DE102021112449A1 - Point level sensor with self-test function, procedure for checking the functionality of a point level sensor - Google Patents

Abstract

The invention relates to a point level sensor (10) with a self-test function, the point level sensor (10) having a sensor unit (16) by means of which reaching a defined point level can be detected. The point level sensor (10) is intended to ensure the safest possible operation of a process with the point level sensor (10).The level limit sensor (10) has at least one means for automatically checking the functionality (20), with at least one means (20) serving to trigger a switching event independently of the level limit being reached and/or to check a switching event to reach the limit.

Description

The invention relates to a limit level sensor with a self-test function according to the preamble of claim 1. The invention also relates to a method for checking the functionality of a limit level sensor according to patent claim 7.

Point level sensors are basically known from the prior art. A typical application for point level sensors is the detection of a predefined filling level in a process container, such as a process tank, a storage tank, a silo or a pipeline in the process industry. Limit level sensors are often used as so-called limit switches, i.e. to determine whether a filling medium is above or below a certain level, the so-called limit level. Point level sensors can be used for different liquids, as well as granulated and powdered bulk goods.

Various types of point level sensors are known, which are selected depending on the area of application, process conditions and properties of the filling medium. Regardless of the measuring principle of the point level sensor, a switching command is usually generated when a defined point level is reached. A switching command from the limit level sensor can, for example, start or stop filling devices or emptying devices in order to prevent the respective process container from overflowing or running empty.

Proper functioning of a point level sensor is particularly important with regard to these switching commands. If the point level sensor does not work properly or emits an incorrect signal, a process vessel may run dry or overflow, causing significant damage, including to other systems.

The underlying object of the invention is therefore to provide a point level sensor and a method by means of which the safest possible operation of a process with a point level sensor can be made possible.

The object is achieved according to the invention with the features of the independent claims. Further practical embodiments and advantages are described in connection with the dependent claims.

• - Eine vibronische Messung, wobei das Sensorelement eine Schwinggabel ist, welche in Schwingungen versetzt wird. Kommt die vibrierende Schwinggabel mit dem Medium in Berührung, so verändert sich die Schwingungsfrequenz und/oder Schwingungsamplitude und das Erreichen des Grenzstandes wird detektiert. Die Schwinggabel ist auf Höhe des Füllstandes angeordnet, welcher als oberer oder unterer Grenzstand definiert ist.
• - Eine kapazitive Messung, wobei das Sensorelement ein Kondensator mit zwei Elektroden ist. Eine der beiden Elektroden kann auch durch eine Behälterwand gebildet sein. Tritt Medium in den Zwischenraum zwischen den beiden Elektroden, so verändert sich die Kapazität und das Erreichen des Grenzstandes wird detektiert. Die Elektroden sind auf Höhe des Füllstandes angeordnet, welcher als oberer oder unterer Grenzstand definiert ist.
• - Eine konduktive Messung, wobei das Sensorelement durch zwei voneinander beabstandete Elektroden gebildet ist. Kommen die Elektroden des konduktiven Grenzstandsensors mit einem leitfähigen Medium in Kontakt, so fließt ein geringer Wechselstrom zwischen den Elektroden und das Erreichen des Grenzstandes wird detektiert. Auch hier erfolgt die Anordnung der Elektroden auf Höhe des Füllstandes, welcher als oberer oder unterer Grenzstand definiert ist.
• - Eine Radarmessung, wobei das Sensorelement einen Mikrowellensender und einen Mikrowellenempfänger umfasst, welche eine sogenannte Mikrowellenschranke (analog zu einer Lichtschranke) bilden. Durchbricht das Medium den Mikrowellenstrahl zwischen dem Mikrowellensender und dem Mikrowellenempfänger, so wird das Signal gedämpft. Diese Veränderung wird vom Empfänger erfasst und in ein Schaltsignal umgesetzt. Die Anordnung des Mikrowellensenders und des gegenüberliegend angeordneten Mikrowellenempfängers erfolgt auf Höhe des Füllstandes, welcher als oberer oder unterer Grenzstand definiert ist.
• - Eine radiometrische Messung, wobei das Sensorelement einen Sender und einen Detektor umfasst. Bei der radiometrischen Messung sendet der Sensor von einem Isotop generierte Gammastrahlen aus. Der Detektor auf der gegenüberliegenden Seite des Behälters empfängt die Gammastrahlung und wandelt diese in Signale um, deren Anzahl erfasst und ausgewertet wird. Tritt ein Medium zwischen den Sender und den Detektor, wird die Intensität der Strahlung abgeschirmt. Auch hier erfolgt die Anordnung auf Höhe des Füllstandes, welcher als oberer oder unterer Grenzstand definiert ist.

A limit level sensor according to the invention with a self-test function has a sensor unit, by means of which the reaching of a defined limit level can be detected. Depending on the measuring principle, the point level sensor can be equipped with a different sensor unit. In particular, the following measuring principles and corresponding sensor units come into question:

• - A vibronic measurement, whereby the sensor element is a vibrating fork, which is made to vibrate. If the vibrating tuning fork comes into contact with the medium, the vibration frequency and/or vibration amplitude changes and reaching the limit level is detected. The tuning fork is positioned at the height of the fill level, which is defined as the upper or lower limit level.
• - A capacitive measurement, where the sensing element is a two-electrode capacitor. One of the two electrodes can also be formed by a container wall. If medium enters the space between the two electrodes, the capacity changes and reaching the limit level is detected. The electrodes are arranged at the filling level, which is defined as the upper or lower limit level.
• - A conductive measurement, the sensor element being formed by two spaced-apart electrodes. If the electrodes of the conductive point level sensor come into contact with a conductive medium, a small alternating current flows between the electrodes and reaching the point level is detected. Here, too, the electrodes are arranged at the height of the fill level, which is defined as the upper or lower limit level.
• - A radar measurement, with the sensor element comprising a microwave transmitter and a microwave receiver, which form a so-called microwave barrier (similar to a light barrier). If the medium breaks through the microwave beam between the microwave transmitter and the microwave receiver, the signal is attenuated. This change is recorded by the receiver and converted into a switching signal. The arrangement of the microwave transmitter and the microwave receiver arranged opposite takes place at the height of the fill level, which is defined as the upper or lower limit level.
• - A radiometric measurement, where the sensor element comprises a transmitter and a detector. In the radiometric measurement, the sensor emits gamma rays generated by an isotope. The detector on the opposite side of the container receives the gamma radiation and converts it into signals, the number of which is recorded and evaluated. If a medium occurs between the Sen the and the detector, the intensity of the radiation is shielded. Here, too, the arrangement is at the height of the fill level, which is defined as the upper or lower limit level.

A limit level sensor according to the invention has at least one means for automatically checking the functionality, with at least one means serving to trigger a switching event independently of the reaching of the limit level and/or with at least one means serving to check a switching event after the limit level has been reached.

An automatic check here means that the simulation or check of the switching event takes place without manual operation. In particular, it is not necessary to remove the point level sensor. No additional access to the point level sensor at the measuring point is required, no pressing of a test button and no manual attachment of a magnet. The point level sensor can test itself.

Triggering a switching event means that regardless of whether a defined limit level is actually reached at the moment, it is simulated that this limit level has been reached. As a result of the simulated limit level, the limit level sensor should trigger a switching event. If the point level sensor triggers such a switching event, it can be assumed that the point level sensor is functioning properly. The simulation of a limit level and the subsequent checking of a switching event can take place at any time and in particular independently of the actually prevailing limit level. The form in which the means simulate a limit level is explained in detail below.

A check of the switching event means that after a defined limit level has actually been reached and a switching event triggered as a result, the means are used to check whether the measured limit level is really due to an increase or decrease in the fill level or whether, for example, buildup of the sensor unit or jammed bulk material have led to a false triggering of a switching event.

Overall, reliable operation of the point level sensor can be implemented by at least one means for automatically checking the functionality. In particular, one or more means are provided so that both the simulation of a switching event and the checking of a switching event can be carried out and the point level sensor can thus be operated particularly reliably. A point level sensor according to the invention can test itself using the means for checking the functionality. Above all, the possibility of simulating a switching event enables simplified predictive maintenance of the point level sensor.

The means for automatically checking the functionality are described in detail below. The means are designed in such a way that they influence the measurement at the sensor element or generate a signal at the level of the sensor electronics.

The at least one means for automatically checking the functionality is, in particular, an electrical signal. This serves in particular to trigger a switching event independently of the actual limit level by simulating a limit level.

Which electronic signal makes sense depends on the type of point level sensor used. If it is a point level sensor that determines the point level capacitively or conductively, an additional capacitance, an additional inductance and/or an additional resistance (or current or voltage) can be coupled in as an electrical signal at the level of the sensor electronics. The additional capacitance or inductance or the additional resistance (or current or voltage) are each designed in such a way that this corresponds to a resulting capacitance or conductivity that would be present if an actual limit level were reached.

If a limit level sensor is used that performs a radar measurement using microwaves, the electrical signal can be a microwave signal of a specific frequency and amplitude, which then leads to a resulting signal that corresponds to the signal when the defined limit level is reached.

If it is a point level sensor that works according to the radiometric principle, a flash of light, e.g. by means of an LED, can be coupled in as an electrical signal.

The electrical signals mentioned above, which are suitable as a means of checking the functionality, are particularly suitable for simulating reaching a limit level and triggering a switching signal independently of an actual limit level.

In particular, the electrical signal is specifically tailored to the application or the medium to be measured. The electrical signal can are generated depending on the existing density or DK value of the medium, for example. This means that the functionality check corresponds as closely as possible to an actual switching event, and it can be assumed that the point level sensor is also functioning properly when the point level is actually exceeded or fallen below.

The at least one means for checking the functionality can also be a mechanical unit. In particular, the mechanical unit can be used to simulate reaching a limit level and/or to check a switching event.

The mechanical unit can also be designed depending on the measuring principle of the point level sensor.

A vibronic point level sensor has in particular an oscillating sensor unit and in particular an oscillating fork. In order to simulate reaching a limit level here, mechanical damping can be arranged on the limit level sensor. In particular, a clamping ring or a displaceable tube can be used, the clamping ring or tube being movable relative to the tuning fork, so that the clamping ring or tube is guided over the tuning fork and mechanically blocks the vibrations of the tuning fork. The tube preferably has a conical inner surface. Due to the taper, the strength of the damping can be variably and steplessly adjusted. The clamping ring or the tube is guided so far over the tuning fork that the tuning fork reaches an oscillating frequency that corresponds to a defined limit level and a switching event is triggered. The relative movement can be realized either by moving the clamping ring or tube or by moving the tuning fork.

In the case of a capacitive or conductive point level sensor, damping or an electrode can be provided as a mechanical unit, which can be automatically moved relative to the sensor element. The damping or the electrode is brought into the area of the sensor element and the measured capacitance or conductivity changes accordingly. The change takes place in such a way that reaching a limit level is simulated and a switching event is triggered.

For a microwave sensor, a cover can be introduced in the area of the microwave barrier, which weakens the signal and thus simulates reaching a limit level.

In a practical embodiment of the limit level sensor according to the invention, the mechanical unit is a telescopically extendable tube, by means of which the sensor element can be moved. On the one hand, this mechanical unit can be used to move the sensor element into the area of a clamping ring, conical tube, damping, an electrode or a cover.

Alternatively or in addition to this, the telescopically extendable tube is used to check a switching event. If it is determined that a limit level has actually been reached and a switching event is then triggered, the sensor element can be moved so that it moves out of the medium (in the case of an upper limit level) or back into the medium (in the case of a lower limit level). Changing the position of the sensor element is intended to change its switching state so that it can be checked whether the original triggering of the switching event is due to the change in fill level or not.

The variants of the mechanical unit described above are designed in particular in such a way that they are sealed against the ingress of dust and liquid. In particular, the telescopically extendable tube has at least one seal that prevents liquid or dust from penetrating between the tube elements that can be moved relative to one another.

In particular, it can be provided that the mechanical unit has a sensor for monitoring the position. This means that the position can be recorded automatically, particularly in the case of a movable mechanical unit.

The means for checking the functionality are designed in particular in such a way that they enable a limit level to be reached depending on the density, the dielectric constant, the viscosity of the filling material to be measured, a prevailing pressure and/or possibly the installation conditions in order to to be able to simulate individual limit values. For example, depending on the medium, the exact value of the necessary damping of the vibration frequency of a vibrating fork can be selected via the contact pressure through a tube with a conical inner surface. This ensures that the damping works with the product in hand.

The design of the means for automatically checking the functionality for the respective concrete process can already take place before the installation of the sensor or also in the installation position. the Tuning is done in particular by the sensor itself.

The means for automatically checking the functionality are supplied with energy via a bus system with an integrated energy supply, e.g. APL or PoE. Other field buses, e.g. 4-20 mA, IO-Link, a relay or transistor connection are also conceivable. Sufficient energy is provided by the bus system without additional cabling to operate the means for automatically checking the functionality.

The invention also relates to a method for checking the functionality of a limit level sensor as described above with a sensor element. A switching event is triggered via a means for automatically checking the functionality independently of the reaching of the limit level and/or a switching event is checked after a limit level has been reached by a means for automatically checking the functionality.

For the advantages of the method, reference is made to the above description.

As already described in detail above, a switching event is simulated by coupling in an electrical signal and/or by moving a mechanical unit. The choice of the means depends in particular on the measuring principle of the point level sensor.

In particular, a switching event is checked by moving and/or pivoting the sensor element. In particular, the sensor element is moved and/or pivoted so far that the sensor element is no longer covered with filling material at an upper limit level or until the sensor element is again covered with filling material and a new switching event is registered accordingly at a lower limit level. The sensor element switches accordingly from "Limit level reached" to "Limit level not reached". If such a new switching event is registered, it can be assumed that reaching the limit level was not incorrectly triggered by buildup or other effects. In particular, only after such a validation of the switching signal is a switching command output via a fieldbus, a radio module or an output. The sensor element can then be moved back to its original position. Alternatively, the sensor element can also remain in the moved position until the "limit reached" signal is determined again. In connection with a time measurement and knowledge of the container geometry, it is also possible to record the filling speed.

The automatic checking of the functionality takes place in particular cyclically. Above all, the check is carried out regularly according to the prescribed maintenance intervals. For example, after a few months or after a year. In particular, the check is automatically documented. The check can also be event-oriented, for example when a switching process has been triggered.

In particular, the measurement parameters determined during an actual switching event for the respective sensor element are stored and subsequently taken into account by the means for automatic checking when a switching event is triggered, regardless of whether a limit level is reached. In particular, the means for automatically checking the functionality during operation of the point level sensor are adjusted. It is then an adaptive point level sensor. For example, the frequency or amplitude of a microwave signal can be stored when the level limit is reached and reused when simulating the level limit due to the damping.

• 1 einen erfindungsgemäßen Grenzstandsensor in einer ersten Ausführungsform mit einer mechanischen Einheit in einer ersten Position in einer Seitenansicht,
• 2 den Grenzstandsensor aus 1 mit der mechanischen Einheit in einer zweiten Position,
• 3 einen erfindungsgemäßen Grenzstandsensor in einer zweiten Ausführungsform in einer Seitenansicht, und
• 4 den Grenzstandsensor aus 3 an einem Behälter, wobei der Grenzstandsensor in drei verschiedenen Positionen gezeigt ist.

Further embodiments and advantages are described below in connection with the figures. Show it:

• 1 a limit level sensor according to the invention in a first embodiment with a mechanical unit in a first position in a side view,
• 2 the level sensor off 1 with the mechanical unit in a second position,
• 3 a limit level sensor according to the invention in a second embodiment in a side view, and
• 4 the level sensor off 3 on a container, with the point level sensor shown in three different positions.

In the 1 and 2 a limit level sensor 10 is shown in a first embodiment. The limit level sensor 10 is a limit level sensor 10 that works according to the vibronic measuring principle. The limit level sensor 10 has a sensor housing 12 in which sensor electronics with a supply and evaluation unit are arranged. Furthermore, the point level sensor 10 has a process connection 14 for connection to a container. An oscillating fork 18, which can be excited to oscillate, is used here as the sensor element 16. If the vibrating fork 18 is covered with filling material when an upper limit level is reached or is no longer covered with filling material when a lower limit level is reached, the oscillation frequency and the changes Oscillation amplitude and reaching a limit level is detected and a switching event is registered.

In addition, limit level sensor 10 has a means for automatically checking functionality 20 . This means 20 is a mechanical unit in the form of a tube 22 with a tapered inner surface. The tube 22 extends into the process connection 14 . As in a synopsis of 1 and 2 As can be seen, the tube 22 can be moved in the axial direction and can be moved out of the process connection 14 to over the tuning fork 18 . Depending on how far the tube 22 is moved over the tuning fork 18 and to what extent the tuning fork 18 is surrounded by the tube 22, the vibration of the tuning fork 18 is damped.

In order to trigger a switching event independently of a limit level being reached, the tube 22 travels so far over the tuning fork 18 that a damped oscillation is achieved with an oscillation frequency that would be present if an actual limit level was reached. If a switching event is triggered as a consequence, it can be assumed that the limit level sensor 10 is functioning properly.

In connection with the 3 and 4 a second embodiment of a point level sensor 10 is described, the same reference numbers being used to describe identical or at least functionally identical components as for the description of the first embodiment.

In 3 a point level sensor 10 is shown, which works according to a capacitive principle. In this respect, the sensor element 16 has an electrode 24 . The limit level sensor 10 also has a housing 12 with sensor electronics arranged therein and a supply and evaluation unit. The limit level sensor 10 also has a process connection 14 .

As a means for automatically checking the functionality 20, a mechanical unit is also arranged on the point level sensor, this being a telescopically extendable tube 26, by means of which the sensor unit 16 can be moved up and down in the axial direction.

The tube 26 of telescopic design has an inner tube 28 which is firmly connected to the process connection 14 and an outer tube 30 which can be moved relative to the inner tube 28 . The sensor element 16 is connected to the outer tube 30 . The outer pipe 30 and the inner pipe 28 are connected to one another in a sealed manner via sealing rings (not visible), so that no moisture or dust can get between the pipes 28, 30.

In 4 the same point level sensor 10 is shown in three different positions on a container 32 in each case. A filling material 34 is arranged in the container 32 .

In the first position I, the sensor element 16 is in an extended position through the tube 26 . In position I, the sensor element 16 is covered by the filling material 34 and the limit level sensor 10 determines that the filling material 34 in the container 32 has reached an (upper) limit level and outputs a switching event “limit level reached”. In order to check this switching event, the sensor unit 16 is moved upwards out of the filling material by means of the telescoping tube 26 (position II). In this position II, the point level sensor 10 should then switch back to the “point level not reached” state. If this switching event occurs, it can be assumed that limit level sensor 10 is functioning. Thereafter, the sensor element 16 is moved to position III, which corresponds to the first position I, and the sensor element 16 should again detect that the limit level has been reached. The switching event is then validated and a switching command can be issued.

If no new switching event is triggered after the respective procedure in positions II or III, the sensor is brought into a safe state and an error is output.

Reference List

10

level sensor

12

Housing

14

process connection

16

sensor element

18

tuning fork

20

Means for automatically checking the functionality

22

Tube with a conical inner surface

24

electrode

26

telescopic tube

28

internal tube

30

external tube

32

container

34

contents

Claims (11)

Limit level sensor with a self-test function, the limit level sensor (10) having a sensor unit (16) by means of which reaching a defined limit level can be detected, characterized in that the limit level sensor (10) has at least one means for automatically checking the functionality (20), wherein at least one means (20) serves to trigger a switching event independently of the reaching of the limit level and/or to carry out a check of a switching event after the limit level has been reached. Limit level sensor according to the preceding claim, characterized in that the at least one means for automatically checking the functionality (20) is an electrical signal. Limit level sensor according to the preceding claim, characterized in that the electrical signal is a capacitance, an inductance, a resistance, a voltage, a current, a light signal and/or a microwave signal. Limit level sensor according to one of the preceding claims, characterized in that the at least one means for automatically checking the functionality (20) is a mechanical unit. Limit level sensor according to the preceding claim, characterized in that the mechanical unit is a clamping ring, a conical tube (22), a damping, an additional electrode and/or a cover. Limit level sensor according to one of the two preceding claims, characterized in that the mechanical unit is a telescopically extendable tube (26) by means of which the sensor element (16) can be moved. Method for checking the functionality of a point level sensor (10) according to one of the above Claims 1 until 6 with a sensor element (16), a switching event being triggered via a means for automatically checking the functionality (20) independently of the reaching of the limit level and/or a switching event being checked by a means for automatically checking the functionality (20) after a limit level has been reached . Method according to the preceding claim, characterized in that a switching event is simulated by coupling in an electrical signal and/or by moving a mechanical unit (22, 26). Method according to one of the two preceding claims, characterized in that a switching event is checked in such a way that the sensor element (16) is moved and/or pivoted and a new switching event is awaited. Method according to one of the preceding claims, characterized in that the functionality is automatically checked cyclically and/or in an event-oriented manner. Method according to one of the preceding claims, characterized in that the measurement parameters determined during an actual switching event for the respective sensor element (16) are stored and are subsequently taken into account by the means for automatic checking when a switching event is triggered, regardless of whether a limit level is reached.

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