WO2019106025A1

WO2019106025A1 - Impedance limit level sensor

Info

Publication number: WO2019106025A1
Application number: PCT/EP2018/082869
Authority: WO
Inventors: Karl Griessbaum; Christian WEINZIERLE; Jürgen Haas
Original assignee: Vega Grieshaber Kg
Priority date: 2017-11-30
Filing date: 2018-11-28
Publication date: 2019-06-06
Also published as: DE102017128440A1

Abstract

An impedance limit level sensor (100) having: - a measurement probe (102), the capacitance of which can be influenced by a medium surrounding the measurement probe (102), - a measurement oscillating circuit, in which the measurement probe (102) is arranged as a capacitance-determining element, - an electronics unit (101) having a signal generator () for exciting the measurement oscillating circuit and a signal detector (104) for determining a response signal of the measurement oscillating circuit, - a signal processing unit () for generating a measurement signal, which is connected to the electronics unit (101) and wherein the impedance limit level sensor (100) is formed as a two-wire field device and has an intermediate energy store (304) for at least partially supplying the impedance limit level sensor (100) with energy.

Description

Impedance level sensor

The present invention relates to an impedance limit

Standensor according to the preamble of patent claim 1 and a method for operating such a sensor.

Impedanzgrenzstandsensoren are basically known from the prior art, for example. For the measurement of limits or levels be known. Typical applications for detecting a predefined level are process vessels, such as process tanks, storage tanks, silos or pipelines in the process industry. Impedance threshold sensors are often referred to as so-called limit switches, i. to determine whether a filling medium exceeds or falls below a certain filling level, the so-called limit level, in different liquids, as well as granulated and pulverized bulk materials.

There are also other types of limit switches or limit sensors known, the conditions depending on the application, process conditions and properties of the filling medium are selected. In addition to impedance limit sensors, sensors that operate according to the TDR (Time Domain Reflectometry) principle, or vibration level sensors or capacitive sensors are used. A switching command of the limit switch can example as filling or emptying start or stop to accordingly avoid overflowing or emptying of the respective process container.

In the present application, instead of the term impedance threshold sensor for simplicity, the Be handles impedance sensor and limit switch equivalent used.

A known impedance sensor 100 is shown in FIG. FIG. 1 shows a simplified sectional view with circuit gaps of an impedance sensor 100 according to the prior art. Essentially, the impedance sensor 100, hereinafter also referred to as a limit level sensor or limit level detector, according to the prior art from an electronics unit 101 and a probe 102. The probe 102, in the present embodiment Ausfüh approximately as a series resonant circuit formed between egg ner measuring electrode 106 and a reference electrode 108 forms a measuring capacitance 110, which is connected to a discrete inductance 109 to the designed as a resonant circuit resonant circuit.

The measuring electrode 106 is rotationally symmetrical to a longitudinal axis L of the impedance sensor 100 is formed and separated via an insulation 107 of a process chamber 90. Advantageously, the discrete inductance 109 is selected so that a resonant frequency fres of the resonant circuit for different media or cover conditions (empty, full and dirty) is set between 100 MHz and 200 MHz.

An amount of a frequency-varying complex impedance | Z | This measuring resonant circuit is advantageously analyzed between 100 MHz and 200 MHz, ie the measuring resonant circuit is excited by means of a frequency generator 103 with a frequency sweep with frequencies between 100 MHz and 200 MHz and a response signal (frequency response) of the measuring resonant circuit is detected by a frequency detector 104. Be is a medium in the range of the measuring probe 102, the impedance behavior of the measuring resonant circuit changes, ie in particular special shifts its resonant frequency fres, at which a minimum of the impedance is formed. A frequency sweep is understood to mean the sequential excitation with a plurality of successive frequencies within a frequency range, wherein the frequency range should ideally contain all possible resonance frequencies of the measuring oscillating circuit.

Specifically, the frequency response with respect to a frequency change Af and a change in the amplitude of a mini mum of the impedance DZ, also referred to as a change in amplitude, is evaluated and derived therefrom Switching command generated.

In Figure 2, the Fre quency responses of the impedance sensor 100 are listed by way of example for the medium ketchup according to the prior art.

A first curve 200 shows the resonance behavior of a clean probe 102. Shown is the magnitude of the impedance Z over the frequency f.

The behavior of a ketchup-adhered measuring probe 102 is shown in a second curve 201 and that of a completely ketchup-covered measuring probe 102 in a curve 202.

Switching commands (empty, full) are realized by the evaluation and control unit 105, wherein according to the prior art only the minima of the resonance curves are used for the evaluation. These are evaluated with respect to a Fre quenzänderung Af and amplitude change DZ. If the minimum of the resonance curve is in a first region I, then the evaluation and control unit 105 transmits the switching If the minimum is, however, in a second area II, the switching command "full" is output. The two defined switching ranges I, II can be factory-programmed into the impedance sensor 100 or adjusted and changed by egg NEN customer comparison. Ideally, the ranges should be defined so that the default settings are sufficient for as many different media as possible, since customer matching is time-consuming and therefore undesirable.

The state-of-the-art level sensors 100 signal the switching state by means of one or more switching outputs, e.g. in the form of a transistor output, and are powered by a separate line. The limit state sensors 100 according to the prior art are offered only with one or two switching outputs. These Schaltaus output lines and the two supply lines are placed on a connector of the sensor and must be wired accordingly with additional effort. This cabling Ver is perceived as a disadvantage.

It is the object of the present invention to provide an impedance proximity sensor, which allows a verrin siege cabling.

This object is achieved by an impedance threshold sensor having the features of claim 1.

Advantageous developments are the subject of dependent claims.

An inventive impedance threshold sensor with a measuring probe by a medium surrounding the probe in a Capacitance can be influenced, a measuring resonant circuit in which the probe is arranged as a capacitance determining element, an electronic unit with a signal generator to the movement of the measuring resonant circuit and a signal detector for He mediation one response signal of the resonant circuit and a signal processing unit for generating a measurement signal, which is connected to the electronic unit is characterized by the fact that the impedance threshold sensor is designed as a two-wire field device and an energy buffer for at least partially supply the impedance limit sensor with energy.

A two-wire field device according to the present inven tion is understood to be a field device which is connected via two lines to a higher-level unit, wherein both a power supply and a measured value transmission takes place via these two lines.

The energy and / or signal transmission between the Zweilei ter field device and the superordinate units is carried out according to the known 4 mA to 20 mA standard, in which a 4 mA to 20 mA current loop, i. a two-wire line is formed between the field device and the higher-level unit. In addition to the analogue transmission of signals, there is the possibility that the measuring devices, according to various other protocols, in particular digital protocols, transmit or receive further information from the higher-level unit. By way of example, the HART protocol or the Profibus PA protocol may be mentioned here.

The power supply of these field devices is also via the 4 mA to 20 mA current signal, so that in addition to the Zweidrahtlei device no additional supply line is necessary. Around the wiring and installation costs and the security measures, for example, when used in Explosions protected areas to keep as low as possible, it is also not desirable to provide additional power supply lines.

With the impedance threshold sensor according to the invention, it is thus possible to significantly reduce the required cabling effort and, despite the limited availability of energy which is made available via the two-wire line, to enable a reliable measurement.

The energy store can advantageously be designed as a capacitor or as an accumulator. In this way, a high number of charging cycles, high availability and high energy density of the energy storage can be achieved.

In one development, the impedance sensor can have an energy management device which is connected to the energy intermediate memory and / or a controller, for example, in an evaluation and control unit and / or measuring electronics. In this way, efficient energy management can be achieved, for example, the controller and / or the Mes selektronik for the duration in which energy must be cached, disabled or put into a power saving mode ver.

For communication, for example with external operating units, external display units, external display and operating units or other devices, the impedance threshold sensor may additionally have a near-distance radio module. The term Nahdistanzfunkmodul should be understood in the present application radio modules that have a maximum range of a few meters. These are, in particular, radio modules that operate in accordance with one of the Bluetooth, Bluetooth Low Energy, ZigBee, WirelessHART, ISAIOO wireless solutions, WLAN or NFC standards.

The near distance radio module preferably has its own

Microcontroller as a second controller, which controls the radio communication. Since the input of messages via the radio communication is not predictable, the microcontroller of the Nahdistanzfunkmoduls is only so far placed in a power saving mode that a reception of messages via the radio module remains guaranteed.

Preferred is an embodiment with a second controller and a Bluetooth low-energy radio module.

A method according to the invention for operating an impedance proximity sensor according to the present application has the following steps:

- Checking a currently available amount of energy,

- if the minimum amount of energy required for a successful measurement is available,

i) activating a controller and measuring electronics, ii) performing an impedance measurement,

iii) output a measured value and

after completion of the measurement or when the minimum energy level is not reached

iv) buffering the energy transmitted by the two-wire line. In order to be able to carry out a new measurement more quickly, the controller and / or the measuring electronics can also be deactivated or put into an energy-saving mode.

The present invention will be explained below with reference to Ausfüh tion examples and with reference to the accompanying Figu ren in detail. Show it:

1 shows a simplified sectional view of an impedance sensor according to the prior art (already discussed),

FIG. 2 shows the impedance behavior of the impedance sensor according to FIG. 1 (already treated),

Figure 3 is a simplified block diagram of an impedance

proximity sensor according to the present application and

FIG. 4 shows a method sequence for operating the sensor according to FIG. 3.

FIG. 3 shows a simplified block diagram of an impedance level sensor 100 in accordance with the present application.

In order to be able to execute the impedance sensor 100 as a two-wire field device, the latter has a power supply unit 301-304 which forms a two-wire interface and essentially has a current regulator 301, a voltage regulator 302, an energy management device 303 and an energy buffer 304.

Since both a power supply and an output of the switching state via two lines, the power supply has the current controller 301, which can output the possible switching states "uncovered" and "covered" as a loop current of, for example, 8 mA or 16 mA. In addition, the current controller 301 is also designed to output a device error, for example. In the form of a third current value, which differs from the two switching states.

In the simplest case, such a current regulator 301 is designed as a longitudinal transistor, which depends on the detected state of the sensor, e.g. impresses the current value 8 mA in the state "uncovered" and 16 mA in the state "covered" in the supply loop. For the signaling of Fehlerzu conditions, it is common to let a current value less than 3, 6 mA or greater than 21 mA to flow.

About the additional voltage control 302 is sicherge notes that the energy which is available in the energy storage 304 for the subsequent sensor and the evaluation and Steuerein unit 105 is not fed back into the two-wire line and thus distorts the switching state. Furthermore, a voltage applied to the energy buffer 304 is limited to a maximum value so that it is not operated outside the values permissible for operation. The energy buffer 304 has the task of buffering the power available through the two-wire supply for the subsequent measurement, i. to save between.

In this case, the situation may arise that a power consumption of the sensor system 306, which in this case particularly includes the frequency generator 103, the frequency detector 104 and the measuring probe 102, the evaluation and control unit 105 for the duration of a measurement, the instantaneous power, which over the two Supply lines is available exceeds. In this case, the available de energy is buffered in the energy storage 304 over a long time, so long that sufficient energy is present in this memory for a measurement. The current state of charge of the intermediate energy storage 304 is checked by the energy management unit 303. To shorten the time to reach this state, for example, the sensor 306 can be deactivated during this time and the controller of the evaluation and control unit 105 can be in a power-saving mode.

These differences in power consumption are suitably controlled by an energy management and organized accordingly.

A possible sequence for operating the arrangement according to FIG. 3 is shown in FIG.

Before beginning a measurement, the current status of the energy buffer 304 is detected in step 401. On the basis of the stored energy, a decision is made in step 402 as to whether a measurement can be carried out. If sufficient energy is stored, an impedance measurement is performed in step 403 and the result is evaluated in step 404. Dependent on a position of the minimum of the impedance curve, a corresponding switching state is output in step 405.

If it is determined in step 402 that too little energy is still stored for performing a measurement in the energy buffer 304, or after performing a measurement, the system returns to step 401. Refer to the list of signs

90 process space

100 impedance sensor

101 electronics unit

102 measuring probe

103 frequency generator

104 frequency detector

105 evaluation and control unit

106 measuring electrode

107 insulation

108 reference electrode / housing

109 inductance

110 measuring capacity

200 first turn

201 second turn

202 third turn

301 current regulator

302 voltage regulator

303 energy management unit

304 energy intermediary

401-405 procedural steps

I first area

II second area

Af frequency change

Dz amplitude change

fres resonance frequency

Claims

claims

1. Impedance level sensor (100) with

a measuring probe (102) passing through a measuring probe

(102) surrounding medium can be influenced in a capacity,

a measuring resonant circuit in which the measuring probe 102 is arranged as a capacitance-determining element,

- An electronics unit (101) with a signal generator

(103) for exciting the measuring resonant circuit and a signal detector (104) for determining a response signal of the measuring oscillating circuit,

- A signal processing unit (105) for generating a measurement signal which is connected to the electronic unit (101) and

That is, the impedance threshold sensor (100) is configured as a two-wire field device and has an energy buffer (304) for at least partially supplying the impedance level sensor (100) with energy.

2. Impedance threshold sensor (100) according to claim 1,

That is, the energy buffer (304) is designed as a capacitor or as an accumulator.

3. Impedance threshold sensor (100) according to one of the preceding claims,

marked by

an energy management device (303), which is connected to the energy buffer (304), a controller of an evaluation and control unit (105) and a measuring electronics (101).

4. Impedanzgrenzstandsensor (100) according to one of the preceding claims,

marked by

the complete power supply of the sensor through the two-wire line.

5. A method for operating an impedance threshold sensor (100) according to one of the preceding claims, comprising the following steps:

- Checking a currently available amount of energy,

i) performing an impedance measurement,

(ii) outputting a reading, and after completion of the measurement or when the minimum amount of energy has not been reached,

iii) buffering the energy transmitted by the two-wire line.

6. The method according to claim 5,

That is, a controller of an evaluation and control unit 105 and / or an electronics unit 101 is activated before performing the measurement, and a

after completion of the measurement or if the minimum energy quantity is not reached, the controller and / or the measuring electronics (101) is deactivated or put into energy-saving mode.