result is obtained by ascertaining a characteristic of the signal spectrum. To this end, the course of the signal may be analyzed as a function of the frequency, e.g., by ascertaining a peak position or a peak amplitude. As an alternative or in addition thereto, the course of the signal may be analyzed as a function of time by ascertaining a change in the form of the signal between the time when the signal was transmitted and when it was received. When the measurement signal has a course over time with a certain pattern, e.g., a square or gaussian pattern, a deformation of the pattern caused by an interaction of the measurement signal with a material may be ascertained in the evaluation signal and evaluated. This time-based method is equivalent to the frequency analysis of the signal described above. This is known from Fourier theory and will not be described in greater detail here.

It is also provided that the signal unit is provided for ultra-broadband operation. A good measurement result may therefore be attained with a low spectral energy density. “Ultra-broadband operation” means the use of a frequency range with a band width of at least 500 MHz or at least 15% of the mid-frequency of the frequency range. The mid-frequency is preferably selected in the frequency range of 1 GHz to 15 GHz.

Ultra-broadband operation may be attained by transmitting pulse sequences, by transmitting “pseudo-noise sequences”, by using a frequency-modulated, continuous signal, or by using a frequency shift system.

When the evaluation unit is provided for determining a characteristic value for moisture, a greater level of user comfort may be attained. The evaluation unit is preferably provided to determine moisture, in interaction with the signal-processing unit. In particular, the generate signal may be shifted into a measurement-frequency range in which interactions with water molecules of an object under investigation may be evaluated by the evaluation unit in order to determine a moisture level.

In a further embodiment of the present invention, it is provided that the signal-processing unit is provided for shifting the generate signal to at least two measurement-frequency ranges. As a result, a high level of flexibility may be attained in the evaluation of the measurement signal.

Flexible measurement procedures may be attained, in particular, when the measuring device includes at least two measurement modes, which are provided for measuring a characteristic value, and each of which is assigned to one of the measurement-frequency ranges.

When the signal-processing unit is provided to shift the generate signal to the measurement-frequency ranges at least essentially simultaneously, a broad measurement signal that extends across at least two measurement-frequency ranges may be attained.

These measurement ranges may be separated from each other. As a result, certain ranges of the frequency scale may be blocked out, thereby making it possible to prevent an undesired energy distribution of the measurement signal across frequency ranges that are not adapted for a measurement, and to eliminate the need for filtering.

The measurement-frequency ranges advantageously form a continuous measurement-frequency section. As a result, the use of complex expansion methods for expanding the generation-frequency range may be advantageously avoided.

In addition, existing, cost-favorable circuits may be used for the signal-processing unit when they include a modulation unit for modulating the generate signal with at least one modulation signal.

It is furthermore provided that, during operation, the evaluation unit is supplied with a processing signal from the signal-processing unit, which is provided to shift the generate signal. As a result, components for processing the evaluation signal may be advantageously eliminated.

The measuring device is advantageously designed as a locating device. Objects may therefore be located with a high level of accuracy.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

A measuring device designed as a locating device10is shown inFIG. 1. In a first measurement mode, locating device10delivers information about objects that are hidden in or behind an object under investigation, e.g., a wall, a floor, a ceiling, etc. These objects are, e.g., water lines, electrical cables, etc. The figure shows a schematic depiction of a wall12in which an object14of this type is located. Locating device10, which is moved close to wall12, enables a user to visualize, in a display16, the wall12being investigated, a characteristic value P depicted as a position of object14in wall12, and the expansion and/or depth of object14. This is realized using a measuring unit18, which is provided to determine this information by processing high-frequency signals. To this end, measuring unit18includes a signal unit20, via which high-frequency measurement signals22.1,22.2are generated and coupled into wall12. To determine characteristic value P of object14, and to visualize the wall structure, to measurement signals22.1and22.2are transmitted in two measurement directions32,33. Transmission in measurement direction32takes place via sensor means24.1designed as an antenna element, while measurement signal22.2is transmitted via sensor means24.2, which are also designed as an antenna element. For clarity,FIG. 1shows only measurement direction32and only one sensor means24.1(see alsoFIG. 2). Measurement directions32,33may also be depicted as, e.g., a horizontal direction and a vertical direction. In a further embodiment, it is also feasible that transmission takes place in both measurement directions32,33via sensor means, e.g., sensor means24.1designed as an antenna element. It is also feasible that a measurement signal is transmitted in only one direction, e.g., direction32. In addition, sensor means24.1,24.2may be designed as monostatic and/or bistatic antenna elements.

Transmitted measurement signals22.1,22.2are generated in signal unit20via a generate signal26, which is produced in a signal-generating unit28and is processed in a signal-processing unit30. Measurement signals22.1,22.2excite evaluation signals34.1,34.2in wall12, which are then received by sensor means24.1,24.2.

After measurement signals22.1,22.2are received, they are forwarded to an evaluation unit36. Evaluation unit36evaluates the frequency spectrum of evaluation signals34.1,34.2and obtains measurement results, which are displayed in display16. Wall12, characteristic value P of object14, locating device10itself, and its direction of motion relative to wall12are shown in display16.

In a second measurement mode, the operator may also be informed of a characteristic value F, which represents the moisture content of wall12. To this end, generate signal26is processed in signal-processing unit30such that measurement signals22.1,22.2are adapted for a measurement of characteristic value F in wall12. The design and mode of operation of signal-processing unit30are illustrated inFIG. 2. The operator may select various measurement procedures via a control unit38, e.g., measurement procedures in which only the first measurement mode is activated, i.e., determining the location of object14, measurement procedures in which only the second measurement mode is activated, i.e., determining characteristic value F, or measurement procedures in which both measurement modes are activated. As an alternative or in addition thereto, a graph of moisture in wall12may be ascertained in this second measurement mode.

A schematic depiction of measuring unit18is shown inFIG. 2. The description in this section also refers toFIGS. 3 through 5. Of the elements depicted inFIG. 1, the following are shown: Signal-generation unit28, signal-processing unit30, sensor means24.1,24.2of signal unit20, and evaluation unit36.

It is assumed that the operator of control unit38selects a measuring procedure in which the first and second measurement modes are carried out. With the first measurement mode, the aim, in particular, is to detect a certain type of plastic of which object14is made, in order to locate object14. With the second measurement mode, the aim is to determine characteristic value F of wall12.

First, signal-generation unit28, which is designed as an SR diode (step recovery diode), is put into operation by a control unit40. Generate signal26, which is designed as an UWB (ultra-wide band) signal and is produced by signal-generation unit28, is shown inFIG. 3as a plot of amplitude versus time. The plot shows a sequence42of pulses44. Pulses44are generated with a pulse duration Δt of 0.5 ns and occur in regular succession. It is also feasible to use a transistor or a transistor circuit to generate pulses44. A time interval between two directly successive pulses44, which is selected to be constant in this exemplary embodiment, may also be designed as a random variable. The sequence may be designed, e.g., as a PN (pseudo-noise) sequence. As an alternative to the generation of pulses44, generate signal26may also be produced as a frequency-modulated, continuous signal (FMCW—frequency-modulated continuous wave).

After generate signal26is created, it is sent to a filter46. After it is filtered, generate signal26has the frequency spectrum shown inFIG. 4as a plot of amplitude versus frequency. Generate signal26has a mid-frequency νEMof 5 GHz and extends across a generation-frequency range48that corresponds to a bandwidth Δν of 2 GHz around mid-frequency νEM. A lower frequency is νEU=1 GHz and an upper frequency of generation-frequency range48is νEO=3 GHz. All of the frequency values described here are examples. Further frequency values are also feasible, of course.

Generate signal26is then sent to signal-processing unit30. It is designed as a modulation unit that includes a signal-generation unit50, a switching device52, and a mixing unit54. Signal-generation unit50is designed as a dielectric oscillator and generates two processing signals56,58, which have a frequency f1=4 GHz or f2=6.5 GHz, and which are sent to switching device52. As an alternative, signal-generation unit50may be designed as a voltage-controlled oscillator (VCO), an oscillating circuit, a variable capacitance diode with quartz, or as a digital circuit, e.g., a FPGA (field-programmable gate array). Via switching device52, one of the processing signals56,58may be designed as a modulation signal for modulating generate signal26, or generate signal26may be processed with both processing signals56,58, which are designed as modulation signals. It is feasible for generate signal26to be processed with more than two processing signals. In this exemplary embodiment, processing signal56or58is assigned to the first or second measurement mode.

In the first measurement mode, processing signal56is sent to mixing unit54, and generate signal26is thereby shifted from generation-frequency range48to a first measurement-frequency range60. This is depicted inFIG. 4as a solid arrow. Generate signal26, which is shifted to first measurement-frequency range60, is a measurement signal22that is divided and then transmitted as measurement signal22.1,22.2. Generate signal26is shifted with frequency f1when processed. Measurement signal22therefore has a mid-frequency νM1of 6 GHz and extends across first measurement-frequency range60with bandwidth Δν=2 GHz. First measurement-frequency range60is selected such that measurement signals22.1,22.2coupled into wall12interact with molecules of the plastic to be detected, thereby making it possible to perform an evaluation based on the frequency spectrum of evaluation signals34.1,34.2in order to determine position P of object14. After the first measurement mode has been carried out, switching device52is controlled by control unit40, and processing signal58is sent to mixing unit54, thereby shifting generate signal26from generation-frequency range48to a second measurement-frequency range62. This is indicated by a dashed arrow. Measurement signal22generated as a result has a mid-frequency νM2of 8.5 GHz and extends across second measurement-frequency range62, also with bandwidth Δν=2 GHz. Second measurement-frequency range62is tuned such that measurement signals22.1,22.2interact with water molecules in wall12, thereby making it possible to determine characteristic value F by performing a spectral evaluation of related evaluation signals34.1,34.2.

Locating device10is designed to perform a further measuring procedure, with which generate signal26is shifted simultaneously from generation-frequency range48into two measurement-frequency ranges. In a first example, generate signal26is shifted simultaneously to measurement frequency ranges60,62by switching device52sending both processing signals56,58to mixing unit54. As an alternative, signal-processing unit30may include two modulation units, which may serve to modulate generate signal26with a processing signal. They may be connected in series, in which case generate signal26is modulated successively, or they may be connected in parallel, in which case generate signal26is divided into two partial signals, each of which is modulated by a processing signal. The partial signals are combined with each other after they are modulated. Via the selection of the processing signals, a measurement-frequency section of the frequency scale that is tailored to a certain measurement may be attained easily and with great flexibility. A measurement-frequency section64of measurement-frequency ranges60,62, which are separated from each other, are depicted in this example and in the example shown inFIG. 4. As a result, it is possible, in particular, to specifically eliminate intervals in the frequency scale—e.g., interval Δf in this case—which are not adapted for a measurement, thereby avoiding the use of a signal filter and realizing a particularly effective use of the signal output.

A continuous measurement-frequency section66of two overlapping measurement-frequency ranges68,70is depicted in a further example, and in the example shown inFIG. 5, in which generate signal26(shown as a dashed line in the figure) is shifted simultaneously by signal-processing unit30. As a result, a broad interval of the frequency scale for a measurement may be easily attained without the need to use complex methods to expand generation-frequency range48. In a further example, generate signal26—which has not been shifted—may represent measurement signal22, in that signal-processing unit30is switched off, or generate signal26is modulated with a constant processing signal.

After processing, measurement signal22is sent to a signal divider72, in which it is divided into two measurement signals22.1,22.2. After they are divided, measurement signals22.1,22.2have essentially the same signal output, which is equal to half the output of measurement signal22. An alternative division of the signal output of measurement signal22into measurement signals22.1,22.2is also feasible. While they are being divided, it is also possible for one of the measurement signals22.1or22.2to be phase-shifted relative to the other measurement signal22.2or22.1. Measurement signals22.1,22.2are then sent via a signal-dividing unit74.1or74.2to a switching device76.1or76.2. Via switching device76.1or76.2, which is controllable by control unit40, measurement signal22.1or22.2may be sent to a reference circuit78for calibrating locating device10, or it may be sent to sensor element24.1or24.2for transmission in a measurement direction32or33. Measurement signals22.1,22.2, which are transmitted by sensor elements24.1,24.2in the form of electromagnetic radiation, have different polarization directions. It is also feasible that signal unit20includes sensor means for each measurement-frequency range, e.g., measurement-frequency ranges60,62of measurement signal22.

Measurement signals22.1,22.2excite evaluation signals34.1,34.2, which are received by sensor elements24.1,24.2. Evaluation signals34.1,34.2are separated from measurement signals22.1,22.2in signal-dividing unit74.1or74.2, which is designed as a circulator, and they are transmitted to evaluation unit36. Evaluation unit36includes two modulation units80,82, for demodulating evaluation signals34.1,34.2.

Modulation units80,82are connected with signal-processing unit30. At least one processing signal is sent via a line84to modulation units80,82. Processing signal, e.g., processing signal56and/or processing signal58, is used to process generate signal26. After demodulation, evaluation signals34.1,34.2are sent to a signal-processing device86. It includes an analog-digital converter88and a data-processing unit90, which is provided for performing a spectral evaluation of evaluation signals34.1,34.2. It is designed, e.g., as a digital signal processing (DSP) unit. Before digital conversion, the mean of evaluation signals34.1,34.2may be calculated, as an option, thereby making it possible to increase the signal-to-noise ratio.

When a PN sequence is generated for generate signal26, it is possible, as an option, to correlate evaluation signals34.1,34.2with a reference signal92in signal-processing device86. The result of the correlation is then sampled and run through an analog/digital conversion. Before this conversion, the mean of evaluation signals34.1,34.2may be calculated, and/or high-frequency components may be filtered. Generate signal26is used as reference signal92in this exemplary embodiment. Measurement signal22may be used as an alternative. In a further variant, after analog/digital conversion, evaluation signals34.1,34.2may be correlated with reference signal92, e.g., in data-processing unit90. It is feasible to use digital filters before correlation, thereby making it possible to improve a measurement result. After evaluation signals34.1,34.2are evaluated, evaluation results are sent to display16(FIG. 1), where they are displayed. In a further embodiment of locating device10, it is also possible—in order to expand the functionalities available for detecting hidden objects—to use further measuring units, which are based on inductive and/or capacitive methods, in addition to measuring unit18. A user could switch between these measuring units and measuring unit18manually or automatically.