Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
  • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
  • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
  • G01V3/088—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices operating with electric fields
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
  • G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
  • G01R27/26—Measuring inductance or capacitance; Measuring quality factor, e.g. by using the resonance method; Measuring loss factor; Measuring dielectric constants ; Measuring impedance or related variables
  • G01R27/2605—Measuring capacitance

Definitions

• the invention relates to a device and a method for error-free capacitive detection of objects behind a sheet-like object permeable to electromagnetic radiation, for example a plate, according to the preamble of claims 1 and 5, respectively.
• the sensor unit is firmly connected to the plate to be penetrated and, viewed from the sensor unit, the object to be detected moves behind this plate. Due to the mechanical arrangement, the sensor and the plate have a fixed capacitance with each other, which is reflected in the measured value as a constant basic capacity.
• Another application is sensors that need to be moved over the sheet to locate objects behind it, e.g. from EP 0 657 032 B1 and EP 1 740 981 B1. These include the so-called “bar finders” (Stud-Detector) . Bar finders are general auxiliary devices for do-it-yourselfers and professionals,
• CONFIRMATION COPY to detect, for example, in prefabricated houses behind a closed timber cladding or planking beams, posts or pipe or power lines. For this, the sensor is guided over the wall. It uses an electrode to measure the capacitance to the wall. If a wooden beam, a pipe or a power line is within the detection range, the capacitance increases as a result of the change in the dielectric. This is evaluated accordingly and brought to the user for display. As long as the sensor is moved with exactly the same distance to the flat object or to the plate, the capacitance between the sensor and the flat object or the plate does not change. As in the first two examples, it only enters the measurement signal as a constant value.
• the beam finder is chosen as an exemplary embodiment.
• the basic capacity formed by the wall structure is substantially higher than the capacity increase by an object behind the wall. If the beam finder moves over the wall, even the slightest tilting, caused by wall unevenness, can cause a strong decrease in capacity, so that the object to be detected can no longer be detected. This effect is particularly noticeable in structural plaster, woodchip wallpaper or transitions between wallpaper layers. The structure plaster not only leads to tilting of the sensor, it is also usually applied unevenly.
• the basic capacity also includes local inhomogeneities of the wall structure, especially if they are located near the surface, ie near the sensor.
• FIG. 11 shows a sensor 1.3 with an electrode 5.12 for determining the capacitance by means of an electromagnetic field 5.15.
• the associated electronics is not shown, the operation is assumed to be known.
• the capacitance value C changes to higher values until the closest possible approach to the wall 1.1 is established.
• An ideal one Movement along the wall does not change the reading as long as there is no post, beam 1.2 or similar behind the wall.
• a threshold value 1.6 can be set above the measured value 1.7 such that it is exceeded when the bar 1.2 passes over due to the resulting increase in measured value 1.8. is exceeded.
• Fig. 2 shows a measurement curve, as it often occurs in reality. Shown is the wall 1.1 with a plaster coating 2.5, irregularities 2.1 and inhomogeneities 2.2.
• the irregularity may e.g. a slightly thicker place in the plaster or a wallpaper pile. If the sensor 1.3 encounters the irregularity 2.1, it forcibly lifts its sensor surface slightly off the wall. As a result, the capacity decreases, the measurement curve 1.7 decreases accordingly (Fig. 2, 2.3). Since the threshold 1.6 is not exceeded, this is initially no problem.
• FIG. 6 D The detected capacitance decrease of the sensor when tilted or lifted off the wall according to the prior art is shown in FIG. It can be clearly seen that, in the prior art, the strongest change in the capacitance curve 6.1 occurs in the first few millimeters of tilting or removal of the sensor from the surface (FIGS. 6, D).
• a device for converting the capacitive signal change of a differential capacitor, which is used in acceleration sensors, in a digital signal is known.
• a sigma-delta modulator is used.
• the principle of sigma-delta modulation is based on a coarse measurement of a signal by means of a quantizer.
• the resulting measurement error is integrated and continuously compensated by a negative feedback.
• the individual blocks of the sigma-delta modulator are digital or analog.
• the differential capacitor is integrated in the negative feedback path and the reference feedback structure. This allows a capacity change directly from one analog value are converted into a digital signal.
• the output signal of the converter in the form of a binary current in the first approximation only depends on the deflection of the seismic mass of the differential capacitor.
• different reference voltages are applied, which are selectable in a certain temporal pattern with a certain amplitude. Through different selected reference voltages different ranges of values and resolutions of the signal to be digitized can be displayed. By a suitably selected sequence of reference voltages, a polarity change of the input signal is realized.
• a force can be exerted on the movable electrode via the sequence of the reference voltages and a suitable clock scheme for applying the reference voltages to the electrodes.
• a capacitive proximity switch a method and a circuit arrangement for the evaluation of small capacity changes.
• a bridge circuit is used in whose bridge branches there is one capacitor each as reactances.
• the two bridge branch voltages are rectified separately after the respective bridge branch, after which the bridge diagonal voltage is evaluated as a DC voltage changing in accordance with the capacitance change of the capacitance.
• the proximity switch consists of a multi-layer board with two electrically insulating layers, between which a metallic intermediate layer is the first face of a capacitor. On one of the two layers, a flat support is applied as a probe, which forms the second surface of the capacitor.
• a metal surface is movably disposed relative to the probe and forms with it a second variable capacitor.
• US Pat. No. 7,148,704 B2 shows a capacitive detection of the position of an object, namely a finger on a touchpad.
• the sensor used for this purpose comprises two measuring channels, which are each connected to an electrode.
• the channels are syn- chronologically, each channel giving a non-linear response to a capacitive influence of the finger.
• These respective output signals are linearly combined to provide position signals that vary linearly with the position of the finger, which is why the sensor operates as a ratiometric sensor.
• US 5,585,733 shows an apparatus and method for measuring the capacitance change of a capacitive sensor.
• means for applying a constant electric current to an electrode and means for generating a first series of clock pulses are provided.
• the voltage of the capacitor is compared with a reference voltage, whereby a signal is generated when the voltage of the capacitor exceeds the reference voltage.
• the capacitive sensor is used to measure the change in dimension of a dimensionally variable article, such as a telescope device.
• the capacitor is formed by two electrically conductive layers which enclose dielectric sleeves of a piston. The movement of the piston and thus of the sleeves changes the capacitance of the capacitor. This change is detected and evaluated by the controller, which detects the change in the position of the piston.
• DE 39 42 159 A1 shows a circuit arrangement for processing sensor signals, which are detected by means of a capacitive sensor.
• the sensor comprises a measuring capacitance which can be influenced by the physical measured variable to be detected and a reference capacitor which has a reference capacitance and supplies a measuring effect dependent on the measuring capacitance and the reference capacitance.
• First electrodes of the capacitors of the sensor are at a fixed potential, while second electrodes for carrying out the charge transport are connected to a first input of an input operational amplifier whose second input is at a reference potential.
• the transhipment of the capacitors of the sensor required to form the transported charge takes place by switching over the reference potential of the input operational amplifier.
• both inputs of the operational amplifier are essentially virtually at the same potential.
• the object of the invention is to provide a capacitive sensor that reduces and, in the best case, does not respond to tilting to the surface or small changes in the distance to the surface.
• the surrounding electrode suppresses electrical influences, e.g. through moisture films on the sensor surface.
• an opposite control of a sensor electrode and a further electrode surrounding the sensor electrode results.
• the signals may preferably be amplified so much that a significantly higher range, e.g. becomes possible behind the swept flat object or the objects become clearer. If a measured value calculation takes place from a plurality of sensor electrodes for positional representation and / or thickness depiction of the object, this can be displayed on a display. This also applies to the representation of inhomogeneity, e.g. a screw as a single object on the display.
• a small-sized capacitive sensor can be realized which detects the position of a finger in which the finger is merely tilted from a fixed support point, or slightly “rolled out” of the position can then be used eg for cursor control
• the surface is pressed to trigger a function, eg to actuate a mechanical microswitch If, for structural reasons, the capacitive sensor is not integrated in the moving part, it will still work movement of the surface during the printing process does not "break" the detected position.
• a mouse function can be displayed as a result of the billing of the measured curves of several sensor sections. Because of the high sensitivity of the system, it is also possible to detect the distance of an approaching object such as a finger in the Z-axis direction.
• a "stud finder” not only the presence but also the position of a bar behind the wall is shown.
• Fig. 2 shows a movement of a sensor according to the prior art along the flat
• FIG. 4 shows an embodiment of sensor electronics with closed-loop control for the constant maintenance of the signal amplitude at the sensor electrode
• FIG. 4.1 Embodiment of a sensor electronics with impedance transformers
• Fig. 5 a sensor according to the invention
• FIG. 8 shows an exemplary embodiment of a further sensor according to the invention with measured value profiles of different capacitance ratios and a display unit in the case of a perpendicular and in a diagonally located bar or post
• FIG. 10 shows an embodiment of an external circuit for realizing the invention with an IC
• FIG. 11 shows a sensor with an electrode for determining the capacitance according to the prior art. Detailed description of preferred embodiments
• Fig. 5 shows a possible arrangement.
• An annular electrode 5.3 surrounds the sensor electrode 5.2.
• the shielding electrode thus follows this potential.
• potential a sine or square-wave voltage can be applied to the measuring electrode with high resistance, an increase in capacitance at the measuring electrode leads to a deformation or at a corresponding frequency to a decrease in the alternating voltage.
• High-impedance coupling means in the further illustration that a change in capacitance, for example by a bar behind the wall, leads to an evaluable change in the signal at the measuring electrode. ßig large capacity change by approximating the sensor to the wall does not lead to a significant influence on the waveform of the AC voltage.
• a "high-impedance" coupling of the measuring electrode to the transmitting electronics can be effected, for example, by means of a 470KOhm resistor (at a frequency of, for example, 100 kHz.) Small changes in capacitance at the measuring electrode can also be clearly seen in the course of the curve. at resistance values around 100 ohms before, a small change in capacitance at the connected electrode leads to a hardly measurable signal influencing.
• the surrounding electrode 5.3 is not tracked at the potential of the sensor electrode 5.2 or measuring electrode. Rather, the sensor electrode is kept constantly at a fixed constant potential.
• the potential of the surrounding electrode 5.3 is readjusted until the fixed constant potential is reached again at the sensor electrode 5.2. The value of the readjustment is then the value of the capacitance change at the sensor electrode.
• a rectangular alternating voltage with a frequency of 100 kHz is applied.
• the amplitude at the sensor electrode 5.2 changes when the capacitance changes.
• An amplitude change when approaching a wall is then e.g. 10%, an additional bar 1.2 behind the wall also changes the amplitude, e.g. by 0.1%.
• a clock generator 4.8 supplies a first clock signal 4.13 having a frequency of eg 100 kHz to a first regulated voltage source 4.10 and a second inverted clock signal 4.12 to a second regulated voltage source 4.9.
• the first regulated voltage source 4.10 feeds the low-resistance voltage divider of R6 and R8, at the center of which lies the electrode 5.3.
• the same voltage source 4.10 feeds the high-impedance voltage divider R2 and R3.
• the base of R3 is at the input of AC amplifier 4.5.
• the ratio of R2 to R3 preferably corresponds to the ratio of R6 to R8.
• the second regulated voltage source 4.9 feeds the low-ohmic voltage divider R5 and R7 and the high-impedance voltage divider R1 and R4.
• the sensor electrode 5.2 forms a capacity against the environment, e.g. opposite the housing of the sensor.
• the capacitance of the capacitor C2 is selected to be about as large as this capacitance.
• the capacitance of the capacitor C1 is selected to be about as large as this capacity.
• C2 thus forms the fixed reference capacitance for the sensor electrode 5.2.
• the values of R5, R7, R1 and R4 correspond to the values for R6, R8, R2 and R3. This circuit part thus forms a total of a reference path to the sensor 5.1, 8.1 comprehensive transmission path.
• the measured value calculation from a plurality of sensor electrodes or sensor subareas SA, SB, SC, SD can thus be used to display the position and / or thickness of the object behind a wall on a display or to display an inhomogeneity such as a screw as a single object on the display.
• a mouse function on the display is also conceivable. Instead of the "bar" then the mouse function is shown on the display, wherein the billing of the traces can be done in the same way.
• the amplifier 4.5 Since the amplifier 4.5 sees only rough at the input in the regulated state of the circuit, it can amplify very high, or be designed as a high-gain limiting amplifier.
• the output signal of the amplifier 4.5 is the synchronous demodulation tor 4.6 supplied. This receives its necessary for demodulation clock signal over 4.18 from the clock generator 4.8.
• the synchronous demodulator 4.6 synchronously supplies the output signal of the amplifier 4.5 to the corresponding inputs of the integrating comparator 4.7 during the entire portion of a clock phase. However, it is also possible to demodulate only in sections.
• the output signals of the synchronous demodulator 4.6 that can be assigned to the two clock signals 4.12 and 4.13 are examined by the integrating comparator 4.7 for amplitude differences.
• the comparator 4.7 can be designed as a high-gain comparator circuit. Any deviation of the input voltages 4.15 and 4.17 leads to a corresponding deviation of the control value 4.16 from the current value. Due to the high sensitivity of the system, i. Due to the high gain, an approach function to the sensor in the direction of a Z-axis is also possible.
• the associated information can be taken from the amplitude of the traces. For example, e.g. in a mouse function, a finger detection e.g. up to 50 mm possible.
• the regulated voltage sources 4.9 and 4.10 are controlled inverted by means of inversion stage 4. 1 against each other with the control value 4.16. If the voltage of one of the regulated voltage sources rises, it drops accordingly in the other one. For the function of the sensor according to the invention, however, the voltage sources 4.9 and 4.10 need not necessarily be controlled against each other, it is also sufficient to control a voltage source.
• the control loop is closed via the voltage divider formed by R1, R4 and R2, R3.
• the route via R1 and R4 accordingly forms the reference to the route via R3 and R2.
• the control output 4.16 will thus assume a specific electrical value, which corresponds to a specific constructional capacitance value of the sensor electrode 5.2. If, for example, the sensor is placed on the wall, the capacitance of the two electrodes 5.2 and 5.3 changes. In this case, the area of the surrounding electrode 5.3 which actively acts on the surface of an object is preferably approximately the same size as the area of the sensor electrode 5.2.
• the capacitance change at the surrounding electrode 5.3 has virtually no effect on the control loop.
• the situation is different with the sensor electrode 5.2.
• the voltage will decrease due to the high resistance of R2, R3.
• an isochronous signal component arises at the input of the amplifier 4.5, which is immediately corrected again to "0.”
• the control value 4.16 changes accordingly.
• the voltage at the sensor electrode 5.2 is thus always kept equal to the voltage at C2.
• An increase in the capacitance at the sensor electrode thus causes no change in the voltage value at the sensor electrode, but leads to an increase in the voltage and thus the electric field 5.4 of the surrounding electrode 5.3.
• FIG. 6 shows the capacitance curve 6.1 of a sensor according to the prior art.
• a sensor When tilted or easily removed from the wall, there is an immediate change in capacity. If such a sensor is guided over a wall with irregularities, the error initially described in FIG. 2 arises.
• Fig. 7 shows the capacitance change, as it arises with the same tilting or easy removal of the sensor from the wall according to the method of the invention. Changes in the vicinity of the wall lead to almost no change in the capacity and thus also in the control value. Capacitance changes in areas further away from the sensor are however detected correctly.
• the high-resistance resistors R3 and R4 serve for the high-impedance decrease of the voltage signal at the sensor electrode 5.2. If their values are chosen equal to the values of R1 or R2, the signal to be detected is correspondingly reduced.
• the signal of the sensor electrode 5.2 or of the capacitor C2 can be taken directly via corresponding impedance transformers 4.21 and further processed with a subsequent differential amplifier 4.23.
• the signals of the voltage sources 4.9 and 4.10 are in common mode.
• the resistors R9 and R10 are then preferably equal to the input impedance of the input impedance of the impedance converter 4.21 selected or can be omitted with correspondingly high impedance input impedances of 4.21.
• the transmission clocks 4.12 and 4.13 have no phase shift.
• FIG. 8 A further embodiment of a sensor 8.1 according to the invention is shown in FIG. 8.
• the sensor area 5.2 was divided into four sensor subareas, ie SA, SB, SC and SD.
• Each sensor subarea is, according to FIG. 5, in each case encompassed by the corresponding surrounding electrode subarea 8.11.
• the sensor subregions may themselves in each case be completely or partially surrounded by a respective respective electrode.
• a measurement can now take place in such a way that in each case one electrode subarea is measured against the reference capacitance C2.
• the sensor portions may be measured against another portion, e.g. to decide whether it is an elongated beam or a small individual object behind the sensor.
• the measurement profiles of the sensor subarea SD against SB and SA against SC are shown.
• a bar 8.2 is performed from left to right under the sensor 8.1.
• the measurements of the sensor subareas SA to SD with respect to the reference capacitance C2 yield the measured value profiles 8.3, 8.4, 8.5 and 8.6.
• the position of the bar alone can be calculated from these measured value curves and displayed on a display 8.9 as bar 8.10. Additional information provides the ratio of the capacities of the sensor sections to each other.
• the capacitance ratio of the sensor subarea SD against the sensor subarea SB is shown in the measured value course 8.7, and the capacitance ratio of the sensor subarea SA against the sensor subarea SC in the measured value course 8.8.
• the measured value course 8.8 does not contain any information, for example, since the bar influences the sensor subareas SA and SC the same during its movement. Thus, the exact position of the bar can be calculated and displayed accordingly. From the size of the measured value changes in the measured value course can be additionally closed on the width of the bar and this is shown accordingly in the display.
• the IC 909.05 includes five freely configurable regulated current sources 10.1 to 10.5, (corresponding to the regulated voltage sources 4.9, 4.10) an input 10.6, the digital version of the signal processing described in the invention, an internal Data processing option and a corresponding data transfer 10.7.
• Fig. 10 is shown by the example of the wiring of the regulated current source 10.1, as the resistors used in the invention described above can be connected for a sensor electrode or surrounding electrode, as well as the wiring for a reference capacitance C2.

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• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Remote Sensing (AREA)
• Geology (AREA)
• Environmental & Geological Engineering (AREA)
• Electromagnetism (AREA)
• General Life Sciences & Earth Sciences (AREA)
• General Physics & Mathematics (AREA)
• Geophysics (AREA)
• Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)
• Geophysics And Detection Of Objects (AREA)
• Electronic Switches (AREA)

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• 2009
  • 2009-12-09 DE DE102009057439A patent/DE102009057439B4/de not_active Revoked
• 2010
  • 2010-10-25 WO PCT/EP2010/006507 patent/WO2011054459A1/de not_active Ceased
  • 2010-10-25 EP EP10776306.2A patent/EP2494382B1/de active Active
  • 2010-10-25 JP JP2012535668A patent/JP5836960B2/ja active Active
  • 2010-10-25 CA CA2775638A patent/CA2775638A1/en not_active Abandoned
  • 2010-10-25 CN CN201080048964.3A patent/CN102741711B/zh active Active
  • 2010-10-26 US US12/911,806 patent/US9035662B2/en active Active

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