EP1966569A2

EP1966569A2 - Level measuring arrangement with a safety cut-out at high temperatures

Info

Publication number: EP1966569A2
Application number: EP06829332A
Authority: EP
Inventors: Adrian Frick; Siegbert Woehrle
Original assignee: Vega Grieshaber KG
Current assignee: Vega Grieshaber KG
Priority date: 2005-12-27
Filing date: 2006-12-06
Publication date: 2008-09-10
Also published as: WO2007073837A3; WO2007073837A2; DE102005062813B4; DE102005062813A1; CN101331388B; CN101331388A

Abstract

The invention relates to a vibration limit switch arrangement comprising a control device (19, 16) for producing an excitation signal (s) and/or for processing a receiver signal (e), a piezoelectric oscillation device (10, 12) for generating a mechanical oscillation according to the excitation signal and/or for converting a mechanical oscillation into a receiver signal, and an oscillation arrangement (3) for emitting the mechanical oscillation generated by the oscillation device into the surroundings of the oscillation arrangement. A temperature determination device (19, 17) is used to determine the temperature (T) of the oscillation device (10, 12) and/or the temperature of the surroundings of the oscillation device, and the control device (19) is embodied in such a way as to generate a switching signal (sw) and/or a warning signal (w) when a threshold temperature is reached or according to the temperature (T). The invention also relates to a correspondingly designed method for operating the vibration limit switch.

Description

description

Level measuring system with safety shutdown at high temperatures

The invention relates to a vibration limit switch arrangement with the preamble features of claim 1 and to a method for operating a vibration ons limit switch with the Oberbegriffliehen features of patent claim 9.

Typically, a vibration limit switch assembly for monitoring a level of a medium in a container comprises a vibration assembly for generating a mechanical vibration. The vibration arrangement is doing with a

Vibration device coupled, wherein the vibration device is designed to generate a to be transmitted to the vibration assembly mechanical vibration due to an electrical excitation signal. Preferably, the same vibration device is at the same time designed to convert a mechanical vibration transmitted by the vibration arrangement into an electrical reception signal. The excitation signal is generated by a control device, wherein the control device preferably also serves to process the received signal.

A vibration limit switch usually consists of a piezoelectric transmitting / receiving unit in the form of such a vibration device and from a coupled thereto mechanical see vibration structure in the form of the vibration arrangement, which is preferably designed as a tuning fork. The electrical drive energy of the transmitting unit is thereby converted into mechanical vibration energy, whereby the above-driven ^¬ ne vibrating structure begins to oscillate at its resonant frequency. Conversely, an electrical reception signal is received at the receiving unit formed by the vibrator. Frequency and amplitude of this sensor Capture signal are dependent on the coverage condition of the Schwingga ^¬ bel and thus the level of the container and can therefore be used for the evaluation.

The object of the invention is to propose a full-level measuring arrangement, in particular a vibration limit switch arrangement or a method for operating such an arrangement, which can be operated more safely.

This object is achieved by an arrangement having the features of patent claim 1 and by a method having the features of patent claim 9.

Advantageous embodiments are the subject of dependent claims.

Accordingly, a vibration limit switch arrangement is preferably provided with a control device for generating an electrical excitation signal and / or for processing an electrical reception signal, a vibration device, in particular a piezoelectric vibration device for generating a mechanical vibration on the basis of the excitation signal and / or for converting a mechanical vibration in the received signal and a vibration arrangement, wherein a temperature determination device for determining a temperature of the vibrator and / or a temperature of an environment of the vibrator is provided and wherein the control device is designed, a switching signal and / or a warning signal when reaching a threshold temperature or depending on the temperature.

The control device preferably has an output for outputting the switching signal for controlling a connected device, in particular filling or emptying device, and / or for displacing the vibration limit switch arrangement and / or a connected device m to a specially defined state. The control device has preferential also has an output for outputting the warning signal for signaling a critical operating state.

A storage device preferably serves for storing at least one previously determined temperature for an analysis according to a fault state of the vibration limit switch arrangement or a higher-level device.

The temperature determination device preferably has a thermocouple with compensation lines for generating a thermal voltage. Preferably, two thermo-electrodes with mutually different thermoelectric coefficients adjacent to each other (and in particular between a ceramic and a piezoelectric element of the vibrating device arranged).

A temperature evaluation device, in particular in the form of the control device, is connected to thermoelectrodes with mutually different thermoelectric coefficients via insulated compensating lines whose thermoelectric coefficient of the individual cores coincides with the thermoelectrical electrode connected thereto or is in a defined ratio.

Preferably, at least one thermal electrode of the temperature-determining device is at the same time designed and connected as a connection electrode for a piezo element of the vibration device.

In particular, a method is also preferred for operating a vibration limit switch, in which an excitation signal is generated and applied to a vibration device, wherein the vibration device generates a mechanical vibration, wherein a temperature of the vibration device and / or a temperature of an environment of the vibration device is determined and / or a switching signal and / or a warning signal is generated depending on the determined temperature or a threshold temperature. The switching signal is preferably generated upon reaching a threshold temperature in order to set a further device for filling or emptying a monitored container in a defined state. The warning signal is generated in particular when reaching a threshold temperature for signaling a critical operating state. In a storage device, at least one previously determined temperature is preferably stored for analysis after a fault condition at a later time. From the temperature and a temperature value of a product of a monitored container can be determined.

In such an arrangement and in such a method, the threshold temperature is set so far below the Curie temperature of the piezo material used that the vibration device can produce the mechanical vibration from the excitation signal and / or the received signal from the mechanical vibration trouble-free. The threshold temperature is preferably less than 10%, in particular less than 5%, in particular less than 2% below the Curie temperature. This allows a safe use of a vibration device, which is formed by at least one piezoelectric element.

When the Curie temperature is exceeded, depolarization would occur, which would result in the transmitting or receiving elements in the drive constructed in this way losing their piezoelectric properties. Depending on the mechanical and electrical execution of a sensor constructed in this way, this could lead to a dangerous error if, for example, a container runs dry or overflows a container.

By providing a temperature determination

Device can be exceeded by introducing a critical threshold temperature below the Curie temperature by initiating preventive measures are prevented or a mechanism can be activated, which causes, for example, a shutdown of the entire system or activation or deactivation of certain devices such a system. When reaching or preferably sufficiently before reaching the Curie temperature is preferably causes an output of a level detector equipped in such a way in a defined secure position, so that, for example, an overflow or dry running of a parent system is prevented. Also useful is the output of a warning message when approaching the depolarization limit, so that if necessary countermeasures can be initiated in good time. The storage of the maximum drive temperature by means of preferably a drag pointer in a storage device such as an EEPROM allows after a failure of a vibration limit switch arrangement or after any other disturbance the manufacturer or operator to limit the possible causes of failure of such a vibration limit switch arrangement ,

Preferably, a temperature sensor of the temperature determination device is mounted in the immediate vicinity of the piezoelectric transmitting / receiving unit. If the specific temperature is transmitted to the control device or to a control center, then the control device or the control center or an operator can additionally use the opportunity to draw conclusions about the temperature of the full-medium of a monitored container with a small temperature difference between the drive and the product ,

Advantageously, cost-effective and space-saving sensor unit is suggested by the proposed arrangement and method with which it is possible the tempera ture ^¬ a piezo-actuator which is used for forming a vibration device to monitor.

In order to protect piezo elements or other comparable components of such a vibration device, the measuring device Preferably, the temperature is carried out by means of a heat resistance chain, which is placed directly in front of the temperature-sensitive elements. One way of measuring the temperature would be the use of metallic temperature sensors, as they are known as PtIOO or PtIOOO, which change their electrical resistance via the temperature.

Such sensors take up a relatively large amount of space in a drive housing. In addition, optimal placement is not easily accomplished because the most favorable location of the thermal conduction on a diaphragm of the vibrating structure of the vibrator or on an element metallically coupled thereto provides potential separation by means of e.g. a ceramic disc between a pressure plate and a piezoelectric block no longer guaranteed. The temperature sensor of such a temperature-determining device should, however, be located as far as possible in the direction of a possible heat source between the heat source and piezoelectric elements. Therefore, an arrangement with electrodes having mutually different thermoelectric coefficients is particularly preferred.

Embodiments of the invention will be explained in more detail with reference to the drawing. Show it:

1 is a schematic side view of a vibration system and electronics of a vibration limit switch arrangement according to a first embodiment,

Fig. 2 shows an arrangement according to a second embodiment and

Fig. 3 shows an arrangement according to a third embodiment.

In addition to the illustrated embodiments are in particular combinations of their respective aspects as well as others Embodiments with a larger number or a smaller number of such respective components feasible. A key idea is that a temperature measurement takes place in a range of temperature-sensitive components and such a determined temperature is used to influence the operation of a vibration limit switch or other devices monitored therewith. In the description of the various embodiments, the same reference numerals designate identical or similar components or signals, with reference being made in the description of the second and third embodiments to simplifications, to corresponding descriptions of the respective other embodiments.

Fig. 1 shows a subdivision into a vibration system 1 and an electronics 2. As a mechanical vibration assembly 3, a common tuning fork is used. The tuning fork protrudes at least partially into a container in which a filling medium is located, the level of which is to be monitored. On the side opposite the monitored filling medium side of the vibration assembly, a sequence of components is arranged, which consists in the illustrated embodiment, only by way of example of individual components, which are stacked and braced by a threaded rod 4 and a nut 5 against the vibration assembly. In principle, however, other known arrangements and methods for forming a vibration drive in conjunction with a vibration fork can be implemented.

In the arrangement shown by way of example above the vibrating fork forming the oscillation arrangement 3 are a lower pressure disk 6, a ceramic element 7, a first thermoelectric electrode 8, a second thermoelectrode 9, a piezoelectric element 10, a first connecting electrode 11, a second Piezo element 12, a second connection electrode 13, a further ceramic element 14 and an upper pressure plate 15 arranged, which are clamped by the nut 5 against the tuning fork.

The electronics 2 comprises, in addition to further customary components, in particular a transmitting / receiving unit 16 and an ADW

Input (ADW: analog-to-digital converter) of a processor, which serves as a temperature determination device 17. These components and other components, such as a memory device 18, are part of an integrated or higher-level control device 19. The control device 19 can thus be formed from individual interconnected components or from an optionally also single integrated component. An excitation signal s, which is applied to the first connection electrode 11, is generated via the transmission / reception unit 16 of the control device 19. The second connection electrode 13 is connected to ground m, the ground m being connected as circuit ground to the transmitting / receiving unit 16 or other customary ground connections. The temperature determination device 17 is connected to the first thermoelectrode 8 via a first line and receives a thermal voltage t via this line. In addition, the temperature determination device 17 is connected to ground via a ground line 21, the ground line 21 being applied to the second thermal electrode 9. As shown, a common mass m may preferably be used with the transceiver unit 16. In principle, however, it is also possible, a line 20 for the send / receive signal s, e and a separate ground line 21 for the drive unit and a separate line pair of its own ground line 21 and a thermo-voltage line 22 for Temperature determining device 17 to provide. The illustrated ground line 21 and the thermo-voltage line 22 form thermal compensation lines.

In this arrangement, therefore, the first thermal electrode 8 and the second thermal electrode 9, which are attached directly between the ers ^¬ th ceramic element 7 and the first piezoelectric element 10 placed or clamped, a pair of electrodes with different thermoelectric coefficients. Thus, there remains a potential separation and a vessel temperature T0 acting on the vibration arrangement 3 from the container is determined as a temperature T acting on the or the piezo elements 10, 12 immediately before the piezo elements 10, 12. The screw connection of the drive constructed in this way ensures that the electrodes, in particular the two thermo-electrodes 8, 9, are connected to one another. In order to determine the absolute temperature T in this range, a measurement of the reference junction temperatures prevailing at the line ends is necessary in such an arrangement with thermal resistances. This is in the electronics 2 z. B. measured by a processor located in the temperature sensor or the temperature-determining device 17 and output as an absolute temperature T by the controller 19 or used. The absolute temperature T can be calculated, for example, by means of a suitably suitable software from the thermoelectric voltage of the first and the second thermo-electrode 8, 9.

According to a particularly preferred embodiment, insulated output lines in the form of the ground line 21 and the thermo-voltage line 22 are used whose thermoelectric coefficients should correspond as closely as possible to those of the thermoelectrodes 9, 8 connected thereto. Exemplary possible thermocouples z. B. formed by NiCr + / Ni or NiCr + / CuNi-. There is preferably no temperature gradient between the transition of the compensating lines to copper lines for adapting the electronics 2 and the comparison measuring point, since otherwise further thermal voltages develop, which would falsify the measurement result and have to be calculated out accordingly. Preferably, however, it is also possible to compensate the thermal voltage t directly at the transition point between the thermocouple and the copper cable with a corresponding wiring or to measure the temperature at the transition point and to perform a software compensation of the measurement result detected by the processor. If the need for electrical isolation can be dispensed with, it is also possible to dispense with one of the thermoelectrodes and instead use a membrane of such an arrangement as a second thermoelectrode.

To save further costs, the two thermo electrodes can also be replaced by any metallic electrode. For this purpose, the thermoelectric lines, as shown in Fig. 2, connected directly to such an electrode. Due to the much higher thermal conductivity of such a metallic compound compared to air, a thermal voltage t is likewise obtained, which contains the information of the temperature prevailing directly in front of the piezoelements.

Accordingly, FIG. 2, in contrast to FIG. 1, instead of a first and a second thermoelectrode, shows only a first thermoelectrode 8 between the first ceramic element 7 and the first piezoelement 10 and a connection preferably adjacent directly to the thermoelectrode 8 - Site 23, which connects the ground line 21 and the thermoelectric voltage line 22 to each other. A further abstraction and even more compact arrangement is shown in FIG. 3, in which, according to a particularly simple implementation principle, the temperature T is measured in front of a piezoelectric drive applied by means of adhesive technology and / or soldering technology. In this case, a thermoelectrode 8, a piezoelectric element 10 and a connection electrode 13 are glued together and / or soldered directly above a arranged on the oscillation assembly 3 ceramic 1, wherein the individual elements are shown spaced apart as in the other representations to sketch this more clearly. Again, a joint 23 is preferably formed near the thermo-electrode 8 with the joint 23 again connecting the ground line and the thermo-voltage line. The connection electrode 13 is in turn connected via a connecting line 20 for transmitting transmitted signals s and received signals e. All three embodiments show an exemplarily sketched storage device 18, in which optionally in addition to operating parameters through the arrangement certain temperatures can be stored. In the event of a malfunction, this allows a later readout of temperatures determined in this way, in order to be able to determine whether a malfunction was caused by too high a temperature or possibly other causes.

Preferably, the control device 19 is designed to output different types of signals as needed. Preferably, the particular temperature T can be output via a corresponding port. Preferably, a switching signal sw and / or a warning signal w can also be output via further connections. By means of a switching signal, for example pumps or other devices can be activated or deactivated to prevent emptying or overflow of a monitored by the thus formed vibration limit switch arrangement container. For monitoring purposes, the control device 19 preferably also takes into account a threshold temperature T * which should not be exceeded or exceeded in order to ensure fault-free operation in the region of the piezoelectric elements 8, 9. In particular, when such a threshold temperature T * is reached, corresponding switching and warning signals sw, w are output.

Preferably, the threshold temperature (T *) is determined as a function of the piezo elements 10, 12 used, so that a trouble-free operation with respect to the critical operating temperatures of the piezo elements is ensured. The consideration of the Curie temperature is important for vibration devices which are formed from piezoelectric elements or comparable elements with comparable physical properties.

Claims

claims

1. level measuring arrangement with

a control device for generating an electrical excitation signal and for processing an electrical received signal,

- A vibration device, in particular piezoelectric vibration device (10, 12) for generating a mechanical vibration due to the exciter signal (s) and / or for Umwan- a mechanical oscillation in the received signal (e) and e e c e n e e c h e n e t

a temperature determination device (19, 17) for determining a temperature (T) of the vibration device (10, 12) and / or a temperature (T) of an environment of the vibration device (10, 12),

- Wherein the control device (19) is designed to generate a switching signal (SW) and / or a warning signal (W) upon reaching a threshold temperature or depending on the temperature (T).

2. Arrangement according to claim 1, wherein the control device (19) has an output for outputting the switching signal (sw) for controlling a connected device, in particular filling or emptying device, and / or for displacing the vibration limit switch arrangement and / or a connected device in a specially defined state.

3. Arrangement according to claim 1 or 2, wherein the control device (19) has an output for outputting the warning signal (w) for

Signaling a critical operating state has.

4. An arrangement as claimed in any preceding claim, further comprising storage means (18) for storing at least one predetermined temperature (T) for analysis of a fault condition of the vibration limit switch assembly or a higher level apparatus.

5. An arrangement according to any preceding claim, wherein the temperature determining means (17) comprises a thermocouple with compensating leads (8, 9, 21, 22) for generating a thermal voltage (t).

6. An arrangement according to any preceding claim, wherein two thermal electrodes (8, 9) with mutually different ther- moelektrische coefficients adjacent to each other and in particular between a ceramic (7) and a piezoelectric element (10) of the vibrating device are arranged.

7. Arrangement according to any preceding claim, in which a temperature evaluation device, in particular the control device (19) with thermoelectrodes (8, 9) with mutually different thermoelectric coefficients via insulated compensation lines (21, 22) is connected, the thermoelekt - Rischer coefficient of the individual wires with the connected thermo-electrode (8, 9) coincides or is in a defined ratio.

8. An arrangement according to any preceding claim, wherein at least one thermo-electrode of the temperature-determining device at the same time as a connection electrode for a piezo element (10) of the vibration device is formed and interconnected.

9. A method for operating a vibration limit switch, in which - generates an excitation signal (s) and a vibration device (10, 12) is applied, wherein the vibration device generates a mechanical vibration and the mechanical vibration via a vibration assembly (3) is provided thereby in that - a temperature (T) of the vibration device (10, 12) and / or a temperature (T) of an environment of the vibration device (10, 12) is determined, and - A switching signal (SW) and / or a warning signal (W) depending on the particular temperature (T) or a threshold temperature (T *) is generated.

10. The method of claim 9, wherein the switching signal (SW) is generated upon reaching a threshold temperature for moving a further device for filling or emptying a monitored container in a defined state.

11. The method of claim 9 or 10, wherein the warning signal (w) is generated upon reaching a threshold temperature (T *) for signaling a critical operating state.

12. The method according to any one of claims 9 to 11, wherein in a memory device (18) at least one predetermined

Temperature (T) is saved for analysis after a fault condition at a later time.

13. The method according to any one of claims 9 to 12, wherein from the temperature (T) a temperature value of a product of ü monitored a container is determined.

14. Arrangement according to one of claims 1 to 8 or method according to one of claims 9 to 13, wherein the threshold temperature (T *) is set so far below the Curie temperature that the vibration device, the mechanical vibration from the exciter signal ( s) and / or the received signal (e) from the mechanical vibration can generate.

15. Arrangement according to one of claims 1 to 8 or method according to one of claims 1 to 13, wherein the threshold temperature (T *) is less than 10%, in particular less than 5%, in particular less than 2% below the Curie temperature ,

16. Arrangement or method according to one of the preceding claims, wherein the vibration device (10, 12) is formed by at least one piezoelectric element.