EP2511640A1 - Apparatus and method for testing a thermocouple - Google Patents

Abstract

The device has control elements (12a-12f) e.g. push buttons, arranged in proximity of thermocouples (11a-11f). An output signal of the control elements is processed by a system programmable controller (21). The controller tests the thermocouples before operating the control elements. The controller determines difference between temperatures measured by the thermocouples and a reference-thermocouple. The controller corrects the temperatures measured by the thermocouples during operation of an annealing furnace (3). Signal lamps (23a-23f) indicate state of a test procedure. An independent claim is also included for a method for testing a thermocouple in a furnace.

Description

State of the art

The invention relates to a device for testing a thermal sensor according to the preamble of patent claim 1, and to a corresponding method according to the preamble of patent claim 10.

It is known from the prior art to use metal parts, e.g. Ball bearings or drive shafts to harden and temper in special furnace systems. Such furnaces typically include a multi-zone tempering furnace, a quenching device for subsequent quenching of the parts, and a tempering furnace in which the parts undergo a final heat treatment.

In the kiln plant, the parts first pass through the hardening kiln, whose zones have different temperatures and a different C level (carbon level). As they pass through the individual zones, carbon atoms diffuse into the surface of the metal parts, penetrating more or less deeply into the surface, depending on the residence time. By the subsequent quenching and tempering, the parts finally get their required quality.

The quality of the treated parts is highly dependent on the consistent adherence to given process parameters, e.g. a certain temperature, a certain C-level in the atmosphere of the curing oven and a certain duration of the individual treatment steps.

To ensure that the quality of the heat-treated parts remains as constant as possible, the American automotive industry has created the CQI-9 standard for the heat treatment of vehicle parts in particular. CQI-9 means as much as: continuous quality improvement in the heat treatment. However, with the industrial furnaces known today for the hardening of metals, it is not possible to comply with this standard, since in particular the thermal sensors mounted on the industrial furnace can not be tested reliably and in accordance with the standard. In addition, the test data can not be logged so far tamper-proof.

Disclosure of the invention

It is therefore the object of the present invention to provide an apparatus and a method for testing one or more thermosensors mounted on a furnace with which they can be tested reliably and in accordance with standards. The test data should be able to be logged in particular tamper-proof.

This object is achieved according to the invention by the features specified in claim 1, and in claim 10. Further embodiments of the invention are the subject of dependent claims.

According to the invention, it is proposed to arrange an associated operating element in the vicinity of at least one thermosensor mounted on the furnace, the output signal of which is processed by an electronic system. The electronics are designed in such a way that a test of the associated thermal sensor can only be carried out if the operating element, such as e.g. a button, was previously pressed. To carry out a test procedure, it is therefore necessary to first actuate the control element associated with the thermal sensor and thereby to release the test procedure. Thus, the electronics is signaled which thermosensor is to be tested. The electronics can then record the temperature measurement data of the selected thermal sensor, assign it to the tested thermosensor and e.g. save in a database. A confusion of the thermosensor to be tested with another thermosensor is excluded in this way.

The actuating element is preferably arranged close to the associated thermal sensor on the furnace, so that a clear affiliation of the operating element to the respective thermal sensor can be seen. In case of several thermosensors is in near each of the thermal sensors mounted an associated control on the stove.

According to the invention, an operating element may be, for example, a button.

The above-mentioned electronics are preferably a controller, e.g. a PLC (system programmable controller). It preferably comprises a software algorithm which processes the signal of the operating element (s) - and in particular recognizes the state "actuated" or "not actuated". The recording of measured data of a selected thermal sensor is preferably by means of software, the z. B. running on a computer, started, z. By selecting an associated software switch. A thermal sensor test can preferably only be carried out if a test mask of the test software is displayed on the PC and, in addition, the associated control element has been actuated on the furnace. If only one control element has been operated on the oven without the test software being displayed on the PC, the test should preferably not be started. The test procedure should also preferably not be able to be started if the operating element of a first thermal sensor was pressed, but another thermal sensor is selected for testing on the test software. In this case, z. For example, an error may be displayed (eg on the PC or with another display device).

During a thermal sensor test, the temperature measurement data of a selected thermal sensor and a reference element are preferably recorded and processed. The measured data of the thermal sensor and the reference element are preferably compared with each other.

According to a specific embodiment of the invention, the functionality and accuracy of the oven-mounted thermosensors is checked by means of a calibrated reference thermocouple. For the purpose of the test, the reference thermocouple z. B. introduced into the thermal sensor to be tested and connected to the electronics. This then calculates a difference between the temperature measured by the thermal sensor and the temperature measured by the reference thermocouple. If the temperature difference is smaller than a predetermined threshold value, the tested thermal sensor is considered to be in order and can continue to be used. Unless the Temperature difference, however, is greater than a threshold, a warning signal is preferably output, which is displayed for example on a computer screen and the test is aborted with error.

The determined temperature difference represents an offset of the thermal sensor, which is preferably automatically taken into account during operation of the furnace. That is, the temperature value measured by the thermal sensor is preferably corrected by the offset. In the case of a temperature control, the controller is then preferably supplied with a corrected temperature value as the current actual value.

According to a preferred embodiment of the invention, a display unit is provided which displays the state of the test procedure. The display unit may, for example, comprise a signal lamp which lights up differently depending on the state or flashes at a different frequency. For example, while testing a thermal sensor, the indicator may flash slowly. If the test has ended without error after a certain time, e.g. a steady light will be displayed. On the other hand, if the test ended with an error, or if an error was already present at the beginning, the display device may, for example, flash very quickly. An error is preferably detected when the difference between the temperature measured by the thermal sensor and that measured by the reference thermocouple is greater than a predetermined threshold, e.g. greater than 10 ° C.

According to a preferred embodiment of the invention, the test of a thermal sensor can not be repeated immediately after it has been completed without errors. As a result, a manipulation of the test can be prevented. This function can, for. B. be realized by an appropriate software in electronics.

Each thermal sensor is preferably associated with its own display device. The display devices are preferably arranged in the vicinity of the respectively associated thermal sensor on the furnace. This makes it visually immediately visible which thermosensor is currently being tested or possibly has an error.

According to a preferred embodiment of the invention, a permanently installed connection for a reference thermocouple is provided for each thermal sensor. The reference thermocouple thus only needs to be connected to the already prepared connection, e.g. a wire connection to the electronics, be connected to perform a test of the thermal sensor.

A thermal sensor may basically comprise one or more thermocouples, e.g. So-called thermocouples have their sensor signals are each processed and evaluated by the electronics.

According to a preferred embodiment of the invention, a thermal sensor comprises two thermocouples, one of which is used for temperature control and the other serves as a comparison element. During the oven operation, the measured values of the thermocouples are preferably compared with each other regularly in order to detect possible sensor errors in good time.

In case of a defect of one or more thermocouples, a warning signal is preferably generated, the z. B. can be displayed on a computer screen.

According to a special embodiment of the invention, a switching device is provided, by means of which a defect of a thermocouple can be switched to another thermocouple of the same thermal sensor. As a result, an uninterrupted operation of the furnace system can be ensured. The switching device is preferably realized as software.

The method according to the invention for testing the thermosensors mounted on a furnace preferably comprises the following method steps: opening a test mask on the PC, inserting a reference element into the thermosensor to be tested, permanently installed and connected, operating an operating element, such as a probe, which in is mounted close to a thermal sensor on the furnace, performing a test procedure for this thermal sensor as soon as the associated control element has been actuated and storing the test data in a (eg SQL) database in which they are tamper-proof stored. The check will then be sequential for the other thermal sensors performed. The requirement of a prior actuation of a control element has the advantage that the electronics that processes the output signals of the thermal sensors, can be reliably specified, which thermal sensor is currently being tested. Mixing up with other thermosensors is almost impossible.

The condition of the test is preferably carried out on a display device, e.g. B. on the PC and / or on-site at the thermal sensor, which is controlled by the electronics accordingly. The condition of the test is thus clearly visible to the examiner.

According to a specific embodiment of the invention, in the event of a defect of a temperature sensor, which is used for the temperature control, switched to another temperature sensor of the same thermal sensor. Switching can in principle be done manually, but also automatically. In the first case, the defect (e.g., optically or acoustically) could be displayed, whereafter the examiner would have to switch by hand.

Fig. 1

einen aus dem Stand der Technik bekannten Industrieofen zum Härten und Vergüten von Metallteilen;

Fig. 2

einen Härteofen mit mehreren Zonen;

Fig. 3

einen Thermosensor und ein Referenz-Thermoelement im nicht eingeführten Zustand;

Fig. 4

einen Thermosensor und ein Referenz-Thermoelement im eingeführten Zustand;

Fig. 5

eine Prüfvorrichtung mit einem Thermosensor und einer Schalteinrichtung zum Umschalten zwischen zwei Thermopaaren; und

Fig. 6

ein Flussdiagramm zur Darstellung mehrerer Verfahrensschritte einer Prüfprozedur zum Prüfen eines Thermosensors.

The invention will now be described by way of example with reference to the accompanying drawings. Show it:

Fig. 1

an industrial furnace known from the prior art for hardening and tempering metal parts;

Fig. 2

a hardening furnace with several zones;

Fig. 3

a thermal sensor and a reference thermocouple in the uninfeed state;

Fig. 4

a thermal sensor and a reference thermocouple in the inserted state;

Fig. 5

a test device with a thermal sensor and a switching device for switching between two thermocouples; and

Fig. 6

a flowchart illustrating a plurality of process steps of a test procedure for testing a thermal sensor.

FIG. 1 shows a known from the prior art furnace 1 for hardening and quenching of metal parts, such as automotive parts. The furnace 1 comprises a so-called feeding station 2, at which the parts are introduced into a hardening furnace 3. The hardening furnace 3 in the present example has three zones Z1-Z3, in which different temperatures and an atmosphere with different C-level prevail. The metal parts are heated in the curing oven 3 typically to temperatures of about 900 ° C. As the metal parts pass through the individual zones Z1-Z3, carbon atoms diffuse into their surface. Depending on the residence time in the furnace 3, the carbon atoms diffuse more or less deeply into the surface of the parts, resulting in a corresponding hardness after quenching of the parts. Longer cycle times mean, in principle, greater hardness and shorter cycle times in principle lower hardness.

After passing through the hardening furnace 3, the metal parts pass into a quenching bath 4 in which the material structure changes in the region in which the carbon atoms have diffused. This results in a certain hardness. Thereafter, the parts are conveyed by means of a conveyor belt 5 in a washing machine 6, in which they are cleaned, and then pass into a tempering furnace 7, in which a further heat treatment takes place. The tempering furnace 7 here also has three zones Z1-Z3 with different temperatures. When passing through the tempering furnace 7, the material relaxes and finally receives its desired properties and quality.

After passing through the tempering furnace, the parts are finally preserved in a preserving bath 8 and conveyed via a conveyor belt 9 to the removal station 10.

Fig. 2 shows an enlarged view of the two zones Z1 and Z2 of the curing oven 3. The zones Z1, Z2 each include a control device with which the temperature in each zone Z1, Z2 can be controlled individually to a predetermined target value. The control device of each zone Z1, Z2 comprises a thermal sensor 11a or 11d, a control algorithm, which as software in an electronics 21 - here a PLC (System Programmable Control) - deposited and a burner (not shown) forming the actuator of the control. The current temperature in the zones Z1, Z2 is measured by the thermal sensors 11a and 11d and fed to the PLC 21.

In addition to the thermosensors 11a, 11d of the temperature control, each zone Z1, Z2 comprises two further thermosensors 11b, 11c and 11e, 11f. The thermal sensors 11 b, 11 e serve to monitor a predetermined allowable temperature range and the thermal sensors 11c, 11f for measuring the temperature in the oven interior for a C-level control. Depending on the design of the furnace 1, however, it is also possible to provide more or fewer thermal sensors per zone Z1, Z2.

The Figures 3 and 4 show a detailed view of a thermal sensor 11. In the illustrated embodiment, each thermal sensor 11 comprises two thermocouples 20a, 20b, which are arranged in close spatial proximity side by side, so that they measure substantially the same temperature. Each thermocouple - also called thermocouple - consists essentially of two wires of different metals, which are welded together at one end. At the weld, a thermal stress is generated which can be measured and is dependent on the ambient temperature.

The thermal sensor 11 comprises in the front region of a protective tube 19, which projects into the interior of the furnace 3 and in which the thermocouples 20a, 20b are arranged side by side. The thermal sensor 11 further includes a connection head 13 having a plurality of terminals 14a-14d. The terminals 14a-14d are connected via two-core equalizing lines 15a, 15b to corresponding terminals 22 of the PLC 21.

The Figures 3 and 4 also show a reference thermocouple 16 that can be inserted into the thermal sensor 11 for testing purposes. To connect the reference thermocouple, a permanently installed on the PLC 21 line 17 is provided with two terminals 18 for the reference thermocouple 16. The reference thermocouple 16 must therefore be connected only to the terminals 18 and introduced into the thermal sensor 11 to be tested.

As in FIG. 2 can be seen, each of the thermal sensors 11a-11f associated with its own button 12a-12f, which is mounted in each case in the immediate vicinity of the associated thermal sensor 11a-11f to the furnace. The pushbuttons 12a-12f are connected via corresponding lines to the PLC 21 and essentially serve to indicate to the PLC 21 when testing the thermal sensors 11a-11f which of the thermal sensors 11a-11f is currently being tested.

For testing the individual thermal sensors 11a-11f, for example, a test method can be carried out, as exemplified in FIG Fig. 6 is shown. In order to start the test procedure of a thermal sensor, for example of the element 11a, a test mask must first be opened on the PC, whereby the buttons 12a-12f are "armed" (step 29). The reference thermocouple 16 is then placed in the thermal sensor to be tested, for. B. 11a, introduced and connected to the PLC 21. It can also be connected before calling the test mask. In addition, the button, eg 12a, a thermosensor to be tested, for. B. 11a, are pressed.

In step 30 of the method, the PLC 21 determines which button 12a-12f has been pressed. As soon as one of the buttons 12a-12f has been pressed (case J), the PLC 21 knows which thermosensor 11a-11f is to be checked. Thereafter, the temperatures measured by the reference thermocouple 16 and thermocouples 20a, 20b are recorded and logged. The state of the test (for example "test running") is determined by an associated display device, such. B. a signal lamp 23a-23f displayed While the test is running, the associated signal lamp flashes z. B. slow and thus indicates the measurement. If the measurement was aborted with error, the lamp, z. B. 23 a, switched to another mode in which it z. B. fast flashing. The measurement can then be repeated. The measurement data is stored in a tamper-proof database. The database may be z. For example, an Oracle © or MS SQL database.

In addition, a difference between the temperature measured by the reference thermocouple 16 and by the thermocouple 20a or 20b is determined in step 32.

In step 33, it is finally checked whether one of the measured temperature differences is greater than a predetermined threshold value, e.g. 10 ° C. If the deviation of the thermocouples 20a, 20b is less than the threshold (Case N), the signal lamp (e.g., 23a) is placed in another state indicating that the test has completed without error. The signal lamp 23a may be e.g. be set by the PLC 21 in a permanently lit state. On the other hand, if the test of the thermal sensor (e.g., 11a) was unsuccessful, or if the temperature difference Δt has become too high, this is indicated at step 34 on the associated signal lamp 23a. The signal bulb 23a may in this case be e.g. flash fast. The test can then be carried out again. If the test mask is closed on the system PC, the permanent lights in the test buttons go out and the test buttons become inactive.

The temperature difference of the thermocouples 20a, 20b to the reference temperature is preferably stored in each case as an offset, with which the sensor signals are corrected in the future operation of the furnace. The temperature controller 24 (see Fig. 5 ) thus sees only the corrected sensor signal.

If it has been detected in step 33 that the thermocouple, eg 20a, whose signal is processed by the temperature controller 24, is defective, can be switched to the other thermocouple, eg 20b. For this purpose, a switching device 22 is provided, as exemplified in Fig. 5 is shown. The switching device 22 is realized here as a software module in the PLC 21. A sensor error is preferably displayed on a PC screen.

Fig. 5 shows a schematic representation of a test device for testing a thermal sensor 11 with a switching device 22, by means of which can be switched between the thermocouples 20a and 20b. The switching device 22 comprises a plurality of switches 26a-26i, which are implemented here as software switches in the PLC 21. The switches 26a-26i are arranged so that each connection (+/-) of the thermocouples 20a, 20b is selectively connectable to the software controller 24 or via appropriate connections of the PLC 21 with another software module 25. In the present exemplary embodiment, two switches 26 are provided in each case for each connection (+/-) of a thermocouple 20a, 20b. Alternatively, however, only a single changeover switch could be provided.

In the case of a defect of that thermocouple 20a, which is relevant for the temperature control in the normal state, then the comparison thermocouple 20b is switched over. The switching can in principle be carried out by hand or done automatically.

Claims (13)

Apparatus for testing a thermosensor (11; 11a-11f) mounted on a furnace (1), characterized by at least one user-operable control element (12a-12f) disposed on the oven and having an output signal processed by electronics (21), wherein the electronics (21) is designed such that a test of the thermal sensor (11; 11a-11f) can only be carried out when the operating element (12a-12f) has been previously actuated. Apparatus according to claim 1, characterized in that a plurality of thermal sensors (11; 11a-11f) are provided and for each thermal sensor (11; 11a-11f) an associated operating element (12a-12f) is provided. Apparatus according to claim 1 or 2, characterized in that a reference thermocouple (16) is provided, and the electronics (21) a difference between that of a thermal sensor (11, 11 a-11 f) and the reference thermocouple (16 ) measured temperature. Apparatus according to claim 3, characterized in that the electronics (21) corrects the temperature measured by a thermal sensor (11; 11 a-11 f) during the oven operation. Device according to one of the preceding claims, characterized in that a display unit (23a-23f) is provided which displays the state of the test procedure. Apparatus according to claim 5, characterized in that a display unit (23a-23f) is provided for each thermal sensor (11; 11 a-11 f), which is arranged in each case at the furnace. Device according to one of the preceding claims, characterized in that a permanently installed connection (17, 18) for a reference thermocouple (16) is provided for each thermal sensor (11, 11 a-11 f). Device according to one of the preceding claims, characterized in that at least one thermal sensor (11; 11 a-11f) comprises a plurality of thermocouples (20a, 20b) whose signals are each processed and evaluated by the electronics (21). Apparatus according to claim 8, characterized in that a switching device (22) is provided, by means of which in the event of a defect of a thermocouple (20a, 20b) to another thermocouple (20a, 20b) of the same thermal sensor (11; 11a-11f) are switched can. Method for testing one or more thermocouples (11, 11a-11f) mounted on a furnace (1), characterized by the following steps: Actuating a control element (12a-12f) disposed on the furnace, which is associated with a thermal sensor (11, 11a-11f), - Performing a test procedure for a thermal sensor (11; 11 a-11 f), if the associated control element (12 a - 12 f) has been operated, and - Save the test data in a database. A method according to claim 10, characterized in that the state of the test is displayed on a display device (23a-23f). Method according to claim 10 or 11, characterized in that during a test a difference between the temperature value measured by a thermosensor (11; 11a-11f) and a reference thermocouple (16) is determined. Method according to claim 12, characterized in that in the case of a thermal sensor (11; 11a-11f) having a plurality of thermocouples (20a, 20b), another thermocouple (20a, 20b) of the thermosensor (11; 11a-11f) is switched over when the temperature difference is greater than a predetermined threshold.

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