WO2011098287A1

WO2011098287A1 - Method and apparatus for the autonomous calibration of extension or force sensors

Info

Publication number: WO2011098287A1
Application number: PCT/EP2011/000655
Authority: WO
Inventors: Wolfgang Viel; Werner Bonifer
Original assignee: Hottinger Baldwin Messtechnik Gmbh
Priority date: 2010-02-12
Filing date: 2011-02-11
Publication date: 2011-08-18
Also published as: DE102010007937A1; EP2534457A1; CN102741673B; DE102010007937B4; CN102741673A

Abstract

The invention relates to a method and an apparatus for autonomously calibrating extension (1) or force sensors comprising a strain gauge circuit (11) for converting a mechanical load into an electric output signal. In order to calibrate the sensor (1), a defined initial value is assigned in an evaluation circuit (13) in a first or unloaded operating state while a defined final value is assigned in the evaluation circuit (13) in a loaded operating state. In the operating state, the evaluation circuit (13) calculates corresponding displayable measured output values from the assigned initial and final values using a linear function. The invention is characterized in that the calibration is done autonomously in the permanently mounted operational sensor (1) by means of an evaluation circuit (13) that is integrated into the sensor (1). The initial value is stored in the evaluation circuit (13) using a controlled first switch signal, while the final value is stored in the evaluation circuit (13) using a controlled second switch signal, and the calibrated measured output values are calculated from said initial and final values according to the subsequent loads.

Description

Method and device for the automatic calibration of strainers or force transducers

The invention relates to a method for automatic

Calibration of strainers or force transducers according to the

The preamble of claim 1, and a measuring device for carrying out the method according to the preamble of

Patent claim 8.

For commissioning of measuring instruments, these must be in advance

be calibrated in order to be able to assign precise, defined measured values to the output signals. It is also

within the operating period to review the

Measuring accuracy or after repair measures often necessary to recalibrate these meters. Especially at

Measuring devices for strain and force measurement is an accurate calibration and their repetition necessary, as with larger measurement errors, this also easy to damage

Devices and persons can lead. Such strain or force measuring devices are often used to monitor the

Force loading on cranes, containers, bridges, presses,

Rolling mills and similar constructions used. The strain or force transducers are preferably used for direct strain measurement at the container feet,

Hydraulic presses and the like mounted to detect the container contents or the pressing force due to the load.

Such transducers have been known for some time and have so far mainly been delivered before delivery

calibrated calibration weights or special test equipment. In addition, a calibration directly at the customer was often necessary because the assignment of

Strain behavior of the respective deformation body depended on which the strain or force transducer are directly attached.

CONFIRMATION COPY In such an application of the strain or force transducer, for example on a container foot calibration was initially made without container contents, in which the

Transducer then with an external evaluation device

must be connected, then the output signal a

Allocates empty load state. Thereafter, the container was filled to the nominal level with a defined amount, for example, water and the output signal as a full load in the

external evaluation and display device defined. Since such a weight load has a linear course, were in the operating state from the respective output signals by means of a linear function, the load or

Weight values are calculated in the external evaluation device and displayed if necessary. Especially with such large equipment, such calibration methods with external evaluation devices are very expensive and usually have to be carried out by external specialist personnel.

An external device for testing and calibrating container scales is known from DE 102 37 513 B4. In this calibration device, a rigid frame is provided, in which a hydraulic loading device is arranged. Below the loading device, the balance is arranged with at least one load cell, on which a modified container foot is turned off. For calibration, the balance is then loaded with an initial value and at least one end value. For this purpose, in particular a reference load cell is provided by which the initial and final values fixed

Weight or force values are assigned, from which in the balance with an externally assigned evaluation device according to a linear function, the weight values are calculated. With such a calibration device only separate scales or load cells can be calibrated with defined deformation bodies. A calibration of strain or Force transducers on undefined deformation bodies is thus not possible.

From DE 44 33 163 AI a device for calibrating balances is known, fixed in a dynamometer

are installed. It is about the chassis dynamometer

Abutment frame provided on which a

Loading device supported, on the other hand on the

Chassis dynamometer stands. In the loading device, a reference balance is arranged, whose reference values of the balance are assigned as start and end values in an evaluation device arranged externally to the weighing cells. Due to the separate abutment frame and the additional

Loading device is such a calibration very expensive and only suitable for intermediate load cells or scales.

A high-precision calibration method for load cells and load cells is known from DE 199 11 086 C2, which operates with a so-called force-normal measuring machine. In this

Force normal measuring machine, the respective load cells to be calibrated with several dead load weights are charged to at least the nominal force automatically and the output signals of the load cells or load cells assigned to the respective weight of the dead loads. With such a device, however, the calibration on site in the installed state of the strain or force transducer usually can not be done.

The invention is therefore the object of a

To provide method and apparatus with which

different strain or force transducer in the installed operating state automatically, i. without external

Load devices or dead loads can be calibrated easily. This invention is solved by the invention specified in claim 1 and 8. Further developments and advantageous embodiments of the invention are specified in the dependent claims.

The invention has the advantage that by the integrated in the sensor evaluation circuit with automatic calibration without external load devices and without external

Evaluation devices in a simple way, a calibration of the pickup can be made. In particular, no reference load machines or reference sensors are required, but the calibration can advantageously be carried out in the respective application and on the

set measuring range. This procedure has the advantage at the same time that it is normal

Operating state of the transducer can be made without the transducer would have to be dismantled from the measurement object and thus advantageously the calibration can also be done on site of the measurement object.

The invention also has the advantage that this

Calibration procedure by program-controlled

Computing devices also fully automatic and thus can be performed at predetermined intervals without any specialist. This is particularly advantageous if such a transducer is exchanged with integrated evaluation circuit or used later, since this requires no external devices and methods. The inventive device has the advantage that it is very compact executable and thus easy to many reliable machine parts for monitoring or as

Overload protection can be easily used and retrofitted. For this purpose, such a transducer with integrated

Evaluation circuit with the simplest version easy in Loading direction of heavy-duty machine parts are attached to this.

The calibration by means of only two load states not only a zero and nominal load calibration, but also an individual calibration of other load conditions is advantageously possible. So is advantageously a calibration of any load conditions as well as a calibrated monitoring or overload control at any

Machine parts possible, the critical loads

subject.

In a special calibration method, where the zero load of an increased output voltage and the rated load of a reduced output voltage are assigned, there is the advantage that even negative loads and those above the rated load can be accurately displayed or signaled.

The invention will be explained in more detail with reference to an embodiment which is illustrated in the drawing. It shows:

Fig. 1: A block diagram of a strain transducer with

integrated evaluation circuit. In the single Fig. The drawing is a block diagram of a strain 1 or force transducer is shown, in which an electronic evaluation circuit 13 for automatically calibrating the transducer 1 is integrated. The strain 1 or force transducer is as

Tensile strip sensor 10 is formed, which preferably has a plate-shaped deformation body of a

includes elastic special stainless steel or aluminum. On this deformation body 10 are preferably four

Strain gauges 11 applied as resistors, which too a Wheatstone bridge 14 are connected. The plate-shaped deformation body .10 still has at least two mounting holes 12, with which he to a

kraftbelastbares component of a crane, a container or a press is attached as a measuring body whose

Force load to be detected. It delivers the

Measuring bridge 14 an output signal, the strain of the

Measuring body and thus the force load or

Weight load is proportional. The output of the measuring bridge 14 is connected to an integrated in the transducer 1 electronic evaluation circuit 13, which consists essentially of an A / D andler 2, a calibration circuit 3, a

Memory circuit 4, an arithmetic circuit 5 and a D / AWandler 6 consists. Here are the necessary

electronic components mounted on a small circuit board, not shown, preferably in a

Groove 15 of the deformation body 10 is arranged and shed with a plastic sealing compound kraftnebenschlußfrei in this. This creates a compact

Strain sensor 1, which is formed cuboid in a proposed embodiment and preferably has a length of about 90 mm, a width of about 25 mm and a thickness of about 10 mm. Depending on the application but other shapes and dimensions are conceivable.

Such an embodiment can easily

force-loadable parts of many machines or components

be screwed, whose load is to be recorded. For power supply, for calibration and display of the measured value of the transducer 1 is provided with an outwardly guided at least five-core connection cable, not shown. This includes at least one line 17 for calibration, a line 18 for taring, a line 16 for display and two for power. For calibration outside the

Evaluation circuit 13 is still a calibration switch 7 for Generation of a second switching signal is provided, which is electrically connected to the calibration circuit 3. To generate a first switching signal or for taring a taring 8 is still provided, which is also connected to the calibration circuit 3. For display, a display device 9 is provided outside of the pickup 1, which is electrically connected via at least one display line 16 of the connecting cable to the D / A converter 6. For measurement and calibration of the above-described transducer 1 operates according to the following procedure:

First, the strain transducer 1 to a resilient

Machine part attached non-positively, which serves as a measuring body or object to be measured. Due to the mechanical load of the

Measuring body results in a change in length on the measuring body, which is transmitted to the extensometer 1. Due to the change in length, the electrical resistance of the applied strain gauges 11 changes proportionally to the elongation. This resistance change is converted by an unrepresented DC amplifier into an electrical measurement signal at the output of the measuring bridge 14. It is the

Strain transducer 1 preferably for an elongation of 500 pm / m and a transducer output voltage of 0 to 10 V (=

100%).

During calibration, these output voltages can be assigned to specific start or end values according to a linear characteristic. In an unloaded first state, the initial value is at the characteristic zero point, which represents a so-called tare function, and in which a zero-load indication is usually to take place. This uncalibrated output signal is now detected by the measuring bridge 14 and in the subsequent analog-to-digital converter 2 in a

Digital value converted. This characteristic start is at the Calibration of this digital output signal in the calibration circuit 3 associated with an output voltage level of one volt (= +10%). For this purpose, the tare switch 8 is first actuated for zero point calibration in this first, preferably load-free state, by means of its first switching signal in the calibration circuit 3

Initial value is assigned an output voltage of one volt (= 10%), so that preferably also negative strains are displayed. This initial value is now stored as a zero point in the memory circuit 4. The initial value or

However, the starting point may preferably be selected from a range of + 0% to + 20%.

Then, the measurement object or the measuring body is mechanically loaded up to a second state, preferably up to its nominal value. The resulting output signal of the measuring bridge 14 is now digitized in the A / D converter and the

Calibration circuit 3 supplied. In this second

Operating condition at rated load is now the

Calibration switch 7 is actuated, which generates a second switching signal, by which the output signal to the end point of

Characteristic is assigned as end value of an output voltage of 9 V (= 90%) and also stored in the memory circuit 4. By assigning the final value at 9 V, it is achieved that the output values up to 10 V (= 100%) can be precisely recorded even above the nominal value. However, the end value or endpoint may preferably be selected from a range of -0% to + 20% of the endpoint. In the memory circuit 4 additionally defined output measurement values are stored, which are assigned to the predetermined start and end values, and by the for each

Output signal of the measuring bridge 14 a defined

Loading force or a relative percentage load value can be calculated as the initial measured value. With these assignments within the calibration circuit 3 and the stored values in the memory circuit 4, the calibration process is automatically completed for the respective essobj ect. Such a calibration can also be fully automatic

be made. Then, the measurement object is from a first operating state, for example the tare state, in a second operating state, for example the nominal state, by means of a program-controlled, not shown

To control computing device. In this case, then by means of another program-controlled not shown

Switching device, a first switching signal are generated, by which the output signal in the tare state within the calibration circuit 3 an initial value of the characteristic

is assigned. Through this program-controlled

Switching device can when reaching a second

Operating conditions, for example, in the achievement of

Nominal load a second switching signal, by which the characteristic curve end point is determined. The program-controlled computing and switching devices can also be used in the

Evaluation circuit 13 to be integrated.

Such automatic calibration operations can also be done in

time intervals are carried out automatically, so that

Intermediate deviations can also be corrected thereby, which improves the measuring accuracy of the pickup 1. By such a method, a strain transducer 1 can also outside the zero load and outside the rated load

be calibrated. Thus, by triggering the first switching signal of the tare switch 8, only the respective output value of the output signal of the measuring bridge 14 is set to the beginning of the characteristic curve. In a further load can then by triggering the second switching signal by means of the calibration 7 this output value as the respective

Output signal of the measuring bridge 14 to the characteristic endpoint be placed. Insofar the pickups are 1 depending on

Application also individually calibrated.

After this integrated calibration, each detected output signal of the measuring bridge 1 is digitized in the analog-to-digital converter 2 and then fed to the arithmetic circuit 5. The instantaneous load measured value is then calculated as the output measured value in accordance with the calibration values stored in the memory 4. This is then in the digital-to-analog converter 6 in an analog output reading

converted and fed to the display device 9 for display or further processing. These output readings can then be displayed or used to signal or shut down the monitored object under test.

Claims

claims

A method for automatically calibrating strain gauges (1) or force transducers with a strain gauge circuit (11) for converting a mechanical load into an electrical output signal, wherein for calibrating the transducer (1) in a first or load-free operating state, a defined initial value and a defined end value in an evaluation circuit (13) is assigned to a second load-loaded operating state, wherein the evaluation circuit (13) calculates in the operating state from the assigned start and end value corresponding output measured values which can be displayed by means of a linear function, characterized in that the calibration in firmly installed operating state of the transducer (1) with an integrated in this evaluation circuit (13) automatically by by a controlled first switching signal, the initial value and by a controlled second switching signal of the final value in the evaluation circuit (13) we saved and the resulting measured values are calculated according to the subsequent loads.

2. The method according to claim 1, characterized in that in a first load-free operating state, the detected output signal of the measuring bridge (14) in a calibration circuit (3) of the evaluation circuit (13) due to the first switching signal of a tare switch (8) has a starting point of a linear Loaded load characteristic and a second output signal with rated load Operating state in the calibration circuit (3) of the evaluation circuit (13) due to the second switching signal of a calibration switch (7) is assigned an end point of the linear load characteristic.

3. The method according to claim 2, characterized in that the starting point and the end point associated output signals of the measuring bridge (14) and their intermediate values of the characteristic of a memory circuit (4) of the evaluation circuit (13) are supplied and stored there and assigned to defined defined output measured values.

A method according to claim 2, characterized in that the detected output signals due to the first switching signal to a 0 to 20% higher starting point of the load characteristic and the output signal due to the second switching signal are assigned a reduced by 0 to 20% end point of the load characteristic.

A method according to claim 1 to 4, characterized in that the respective output signals of the measuring bridge (14) with their assigned defined output measured values in an arithmetic circuit (5) of the evaluation circuit (13) are converted into calibrated output measured values.

The method of claim 1 to .5, characterized in that the calibrated output measured values in a display device (9) can be displayed or signaled at a threshold value exceeded.

A method according to claim 1, characterized in that the first and second operating state of the transducer (1) provided with the measuring object ^' by means of a program-controlled ^' computing device automatically controlled and thereby with the program-controlled

Computing device, the first and second switching signal is generated automatically, whereby the calibration in

Initial operating state or at intervals fully automatically.

Device for carrying out the method according to one of claims 1 to 7, characterized in that the transducer has a flat rectangular deformation body

(10) with strain gauges (11) applied thereto and at least two attachment regions (12), wherein an electronic evaluation circuit (13) is integrated in the transducer (1), the at least one calibration circuit

(3), a memory circuit (4) and an arithmetic circuit

(5).

Apparatus according to claim 8, characterized in that the calibration circuit (3) of the evaluation circuit (13) with at least one calibration (7) and a tare switch (8) is connected, with the aid of which in a first operating state, a first switching signal and at a second loaded operating state, a second switching signal is generated.

Apparatus according to claim 8 or 9, characterized in that the arithmetic circuit (5) or a digital-to-analog converter (6) of the evaluation circuit (13) with a display device (9) is connected, which serves to display the calibrated output measured values.