DE19903183A1 - High frequency distance measuring device, especially a proximity measuring device or proximity switch, comprises a sensor having a hollow conductor antenna with an open end closed by a damping element - Google Patents

Abstract

A distance measuring device, comprising a sensor having a hollow conductor antenna with an open end closed by a damping element. An Independent claim is also included for a method of determining the distance of an object from a device, especially the above device, by measuring the resonant frequency of a hollow conductor. Preferred Features: The hollow conductor is operated at just above its cut-off frequency and is a round hollow conductor filled with a dielectric. The damping element is a disk of dielectric material.

Description

The present invention relates to a Distance measuring device according to the preamble of Claim 1 and a method for determining the Distance.

Conventional distance measuring devices working preferably in the close range of inductive, capacitive, optical or ultra Sound sensors. For a measurement with inductive Sensors must set the calibration curve and that too Material of an object to be measured must be known his. Furthermore, the inductive sensors for example, a 180 ° measuring range so that two sensors lying next to each other influence and thus the calibration curves of each Sensors can change. Beyond that such sensors only in embodiments in Commercially available that are larger in diameter than 4 mm (M4).

The disadvantage for a measurement with capacitive Sensors is that the distance between the Capacitor plates must be known exactly. Further subject to measurement of the influence of the Humidity, the general electro magnetic compatibility or temperature. To make the measurement regardless of these parameters To be able to carry out, depending on the need a reference measurement can be carried out which then eliminates the disturbing influence can be.

The object of the present invention is therefore a distance measuring device and a method for Determining the distance to create which or which overcomes the disadvantages listed above and a continuous distance determination, a easy handling and versatile Possible uses.

This task is accomplished with the device-technical features of claim 1 and with the procedural features of Claim 19 solved.

According to the invention, the sensor has a waveguide, preferably a round waveguide, which is filled with dielectric, preferably Al ₂ O ₃ . With this measure, the advantage is achieved that the smallest designs, for example <M4 <, can be implemented and the possible uses are increased many times over. The size of the waveguide depends on the transmission frequency if it is assumed that the waveguide is operated just above its cut-off frequency. Due to the basic geometry of a waveguide, small distances between several sensors arranged in parallel are possible, since the sensor has a laterally sharply delimited measuring range and its measuring behavior is therefore not influenced by sensors arranged in parallel. As an area of application, it is conceivable, for example, that the distance measuring device according to the invention can be used in the direction detection of movable objects or in a space-saving installation, for example by parallel installation.

Furthermore, the sensor according to the invention can be used as Switch are used with the  Switch point changes without re-dimensioning or changes to the sensor element or adding further electronic components become possible. This has the advantage that the switching point for example via software to the respective Needs is adjustable.

The sensor according to the invention is also in the Location, approaching, conductive or dielectric Detect objects and the distance to the object with accuracy in the submicrometer range measure up. This type of sensor can, for example as a proximity switch, for continuous measurement of the piston travel in the point of reversal of pneumatic and hydraulic cylinders, the stress of Ball bearings, valve positions or for measurement the expansion of pressure membranes can be used.

According to the invention depends on conductive objects the measuring distance does not depend on the size of the object, if you assume that the object is at least like this is the same as the diameter of the waveguide. In addition, a distance measurement is generally too conductive and dielectric objects possible.

If the sensor is used as a switch, then is a change in the switching point or a redimensioning or a change of Sensor element in a simple way accomplish. Since the switching point z. B. about Software is adjustable, is also the advantage given that the entry of multiple switching points through suitable software in a simple way is made possible, which makes a much higher Application flexibility, for example for a parts Size detection, for different machines configurations, for a rotation angle detection via  Cam discs, etc. receives. In contrast, how mentioned at the beginning with inductive sensors Multiple switching points only with great effort will be realized.

Because of the in the invention Distance measuring device used measuring method can also set several switching points via one logic are linked together, the measuring method works continuously. For example advantageous if three switching points when queried a rotary cylinder are required.

Due to a compact design is for Switching distances of, for example, 0.6, 0.8, 1.0, 1.5, 2.0 mm or 5 mm or a basic element in all common housing designs can be used, which means a Cost savings are achieved and thus a ge less logistics is needed.

Further advantageous embodiments are Subject of the further subclaims.

It has turned out to be particularly advantageous if the waveguide is a round waveguide, the operating frequency of which is slightly above its cut-off frequency if it is designed for operation with the H _mnp mode, preferably the H ₁₁₁ mode. Here, the waveguide is operated as an antenna in that one side of the waveguide, preferably one end side, remains open and the electromagnetic wave is emitted on this side. The waveguide, which is open on one side, has an opening angle of approx. 120 °. The reflection factor between the waveguide and free space is ← 10 dB.

If, for example, the cavity resonator is filled with a dielectric, preferably Al ₂ O ₃ , the entire distance measuring device can be made smaller than the z. B. air-filled waveguide. Furthermore, it is now particularly advantageous that between the dielectric and the surrounding medium, for. B. air between the object and the open waveguide side, a transition occurs which leads to the fact that, compared to the air-filled waveguide, a larger part of the electromagnetic wave is reflected and is no longer emitted. The reflection factor is then between 1 dB and

1.5 dB. It is particularly advantageous that now due to the larger reflection factor next to the Antenna function builds a resonance circuit, the Quality, however, compared to conventional HF Cavity resonators (~ 3000 to 5000) by the factor 20 to 30 is worse.

This disadvantage can be avoided according to the invention by placing an attenuator on the open side of the Waveguide between the dielectric of the waveguide and the surrounding medium, e.g. B. air attached becomes. This attenuator preferably consists of dielectric material, e.g. B. Teflon, whose Dielectric constant between the dielectric of the Waveguide and the surrounding medium, e.g. B. air, lies. This allows the reflection factor to be approx.

0.4 dB in the area just above the cut-off Increase frequency and thus a much better one Achieve the quality of the resonance circuit. This is required with sufficient accuracy, e.g. B. determine the resonance frequency in the kilohertz range can. Because the resonance frequency is directly proportional the distance between the object and the one with the Attenuator closed side of the waveguide can be with this arrangement  Distance measurement to the object with an accuracy in the submicrometer range.

Furthermore, the attenuator has the advantage that e.g. B. with Teflon with increasing thickness Focusing the radiation pattern of the antenna is achieved, however, by accepting one Reduction of the range. The use of Teflon as a dielectric for the attenuator the additional advantage that condensing that Measurement falsifying moisture of the surrounding Medium due to the poor adhesion of the Teflon rolls off.

In contrast to the patent application with the File number DE 197 33 109.2 or DE 198 07 593.6 or PCT / EP 98/04 815 the invention has the advantage that a range increase by a factor of 2.5 to 3 is possible.

It has proven advantageous that according to Claim 6 only the surface of the Dielectric with the exception of the attenuator or base with a Adhesive layer, e.g. B. 1 nm TiW and then with a thin gold layer, e.g. B. 1 µm, coated or is sputtered on, so that the metallic Waveguide in the sense of a low price Mass production is replaced.

The distance measuring device according to claim 8 and in particular the waveguide a coplanar Slot coupling preferably on the object facing away from the end of the waveguide, so this arrangement ensures that the Coupling of the electromagnetic wave suitable place and can be done easily.  

Depending on the mode of operation of the distance measuring device the coplanar slot coupling can consist of one Coupling slot for transmitter and receiver according to Claim 9, which are parallel (a slot is attached in the center of the waveguide, the others parallel to this towards the waveguide edge) are arranged and what a transmission mode corresponds, or the coplanar slot coupling a coupling slot for transmitter and receiver consists of what is operating in a reflection mode corresponds.

Alternatively, the distance measuring device according to Claim 11, in particular the waveguide, a Have a microstrip line for coupling, which is used in particular when it The advantage is that the evaluation electronics separated from the waveguide must be built.

If, according to claim 12, the distance _{measuring device is} preferably operated in the H _mnp modes, preferably in the H ₁₁₁ mode, the waveguide can oscillate in a wide range of resonance frequencies in which no further modes are excited, so as to keep the measurement accuracy high .

Further advantageous embodiments of the Invention are the subject of the remaining sub Expectations.

With reference to the following Drawings are intended to illustrate individual embodiments of the present invention.  

Fig. 1 shows a sectional view of the distance measuring device according to the invention;

FIG. 2 shows a rear view of the distance measuring device according to the invention according to FIG. 1;

Fig. 3 shows a block diagram of the circuit for the distance measuring device according to the invention;

FIG. 4 shows the reflection or transmission behavior as a function of the resonance frequency at different distances from the object of the distance measuring device according to the invention;

Fig. 5 shows a diagram of the dependence of distance to the object and resonance frequency;

Fig. 6 shows the mode characteristic of a circular cylinder for dimensioning the resonator of the distance measuring device according to the invention;

Fig. 7a-f the radiation characteristics of H ₀₁₁ and H ₁₁₁ shows modes and the reflection factors for the H ₁₁₁ mode with and without an attenuator.

Fig. 8 illustrates different positions of a particular application for the inventive distance-measuring;

Fig. 9 shows a further possible application of the distance to the invention;

FIG. 10 also shows another registration option for the distance measuring device according to the invention, for example for a shock absorber query;

Fig. 11 shows a possible application for the detection of a piston position in a valve;

Fig. 12 shows a further possible application, for example a pressure measurement by detecting the deflection of a diaphragm;

Fig. 13 shows a further possible application, for example the determination of tangential and axial forces in the wheel bearing of vehicles, and the simultaneous determination of the speed of revolution of the wheel.

Fig. 14 shows a further possible application of the distance according to the invention, for example at the surveying object;

Fig. 15 shows a further possible application of the distance according to the invention, for example for a level sensor.

As shown in Fig. 1, the distance measuring device z. B. a circular waveguide 1 , which is formed from a metallic housing 5 , preferably made of titanium or Kovar. In this metallic housing, which is preferably tapered, a dielectric 7, for example in the form of a ceramic z. B. Al ₂ O ₃ introduced. The ceramic can, as shown in Fig. 1, be inserted into the housing. With the exception of the open side facing object 3 , dielectric 7 itself is metallized, for example gold-plated. This has the advantage that the function over temperature depends only on the temperature coefficient of the dielectric 7 and not on that of the metallic housing. The metallic housing of the waveguide could also be completely eliminated.

The end face of the waveguide, which lies opposite the open end face, is gold-plated and carries the coupling mimic, for example in the form of a coplanar slot coupling or a microstrip line, and the components for the transmitter, receiver and possibly evaluation electronics 11 . The electromagnetic wave is coupled in via this arrangement.

Due to the use of the dielectric 7 it is achieved that the geometric dimensions, for. B. the circular waveguide can be reduced while maintaining the same transmission frequency. If the open side of the waveguide is closed with an attenuator 10 , the reflection factor is so large that the waveguide can be operated in resonance with a sufficiently high quality parallel to its antenna function. As is generally known, the resonance frequency f _{r of} a cylindrical H _{mnp resonator can be} determined from ε, µ, the nth zeros of the derivative of the Bessel function of the mth order, as well as the diameter D of the circular waveguide and the length L of the Determine the round waveguide. The functional relationship between εµ (for _r D) ² and (D / L) ² can be clearly represented in a so-called mode diagram according to FIG. 5. From this so-called mode diagram, it is also relatively easy to identify areas in which no other modes can propagate. A further mode selection can be made by isolating the resonator _top surface from the cylinder _jacket , which corresponds to an open resonator with H _mnp modes. It has proven to be particularly advantageous for the waveguide to be designed such that the H _mnp modes, preferably the H ₁₁₁ modes, can be propagated as the wave type. The H ₁₁₁ mode has the advantage that, unlike the H ₀₁₁ mode, it spreads axially towards the object. The result of the corresponding field simulations is shown in FIG. 7. In order for the geometry of the waveguide to support the propagation of the H ₁₁₁ mode, a section on the line of the H ₁₁₁ mode is to be sought according to FIG. 5, in the vicinity of which no characteristic curve of other modes occurs , so that no other mode is excited even with certain fluctuations in the mechanical waveguide dimensions and when tuning the frequency.

FIG. 2 shows the back of the circular waveguide 1 according to FIG. 1 by way of example. Using this figure, the coupling of the electromagnetic wave into the circular waveguide can be shown more clearly, which corresponds to a coplanar slot coupling in this figure. The end face of the cavity resonator opposite the open side of the circular waveguide is preferably gold-plated. Only the coupling slots 13 and 15 in the circular waveguide 1 are left free . At the, e.g. B. for the H ₁₁₁ mode, place maximum field strength, for example in the center of the dielectric 7 of the circular waveguide, the electromagnetic wave is fed in via the slot coupling. Parallel to the coupling slot, a further coupling slot for coupling out the electromagnetic wave in the direction of the waveguide edge for the receiving electronics is provided in the transmission mode. The slots for sending and receiving are interchangeable. The size of the coupling slots 13 and 15 depends on the dimensions and the dielectric constant of the dielectric 7 and the transmission or resonance frequency relevant to the respective mode. With a diameter of the dielectric 7 of z. B. 6 mm, the size is approximately 0.5 mm by 0.1 mm. The electromagnetic wave itself is brought up to the slot via a coplanar 50 Ω line and via a bonding wire 17 , for. B. 17.5 microns gold wire 17 coupled into the slot 15 . It is important to ensure that the shortest possible wire routing of the ground bonds on one side of the coupling slot and the signal line on the opposite side of the coupling slot ensures optimal coupling of the E-vector.

With this arrangement, the circular waveguide 1 can be operated in both transmission and reflection modes. If the circular waveguide 1 is operated in transmission mode, then the electromagnetic wave is coupled out at a second coupling slot 13 with the coplanar coupling or coupling already described. In the reflection mode, this output is terminated with 50 Ω. As already mentioned above, in the case of smaller diameters of the dielectric 7 , a microstrip line coupling can also advantageously be used. An oscillator 19 , for example a voltage-controlled oscillator (VCO), a broadband HF detector diode 21 and a frequency divider 23 , which are connected to an evaluation electronics, are also provided on the back.

In Fig. 3, an overall diagram or a block diagram of the operation of an advantageous embodiment of the distance measuring device according to the application is shown. Starting from control and evaluation electronics, a ramp generator is controlled via a ramp control, whereby the frequency of the transmission branch I is tuned. At the same time, a resonance detector connected to the detector diode and downstream amplifier is connected via the receiving branch II, for example a comparator which queries a fixed threshold whether a video signal tapped from the receiving branch II indicates resonance. The resonance can be recognized by the fact that it differs from a non-resonance with a high slope in a video signal of the receiving branch with increasing oscillator frequency (see FIG. 4).

Is on the detector due to a drop in performance Resonated, then at that time via the DDS (direct digital synthesizer) associated resonance frequency of the VCO known. For this, the divided oscillator frequency not used directly as a result, but in a frequency and phase control loop one so-called phase-locked loop (PLL) fed. Furthermore, the target frequency is set via the DDS set a frequency that is used as a reference variable in the control loop arrives. Do that of that Receiving branch II recorded video signal Resonance condition, is in one in the Evaluation electronics contained microcontroller already the resonance frequency and thus the Known distance to target. By eliminating the Measuring time for the oscillator frequency and the Use e.g. B. a resonance sequence algorithm in one in the evaluation electronics Microcontrollers can make the cycle time clear be shortened and thus the measuring accuracy we be significantly increased.  

In this way, the resonance frequency in the waveguide is measured. Since the resonance frequency in the waveguide depends on the distance of the object (see FIG. 5), the distance can be determined directly by determining the resonance frequency. The new resonance frequency is determined by changing the transmission frequency until the resonance frequency and transmission frequency match. At this point, a drop in performance is detected on the detector diode. The determination of the distance with a measuring accuracy of 1 µm typically requires, at a distance of 0.5 mm, an accuracy in the frequency determination of at least 0.25 MHz at a transmission frequency of 11 GHz.

To illustrate how the Distance measuring device according to the application in Figs. 4 and 5 serve measured values.

As can be clearly seen in FIG. 4, the reflection and transmission characteristics, which are shown as a function of the resonance frequency at different distances from the object, show clear signal dips that occur when the resonance frequency is reached at a fixed distance from the object. In addition, there is a clear correspondence between the signal dips between the reflection and transmission characteristics.

In Fig. 5 the dependence of the distance and the resonance frequency is shown. It can clearly be seen that at a smaller distance a clearer resonance frequency shift occurs, which the measuring accuracy is measured in particular in objects which are positioned close to the waveguide. It should be noted here that the resonance frequency decreases as the distance to the object increases. In contrast, the resonance frequency for dielectric objects increases with increasing distance from the object. The change in direction of the resonance frequency thus depends on the dielectric constant of the object. In Fig. 6 is a general overview of the modes to be excited is illustrated of a circular cylinder. Depending on the size of the cylinder, the appropriate modes (TM = E field components and TE = H field components) can be selected using this circuit diagram.

FIG. 7 shows the range ratios for the cavity resonator when coupling in an electromagnetic wave in the H ₀₁₁ mode with the circular waveguide of an electromagnetic wave operated in resonance in the H ₁₁₁ mode. The range for object detection in H ₀₁₁ mode can only be increased slightly if the field is additionally focused using a tapered ceramic. If the circular waveguide z. B. excited in H ₁₁₁ mode, then it can only be operated in parallel as an antenna and resonator if the reflection factor at the transition point between the dielectric of the waveguide and the medium to the test object can be made correspondingly high via an attenuator. The differences in the reflection factor for the H ₀₁₁ mode in the resonator and the H ₁₁₁ mode for radiation from the circular waveguide open on one side with and without an attenuator are also shown in FIG. 14.

The following is based on some Areas of application the possible uses of distance measuring device according to the application  a high-frequency proximity sensor shown become.

A. Detection of the piston position

In Fig. 8, the possible sensor arrangements for piston position detection of a linear cylinder drive with the high-frequency proximity sensor according to the distance measuring device according to the application are shown.

A possible sensor arrangement for querying the position of a rotary drive with the high-frequency proximity sensor is shown for a rotary drive in FIG. 9. Since such a high-frequency proximity switch has an extremely flat construction, multiple positions can also be realized with the sensor element in the case of a plurality of switching points, the setting being able to be carried out, for example, via potentiometers or a teach-in logic.

B. Detection of the piston position Shock absorber

In Fig. 10, the schematic structure is shown a shock absorber with an integrated high-frequency proximity sensor.

In general, the principle according to the invention can also be applied to valves with movable mechanical parts (see FIG. 11), the valve flow possibilities being regulated by changing the position of the mechanical part. Previous position queries were implemented in pneumatics using magnetic field-sensitive sensors that react to the permanent magnet on the piston or tappet of the valve. It was shown, however, that for cost-effective solutions, only discrete position areas can be detected by the sensor mounted in a fixed position and adjusted to the positions to be detected. In hydraulic systems, magnetic interrogation is only possible to a limited extent due to the ferromagnetic materials that are usually used.

C. Pressure measurement by detecting the Membrane deflection

In Fig. 12 different pressure measurements, ie, absolute pressure or relative or differential pressure measuring possibilities are shown. In this particular application example, the pressure determination is achieved in that a membrane moving towards or away from the HF proximity sensor is detected at a distance. Compared to today's systems, e.g. B. piezoresistive strain gauges (DM5) or silicon elements, the device according to anmel has the advantage that the sensitive electronics are outside the pressure measuring cell.

D. ball bearings

In Fig. 13, a ball bearing is shown as z. B. is used as part of a wheel bearing in the automobile. In this application the sensor measures e.g. B. at an absolute distance of about 1 mm, the distance change in the operation of the vehicle. 3 physical quantities can be determined from this:

• - Axial force on the ball bearing, the z. B. arise from cornering. So caused by an average middle class car axial force of one kN a change in distance  of approx. 20 µm.
• - radial force over the weight of the Vehicle z. B. on uneven floors Wheel bearing is exercised. So causes one radial force from a kN one Distance change of approx. 1 µm.

The total change in distance is therefore the sum the changes in distance from axial and radial Force. Both can be separated because of as previously mentioned the changes in distance axial force is greater by a factor of 20 and it in contrast to the radial movement a slow loading process acts.

• - Measure the speed of rotation of the wheel by making markings on the circumferential half-shell. When marking it is a continuously tapered milling, such. B. in Fig. 9, act in the circumferential half-shell. An even more advantageous option is to mill transverse grooves in the movable half-shell with an increasing groove width from 0 to 360 °. The evaluation is carried out by subtracting the sum signal (sum signal = total change in distance due to axial and radial force and the revolution).

E. Object measurement

In the object measurement according to FIG. 14, the movement of the measuring tip, which is moved towards or away by an object on the HF proximity sensor, is measured. Because of the distance measuring device according to the application, measurements in the micrometer range can thus also be carried out.

F. Level sensor or monitor

The possible application shown in FIG. 15 relates, for example, to a fill level sensor. In FIGS. 15a, b, different installation locations of the Hochfrequenzan c are illustrated proximity sensor. In the cases of FIGS. 15a and 15b, the distance of the level to be measured is measured in a separate sensor tube, which is arranged externally or internally. In the arrangement according to FIG. 15c, the high-frequency proximity sensor is used externally for monitoring for a corresponding level of the maximum fill level. This advantageously ensures the monitoring of a maximum fill level or a predetermined set detection range, a switching signal being displayed when the fill level falls below the maximum fill level or if the leakage occurs outside the set detection range.

If, on the other hand, the high-frequency proximity switch is used externally as a level switch, the corresponding switching function can be used to indicate whether a predetermined level has been exceeded or fallen below. This external arrangement means that complex integration efforts can be dispensed with. The system according to FIG. 14c can be used for adaptation to existing maintenance devices with HF-transparent shells.

At this point it should be noted that the Distance measuring device according to the application in addition to the  areas of application listed above everywhere there can be used where a distance measurement device down to the micrometer range is required.

Claims (22)

1. Distance measuring device with a sensor and evaluation electronics, characterized in that the sensor has as an antenna a waveguide open on one side, the open side of which is closed with an attenuator. 2. Distance measuring device according to claim 1, characterized characterized in that the waveguide is scarce is operated above its cut-off frequency. 3. Distance measuring device according to claims 1 and 2, characterized in that it is the Waveguide preferably around a circular waveguide acts, its open, with the attenuator shows the closed end face to the object. 4. Distance measuring device according to claim 3, characterized in that the waveguide is filled with a dielectric, preferably Al ₂ O ₃ . 5. Distance measuring device according to claim 3, characterized characterized that it is Attenuator around a disc dielectric material, preferably Teflon, acts. The physical dimensions correspond at least to those of Cross section of the open area of the waveguide. The dielectric constant is between the Dielectric constant of the filling of the  Waveguide and the medium between the waveguide and object. 6. Distance measuring device according to claim 4, characterized characterized in that the surface of the Dielectric, with the exception of the object facing surface with a thin adhesive layer, e.g. B. 20 nm TiW and a final Gold layer, e.g. B. 1 micron coated, preferably sputtered is. 7. Distance measuring device according to claims 4, characterized characterized in that the dielectric in one metallic waveguide, preferably made of Kovar or titanium, is inserted. 8. Distance measuring device according to one of the claims 1 to 7, characterized in that the Waveguide a coplanar slot coupling, preferably on the side facing away from the object Front side of the waveguide has. 9. Distance measuring device according to claim 8, characterized in that the coplanar slot coupling consists of a coupling slot for each transmitter and receiver (transmission mode), which are arranged in a fashion-specific manner. For example, a rectangular slot is provided in the center of the circular waveguide for coupling the H ₁₁₁ mode. The coupling slot for the receiver is shifted parallel to the edge of the circular waveguide. 10. Distance measuring device according to claim 8, characterized characterized that the coplanar  Slot coupling from a coupling slot for There is a transmitter and receiver (reflection mode). 11. Distance measuring device according to one of the claims 1 to 7, characterized in that the Waveguide a microstrip line for Has coupling. 12. Distance _measuring device according to one of claims 1 to 11, characterized in that the coupling and the resonator as the wave type allow the H _mnp modes, preferably the H ₁₁₁ mode. 13. Distance measuring device according to one of the claims 1 to 12, characterized in that the sensor high-frequency electronics with a transmission and has receiving branch. 14. Distance measuring device according to claim 13, characterized characterized in that the transmission branch from a Oscillator, preferably a voltage Controlled Oscillator (VCO). 15. Distance measuring device according to claim 13, characterized characterized that the receiving branch out there is at least one high-frequency diode. 16. Distance measuring device according to claim 14, characterized characterized in that the oscillator frequency above a closed control loop one Target frequency (reference variable) follows. 17. Distance measuring device according to claim 16, characterized characterized in that the control loop (PLL: Phase Locked Loop) from at least one Frequency divider, a phase discriminator and there is a Tielpass filter and the target frequency  via a DDS (Direct Digital Synthesizer) is specified (dynamic frequency control or determination). 18. Distance measuring device according to claim 16, characterized characterized that the control loop out there is at least one frequency divider and preferably via a frequency counter, Microcontroller and digital-to-analog converter is closed (static frequency control or determination). 19. A method for determining a distance of an object to a device, in particular to a distance measuring device according to one of claims 1 to 18, which comprises the steps:

• a) providing a waveguide;
• b) Determination of the resonance frequency in order to determine the distance to the object.

20. The method according to claim 19, characterized records that the determination of the Resonance frequency is such that an im Transmitter provided oscillator in its transmission frequency is detuned until in A drop in performance at a receiving branch Resonance is established. 21. The method according to claim 20, characterized records that the transmit frequency of the oscillator by ramp control and one Ramp generator is detuned. 22. The method according to claim 20, characterized records that the transmit frequency of the oscillator  via a direct digital synthesizer (DDS) is set.