DE102019133249A1 - Passive sensor - Google Patents

Abstract

The invention relates to a passive sensor (1) and a measuring system (1, 2) for controlling the sensor (1) by means of an excitation signal (SHF) and for determining the corresponding measured value based on the received evaluation signal (EHF). The sensor (1) is based on two signal paths (11, 13) each with a diode (111, 131) and an impedance (112, 132) to which the receiving antenna (12) and the transmitting antenna (14) are connected accordingly. According to the invention, the impedance (111) of one signal path (11) is designed in such a way that its value depends on the measured variable. As a result, an electromagnetic evaluation signal (EHF) is generated in a passive manner, the amplitude spectrum of which has constant components (A13) on the one hand, but also components (A11) that are dependent on the measurement impedance. A higher-level unit (2) of the measuring system (1, 2) can use this to determine the measured value as an absolute variable. Since it is not strictly prescribed according to the invention whether the measuring impedance (112) is designed as a resistive, capacitive or inductive component, the sensor (1) can potentially determine many different measured variables.

Description

The invention relates to a passive sensor and a corresponding measuring system for operating the sensor, in particular for use in automation technology.

In automation technology, in particular in process automation technology, measurement systems are often used that are used to record and / or influence various measured variables. The measured variable to be determined can be, for example, a fill level, a flow rate, a pressure, the temperature, the pH value, the redox potential, the conductivity or the dielectric value of a product. To acquire the corresponding measured values, the measuring systems each include suitable sensors or are based on suitable measuring principles. A large number of different sensors and measuring systems are manufactured and sold by the Endress + Hauser group of companies.

Often, the respective measured variable has to be measured in a difficult-to-access location, such as inside a closed container, on movable fixtures, or in places where there is a risk of explosion. This prevents a wired connection and a battery-based energy supply for the sensor. From the publication US20090272814A1 Passive reflectors are therefore known that can be located. In the corresponding method, an excitation signal in the form of an electromagnetic wave is received by a passive sensor and the frequency is doubled with the aid of a diode. The corresponding evaluation signal is then sent back to the evaluation device at twice the frequency. With this method, however, only the presence of the sensor can be detected and no further information can be transmitted. Passive pressure sensors based on surface acoustic waves are known from US publication 4454440 A. In this case, however, the measuring principle cannot simply be transferred to other measured variables.

The invention is therefore based on the object of providing a passive sensor for process automation applications which in principle can be used to measure a wide variety of measured variables.

• - Einen ersten Signalpfad, mit zumindest
  • ◯ einer ersten Diode,
  • ◯ einer von der Messgröße abhängigen Mess-Impedanz, und
  • ◯ einem ersten Anschluss für einen ersten Pol
• - einer zweipoligen Empfangsantenne, deren Impedanz auf die Frequenz eines definierten Anregungssignals angepasst ist,
• - einen quasi parallelen, zweiten Signalpfad mit zumindest
  • ◯ einer zweiten Diode,
  • ◯ einer Referenz-Impedanz, deren Wert vorzugsweise in etwa dem Wertebereich der Mess-Impedanz entspricht, und
  • ◯ einem zweiten Anschluss, and dem der zweite Pol der Empfangsantenne angeschlossen ist,
• - einer zweipoligen Sende-Antenne, deren Pole zur Aussendung eines Auswertungssignals jeweils an einem Pfadanfang und an einem Pfadende der zwei Signalpfade kontaktiert sind. Dabei ist die Sende-Antenne vorzugsweise auf die doppelte Frequenz des Anregungssignals abgestimmt.

The invention solves this problem with a passive sensor for determining a defined measured variable, such as temperature, pressure, humidity or a limit level. The sensor comprises the following components:

• - A first signal path, with at least
  • ◯ a first diode,
  • ◯ a measurement impedance dependent on the measured variable, and
  • ◯ a first connection for a first pole
• - a two-pole receiving antenna, the impedance of which is adapted to the frequency of a defined excitation signal,
• - A quasi-parallel, second signal path with at least
  • ◯ a second diode,
  • Referenz a reference impedance, the value of which preferably corresponds approximately to the value range of the measurement impedance, and
  • ◯ a second connection to which the second pole of the receiving antenna is connected,
• - A two-pole transmitting antenna, the poles of which are contacted for sending an evaluation signal at the beginning of the path and at the end of the two signal paths. The transmitting antenna is preferably tuned to twice the frequency of the excitation signal.

This structure according to the invention enables an electromagnetic evaluation signal to be generated in a passive manner, the amplitude spectrum of which has constant components on the one hand, but also components that are dependent on the measurement impedance. The measured variable can thus be determined from the component that is dependent on the measurement impedance, the constant component of the amplitude spectrum being dependent on the reference impedance. This allows the measured value to be determined as an absolute variable. Because it is not strictly prescribed according to the invention whether the measurement impedance of the sensor is designed as a resistive, capacitive and / or also as an inductive component, the sensor can potentially be used to determine a large number of measured variables. With a resistive design, the measurement impedance can be designed, for example, as a temperature-dependent resistor, in particular as a Pt100 element, or as a strain gauge. In the case of a capacitive design, the measurement impedance can be designed, for example, as a humidity- or pressure-dependent capacitor.

In a possible extension of the sensor according to the invention, a third diode can also be arranged in the first signal path in the same orientation as the first diode (i.e. in relation to the beginning of the path in the opposite orientation to the second diode), the first connection to the first pole of the receiving antenna in this case the first diode and the third diode is arranged. Similarly, in the second Signal path in the same orientation to the second diode (again in relation to the beginning of the path in the opposite orientation to the first and possibly third diode) in turn a fourth diode can be arranged. The second connection to the second pole of the receiving antenna is in turn arranged between the second diode and the fourth diode. In this design variant, the four diodes act as a bridge rectifier circuit, whereby the evaluation signal can be generated with increased efficiency and thus increased power can be transmitted.

• ◯ das Anregungssignal gen Sensor auszusenden,
• ◯ ein von der Sendeantenne des Sensors ausgesendetes Auswertungssignal zu empfangen,
• ◯ im Auswertungssignal eine erste Amplitude, die dem ersten Signalpfad zuordbar ist, zu erfassen,
• ◯ im Auswertungssignal eine zweite Amplitude, die dem zweiten Signalpfad zuordbar ist, zu erfassen,
• ◯ anhand der ersten Amplitude und der zweiten Amplitude die Messgröße zu bestimmen.

According to the invention, the passive sensor is operated as part of a measuring system which, in addition to the sensor according to one of the previously described embodiment variants, includes a higher-level unit for controlling the sensor. The higher-level unit is designed to

• ◯ send the excitation signal to the sensor,
• ◯ to receive an evaluation signal sent by the transmitting antenna of the sensor,
• ◯ to detect a first amplitude in the evaluation signal that can be assigned to the first signal path,
• ◯ to detect a second amplitude in the evaluation signal, which can be assigned to the second signal path,
• ◯ to determine the measured variable based on the first amplitude and the second amplitude.

In the context of the invention, the term “unit” is understood to mean in principle any electronic circuit that is designed to be suitable for the intended use. Depending on the requirements, it can therefore be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit such as an FPGA or a storage medium in conjunction with a program. The program is designed to carry out the corresponding process steps or to apply the necessary arithmetic operations of the respective unit. In this context, different electronic units of the fill level measuring device in the sense of the invention can potentially also access a common physical memory or be operated by means of the same physical digital circuit.

So that the measuring system can be used within the scope of radio approvals, the higher-level unit should preferably be designed in such a way that the excitation signal is generated with a frequency that lies in one of the ISM bands (“industrial, scientific and medical band”).

To determine the measured variable, the higher-level unit can be configured, for example, in such a way that the first amplitude and the second amplitude are determined by means of a Fourier transformation, e.g. B. in that the higher-level unit assigns the corresponding amplitude to the respective signal path via a previously known frequency in the Fourier spectrum. The measured variable can be determined by the superordinate unit calculating a ratio between the first amplitude and the second amplitude, the measured value being subsequently determined by the superordinate unit on the basis of the calculated ratio.

• - Aussenden des Anregungssignals gen Sensor,
• - Empfang des von der Sendeantenne ausgesendeten Auswertungssignals,
• - Erfassung einer erste Amplitude des Auswertungssignals, die dem ersten Signalpfad zuordbar ist,
• - Erfassung einer zweiten Amplitude des Auswertungssignals, die dem zweiten Signalpfad zuordbar ist,
• - Bestimmung de Messgröße anhand der ersten Amplitude und der zweiten Amplitude.

Corresponding to the measuring system according to the invention, the object on which the invention is based is also achieved by a corresponding method for operating the measuring system. Accordingly, the procedure comprises the following procedural steps:

• - Sending the excitation signal to the sensor,
• - Reception of the evaluation signal sent by the transmitting antenna,
• - Detection of a first amplitude of the evaluation signal, which can be assigned to the first signal path,
• - Detection of a second amplitude of the evaluation signal, which can be assigned to the second signal path,
• - Determination of the measured variable on the basis of the first amplitude and the second amplitude.

• 1: Ein erfindungsgemäßes Mess-System an einem Behälter,
• 2: Eine erste Ausführungsvariante des erfindungsgemäßen Sensors
• 3: Eine zweite Ausführungsvariante des erfindungsgemäßen Sensors,
• 4: einen zeitlichen Signal-Verlauf des Auswertungssignals, und
• 5: ein Frequenz-Spektrum des Auswertungssignals.

The invention is explained in more detail with the aid of the following figures. It shows:

• 1 : A measuring system according to the invention on a container,
• 2 : A first variant of the sensor according to the invention
• 3rd : A second variant of the sensor according to the invention,
• 4th : a signal curve over time of the evaluation signal, and
• 5 : a frequency spectrum of the evaluation signal.

For a general understanding of the invention is in 1 a measuring system 1 , 2 on a container 3rd of a process plant. The measuring system is used for this 1 , 2 to determine a measured variable that is related to the corresponding process, for example the temperature or the pressure in the container 3rd , a defined limit level of the product 4th , or a dielectric value or a conductivity of the filling material 4th . This can be the case with the filling material 4th to liquids such as beverages, paints, cement or fuels such as liquefied gases or Trade mineral oils. However, it is also conceivable to use the measuring system 1 , 2 for bulk goods 4th such as grain.

To determine the corresponding measured value, the measuring system includes 1 , 2 a sensor 1 on the inside wall of the container 3rd is arranged and is therefore in contact with the process. If it is, for example, a pressurized container 3rd acts, the sensor can 1 However, it cannot be connected by cable without considerable effort in order to be supplied with energy or to transmit the measured value.

According to the invention is the sensor 1 therefore designed passively and is handled by a higher-level unit 2 by means of an electromagnetic excitation signal S _HF , which has a defined frequency, is driven. Unless the parent unit 2 is designed, the excitation signal S _HF The measuring system requires the transmission to be transmitted at a frequency that lies in one of the freely usable ISM bands 1 , 2 advantageously no radio license.

As in 1 is shown, the sensor is transmitting 1 the measured value by means of a corresponding evaluation signal E _HF to the higher-level unit 2 , where the sensor 1 is designed in such a way that the measured value is based on specific amplitude components contained in the evaluation signal E _HF are contained, is determinable. The higher-level unit is accordingly 2 designed to be in the evaluation signal E _HF a specific first amplitude A ₁₁ and a specific second amplitude A ₁₃ to capture so that based on these two specific amplitudes A ₁₁ , A ₁₃ the measurand can be determined.

The parent unit 2 can with the in 1 The embodiment shown may in turn be connected to a process control system of the process plant (not explicitly in 1 shown). For this purpose “PROFIBUS”, “HART”, “Wireless HART” or “Ethernet” can be implemented as interfaces. This can be used to transmit the measured value, for example. However, other information about the general operating status of the measuring system can also be used 1 , 2 communicated.

2 shows a first variant embodiment of the sensor according to the invention 1 , by means of which upon receipt of the excitation signal S _HF passively the corresponding evaluation signal E _HF is generated: The core of the circuit are two signal paths that are parallel in terms of circuitry 11 , 13th with one diode each 111 , 131 and an impedance 112 , 132 . The beginning of the path 130 , i.e. the potential in front of the respective diode 111 , 131 and the end of the path 135 (i.e. the potential behind the impedance 112 , 132 ) of both signal paths 11 , 13th are each electrically contacted with one another. Here are the first diode 111 and the second diode 131 in relation to the beginning of the path 130 or to the end of the path 135 interconnected in the same direction.

According to the invention, the first impedance 112 depending on the measurand to be measured. In the case of a temperature to be measured, the first impedance 112 be designed as a temperature-dependent resistor, for example as a PT100. In the case of a pressure to be measured, the first impedance 112 be designed as resistive strain gauges or as pressure-dependent capacitance. Depending on the measured variable to be measured, it is in principle also conceivable to use the first impedance 112 designed as a variable inductance.

Regardless of its implementation, it is related to the first impedance 112 advantageous if the value of the reference impedance 132 approximately up to approx. +/- 50% of the value range of the measurement impedance 112 corresponds to. With a PT100 as the first impedance 112 is the value of the reference impedance according to this specification 131 with approx. 50 ohms to 200 ohms, in particular between 80 ohms and 160 ohms.

Between the respective diode 111 , 131 and the impedance 112 , 132 the signal paths 11 , 13th is one connection each 113 , 133 to a corresponding pole of a two-pole receiving antenna 12th educated. The receiving antenna 12th serves to couple the excitation signal S _HF into the sensor 1 . The diodes cause 111 , 114 in the respective signal path 11 , 13th that the excitation signal S _HF in relation to the potential difference between the beginning of the path 135 and the end of the path 130 is rectified, resulting in a frequency doubling of the excitation signal S _HF leads.

How out 2 can be seen are the beginning of the path 130 and the end of the path 135 the signal paths 11 , 13th at the corresponding node, each with one pole of a two-pole transmitting antenna 14th contacted. Accordingly, the rectified excitation signal S _HF via the transmitting antenna 14th as an evaluation signal E _HF gen superordinate unit 2 radiated. As the excitation signal S _HF in relation to the potential difference between the beginning of the path 135 and the end of the path 130 is quasi doubled in frequency by the rectification, it is advantageous if the impedance of the transmitting antenna 14th to twice the frequency of the excitation signal S _HF is adapted.

The course of the evaluation signal over time E _HF , represented as the potential difference between the beginning of the path 130 and the end of the path 135 the signal paths 11 , 13th , is in 4th shown in more detail: As can be seen from the corresponding graph, the rectification of the excitation signal is S _HF can be seen from the fact that every other amplitude A ₁₁ , A ₁₃ of the evaluation signal E _HF either the first Signal path 11 or the second signal path 13th is assignable. It can be seen from this that the first amplitude A ₁₁ depending on the measured value-dependent impedance 112 is, while the respective second amplitude A ₁₃ is constant and of the value of the reference impedance 132 depends. Both amplitudes are here A ₁₁ , A ₁₃ in the same order of magnitude as the measurement impedance 112 and the reference impedance 132 again lie in the same range of values. This simplifies the subsequent evaluation of the evaluation signal E _HF by the higher-level unit 2 .

Since the ratio of the amplitudes A ₁₁ , A ₁₃ approximately proportional to the value of the measuring impedance 112 changes, the parent unit can 2 the measured value based on the evaluation signal E _HF determine by taking a ratio of the two specific amplitudes A ₁₁ , A ₁₃ forms to each other. Can identify the parent unit 2 the respective amplitude A ₁₁ , A ₁₃ beforehand, for example by means of a Fourier transformation. The higher-level unit can 2 the corresponding amplitude via a respectively previously known frequency f ₁₁ , f ₁₃ A ₁₁ , A ₁₃ in the associated frequency spectrum for the respective signal path 11 , 13th assign. In this regard, the frequency f ₁₃ corresponds to that of the amplitude A ₁₃ of the second signal path 13th corresponds to the frequency of the excitation signal S _HF . The one to the amplitude A ₁₁ of the first signal path 11 The corresponding frequency f ₁₁ can in turn be determined, for example, by a calibration measurement series under known measurement conditions. A corresponding Fourier spectrum of the evaluation signal is shown E _HF in 5 .

A second variant for realizing the sensor according to the invention 1 is in 3rd shown. In contrast to the in 2 The embodiment variant shown include the two signal paths 11 , 13th another diode each 114 , 134 that in relation to the first diode 111 or to the second diode 131 in the same direction in the signal path 11 , 13th is arranged. This means the first diode 111 and the third diode 114 in relation to the end of the path 135 in the opposite direction to the second diode 131 and to the fourth diode 134 are interconnected.

Furthermore, the in 3rd The embodiment shown is the first connection 113 to the first pole of the receiving antenna 12th between the first diode 111 and the third diode 114 arranged. The second connection 133 to the second pole of the receiving antenna 12th is between the second diode ( 131 ) and the fourth diode arranged 134. This interconnection of the four diodes 111 , 131 , 114 , 134 corresponds with regard to the coupled-in excitation signal S _HF a bridge rectifier. The advantage here is that the evaluation signal E _HF compared to the in 2 shown variant of the sensor 1 is generated with an increased stability, so that the evaluation signal E _HF from the parent unit 2 for example, even when the distance to the sensor is greater 1 Will be received. Advantageous at the in 2 shown variant of the sensor 1 however, that is the amplitude of the incoming excitation signal S _HF only the breakdown voltage of the two diodes 111 , 131 must exceed so that the evaluation signal E _HF is generated. The higher-level unit can take the measured value 2 at the in 3rd shown variant of the sensor 1 in the same way as the procedure described in 4th and 5 in relation to the variant of the sensor 1 in 2 is described.

List of reference symbols

1

sensor

2

Parent unit

3

container

4th

Filling material

11

First signal path

12th

Receiving antenna

13th

Second signal path

14th

Transmitting antenna

111

First diode

112

Measurement impedance

113

First connection

114

Third diode

130

Beginning of the path

131

Second diode

132

Reference impedance

133

Second connection

134

Fourth diode

135

End of the path

A11

First amplitude

A13

Second amplitude

EHF

Evaluation signal

f11, 13

Frequencies

SHF

Excitation signal

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 20090272814 A1 [0003]

Claims (13)

Passive sensor for determining a measured variable, comprising the following components: - A first signal path (11), with at least o a first diode (111), o a measurement impedance (112) dependent on the measured variable, and o a first connection (113) for a first pole - a two-pole receiving antenna (12), the impedance of which _{is adapted to the frequency of a defined excitation signal (S HF} ), - a second signal path (13), with at least o a second diode (131), o a reference impedance (132), and o a second connection (133) to which the second pole of the receiving antenna (12) is connected, - a two-pole transmitting antenna (14), the poles of which are used to transmit an evaluation _{signal (E HF} ) at a path start ( 130) and at a path end (135) of the signal paths (11, 13) are contacted. Sensor after Claim 1 , wherein the value of the reference impedance (132) corresponds approximately to the value range of the measurement impedance (112). Sensor after Claim 1 or 2 , wherein a third diode (114) is arranged in the first signal path (11) in the same orientation as the first diode (111), the first connection (113) to the first pole of the receiving antenna (12) between the first diode (111) and the third diode (114) is arranged, and / or wherein a fourth diode (134) is arranged in the second signal path (13) in the same orientation as the second diode (131), the second connection (133) to the second pole of the receiving antenna (12 ) is arranged (134) between the second diode (131) and the fourth diode. Sensor according to one of the preceding claims, wherein the measuring impedance (111) is designed as a resistive component. Sensor after Claim 4 , wherein the measuring impedance (111) is designed as a temperature-dependent resistor, in particular as a Pt100, or wherein the measuring impedance is designed as a strain gauge. Sensor after Claim 1 to 3rd , the measuring impedance (111) being designed as a capacitive component. Sensor after Claim 6 , wherein the measuring impedance (111) is designed as a humidity or pressure-dependent capacitor. Measuring system, comprising: - a sensor (1) according to at least one of the preceding claims, - a superordinate unit (2) which is designed to o _{transmit the excitation signal (S HF} ), o one transmitted by the transmitting antenna (14) Evaluation signal (E _HF ) to be received, o in the evaluation signal (E _HF ) a first amplitude (A ₁₁ ), which can be assigned to the first signal path (11), to be recorded, o in the evaluation signal (E _HF ) a second amplitude (A ₁₃ ) which can be assigned to the second signal path (13), o to determine the measured variable _{on the basis of the first amplitude (A 11} ) and the second amplitude (A _13). Measuring system according to Claim 8 , wherein the superordinate unit (2) is designed _{to generate the excitation signal (S HF} ) with a frequency which is in one of the ISM bands. Measuring system according to Claim 8 or 9 , the higher-level unit (2) being designed to determine the amplitudes (A ₁₁ , A ₁₃ ) by means of a Fourier transformation. Measuring system according to Claim 10 , the higher-level unit (2) being designed _{to assign the corresponding amplitude (A 11} , A ₁₃ ) to the respective signal path (11, 13) via a previously known frequency (f ₁ , f _{2) in the Fourier spectrum.} Measuring system according to Claim 8 to 11 , wherein the superordinate unit (2) is designed _{to calculate a ratio between the first amplitude (A 11} ) and the second amplitude (A ₁₃ ), and the measured variable is determined on the basis of the calculated ratio. Method for determining the measured variable by means of the measuring system according to one of the Claims 8 up to twelve, comprising the following process steps: - sending the excitation signal (S _HF ) to the sensor (1), - receiving the evaluation signal (E _HF ) sent out by the transmitting antenna (14), - detecting a first amplitude (A ₁₁ ) of the evaluation signal (E _HF ), which can be assigned to the first signal path (11), - Detection of a second amplitude (A ₁₃ ) of the evaluation _{signal (E HF} ), which can be assigned to the second signal path (13), - Determination of the measured variable on the basis of the first amplitude (A ₁₁ ) and the second amplitude (A ₁₃ ).

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