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WO1997017597A1 - Balance - Google Patents

Balance Download PDF

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Publication number
WO1997017597A1
WO1997017597A1 PCT/EP1996/004874 EP9604874W WO9717597A1 WO 1997017597 A1 WO1997017597 A1 WO 1997017597A1 EP 9604874 W EP9604874 W EP 9604874W WO 9717597 A1 WO9717597 A1 WO 9717597A1
Authority
WO
WIPO (PCT)
Prior art keywords
sensor
temperature
calibration
pressure
conditioning
Prior art date
Application number
PCT/EP1996/004874
Other languages
German (de)
English (en)
Inventor
Jürgen Hermann
Original Assignee
Hermann Finance Corporation Ltd.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US08/575,792 external-priority patent/US5764541A/en
Application filed by Hermann Finance Corporation Ltd. filed Critical Hermann Finance Corporation Ltd.
Publication of WO1997017597A1 publication Critical patent/WO1997017597A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01G—WEIGHING
    • G01G5/00—Weighing apparatus wherein the balancing is effected by fluid action
    • G01G5/04—Weighing apparatus wherein the balancing is effected by fluid action with means for measuring the pressure imposed by the load on a liquid
    • G01G5/06—Weighing apparatus wherein the balancing is effected by fluid action with means for measuring the pressure imposed by the load on a liquid with electrical indicating means

Definitions

  • the invention relates to a balance according to the preamble of claim 1.
  • DE-A1-40 32 955 shows a pressure sensor in which the pressure sensor is arranged in the interior of a housing in direct contact with the pressure-transmitting liquid medium.
  • the volume of the liquid medium is kept as small as possible.
  • DE-A1-43 15 962 describes a pressure sensor in which a pressure sensor is arranged between two pressure-medium chambers filled with a liquid pressure-medium medium. Such a sensor has been proposed in particular for measuring pressures of corrosive media.
  • EP-A1-0 658 754 in turn shows an arrangement in which influences by electromagnetic radiation or by electrical charging of the oil filling on the pressure-dependent changes in resistance of the strain gauges made of polycrystalline silicon are to be avoided by providing metallic separating foils.
  • One of these foils is arranged in the immediate vicinity of the strain gauges, covering them.
  • a temperature compensation circuit is provided to compensate for temperature influences.
  • the object of the present invention is to provide a balance which is based on the principle of measuring a weight force via the change in pressure generated by it in a pressure medium.
  • the scale according to the invention has advantageous features compared to known scales - scales which are used in particular for weighing small weights and people for weighing ranges between approximately 2 and a few hundred kilograms.
  • the principle on which the scale is based such as measuring the weight force to be determined via the pressure which this weight force generates in a pressure medium, makes mechanical parts, such as weighing beams, unnecessary. There are therefore no torques to be compensated, and strain gauges which are difficult to assemble with known low output signals and thus necessary, current-intensive amplifier circuits with large temperature and inherent errors to be compensated for can also be dispensed with.
  • the balance according to the invention has a pressure sensor embedded in a pressure medium - wherein, if appropriate, further electronic components can also be embedded in the pressure medium.
  • the pressure medium is arranged within a basic structure with a corresponding recess and between this and a weighing plate and is hermetically sealed to the outside.
  • the pressure sensor is in particular a piezoresistive pressure sensor (other pressure sensors, such as, for example, electroresistive ones, are also possible).
  • the preferred measuring electronics which can optionally also be embedded in the diaphragm seal medium, has a programmable amplifier circuit for adjusting the offset and yarn, a programmable sensor supply for rough adjustment of the sensor output signal, a temperature compensation circuit, an A / D converter for converting the analog measurement signal, a memory, for example an EEPROM, for storing the resultant Compensation and setting parameters, a serial or parallel interface to an externally connectable microprocessor and a program for executing the error compensation and separation of the sensor useful signal from the sensor error signal and for converting the pressure values into weight values.
  • system can be designed as a modular system due to the differently arrangeable electronic components.
  • the sensor-measuring electronics arrangement described will be an arrangement which is preferable in many respects, since not only can this drastically reduce the manufacturing costs, but also the calibration of the balance is simple at the same time high accuracy regardless of the respective weighing range.
  • Such an arrangement enables the compensation of sensor, housing, temperature and intrinsic errors of the electronics with the balance fully assembled; the error compensation data and setting parameters that can be obtained during the calibration are stored in a non-volatile memory.
  • the measuring electronics could also be designed as "classic", so-called textbook electronics, consisting of an adjustable amplifier circuit (offset and gain adjustable), a current or voltage supply to the sensor, an A / D converter and a microprocessor with display.
  • an adjustable amplifier circuit offset and gain adjustable
  • a buffer and a high-resolution A / D converter (16 bits or more) can also be provided in order to separate the sensor error signal from Separate the useful sensor signal only in the microprocessor.
  • space requirements, power consumption, manufacturing and assembly complexity, and thus sources of error to be additionally calculated in, as well as higher component costs are generally to be regarded as disadvantageous. It is understood that these classic arrangements are within the scope of the present application.
  • the pressure medium is - at least against the weighing plate too - at least partially covered by a membrane which - at least indirectly - as a support for the weighing plate or for correspondingly dimensioned partial areas of the weighing plate, for example in the form of nipples, webs or foot-like projections or as part of the weighing plate itself.
  • the membrane is thus provided as an optionally force-transmitting element.
  • the design of the weighing plate and specifically by the choice of the size of the force-transmitting surface, gives the possibility, with the sensor-measuring electronics arrangement configured in the same way, of the weighing range of a weighing arrangement according to the desired use against lower or higher To move areas.
  • F ⁇ g.1 a representation of the principle of a scales according to the invention in section;
  • 6a shows a plan view of a balance
  • 6b shows a section according to AA of FIG. 6b; b
  • FIG. 6c shows detail I of FIG. 6b
  • FIG. 7a shows a plan view of a balance with the weighing plate removed, wherein
  • Figures 7b and 7c each show a section along B-B of Figure 7a for different designs
  • FIG. 8 shows a representation corresponding to FIG. 7a of an alternative design for an inventive one
  • FIG. 9 shows a further representation corresponding to FIG. 7a of a further alternative embodiment for a balance
  • FIG. 11 shows a schematic representation of a conditioning IC
  • a pressure-medium medium 3 is introduced between a basic structure 1, which may be in several parts, but is essentially cup-shaped, and a weighing plate 2 in a cavity provided by a corresponding design of the basic structure 1.
  • This pressure medium 3 is an incompressible Liquid, the viscosity of which will have to be selected as required, such as silicone oil, or also a gel, such as silicone gel.
  • the pressure medium 3 is delimited at least on one side by a flat, thin structure, a membrane 5, so that it is held within the cavity given by the shape of the basic structure 1.
  • the membrane 5 is, for example, seated in a clamping connection 7 with a sealing ring assigned to the basic structure 1.
  • this membrane 5 can be made of metal or plastic, the thickness will vary between 0.01 mm and 0.5 mm, depending on the intended use.
  • a pressure sensor 4 is provided in the pressure medium 5, possibly articulated to the basic structure 1, for example a piezoresistive pressure sensor. Since a change in the crystal structure and thus the conductivity takes place in the case of a piezoresistive element when the pressure changes, the pressure change can be measured as a proportional change in resistance. The change in the specific resistance of the piezoresistive pressure sensor is thus a measure of the pressure force acting on it.
  • Battery (s) as a voltage source, amplifier for amplifying the electrical signal obtained,
  • a / D converter in connection with a microprocessor, optionally temperature sensors with corresponding electronic components for compensation of temperature influences on the sensor and pressure medium can be in be ⁇ known way.
  • a programmable circuit consisting of sensor supply and a downstream programmable A / D converter with signal amplifier electronics, is advantageously provided, with this system including memory (preferably an EEPROM) for the sensor- and balance-specific error compensation and calibration values in the oil encapsulates.
  • memory preferably an EEPROM
  • Pressure sensor and possibly also the associated electronics - described in detail below - are embedded in the diaphragm seal medium, the battery (s) - optionally exchangeable - m Basic structure 1 is (are) arranged.
  • the display and, where appropriate, further components, such as a microprocessor with an integrated display driver, RAM, ROM and I / Os (Smgle-Chip-micro-computer) will have to be provided in or on the basic structure (see below) ).
  • a receptacle 6 for the batteries is arranged on the basic structure 1.
  • a frame 13 encompasses the basic structure 1 and weighing plate 2, so that the latter cannot tip over even when the weight supports are unequal and could thus possibly damage the membrane.
  • the gap 14 between the basic structure 1 and the weighing plate 2 is also covered.
  • the membrane 5 delimiting the pressure medium medium 3 will have to be suitably designed.
  • the membrane 5 can be made of a somewhat elastic material, or it can also have expansion areas (see below).
  • the thickness of the membrane should not be kept too thick, so that the force acting on it is transferred correctly to the diaphragm seal medium and is not possibly supported by the membrane itself.
  • the pressure medium medium could also be provided in a cushion-like manner - the membrane would then be the "cushion cover" - between the weighing plate and the basic structure.
  • the geometry to be provided for the pressure medium medium can be of the most varied types, in this way increasing or reducing the force transmission surface, as described by way of example with reference to some figures below.
  • FIGS. 2 to 9 show examples of possible designs for scales in which the engagement surfaces of the weighing plate (pressure medium medium) basic structure are dimensioned differently and / or the membrane is designed differently.
  • the possibility of different weighing ranges is determined by determining the force-transmitting area given for the same sensors and on the other hand - for example in the case of personal scales - an increase in stability is achieved during the weighing process.
  • the choice of the size of the force-transmitting surface on the weighing plate thus provided makes it possible - with the same basic structures and the same electronic components - to select a wide variety of weighing ranges which are matched to the corresponding purposes.
  • FIG. 2 shows a configuration corresponding to that of FIG. 1, in which the weighing plate 2a and membrane 5a are formed in one piece - for example as an injection molded part.
  • the weighing plate 2a is designed here as a more stable, thicker area of the membrane.
  • the membrane 5a can sit tightly clamped on the basic structure 1 in the manner described above, or it can also be welded or glued.
  • the hermetic seal of the pressure medium 3 is essential.
  • FIG. 3 The design according to FIG. 3 is similar to that of FIG. 2, here the membrane 5b being divided several times and alternatingly having thicker areas 5b1 and thin areas 5b2, which - compared to the design of FIG. 1 - gives greater strength .
  • a membrane 5b can also be produced in one piece by injection molding. If necessary, such a membrane 5b with correspondingly large regions 5b1 and comparatively narrow regions 5b2 over the thicker regions 5b1 could also serve as a weighing plate, or a weighing plate 2 arranged above it can be provided, as shown in FIG to avoid possible injuries to the membrane 5b.
  • FIG. 4a and 4b show an embodiment variant for a balance according to the invention, FIG. 4a representing a section along EE of FIG. 4b.
  • the support body 12 is arranged above the scale surface hm, with intermediate, rather small-area membrane parts 5c which are attached to the support bodies 12, for example welded or glued, or in the case of a two-part design of these support bodies, as indicated by dash-dotted lines, held therein, glued, welded or injection-molded in one piece.
  • the weighing plate 2c engages with appropriately shaped, nipple-shaped projections 9c in these membrane parts, as a result of which the force-transmitting area is reduced (or a higher oil pressure is achieved) and the weighing range can thus be shifted towards smaller values.
  • the support body 12 or the lower support body parts can be fixedly arranged on the base structure 1, optionally injection-molded in one piece with this.
  • the membrane possibly with the corresponding upper support body parts (for example also in one piece, similar to FIG. 3), could then be laid over it and firmly connected to the lower support body parts, hermetically sealing the pressure medium.
  • the projections 9c can each be arranged between the individual support bodies 12, but web-shaped projections 9c1 could also be provided, as indicated by dashed lines.
  • the arrangement of the support bodies 12 with the membrane parts 5c lying therebetween, the surface area of which is determined by the number and dimensions of the support bodies 12, enables a large number of weighing plates to be designed differently, with a few or many individual nipple-like projections or with between the supports Ridge-shaped projections engaging the body rows or also with a bridge "net", depending on the weighing range to be provided.
  • a display 11 is arranged on the housing of the scale.
  • Fig. 5 shows another possibility of changing the weighing range - with otherwise the same measuring device.
  • the force-transmitting surface of the weighing plate 2d is enlarged, the lower surface of the weighing plate 2c is corrugated or nubbed, the counter plate of the basic structure 1d is shown in FIG formed approximately opposite, the diaphragm medium 3 covered by the membrane 5 over the entire surface.
  • the pressure sensor 4 is arranged in an extension 17d. The weighing range of such an arrangement can be shifted towards larger values by increasing the area, since the oil pressure is reduced with the same weight.
  • FIGS. 6a, 6b and 6c show an embodiment of a balance in which the basic structure 1e has an annular recess 8.
  • FIG. 6a shows the top view of such a scale.
  • a display 11 in particular a liquid crystal or LED or plasma display, is arranged on the basic structure of the housing of the scale and is excluded in the scale cover.
  • the pressure made available via the sensor arrangement in the chemical seal medium is displayed by the microprocessor after conversion from pressure to weight according to the desired measurement system by the microprocessor.
  • Fig. 6b shows a section along AA of Fig. 6a
  • Fig. 6c shows detail I of Fig. 6b.
  • the pressure medium 3 m is held in a cavity formed by the basic structure 1e.
  • the basic structure 1e could accordingly be formed in this area as a hollow body with supports, which carries the pressure medium.
  • the membrane 5e would then be attached to it - along the upper edges of the recess 8 in a manner corresponding to FIG. 6c.
  • An extension 17e is provided in the center of the area, for receiving at least the pressure sensor 4 or the sensor arrangement comprising the pressure sensor 4 (see further below). The dimensioning of this extension will accordingly depend on the space required for the pressure sensor or sensor arrangement.
  • On the weighing plate 2e there is provided a ring-shaped projection 9e corresponding to the ring-shaped recess 8 which engages in the ring-shaped recess 8.
  • the frame 13e of the housing encompasses the basic structure 1e and the weighing plate 2e.
  • the frame is in two parts executed and is latched, glued, snapped or possibly ultrasonically welded for assembly, so that the base plate and weighing plate cannot fall apart, and the weighing plate cannot be tilted or tilted due to one-sided weight supports and thus the membrane cannot be damaged.
  • the type of pressure sensor or sensor arrangement will depend on the intended use of the balance or on the requirements for accuracy.
  • FIG. 6c The detail I of FIG. 6b is shown in FIG. 6c, the detail II of FIG. 6b being designed correspondingly, but reversed, to this.
  • This shows a possible design variant for the connection between the membrane and the basic structure.
  • the membrane 5e is tightly connected via a connection piece 18 to the base structure 1e, which may be formed from plastic, in particular spot or line-like ultrasonically welded.
  • certain areas of the membrane 5e are designed as so-called stretching areas 10.
  • the membrane 5e can be made particularly thin there and possibly with an oversize, but alternatively or additionally, the membrane 5e as such can also be provided in a stretchable and elastic manner.
  • FIGS. 7a, 7b and 7c show arrangements with individual, discretely arranged recesses 8f and 8f1, respectively, with FIGS. 7b and 7c each showing a section along B-B of FIG.
  • the configurations of FIGS. 7b and 7c differ essentially only in the depth of the recesses 8f and 8f1 and the configuration of the membrane 5f.
  • the display 11 is provided on the cover or the basic structure. According to FIG. 7b, two such recesses 8f are connected to one another via channel-like recesses 16, the recessed extension 17f being provided at the intersection thereof. Correspondingly dimensioned projections 9f arranged on the weighing plate 2f engage in these recesses 8f. Between the basic structure 1f - or within the channels 16 provided in the basic structure 1f - and weighing plate 2f, the diaphragm seal medium 3 is provided, at least partially covered by a membrane 5f. The membrane 5f is fastened in the area of the recesses 8f to the basic structure 1f in a manner corresponding to FIG. 6c.
  • a further projection which engages in the extension 17f and is provided on the weighing plate 2f, could also be provided (not shown).
  • the discrete recesses 8f1 can be provided in a circle on the basic structure 1f1, wherein the pressure medium medium can be filled therein either in the form of a channel - according to FIGS. 7a and 7b - or in a large space.
  • the recesses 8f1 smd are covered by a membrane 5f which is fastened to the basic structure 1f1, corresponding approximately to FIG. 6c, and a thicker membrane part 5f1 approximately corresponding to the configuration in FIG. 3 as a support for the has projection 9f1 provided on the weighing plate 2f1.
  • 8 and 9 show further training options for scales according to the invention.
  • 8 shows four intersecting channels 16g, at the two ends of which a recess 8g is provided for engaging corresponding projections provided on the weighing plate;
  • the expansion 17 accommodating the pressure sensor or the sensor arrangement is provided in the center of the channels 16g.
  • FIG. 9 shows an embodiment in which three intersecting channels, forming recesses 8h, are formed, each of which is covered by a membrane - if appropriate in a manner corresponding to FIG. 7c. Appropriately shaped projections engaging in these channels are then provided on the weighing plate (not shown).
  • a sensor arrangement which proves to be particularly advantageous for the scales according to the invention is a programmable sensor signal conditioner and measurement error compensation circuit, as described in US Pat. No. 5,121,118 by the same applicant and also in US Pat on December 22, 1995, filed by the same applicant, the priority of which is claimed for the present application.
  • the content of US Pat. No. 5,121,118 is hereby fully disclosed.
  • the sensor arrangement open in these two documents relates to a so-called dual
  • 5,121,118 lies in the fact that this arrangement completely accomplishes temperature-dependent offset voltages and sensitivity changes in the sensor, as well as manufacturing tolerance-dependent scatter ranges of the sensor zero-point signal and the sensitivity under microprocessor control can and also compensate for all other error signals from manufacturing tolerances and changes in the signal range such as long-term zero point drifts, changes in the offset of the pressure in the pressure medium medium due to temperature and ambient pressure changes, changes in the bridge voltage due to moisture and Influences of contamination (contamination), voltage drop at the voltage source (battery wear) can be eliminated under program control or can be calibrated in a self-learning programmed manner and can be carried out automatically during the A / D conversion.
  • a second sensor for measurement could possibly be used for precision scales the conductivity in the pressure medium (oil contamination) and possibly also a third sensor for temperature measurement, the temperature determination at the pressure sensor, as described in US Pat. No. 5, 121, 118, should not be sufficient.
  • a piezo-resistive pressure sensor 4 is connected to a sensor signal conditioning circuit (SSC), in particular to an integrated circuit, hereinafter called conditioning IC 22.
  • SSC sensor signal conditioning circuit
  • conditioning IC 22 an integrated circuit
  • a temperature-dependent signal is determined directly on the IC 22 or the IC 22 measures the temperature signal as a bridge supply voltage signal, as described, for example, in the two documents listed above, directly on the piezoresistive pressure sensor 4.
  • the battery is also monitored the IC 22.
  • the conditioning IC 22 enables optimum use of piezoresistive sensors 4 and conversion of the analog measurement signals of the pressure sensor 4 into digital pressure and temperature values adapted to the application.
  • a microprocessor 23 ( ⁇ P), a voltage source (battery 50) and a display 11 are arranged outside the pressure medium 3, as can be seen schematically in FIG.
  • the display / computer unit 15 consisting of microprocessor 23, display 11 and voltage source 50 is connected via an interface 51 in the form of a sealed plug to the sensor arrangement 48 consisting of conditioning IC 22, sensor 4 and EEPROM 21 .
  • the interface 51 can be designed as a parallel or serial interface.
  • conditioning IC 22 and microprocessor 23 - and possibly also EEPROM 21 - are present as single chips and can be arranged within the pressure medium.
  • sensor 4 and EEPROM 21 can also be arranged within the pressure medium, conditioning IC 22 and microprocessor 23 are then located individually or on a single chip outside the same.
  • the sensor signal conditioning circuit 22 comprises means for programmable amplification and A / D conversion, in particular for offset and gam adaptation, means for programmable feeding of the sensors, means for compensating temperature effects in the signals of the Pressure sensor 4, means for determining compensation and adjustment parameters, means for storing the specific compensation and adjustment parameters, which are preferably stored in an EEPROM 21 arranged in the pressure medium 3, and means for checking the conditioning circuit and for connecting it with the external, or outside the
  • the memory means is preferably designed as a separate component (EEPROM), possibly also on the signal conditioning IC, or as a memory area of the microprocessor 23 located outside the pressure medium medium 3.
  • the connections of the conditioning circuit and the EEPROM lead through the housing in a pressure-resistant manner (eg injected plug).
  • a serial MICRO-WIRE interface, four connections
  • Eme 4B ⁇ t parallel microbus interface would result in 8 connections.
  • the piezoresistive sensor 4 is designed as a Wheatstone bridge circuit.
  • the sensor-bridge circuits (pressure sensor 4) are connected directly to the IC 22.
  • the IC 22 comprises a sensor interface 25 and a programmable supply 26 connected to it.
  • the sensor interface 25 is connected via a first one Multiplexer 27 and an intermediate memory / amplifier 28 are connected to an analog part 29 of the A / D converter.
  • This analog part 29 includes an offset, an integration and a comparator stage.
  • a digital part of the A / D converter comprises a counter 33 and a D / A converter 34, the output signal of the D / A converter 34 controlled by the counter 33 passing through the first multiplexer 37 m to the analog part 29 and is used there as a setting value for programming (activation) of offset integration and compensation values.
  • the A / D converter can preferably be operated using the dual slope method and is connected to a control means or the main control unit 30.
  • the main control unit 30 communicates with various parts of the IC via an internal bus 31 and with the external microprocessor 23 via a microprocessor interface 32.
  • a non-volatile memory in particular an EEPROM, is also connected to the external bus 52. for parameters, digital IC settings and error compensation values or reference voltages for A / D conversion. The parameters corresponding to the current temperature are used to compensate for temperature effects.
  • Digital values of the EEPROM are, if necessary directly, or after processing or conversion in the microprocessor 23 from the bus 31 via first register 36, a second one Multiplexer 37 and the D / A converter 34 are fed to the analog part 29 of the A / D converter.
  • the programmable supply 36 is set by the bus 31 via a decoder 43 and a step selector 44 in accordance with the pressure or temperature signal of the pressure sensor 4 to be measured. So that a set supply voltage is also applied to the desired sensor 4 or to its measuring bridge, the supply 26 is connected to the sensor interface 25.
  • the main control unit 30 becomes the output signal of the analog part
  • a versatile conditioning IC has, for example, an oscillator with a selectable frequency, with frequencies in the range from 500 to 800 kHz being expedient for static measurements (1-2 times per second).
  • the dual-slope method used in the IC 22 consists of a neutral phase (auto-zero phase) during which a stable input voltage can be set.
  • the input voltage or offset compensation value programmed on the A / D converter is placed on a capacitor (auto-zero cap) for the start of the A / D conversion.
  • a rising phase sensor signal integration phase
  • the output voltage of an integrator rises in proportion to the slope with the signal voltage of the measuring bridge with the pressure sensor.
  • the increase takes place during a time which is likewise predetermined by the counter 33 and is also programmable and thus leads to a bit precisely adjustable integrator final voltage.
  • the rise time can be selected so that a maximum integrator final voltage is not exceeded.
  • the rise phase is followed by a descent phase (de-integration phase), during which the output voltage of the integrator decreases proportionally to the negative slope starting from the final voltage with a reference voltage programmable on the D / A converter until the original output voltage or Offset voltage is reached again.
  • the reference voltage corresponding to the necessary compensations in particular the temperature compensation, can be applied from the D / A converter 34 to the integrator via the first multiplexer 27 and / or the programmable counter 33 , before the A / D conversion, as a function of the temperature.
  • the rise time is determined by means of counter 33 (full scale, fine range setting).
  • the descent time or the level of the counter 33 at the end of the descent phase is proportional to the ratio of the input voltage to the reference voltage.
  • the counter reading corresponds to the digital A / D value, which is a measure of the sensor voltage compensated by means of the reference voltage.
  • At least one calibration parameter is determined for two, in particular high and low, pressure and temperature values.
  • calibration parameters are determined and stored for four pressure values of the measuring range at two different temperatures.
  • Specific reference voltages (coarse adjustments) for offset and full-scale are determined at the lowest gauge temperature.
  • the values for the full-scale fine adjustments are calculated from the calibration parameters for any temperatures within an approved temperature operating range by interpolation, in particular polynomial interpolation, and - as already described - via the Counter 33 fed to the D / A converter.
  • the full-scale and offset rough settings remain unchanged.
  • the reference voltages are selected in accordance with the pressure or weight range to be measured and the components used, in particular in accordance with the counter 33.
  • a counter 33 with a counting range from 0 to 4096 (12B ⁇ t) for a personal scale with a measuring range of 0- 150kg, it is advisable to choose the reference voltages for the permitted temperatures so that with a weight of 150kg - in essentially independent of the temperature - a counter reading slightly less than 4096, for example 3700 is reached.
  • the counter reading when the scale is not loaded (0kg) should essentially be 700, or between 100 and 1000 depending on the temperature.
  • the coarse adjustment of sensor zero point and sensitivity of the pressure calibration are already taken into account in the analog part, in particular in its integration stage.
  • support points or support values of the calibration curves are interpolated between temperature calibration points (for example 15 ° C and 35 ° C) when the temperature changes according to the current temperature and are stored as current support values.
  • a weight value is interpolated at this determined value using the current base values and the calibration weights assigned to them.
  • a Lagrangian or Newtonian interpolation is preferably carried out.
  • the temperature signal at the pressure sensor 4 is evaluated at regular time intervals.
  • the temperature signal of the pressure sensor 4 is optionally converted into a digital value by means of the A / D converter or its analog and digital part 29, 33, 34.
  • reference voltages of the temperature sensor would have to be supplied to the A / D converter. Because the temperature values are resolved to a maximum of 8 bits for a scale application with only 12 bit resolution, ie there are no high demands on the accuracy of the temperature value, the temperature signal is preferably evaluated via a comparator 35 provided for this purpose.
  • a first input of the comparator 35 is connected to the sensor interface 25 in such a way that the temperature signal of the temperature sensor 4 can be fed to the comparator 35.
  • the second input of the comparator 35 is connected to the D / A converter 34 and this to the counter 33, so that a comparison voltage can be changed step by step.
  • the counter 33 is stopped when the sensor voltage is reached and then contains a value assigned to the temperature.
  • an amplification is selected so that a counter reading of 255 corresponds to a temperature of approximately 100 ° C.
  • the scale is preferably only calibrated in the fully assembled state.
  • Fig. 12 and Fig. 13 illustrate the calibration procedure.
  • Fig. 12 shows the temperature curve during oak.
  • t1 or t2 calibrations are carried out for a first or second temperature (for example 15 ° C. or 35 ° C.).
  • the load on the scales and the associated calibration steps (S1-S18) can be seen from the illustration in FIG.
  • FIG. 13 shows a calibration curve which is shifted through the selection of an offset and a reference voltage for the weight range from 0-150 kg (x-axis) m to a desired range of the digital values (y-axis).
  • the calibration curve is shown as a straight line. Due to the non-linearities of the scale, the real calibration curves deviate from straight lines.
  • the sensor signal area is marked with the area bar drawn in the y direction.
  • the size of the bars increases from the weight of 150kg to 0kg, because all calibration curves are set by programming the counter 33 in such a way that they lead through the point with the x, y coordinates 150kg, 3700 at any temperature (calibration ranges).
  • Different offset signals and zero point shifts of the sensors can therefore lead to increasing deviations from the ideal curve in the negative x direction, characterized by the scattering range upwards and downwards.
  • a calibration program is started by the loading, in which function tests and initializations of the electronics, in particular the capacitor IC 22 and the EEPROM, are carried out as part of the first four calibration steps (S1, S2, S3, S4) 21 (Fig. 10).
  • the scale display shows the calibration steps to be carried out.
  • the balance is brought to a first calibration temperature, preferably to 15 ° C., after the start of the calibration program (first insertion of the batteries) (all scales are in a room kept at 15 ° C.).
  • the calibration program waits during a predetermined time, or until a weight is applied and a high A / D value is read, and then, when the scale is not loaded (0kg, 1bar) in calibration step S5, the supply 26 of the pressure sensor 4 (FIG. 10) Set so that there is a measurement signal in a predetermined range.
  • an offset voltage must be determined and stored at least for the pressure sensor in a calibration step S6, which ensures that the digital pressure value of the unloaded scale is slightly above 0 at 0kg load.
  • the calibration step S6 increases or decreases the digital pressure values.
  • a reference voltage is determined and stored by means of steps S7 and S8, and the counter 33 set so that the digital pressure value at 15 ° C and 150kg is essentially 3700. According to FIG. 13, this corresponds to a change in the mean slope of the calibration curve.
  • the calibration steps S9 and S10 the current temperature value, or the digital value corresponding to this, and using the determined reference voltage for offset and full range and counter setting 33, the digital weight value is recorded and stored.
  • the subsequent calibration steps Sl 1 -Sl 3 are also carried out at 15 ° C with the reference and offset voltages for 15 ° C but each with the calibration loads 100kg, 50kg and 0kg.
  • the digital values corresponding to the calibration loads are saved and form the base values of the calibration curve at 15 ° C.
  • a personal scale is generally used in the temperature range of 15-35 ° C.
  • temperature effects in this or another, correspondingly predetermined, temperature range must be compensated optimally.
  • the support points of a further calibration curve are recorded.
  • the balance to be calibrated is placed in a calibration room at approx. 35 ° C.
  • calibration steps S14-S19 can be carried out analogously to calibration steps S8-S13.
  • the reference voltage for the offset and full range is not reset, only the counter 33 is programmed to the new temperature so that when 150 kg are placed, 3700 ADC counts are read again.
  • a digital temperature value and the digital values corresponding to the calibration loads are then read in and stored at 35 ° C.
  • Base values for pressure calibration curves between 15 and 35 ° C can therefore be determined by linear interpolation.
  • a third degree polynomial interpolation in particular a Lagrange or Newtonian interpolation, is optionally also used for the interpolation between the values known at different temperatures lynomial interpolation is used.
  • values at an intermediate temperature can also be determined, if necessary by linear interpolation (S20).
  • an interpolation of the second degree is expediently provided, in particular a Lagrangian or a Newtonian interpolation.
  • the above-described calibration of the sensor and IC also guarantees a calibration curve with different sensors for every temperature in the operating range, whose digital pressure values for loads from 0kg to 150kg essentially in the range from 700 to 3700 lie.
  • an OK value (check sum via the setting parameters and calibration values stored in the EEPROM) is stored and the balance is set to weighing operation. Since no temperature display is provided, no temperature norms have to be assigned to the digital temperature values. Accordingly, the calculation of ° C units from the recorded temperature calibration curves and the predetermined support points (15 ° C and 35 ° C) can be dispensed with.
  • a set of calibration values corresponding to this current temperature value is loaded. So- as soon as the temperature changes by essentially 1 ° C or more than two digital units, a set of calibration values corresponding to the new temperature is loaded. As already described, the calibration values corresponding to the temperature are determined by interpolation from the values measured during the calibration (self-learning calibration). Likewise, the digital pressure value is converted into an weight value using an interpolation using the current calibration values. In order to enable a display m of the desired weight unit (US / metric), the weight value of the unit is converted accordingly.
  • the weighing mode is designed as a control mode with a minimal power consumption.
  • a temperature value is determined in order to interpolate and load the corresponding calibration values (counter 33 and reference values of the calibration curve) in the event of temperature changes.
  • a weight determination is preferably carried out to check the zero point position. If the determined weight of the unloaded scale is not zero, an offset correction is preferably carried out. This zero point correction can compensate for errors in weight determination, for example, due to atmospheric pressure fluctuations or changes in altitude or temperature-related pressure fluctuations, as well as long-term drifts and other sensor bridge adjustments.
  • display mode is provided in which the weight is determined in shorter time intervals, in particular in intervals of 1 second.
  • the interval for the temperature measurement and the adjustment of the calibration values that may be necessary preferably remains at 1 minute.
  • the display remains on until the weight has stabilized and then switches off after a certain time, approx. 10 seconds.
  • a switch may be provided. The switchover is preferably carried out automatically. For this purpose, when changing from control to display mode, the load on the scale must be recognized within 2 to 3 seconds. Accordingly, a digital value of the pressure sensor signal must be determined at intervals of 2 to 3 seconds.
  • a 10 bit A / D conversion is preferably provided for the load detection. Switching on should take place, for example, when the 10-bit pressure value changes by at least 20 units (4 kg, for personal scales).
  • successive weight values are compared with one another. As soon as the determined weight fluctuates around a fixed value for only about 10 seconds within the double measurement resolution (+/- 0.1kg), the balance is switched back to control mode.
  • the sensor arrangement 48a according to FIG. 14 shows a sensor supply 54 which can be set with R1 and has a current source 53 for operating the pressure sensor 4 and for generating the desired potential difference of the sensor output signal.
  • the resistors R2 and R3 and the potentiometer P1 form the sensor offset and signal zero controller 49 for the sensor 4 and the downstream measuring arrangement, which consists of the buffer / differential amplifier 55, the A / D full-range controller 57 and the A / D converter 56a, wherein the sensor offset signal is roughly adjusted via R2 and R3 and the zero point fine adjustment of the sensor measurement signal via the potentiometer P1.
  • the resistance R4 compensates for the temperature response (TC) of the sensor sensitivity, or reduces it as much as possible.
  • One possibility of compensating for the temperature response (TC) of the sensor zero point would be to regulate the current source 53 at the positive input with an NTC resistor R8 (shown in dash-dot lines) so that the bridge current through the sensor 4 is opposite and changed in proportion to the temperature-dependent increase or decrease in the bridge resistance of the sensor 4 and thus compensate for the temperature response TC of the sensor zero point. It is self-evident that such an analog temperature error compensation can only be done approximately and therefore not with very high accuracy, because all analog error compensation methods have the disadvantage that error quantities caused by temperature effects compensate with the same temperature effects of other components become.
  • the signal gain is adjusted via the potentiometer P2 by trimming the reference voltage of the A / D converter 56a on the A / D full-range controller 57.
  • the corresponding specifications of the sensor 4 are used and these resistors are selected so that both maximum and minimum sensor offset and sensor sensitivity signals are sent via the potentiometer P1 and P2 can be compared and so that the area of the A / D converter 56a can be fully utilized, or the calibration points for zero point and full area can be placed on the desired A / D points.
  • the resistances R2, R3 and R4 can be found in the data sheet for each individual sensor, or else for each individual sensor by measuring the same in a test arrangement and for coordination (pairing of sensor and measuring circuit) on the sensor arrangement to equip.
  • each sensor arrangement has to be equipped with different resistances R2, R3 and R4, which are adapted to the respective sensor error behavior, as a result of which production and calibration become more complex and, compared to the sensor arrangement of FIG. 13, a not insignificantly higher current ⁇ Consumption results, even if on and off switches should be provided for all blocks of the analog measuring circuit consisting of 54, 55, 57 and 56a.
  • FIG. 15 shows a further "classic" sensor arrangement 48b which, in comparison to the arrangement 48a shown in FIG. 14, is also suitable for scales with higher accuracy requirements. This also enables, as in the case of the sensor arrangement 48 of FIG. 13, a self-learning automatic calibration, and that without individual coarse resistance adjustments and without iterative potentiometer femalignments.
  • the sensor arrangement 48b shows a sensor supply 54a with a current source 53a that can be adjusted via a resistor R1a in order to generate the desired potential difference of the sensor output signal.
  • the two ⁇ ensor bridge paths S1 and S2 are brought together here directly. Production-related sensor offset and zero point signal shifting of the downstream measuring arrangement are thus fed to the A / D converter 56b without fine or coarse adjustment of the measuring signal.
  • the measuring arrangement consists of the buffer / differential amplifier 55a with a permanently set gain 1 to A, which is appropriately adapted to the sensor signal range, the A / D full-range setting 57a with a reference voltage which is permanently set by the resistor R7, but which is adapted to the sensor signal range, and the A / D converter 56b.
  • the separation of useful and error signals takes place in software in the microprocessor, ie only after the A / D conversion. If the temperature response (TC) of the sensor sensitivity, the sensor zero point and the measuring arrangement itself is also to be compensated, then a temperature measurement must also be provided and the entire sensor arrangement 48b has a pressure / temperature calibration profile which corresponds to FIG. 12 ⁇ accordingly, but with significantly more support points, are exposed.
  • This temperature measurement can be carried out via a switching arrangement connected in parallel, a current supply 58a, a thermistor T8, a current limiting resistor R9 and a second A / D converter 58c or a multiplexer (not shown) for using the A / D converter 56b can be provided.
  • the recorded support points (A / D values for pressure (weight) and temperature) are stored in a matrix and with the equivalent pressure and temperature nominal values specified in the ROM with a correspondingly complex, polynomial interpolation of a higher degree and the associated correction calculation converts m error-compensated, calibrated weight units.
  • a high-resolution A / D converter 56b is required, which has at least 16, but preferably 18 bit resolution, over the entire bandwidth of the uncompensated, unconditioned sensor signal, which is associated with all possible error signals is superimposed, to be able to convert and to obtain 12 to 13 good bits, calibrated in weight units, for the display after the software separation of the useful and error signals in the microprocessor.
  • this sensor arrangement as elegant as it may seem, requires expensive, power-intensive components such as an 18-bit A / D converter and a high-performance microcontroller , as well as complex calibration due to the large number of pressure and temperature support points.
  • Eme scales with an arrangement according to Fig. 15 will therefore be of interest for the laboratory and industrial sectors. However, this will generally be too expensive for inexpensive consumer products with low power consumption.
  • a combination of the sensor arrangement 48a in FIG. 14 and the sensor arrangement 48b in FIG. 15 could also be provided, and an intermediate solution could thus be implemented which provides both analog and software-based error compensation circuits and thus the disadvantages of the two classic methods for taken all, reduced by a more advantageous third combination arrangement of 48a and 48b.
  • FIGS. 14 and 15 are exemplary; It goes without saying that these can be replaced by arrangements having the same effect and familiar to any person skilled in the art.
  • the individual components of the circuit arrangements of FIGS. 14 and 15 or also possible combinations (see above) can be in discrete form, or can also be implemented on an integrated circuit (IC) as an A / D mix, the ones to be adjusted externally Resistors can be trimmed with a laser and the potentiometers can also be available as digital potentiometers that can be set by the microprocessor.
  • IC integrated circuit

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  • General Physics & Mathematics (AREA)
  • Measuring Fluid Pressure (AREA)

Abstract

L'invention concerne un dispositif permettant de déterminer des poids, qui comprend une structure de base (1), un plateau de pesée (2) monté dessus et un système de détection disposé entre. Après avoir été convertis de manière appropriée, les signaux de mesure fournis par le système de détection sont disponibles sur un système d'affichage. Un espace hermétique situé entre la structure de base (1) et le plateau de pesée (2) contient un fluide de mise en pression (3). Le système de détection comprend au moins un détecteur de pression (4), éventuellement piézorésistif, ledit capteur (4) se trouvant dans le fluide de mise en pression (3).
PCT/EP1996/004874 1995-11-10 1996-11-07 Balance WO1997017597A1 (fr)

Applications Claiming Priority (6)

Application Number Priority Date Filing Date Title
EP95117790.6 1995-11-10
EP95117790 1995-11-10
US08/575,792 1995-12-22
US08/575,792 US5764541A (en) 1995-12-22 1995-12-22 Microprocessor controlled sensor signal conditioning circuit
EP96101983 1996-02-12
EP96101983.3 1996-02-12

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10030245A1 (de) * 2000-06-20 2002-01-03 Marco Heyd Wiegeeinrichtung für auf diese auffahrende Transportfahrzeuge
WO2002063254A1 (fr) * 2001-02-07 2002-08-15 Rigobert Opitz Capteur de pesage
WO2010010144A1 (fr) * 2008-07-25 2010-01-28 BSH Bosch und Siemens Hausgeräte GmbH Robot ménager comportant une base munie de plusieurs pieds
DE102016206165B3 (de) * 2016-04-13 2016-09-29 Ifm Electronic Gmbh Druckmessgerät mit einer Messbrücke und einer Abgleicheinheit
DE102016117539A1 (de) 2016-09-16 2018-03-22 Minebea lntec Bovenden GmbH & Co. KG Waage mit einer Wägeplattform
DE102018214801A1 (de) * 2018-08-31 2020-03-05 Audi Ag Brennstoffzellensystem und Verfahren zum Bestimmen des absoluten Feuchtegehalts bei einem Brennstoffzellensystem
CN111442876A (zh) * 2020-01-03 2020-07-24 武汉钢铁有限公司 一种变送器智能校验系统
CN113295196A (zh) * 2021-05-28 2021-08-24 东华大学 用于过滤设备的三位一体化装置及其校准方法
CN113324729A (zh) * 2021-07-08 2021-08-31 中国空气动力研究与发展中心高速空气动力研究所 一种风洞天平温度漂移物理补偿方法

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GB1443624A (en) * 1974-07-31 1976-07-21 Collier J C Weighing devices
EP0221736A2 (fr) * 1985-10-30 1987-05-13 Appliance Control Systems (Holdings) Pty. Ltd. Dispositifs de pesage
US4836308A (en) * 1988-04-04 1989-06-06 General Electrodynamics Corporation Highly accurate platform weighing system
WO1989008819A1 (fr) * 1988-03-15 1989-09-21 Divetronic Ag Procede et dispositif pour la compensation des erreurs de mesure
US5076375A (en) * 1987-11-30 1991-12-31 Mettler-Toledo, Inc. Load cell
DE4036994A1 (de) * 1990-11-20 1992-05-21 Divetronic Ag Anzeigevorrichtung als elektrische/elektronische instrumente, insbesondere tauchcomputer

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Publication number Priority date Publication date Assignee Title
DE2263145A1 (de) * 1972-12-22 1974-06-27 Pietzsch Ludwig Messaufnehmer fuer rad- oder achslasten von strassenfahrzeugen
GB1443624A (en) * 1974-07-31 1976-07-21 Collier J C Weighing devices
EP0221736A2 (fr) * 1985-10-30 1987-05-13 Appliance Control Systems (Holdings) Pty. Ltd. Dispositifs de pesage
US5076375A (en) * 1987-11-30 1991-12-31 Mettler-Toledo, Inc. Load cell
WO1989008819A1 (fr) * 1988-03-15 1989-09-21 Divetronic Ag Procede et dispositif pour la compensation des erreurs de mesure
US4836308A (en) * 1988-04-04 1989-06-06 General Electrodynamics Corporation Highly accurate platform weighing system
DE4036994A1 (de) * 1990-11-20 1992-05-21 Divetronic Ag Anzeigevorrichtung als elektrische/elektronische instrumente, insbesondere tauchcomputer

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE10030245A1 (de) * 2000-06-20 2002-01-03 Marco Heyd Wiegeeinrichtung für auf diese auffahrende Transportfahrzeuge
WO2002063254A1 (fr) * 2001-02-07 2002-08-15 Rigobert Opitz Capteur de pesage
WO2010010144A1 (fr) * 2008-07-25 2010-01-28 BSH Bosch und Siemens Hausgeräte GmbH Robot ménager comportant une base munie de plusieurs pieds
DE102016206165B3 (de) * 2016-04-13 2016-09-29 Ifm Electronic Gmbh Druckmessgerät mit einer Messbrücke und einer Abgleicheinheit
DE102016117539A1 (de) 2016-09-16 2018-03-22 Minebea lntec Bovenden GmbH & Co. KG Waage mit einer Wägeplattform
DE102016117539B4 (de) 2016-09-16 2024-02-22 Minebea lntec Bovenden GmbH & Co. KG Waage mit einer Wägeplattform
DE102018214801A1 (de) * 2018-08-31 2020-03-05 Audi Ag Brennstoffzellensystem und Verfahren zum Bestimmen des absoluten Feuchtegehalts bei einem Brennstoffzellensystem
CN111442876A (zh) * 2020-01-03 2020-07-24 武汉钢铁有限公司 一种变送器智能校验系统
CN111442876B (zh) * 2020-01-03 2021-08-17 武汉钢铁有限公司 一种变送器智能校验系统
CN113295196A (zh) * 2021-05-28 2021-08-24 东华大学 用于过滤设备的三位一体化装置及其校准方法
CN113324729A (zh) * 2021-07-08 2021-08-31 中国空气动力研究与发展中心高速空气动力研究所 一种风洞天平温度漂移物理补偿方法

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