EP2979067A1

EP2979067A1 - Load cell diagnostics

Info

Publication number: EP2979067A1
Application number: EP14711793.1A
Authority: EP
Inventors: Daniel Schrag; Daniel Rupp; Christoph Trautweiler; Hans-Rudolf Burkhard
Original assignee: Mettler Toledo AG
Current assignee: Mettler Toledo Schweiz GmbH
Priority date: 2013-03-28
Filing date: 2014-03-24
Publication date: 2016-02-03
Also published as: US20160011038A1; US9964429B2; CN105074397B; JP2016514836A; WO2014154633A1; EP2784454A1; JP6336034B2; EP2784454B1; CN105074397A; PL2784454T3

Abstract

The force measuring apparatus comprises a stationary parallel limb (11, 111) and a movable parallel limb (12, 112) which receives the load of an applied material to be weighed and is connected to the stationary parallel limb (11, 111) by means of parallel guides (14, 114). The force measuring apparatus also comprises a measuring sensor (20, 120) which is connected in a force-transmitting manner to the movable parallel limb (12, 112) and comprises a coil (25, 125), which can move in a magnet system (27, 127) and through which an electrical current (24) can flow, and a position sensor (21, 28) which determines the deflection of the coil (25, 125), caused by the application of a load to the movable parallel limb (12, 112), from the adjusted position thereof with respect to the magnet system (27, 127). The electrical current (24) through the coil (25, 125) is used to return the coil (25, 125) and the movable parallel limb (12, 112) connected to the coil (25, 125) or to the magnet system (27, 127) to the adjusted position and/or to hold said elements there by means of the electromagnetic force between the coil (25, 125) and the magnet system (27, 127). According to the invention, at least one system identification means (29) of the force measuring apparatus (1) is created using a processing unit (26), and the system identification means (29) is compared with at least one invariable system reference means (30) which is persistently stored in the processing unit (26), wherein the functionality of the force measuring apparatus (1) is determined on the basis of the comparison and an action of the force measuring apparatus (1) is then carried out, and wherein the magnitude of the electrical current (24) and the magnitude of the deflection of the coil (25, 125) from the adjusted position thereof are used to check the functionality.

Description

Wägezellendiagnostik

The invention relates to a method for checking the operability of a force measuring device.

A load cell is a mechanical mass converter for determining the mass, in which the weight force exerted by the sample is converted into an electrical signal, examples being a strain gauge load cell, string load cell or EMFR (electro-magnetic force restoration) load cell. Frequently, a load cell finds its use in force measuring devices, in particular scales, which convert the weight of an applied load into an electrical signal. In load cells, which operate on the principle of electromagnetic force compensation, the weight of the sample is either directly or by one or more, mounted on bearings (s) power transmission lever to a

transmitted electromechanical sensor. The sensor generates a compensation force corresponding to the weight of the weighing sample and thereby provides an electrical signal which is further processed by a weighing electronics unit, the processing unit, and displayed.

An EMFR load cell usually has a parallelogram with a fixed parallel leg and connected to this by two parallel guides movable parallel leg, which serves as a load receiving area. In

Lever systems, the weight is transmitted via a coupled to the load receiving, longitudinally rigid, flexible coupling element to a load beam, which is supported on the fixed parallel leg. The purpose of such a weighing cell is to reduce the weight force corresponding to the applied load to such an extent that the measuring sensor generating the compensation force can output a measuring signal corresponding to the weight force. As is known, the connecting points of the individual elements are in

High-resolution load cells designed by Biegelager. Bend bearings define an axis of rotation between the two coupled elements and can at a one-piece load cell, also called monolithic load cell or monoblock, designed as a thin material locations.

In EMFR load cells in which the weight force directly, ie without reduction of the compensation force by means of levers, of the generated by the sensor

Compensating force is compensated, the parallel guides are usually as

Spring elements or spring joints or membranes designed. In such

Weighing cells, also called direct measuring systems, are characterized by a single

Sensor one of the weight of the load corresponding to the same size

Countering force, or with several arranged in a composite sensors a corresponding partial compensation force.

In high-resolution force measuring devices, the Biegelager are thinner and therefore more prone to damage that may affect the weighing result or make the force measuring device unusable. For example, a shock to the pan or an impact on the ground can lead to excessive stress on the parallel guides and other components. The possible consequences range from bent Biegelagern, spring joints or

Diaphragms, over torn places in the flexure bearings, spring joints or membranes, up to a break of a bending bearing, spring joint or a

Membrane. For example, a sensor used in an EMFR load cell may be configured as a current-carrying coil in a permanent magnet. In this case, usually the coil is arranged on the weighing beam and the permanent magnet on

attached fixed parallel leg, but also the variant in which the permanent magnet on the load beam and the coil is arranged on the fixed parallel leg is possible. In the operation of a force measuring device, the coil is traversed by an electric current, whereby an applied load

compensating compensation force is generated. A position measuring device detects the deflection of the coil from its Einspiellage, whereupon a control unit regulates the current due to the position measurement signal so that the coil is returned to the Einspiellage again. Is the coil in the single-play position, ie if all on System attacking forces are equal to zero, the magnitude of the electric current to determine the weighing result is measured and displayed.

Likewise, an excessively high stress, as mentioned above, also affect the coil in the magnet system or the position measuring device. in the

Manufacturing process of a force measuring device, the adjustment of the load cell is an important step to adjust the sensitivity and accuracy. These

Settings apply only to the configuration in which the adjustment was performed. In the event of excessively high stress, the orientation of the coil in the magnet system may change or the position device may shift relative to the weighing beam, with the result that the weighing result is not determined correctly.

Is despite damage to the load cell, be it at a Biegelager or through

Position changes of the coil in the magnet system or on the

Position measuring device relative to a position in which the

Force measuring device was calibrated, an alleged measurement of the weighing still possible, such damage is not apparent with today's means.

Nevertheless, a weighing result is output by the force measuring device, which is not correct because the force measuring device seems to work unscathed or without errors. EP 1 785 703 A1 discloses a method for monitoring and / or for

Determining the state of a force measuring device. The force measuring device in this case has a force measuring cell arranged in an interior of a housing, as well as a sensor, which has a life span of the force measuring device

influencing parameter of indoor climate measures. By means of the method, the state of a force-measuring device can be monitored without the housing having to be opened in order to determine the state of the force-measuring device.

The disadvantage here is that damage to the load cell, be it on a

Biegelager or a change in position of the coil or the

Position measuring device, after an excessively high stress is not recognizable. In order to ensure that the force measuring device functions correctly and the user can rely on the displayed measured value, the load cell must be checked at regular intervals. This periodic check is usually done by the manufacturer, which means a failure of the force measuring device and is associated with costs for the user.

The object of the present invention is to provide a method by which the functionality of a force measuring device can be checked.

In addition, it should be possible that the procedure at the place of operation of

Force measuring device and can be carried out by themselves.

According to the invention, the objects are achieved by a method for checking the functional capability of a force measuring device according to claim 1 which works according to the electromagnetic force compensation principle.

The force measuring device comprises a fixed parallel leg and a load of an applied weighing sample receiving movable parallel leg, which is connected by parallel guides with the fixed parallel leg. Furthermore, the force measuring device comprises a movable with the

Parallel shank in a force-transmitting manner connected sensor comprising a movable in a magnet system coil, which can be traversed by an electric current, as well as a caused by the application of a load on the movable parallel leg deflection of the coil from its Einspiellage with respect to the magnetic system detecting position sensor. The electric current through the coil serves to cause the coil and the movable parallel leg connected to the coil or the magnet system to move through the electromagnetic force between the coil and the magnet system

Attributed to and / or keeping one-game days.

According to the invention, at least one system identifier of the force measuring device is created by means of a processing unit, and the system identifier with at least a fixed in the processing unit persistently stored fixed system reference means, which is determined on the basis of the comparison, the operability of the force measuring device and according to which an action of the

Force measuring device is carried out, and wherein the size of the electric current and the size of the deflection of the coil are used from their Einspiellage to check the functionality.

By the inventive method, the force measuring device is capable of

Deflection of the coil from its Einspiellage or their position in the magnet system to be included in the check of the functionality, since the size of the deflection of the coil from its Einspiellage additionally supplied to the processing unit.

The sensor can be arranged in various ways in the force measuring device. Either the coil on the movable parallel leg and the magnet system on the fixed parallel leg, or the coil on the fixed parallel leg and the magnet system is attached to the movable parallel leg. In both cases, the coil and the magnet system can move relative to each other. The electrical current through the coil, usually regulated by a PID controller, in both cases causes an electromagnetic force between the coil and the magnet system which returns the coil to its Einspiellage relative to the magnet system and / or there holds when a load on the load receiving area is hung up. The coil, which is arranged movably in the magnet system, can be configured by one or more windings. The magnet system itself may be a permanent magnet or a current-carrying electromagnet. The

most common way is to attach the magnet system to the fixed area and the coil directly or coupled via one or more levers on

Load-receiving portion. This is usually useful because the lower

Mass inertia, in this case the inertia of the coil, a faster

Returning to or more stable holding of Einspiellage allows. But there are also force measuring devices in which the magnet system is arranged as a permanent magnet on the movable part, for example, to simplify the power supply of the coil. The Einspiellage is the position of the coil in the magnet system, in which there is a balance between all forces acting on the system forces. For lever systems, this also corresponds to a weighing beam position equal to zero. Due to the

Connection of the coil with the weighing beam is a deviation of the balance beam from the Einspiellage synonymous with a deflection of the coil from its Einspiellage. The same applies if instead of the coil, the magnet system with the

Weighing bar is connected. For the purposes of this application, the weighing beam is that one-sided or two-sided lever of the force-transmitting connection to which the position sensor monitors the single-play position. Preferably, the axis of rotation of the balance beam, the center of gravity of the balance beam, the connection of the first lever arm with the coupling, and the force generation center of the sensor, lie together on one level. If this is true, then that is

Weighing beam without applied load, always free of momentum and always in balance, regardless of any inclined surface. The level formed by the above points is also called level-neutral plane.

In a direct measuring system, the coil or the magnet system of the

Sensor attached to a power transmission linkage, which is directly connected to the load receiving area, which means that no levers for

Reduction of the applied force are present. A deflection of the coil or of the magnet system from its / their Einspiellage is in direct measuring systems synonymous with a deviation of the power transmission linkage from its Einspiellage.

Preferably, such an inventive method is used in microbalances

Application, as these usually have very thin Biegelager. These balances can determine a weighing load of 10g with a resolution of 0.001 mg, i. to the nearest ten millionths. Relatively small overloads are therefore already sufficient in order to cause damage to a bending bearing in the case of a microbalance.

The invention is suitable both for force measuring devices with sensors, which according to the push principle, as well as those according to the push-pull principle, the Create compensation force. Their difference lies in the generation of the

Compensation force: a push system can generate the compensation force in only one direction, while a push-pull system is capable of producing one

To generate compensation force in two opposite directions. The deflection of the coil from its Einspiellage is determined and quantified by the position sensor, which serves a position control unit to regulate the electrical current through the coil so that the coil and connected to the coil or the magnet system movable parallel leg through the electromagnetic force between the Coil and the magnet system in the

Einspiellage be traced back. Alternatively, the size of the deflection of the coil from its Einspiellage can also be determined by means of an additional position sensor. As additional sensors sensors are possible, which the same information about the size of the deflection of the coil within the magnet system as

Detect the sensor signal as detected by the position sensor of the position measurement. For example, this sensor signal could be from an acceleration,

Speed, angle or position sensor are provided to provide this information to a processing unit.

The position sensor used is preferably an optoelectronic position sensor whose sensor signal corresponds to the displacement of the interconnected moving parts of the load cell caused by the application of the load to the load receiver from a single-play position. Such an optoelectronic

Position sensor typically includes a light emitter and a light receiver, which are fixed with a gap on the fixed parallel leg, as well as a passing through the space and the deflection of the moving parts mitmachende shutter. The signal of the position sensor is fed to the position controller, which then regulates the electrical current through the coil so that the diaphragm and its associated movable parts of the load cell are returned by the electromagnetic force between the coil and permanent magnet in the Einspiellage. In other words, the control ensures that the electromagnetic force between the coil and the magnet system keeps the balance balanced. As a system here is the load cell with all its characteristics of the components

(Parallelogram, lever reduction, Biegelager, sensor, position sensor) and their influencing factors meant. Properties such as material properties, resistance moments, homogeneity of the magnetic field and linearity of the

Position sensors are dependent on various influencing factors.

Temperature changes, vibrations and vibrations of the substrate or impacts on the load cell influence the system or can even permanently change it. The reference means of the system describes the perfect condition or the functionality of the system after completion of production and assembly or when delivered to the user. This system reference means is persistently stored in the processing unit of the force measuring device. The identifier of the system identifies the current state or the

Operability of the system and is determined if necessary and / or in a predetermined time interval. The system identifier thus identifies the current state or the functionality of the force measuring device. A deviation of the system identifier from the system reference means therefore indicates a changed state or an altered functionality.

A development of the invention provides that the at least one

System identifier and the at least one system reference means each make a reference between the size of the electric current and the size of the deflection of the coil from their Einspiellage.

An advantageous development of the invention provides that the at least one system reference means the functioning of the force measuring device at the time of initial adjustment, in particular an adjustment during manufacture or near completion of the force measuring device, and / or the condition of proper functioning of the force measuring device.

A development of the invention provides that the at least one

System identification means and / or the at least one system reference means in each case a system table with the size of the deflection of the coil from its Einspiellage and the magnitude of the electric current associated values of the weight of the and / or comprises a system function with at least one parameter and at least the magnitude of the deflection of the coil from its Einspiellage and the size of the electric current as input variables. In the context of this invention, the at least one parameter of the system function is to be understood as a variable of a mathematical function which describes the relationship between the magnitude of the deflection of the coil from its insertion position and the magnitude of the electric current.

A system table is used to compare the system identifier with the

System reference means the corresponding value from a table, which has values depending on the size of the deflection of the coil from its Einspiellage and the magnitude of the current selected. A system function is a mathematical function with at least two input quantities and at least one parameter.

A further embodiment of the invention provides that the at least one

Parameter of the system function is stored as a parameter table. From a parameter table, the corresponding parameter of the system function in

Depending on the size of the deflection of the coil from its Einspiellage and the size of the current selected. In addition, the at least one parameter of the system function may be load-dependent. Another advantageous development of the invention provides that the determination of the values of the system table and / or the determination of the at least one parameter of the system function by varying the deflection of the coil and substantially simultaneous measurement of the size of the electrical for the deflection of the coil from its Einspiellage associated Current takes place, and / or by varying the size of the electric current and substantially simultaneous measurement of the size of the electric current associated deflection of the coil from its Einspiellage done.

An advantageous development of the invention provides that the determination of the values of the system table and / or the determination of the at least one parameter of the system function respectively without and with the movable parallel leg acting weight is carried out, wherein it may be in the weight to an externally levitated or an internally be applied by means of a device weight. The determination of the values and / or the at least one parameter under different load conditions improves the accuracy of the checking of the functionality over the entire weighing range of the gravimetric

Force measuring device.

Another aspect of the invention provides that the at least one

System reference means for each force measuring device individually or for the same type of force measuring device is generically created. It is obvious that each force measuring device, characterized by the individual manufacturing tolerances on the

Magnetic system, on the flexure bearings, on the position measurement and the

Leverage, own values and / or parameters, which then apply only to the one force measuring device. To be in production of

Force measuring devices to determine these values and / or parameters

can accelerate a system reference in the processing unit

stored, which was generically created from the arithmetic mean of previously determined system reference means.

A particularly advantageous development of the invention provides that by means of the comparison, a break or crack and / or bending of a joint of the

Parallel guidance and / or a change in position of the coil in the magnet system with respect to an original position and / or a position change of the position sensor is compared to an original position checked, the original positions respectively for the state of the force measuring device, in which the system reference means was created. A preferred embodiment of the invention is characterized in that from the created system identifier and the previously created system identification means a course of functioning is created, by means of which a prediction of the functionality, in particular the remaining time to the next maintenance of the force measuring device, can be made , A load cell for electromagnetic force compensation gravimetric force measuring apparatus having a force transmitting mechanical connection between a sensor, comprising a movable in a magnet system coil and a movable parallel leg, wherein either the coil or the magnet system is in communication with the movable parallel leg, characterized by characterized in that the force measuring cell has a position sensor which detects the deflection of the coil from its inserting position by the application of a load on the movable parallel leg, by means of which the size of the deflection of the coil from its inserting position can be determined, the size of the deflection of the coil from its inserting position can be used in a procedure for checking the functionality.

In a computerized program for carrying out the procedure for

Checking the operability by means of a working according to the electromagnetic force compensation principle gravimetric force measuring device, a signal for triggering an action by the force measuring device, such as a release or a blocking of the force measuring device, brought to the output. The force measuring device in this case has a movable in a magnet system coil, which can be traversed by an electric current, which serves the coil and connected to the coil or the magnet system movable parallel leg, by the electromagnetic force between the coil and the magnet system in to return and / or maintain the single-play days, and a force-transmitting mechanical connection between the coil and a

movable parallel leg, and the one caused by the application of the load on the movable parallel leg deflection of the coil from one of their Einspiellage detecting sensor. As inputs to the computerized program, at least the magnitude of the electrical current and the magnitude of the deflection of the coil from its insertion position are used.

A further development of the computerized program provides that the

computer-based program accesses a system reference means and at least one system identifier. The system identifier can in the memory of the program-executing unit stored and the system reference means persistently stored.

In the following, the subject invention is based on preferred

Embodiments, which are illustrated in the accompanying drawings explained. Show it:

Fig. 1 is a schematic sectional view of a load cell of a

upper-shell force measuring device as a lever system in the side view;

Fig. 2 is a monolithic load cell as a lever system in the

Side view;

3 shows a load cell as a direct measuring system;

4 is a block diagram with the aid of the functional sequence of a

will be described force measuring device according to the invention;

Fig. 5 is a block diagram with the help of the life cycle of a

will be described force measuring device according to the invention;

Fig. 6 is a position-current diagram, over the entire deflection range of

Coil, with the system functions SEI, S _E 2 and S _E 3 one

System reference means and an ideal system function A;

Fig. 7 is a position-current diagram, over the entire deflection range of

Coil, with the system functions S _K i, S _K2 and S _K3 a system identifier of a force measuring device with damaged Biegelagern or

Spring joints or membranes;

Fig. 8 shows a detail of the position-current diagram of Fig. 6, with the

System functions S _K i, S _K2 and S _K3 a system identifier of a force measuring device with damaged Biegelagern or spring joints or membranes, and with possibilities of thresholding the system functions;

Fig. 9 A position-current diagram, over the entire deflection range of

Coil, with a system function SK of a system identifier and a force measuring device with shifted position measurement in comparison with a system function SE of a system reference means;

10 is a position-current diagram, over the entire deflection range of

Coil having a system function SK of a system identifier of a force measuring device with an eccentrically shifted coil in the magnet system in comparison with a system function SE of a system reference means;

Features having the same function and similar configuration are given the same reference numerals in the following description.

Figure 1 shows a schematic representation of a load cell 10 of a

Force measuring device 1 as a lever system from the side in a sectional view. About the stationary parallel leg 1 1, the force measuring device 1 is supported on a base. On the movable parallel leg 12, which is connected by two parallel guides 14 with the fixed parallel leg 1 1, the load to be measured is placed on a shell 1 5. The parallel guides 14 are each by Biegelager 16 with the movable parallel leg 12,

or connected to the stationary parallel leg 1 1. Bend bearings 16 define an axis of rotation and behave transversely to the axis of rotation as a substantially rigid force transmitting element. The variant shown here as oberschalige

Execution is not mandatory. The force measuring device 1 can also be designed as undershielded, usually having a hanger. The coupling 13 transmits the weight to the first lever arm 1 8 of the balance beam 17, which is mounted on a bearing point. At the other end of the balance beam 17, the second lever arm 19, the measuring sensor 20 is positioned at its outer end, which compensates the reduced weight of the load with a compensation force. The sensor 20 shown here is as one in a Magnetic system 27 movably mounted current-carrying coil 25 shown.

Corresponds to the generated compensation force of the sensor 20 on the second lever arm 19 of the weight of the load on the first lever arm 18 so is the

Weighing bar 1 7 in balance and thus in the Einspiellage. This Einspiellage is monitored by a position sensor 21st

By placing a mass or applying a force on the shell 15, the movable parallel leg 12, guided in parallel through the parallel guides 14, lowers. Connected via the coupling 13 with the movable parallel leg 12, the balance beam 17 transmits this movement with a defined translation to the other, the transmitter 20 facing the end of the balance beam 17. By means of

Position sensor 21, a position signal 22 corresponding to the deflection of the coil 25 is determined from the Einspiellage. This position signal 22 is the

Input signal for a position control unit 23, which regulates an electric current 24 through the coil 25 so that the resulting compensation force, the coil 25 and connected to the coil 25 weighing beam 1 7 back to the Einspiellage. In the adjusted state (coil 25 is again in the

Einspiellage) is the strength of the electric coil current 24 is a measure of the determined to be determined, applied mass or force applied to the moving

Parallel leg 12. The strength of the electric coil current 24 is measured, processed by means of a processing unit 26 (see FIG. 3), and then displayed as a display value on a display.

In Figure 2 is a possible embodiment of a load cell 10 of a

Force measuring device 1 as a monolithic cell from the side in one

Sectional view shown. The fixed parallel leg 1 1, the movable parallel leg 12, the coupling 13, the parallel guides 14 and the balance bar 17 are in direct material connection of a single homogeneous

Material block worked. All these elements are suitable

Fabrication techniques from a metal cuboid by separation, e.g. machining, cutting, or eroding. The Biegelager 1 6, the fulcrum of the balance beam and the connection points of the coupling 1 3 are as thin

Material bridges formed, wherein the Biegelager 16 depending on the weighing range of Force measuring device 1 can be adjusted in their material thickness, ie that the material bridge of the bending bearing 1 6 fails at higher weighing ranges thicker.

Figure 3 shows a possible embodiment of a load cell 100 as

Direct measurement system. The fixed parallel leg 1 1 1 is supported on the ground. The movable parallel leg 1 12, which serves the load bearing is connected to a power transmission link 1 17 and is through

Parallel guides 1 14, designed here in Figure 3 as a membrane, out. In this embodiment, the sensor 120 is at the lower end of the

Power transmission linkage 1 17 arranged, in which case the coil with the

movable parallel leg 1 12 is in communication and the magnet system 127 is disposed on the fixed parallel leg 1 1 1. Further embodiments would be possible by attaching the sensor 120 in the area between the

Parallel guides 1 14 and / or by a reversed arrangement of magnet system 127 and coil 1 25. The thinner a material bridge of a material connection or a spring joint or a diaphragm, the more damage is a load cell 10, 1 00 in case of impacts on the movable parallel leg 12, 1 12, an impact on the ground or an excessively high load. As a result, the material connection or the spring joint or the membrane may be bent, have torn places or even break or be completely severed.

The position sensor 21 and the sensor 20, 1, 20 are also susceptible to impacts, overloads and / or impact with the ground. These components of a force measuring device 1 are positioned and aligned during manufacture or near completion of a force measuring device 1. A subsequent adjustment of the force measuring device 1 thus always refers to the position in which the force measuring device 1 has been positioned and aligned. A position deviating from this position of a component falsifies the weighing result without being noticed by the user. Despite damage to the load cell 10, 1 00, be it on a material connection or on a spring joint or on a membrane or by changes in position of the coil and / or the position sensor relative to a position in which the force measuring device 1 has been adjusted, a supposed weighing is still possible However, such damage can not be detected by today's means. Nevertheless, a weighing result is output from the force-measuring device 1, but this is not correct, since the force-measuring device 1 appears to function unscathed or without errors.

The following is the functional sequence for an in-service

Force measuring device 1 with reference to the block diagram of Figure 4 in more detail

described. An applied to the shell 1 5 load exerts a force F on the movable parallel leg 12, 1 12. The balance beam 17 and connected to the balance beam 1 7 coil 25 or connected to the balance beam 1 7 magnet system 27, or the power transmission linkage 17 and the with the

Power transmission link 1 17 connected coil 125 or with the

Transmission linkage 1 17 connected magnetic system 127 are deflected from their Einspiellage, that is, they take a different position. The new position x is determined by the position sensor 21 and forwarded as a position signal 22 to a position control unit 23. Based on the position signal 22, the position control unit 23, usually having a PID controller, constantly determines the necessary for the return of the system in the Einspiellage electric coil current 24. By the electric coil current 24, the coil 25, 125 forms a magnetic field and generated in the magnet system 27th , 127 a compensation force, which brings the balance beam 1 7 and the transmission rod 1 17 and thus the coil 25, 125 back to the Einspiellage. The whole process is constantly repeated in the sense of regulating or holding the system in the single-play days. This control circuit detects the deflection of the balance beam 1 7 or the power transmission link 1 1 7 so dynamic, that is several times per second, for example in the range of 500Hz - 10kHz. Since the electric coil current 24 is a direct measure of the compensation force, the electric coil current 24 is measured and from this the weight of the applied load as a display value calculated by the processing unit. to

Calculation of the display value also takes the processing unit 26

Additional factors, such as the ambient and magnetic temperature and time-dependent dynamic effects. The inventive method for checking the functionality is characterized in that the processing unit 26 in addition to the size of the electric current 24, the position signal 22 of the position sensor 21, so the size of the deflection of the coil 25, 125 used from their Einspiellage to assess the functionality. This is shown in FIG. 3 by the dashed line

shown. Also possible instead of the position signal 22 are input signals to the processing unit 26, which contain the same information about the position x or about the position of the coil 25, 125 within the magnet system 20, 120. In FIG. 4 this is represented by the dot-dashed path. For example, a second additional sensor 28, e.g. an acceleration, speed,

Angle measurement or position sensor, this information in the form of a position signal 22 'to the processing unit 26 supply.

The force measuring device 1 is thus able to incorporate the size of the deflection of the coil 25, 1 25 from its Einspiellage in the assessment of functionality, and so also damage such as the magnetic system 20, 120, at the position measurement, to the Parallel guides 14, 1 14 especially the bending bearing 16 or the spring joints or the membranes and to take into account the lever translation.

Stored in the processing unit 26 is the system reference means 30, which was created during an adjustment of the force-measuring device 1 (see the

Description of Figure 5). The system reference means 30 is stored persistently, ie permanently and can only be overwritten when the force measuring device 1 is readjusted. This is indicated in Figure 4 by the symbol of the closed lock. The system identifier 29, however, can be updated during operation of the force measuring device 1, for example after a successful

Checking the functionality. The out-of-date system identifier 29 ' but must not be deleted, but can continue to be stored in the processing unit 26 to give, for example, in a history information about the course of the functioning of a force measuring device 1 can.

Under a calibration, the detection of a deviation between the

Measured value and the true value of the measurand at given

Measuring conditions without making any change understood. If, however, a change made one speaks of an adjustment. For example, in the case of a balance, when adjusting by fine-tuning its functions with the parts provided by trained personnel (manually), or semi-automatically by the user, placing an external reference weight built into the balance, or automatically, if the balance one

Has adjustment mechanism with reference weight, the change compensated.

FIG. 5 shows the life cycle of a force-measuring device 1 as a block diagram. At the beginning, all components or components of a force-measuring device 1 are manufactured and assembled into a force-measuring device 1. Subsequently or promptly to the completion of the force measuring device 1 is usually carried out a calibration of the force measuring device 1 and an adjustment of the components and parts of the force measuring device. 1 In this case, a system reference means 30 is created, which maps the state of perfect functionality. This system reference means 30 is stored persistently in the processing unit 26. The

System reference means 30 can be in the form of a system table or a

System function be stored with at least one parameter. In addition, other setup settings of the force measuring device 1 in the

Processing unit 26 are stored. A system reference means 30 can be determined individually for each individual force-measuring device 1, or generically for one and the same type of force-measuring device 1. In this generically determined system reference means 30, an average value is determined from a plurality of previously determined system reference means 30, which can then be used for all force measuring devices 1 of the same type. The force measuring device 1 can now be delivered to the user and put into operation. For special, on the operating conditions, such as a constantly existing preload, adapted force measuring devices 1, can be maintained with the creation of the system reference means 30 and done only at the site. Today's force measuring devices must be checked and tested for their functionality by the manufacturer in a certain time interval in order to meet certain accuracy requirements from national regulations, calibration regulations and / or industry standards. This can be done locally by a service technician or by the manufacturer of the force measuring device 1. If a damage is discovered in the functional test by the manufacturer and it turns out that the cost of a repair will not be worthwhile

Force measuring device 1 taken out of service. Is the result of

Function test positive, the user can continue to operate the force measuring device 1 for the next time interval. Is the force measuring device to a

Communication network connected, a message to the manufacturer can be triggered. Because of the message, the manufacturer knows as well about the

Functioning of the force measuring device is ordered and can take appropriate steps if necessary.

As a third possibility, those components which have suffered a defect or whose damage can be exchanged when identifying a damage

Functioning is faulty. Subsequently, a new adjustment of

Components and parts of the force measuring device 1 by the manufacturer necessary.

Here, a system reference means 30 is again created and in the processing unit

26 persistently stored, wherein the previous system reference means 30

is overwritten. Additional additional setup settings can also be stored in the processing unit 26. The force measuring device 1 is then released again for operation by the user.

The inventive method, represented by dashed lines in FIG. 5, fits into this life cycle prior to the periodic maintenance by the manufacturer and checks the functionality during the time interval between two maintenance operations the force measuring device 1. As a result, it can be detected even before an actual maintenance whether the functionality is given or limited. This prevents the use of the force measuring device 1 if damage to the

Force measuring device 1 would be present and the force measuring device 1 seems to be undamaged or seems to work without errors. On the other hand, the time interval between two servicing can also be prolonged if the check of the functionality is positive in each case, whereby the user saves costs which arise due to the failure of the force-measuring device 1.

The inventive method compares each of the at least one

System reference means 30 with at least one system identifier 29 and determined on the basis of the comparison, the operability of the force measuring device. 1 The system identifier 29 and the system reference means 30 each relate the magnitude of the electrical current 24 to the magnitude of the deflection of the coil 25, 125 from their single-player locations, and may take the form of values in a system table or system function with at least one parameter to be available. The persistently stored in the processing unit 26

System reference means 30 represents the state of the force measuring device 1 with perfect functionality and the system identifier 29 the state of the force measuring device 1 with the current, current functionality. Previously, in order to compare the system identifier 29 with the system reference means 30, the system identifier 29 must be created in the form of values in a system table or system function with at least one parameter. The determination of the values of the system table or the system function with at least one parameter as a step before the comparison of the system identifier 29 with the system reference means 30, as well as the determination of the values of a system table or the system function with at least one parameter of the system reference means 30 during the adjustment, can different types take place.

In the following, possibilities for determining the values of a system table and the system function with at least one parameter are shown. The determination is advantageously carried out during the production of the force-measuring device 1, especially during the adjustment phase. As a first possibility, the determination is made by varying the deflection of the coil 25, 125 and in

Substantially simultaneous measurement of the deflection of the coil 25, 125 associated size of the electric current 24. Alternatively, as a second possibility, the determination by varying the size of the electric current 24 and in the

Substantially simultaneous measurement of the size of the electric current 24 associated deflection of the coil 25, 1 25 done. In order to be able to vary the deflection of the coil 25, 1 25 or the size of the electric current 24, the processing unit can specify a desired position or a nominal current by means of two interfaces to the position control unit 23.

The two processes described above for determining the values of a system table and / or of a system function having at least one parameter can additionally be carried out with an additionally applied calibration weight. From the measurement with calibration weight and a measurement without calibration weight can then each have a separate system reference means 30 and system identifier 29 for the magnet system 20, 120, for the parallel links 14, 1 14 and their Biegelager 16 or their spring joints, the position sensor 21 and / or of

Lever transfer ratio are formed.

From the created system identifier 29 and the previously created

System identifier 29 'can be created a course of operability, by means of which a prediction over the remaining time until the next maintenance of the force measuring device can be made.

If the force-measuring device 1 has an internal calibration weight that can be connected to the movable parallel leg 12, 12, the force-measuring device 1 can use one or more of the abovementioned possibilities for determining the values of a system table and / or the system function perform menu-controlled or autonomous with at least one parameter. After checking the operability of the processing unit 26 may be a release of the force measuring device 1, a blocking of the force measuring device 1, or a warning to the user, or generally an action of

Force measuring device 1 done. Such a warning may include the information that maintenance is imminent or operability

is restricted.

FIGS. 6 to 10 show various system functions of force-measuring devices 1 based on position-current diagrams. The system function establishes a relationship between the magnitude of the electrical current 24 and the magnitude of the deflection of the coil 25, 125 from its single-play position, and is one way to represent a system identifier 29 and a system reference 30, respectively. The

Markings 100% and -100% and 10% and -10% on the horizontal axis define the deflection position of the coil 25, 125 in the magnet system 20, 1 20.

FIG. 6 shows a system function A of an idealized force-measuring device 1 with ideal behavior of the flexure bearings 16 or of the spring joints and of the magnet system 20, 1 20 as a straight line, which means that a deflection of the coil 25, 125 from their single-play position results in a linear change of electric current 24 results. In contrast to the system function A, the system functions S _EI , S _E2 and S _E3 correspond to the real behavior of the magnet system 20, 1 20 and at the same time constitute a system reference means 30.

If the force measuring device 1 experiences an excessively high load, be it a blow to the weighing pan 15 or an impact on the ground, the system functions also change. FIG. 7 shows a system identifier 29 created by the processing unit 26 with the system functions S _K i, S _K2 and S _{K3 of} a force measuring device 1 in which at least one flexure bearing 16 or spring joint or membrane has been damaged by an excessively high load, shown. Good to see are the not even running

System functions or the characteristics of the system functions at the deflection position P. Such characteristics of a damaged bending bearing 16 or spring joint or a damaged membrane can be of various shapes accept. For example, as shown at system function SK2, over a small range of deflection position associated with a large deviation of coil electric current 24, or as shown at system function S _K 3, over a large range of deflection position associated with a small deviation of coil electrical current 24 ,

FIG. 8 is an enlarged section of the dashed rectangle in FIG. 7. A comparison between a system reference means 30 and a system identifier 29, as shown in FIG. 8, is to quantify the extent of the deviation and to qualify it by means of a threshold value. As a threshold value, for example, a tolerance band may be set, whose included range may not be exceeded, or it may, as shown in the system function S _K 3, for the

included area between the system reference means 30 and the

System identifier 29 be set a threshold, or combined both possibilities. The tolerance band does not have to be the same width over the entire deflection range, but can also be set depending on the deflection. This ensures that a deviation of the system function of a

Systemkennmittels 29 must have a lower tolerance in the field of Einspell days for the qualification. It can thus be ensured that the most varied types of system functions are quantified and qualified according to their significance.

FIG. 9 shows how a displacement of the position sensor 21 results in a system function SK of a system identifier 29. If the position sensor 21 is no longer at the position at which the adjustment was made deviates

System function SK of the system identifier 29 in the position-current diagram in the horizontal direction of the system function SE of the system reference means 30 from. A deviation is thus easily and quickly detectable.

In Figure 10, the effect of an off-center, off-center displacement of the coil 25, 125 in the magnet system 27, 127 on the system identifier 29 is shown. Analogously to the deviation in FIG. 9, a system function S _K of FIG

System identifier 29, which in the direction vertical to the system function SE of System reference means 30 is shifted, which means that at all deflection positions of the coil 25, 125, a stronger current 24 flows through the coil 25, 125, as in the adjusted state. In both cases, the off-center

Displacement of the coil 25, 125 in the magnet system 27, 127 and the displacement of the position sensor 21, suitable tolerances or thresholds are set, preferably with tighter tolerances in the field of Einspiellage.

It has been found that a system reference means 30 and a system identifier 29 are dependent on the mass of the applied load, ie the values of the system table and / or the system function parameters of a system reference means 30 or a system identifier 29 apply to a specific applied load. In FIGS. 6, 7 and 8 this is illustrated with different system functions SEI, S _E 2 and S _E 3 or S _K i, S _K 2 and S _K 3. The stronger the associated on the moving

Parallel leg 12, 1 12 applied force, the greater is the curvature of a system function in the position-current diagram. The system function SE3 or Siowe has an upward curved characteristic. This arises when the direction of force of the measuring sensor 20, 120 changes, as occurs, for example, in push-pull systems. The system reference means 30 and the system identifier 29 therefore contain at least one system table and / or one system function with the corresponding parameters which is then used to check the functionality if the system table or the system function corresponding to the

best match the applied force, or it interpolates between two values of the system table or between two system functions.

Although the invention is characterized by the illustration of several specific

Having described embodiments, it is obvious that numerous other embodiments can be provided with knowledge of the present invention, for example by the characteristics of the individual

Embodiments combined with each other and / or individual functional units of the embodiments are exchanged. LIST OF REFERENCE NUMBERS

1 force measuring device

10 load cell of a lever system

100 load cell of a direct measuring system

1 1, 1 1 1 fixed parallel leg

12, 1 1 2 movable parallel leg

13 paddock

14, 1 14 parallel guide

15 weighing pan

16 Bearing

17 balance beam

1 1 7 Power transmission linkage

18 First lever arm of the balance beam

19 Second lever arm of the load beam

20, 120 sensors

21 position sensor

22 position signal

23 position control unit

24 coil current

25, 125 coil

26 processing unit

27, 127 magnet system

28 Additional position sensor

29 System Identifiers

29 'preceding system identifier

30 system reference means

A ideal system function

SE, SEI, S _E 2, S _E 2 System function of the system reference means

SK, SKI, S _K 2, S _K 3 System function of the system identifier

F Weight of the load applied

x Position of the balance beam or of the power transmission linkage disturbance

temperature signal

time signal

Claims

A method for checking the functionality, one after the

electromagnetic force compensation principle working

Force measuring device (1) comprising

- a fixed parallel leg (1 1, 1 1 1)

a movable parallel leg (12, 12) receiving the load of an applied weighing product, which is connected to the stationary parallel leg by means of parallel guides (14, 14),

- A sensor connected to the movable parallel leg (12, 1 12) in a force-transmitting manner transducer (20, 1 20) comprising a in a magnet system (27, 127) movable coil (25, 125), which flows through an electric current (24) can be,

- the one by placing a load on the movable

Parallel leg (12, 1 12) caused deflection of the coil (25, 1 25) from its Einspiellage with respect to the magnetic system (27, 1 27) detecting position sensor (21, 28),

wherein the electrical current (24) through the coil (25, 125) serves the coil (25, 1 25) and the movable parallel leg (12, 1) connected to the coil (25, 125) or the magnet system (27, 127) 1 2) through which

electromagnetic force between the coil (25, 125) and the

Magnetic system (27, 127), attributable to the one-play days and / or to keep there, characterized in that

at least one system identification means (29) of the force-measuring device (1) is created by means of a processing unit (26), and

the system identifier (29) is compared with at least one immutable system reference means (30) persistently stored in the processing unit (26),

whereby due to the comparison the functionality of the

Force measuring device (1) is determined, and

wherein the size of the electric current (24) and the size of the deflection of the coil (25, 1 25) are used from their Einspiellage to check the operability.

2. A method for checking the functionality according to claim 1, characterized in that

the at least one system identifier (29) and the at least one

System reference means (30) each establish a relation between the magnitude of the electric current (24) and the magnitude of the deflection of the coil (25, 125) from their Einspiellage.

3. A method for checking the functionality according to claim 1 or 2, characterized in that

the at least one system reference means (30) represents the functionality of the force measuring device (1) at the time of the first adjustment, in particular an adjustment during manufacture or near completion of the force measuring device (1), and / or the condition of proper functioning of the force measuring device (1) ,

4. A method for checking the functionality according to one of claims 1 to 3, characterized in that

the at least one system identifier (29) and / or the at least one system reference means (30) each comprise a system table with values of the weight of the applied load associated with the size of the deflection of the coil (25, 125) and the magnitude of the electrical current (24) and / or comprises a system function with at least one parameter and with at least the magnitude of the deflection of the coil (25, 125) and the magnitude of the electrical current (24) as input variables.

5. A method for checking the functionality according to claim 4, characterized in that

the at least one parameter of the system function is stored as a parameter table, wherein the at least one parameter of the system function may be load-dependent.

6. A method for checking the functionality according to claim 4 or 5, characterized in that the determination of the values of the system table and / or the determination of the at least one parameter of the system function by varying the

Deflection of the coil (25, 125) and substantially simultaneous measurement of the deflection of the coil (25, 1 25) associated size of the electric current (24), and / or by varying the size of the electric current (24) and substantially simultaneous measurement of the size of the electric current (24) associated deflection of the coil (25, 125) takes place.

Method for checking the functionality according to claim 6, characterized in that

the determination of the values of the system table and / or the determination of the at least one parameter of the system function is carried out in each case without and with a load acting on the movable parallel leg (12, 11), the weight being an externally deployable or an internally can act by means of a device attachable weight.

Method for checking the functionality according to one of claims 1 to 7, characterized in that

the at least one system reference means (30) is generated generically for each force measuring device (1) individually or for the same type of force measuring device (1).

Method for checking the functionality according to one of claims 1 to 8, characterized in that

by means of the comparison a break or crack and / or bending of a

Joint of the parallel guide (14, 1 14) and / or a change in position of the coil (25, 1 25) in the magnet system (27, 127) compared to an original position and / or a change in position of the position sensor (21, 28) compared to an original position checks becomes, whereby the

original positions respectively for the state of the force measuring device (1), in which the system reference means (30) was created. Method for checking the functionality according to one of claims 1 to 9, characterized in that

From the system identifier (29) created and the previously created system identification means (29 ') a course of functionality is created, by means of which a prediction of the functionality, in particular the remaining time until the next maintenance of the force measuring device (1), can be made.

Gravimetric force measuring device (1) operating according to the electromagnetic force compensation principle, with a method for checking the functioning of the gravimetric force measuring device (1) according to one of claims 1 to 10.

Computer-aided program for carrying out a method for

Checking the functionality according to one of claims 1 to 1 1 with output of a signal to trigger an action by the

Force measuring device (1) and at least the magnitude of the electric current (24) and the magnitude of the deflection of the coil (25) from their Einspiellage using as input variables for a working according to the electromagnetic force compensation principle gravimetric force measuring device

(1) - 13. Computerized program for carrying out the procedure for

Checking the functionality according to claim 12, characterized

marked that

the computerized program accesses a system reference means (30) and at least one system identifier (29) according to any one of claims 1 to 10.