JP5679704B2 - Strain gauge type load cell fault diagnosis device - Google Patents

Description

The present invention relates to a failure diagnostic apparatus for a strain gauge type load cell using a strain gauge such as an electric resistance wire strain gauge or a semiconductor strain gauge.

  As this type of failure diagnosis apparatus, there is one proposed in Patent Document 1, for example.

JP-A-5-172661

  In the failure diagnosis device according to Patent Document 1, the weighing instrument is in a specific state, for example, the operator judges that there is no object to be weighed on the weighing table, and manually operates the zero adjustment device, In the case of automatic, the two half-bridge circuits constituting the full-bridge circuit of the load sensor are received by receiving the zero point determination by the zero-point automatic detecting means by detecting the presence or absence of an object to be weighed on the weighing table by the article sensor. Each output is compared with a predetermined allowable value based on the zero point output, and if the result of the comparison is that the output of any half-bridge circuit exceeds the allowable value, a failure notification is made.

  However, when the failure diagnosis apparatus according to Patent Document 1 is applied to a measuring instrument, there are the following problems.

  Some weighers, such as conveyor scales and hopper scales, continue to be loaded for a long period of time, and there is rarely a condition where the object to be weighed disappears on the weighing table, and it does not return to the zero point. Failure notification cannot be made in the state of use.

  Non-automatic scales such as track scales, platform scales, and fee scales are typically equipped with an automatic zero-point tracking function. For this reason, even if the zero point or span of the load sensor drifts due to a failure, the automatic zero point tracking function operates to keep the displayed weight measurement value at zero when there is no object to be weighed on the weighing platform. become. If the display value of the weight measurement value is zero, the operator does not operate the zero point adjustment key switch that is the zero point adjustment device, and therefore no failure alarm is output even if the strain gauge has failed.

  In Patent Document 1, there is also proposed a method for detecting a state in which there is no object to be weighed on a weighing table by providing an article sensor such as a photoelectric detector, and determining a zero point to perform failure detection. A sensor having a single optical axis cannot be used to reliably detect that the object to be weighed is not placed on the weighing table due to the relationship between the size of the object and the size of the object to be weighed.

  Further, in the failure diagnosis apparatus according to Patent Document 1, the outputs of the two half bridge circuits are compared with corresponding allowable values, respectively, and the presence or absence of a failure is determined. For this reason, it is not possible to distinguish between a zero point drift factor caused by a failure of the bridge circuit of the load sensor, such as mud, water drops, and dust adhering to the weighing table, and a zero point drift factor caused by a failure of the bridge circuit. Therefore, an allowable value must be set in anticipation of a drift amount of a factor that is not a failure. However, it is difficult to grasp a drift amount due to a factor that is not a failure, and an accurate failure determination cannot be performed.

  Moreover, in the failure diagnosis apparatus according to Patent Document 1, a specific state that can be created without a worker's special hand is a state in which there is no object to be weighed on the weighing table. However, in the case of a measuring instrument with a small tare load as a measuring instrument, as shown in FIG. 8, even if the span of the half-bridge circuit varies, the change Δe of the load signal near the zero point as a measuring instrument is small. Even if an abnormal change in the span exceeding the allowable accuracy occurs, a failure cannot be detected.

  Moreover, in the failure diagnosis apparatus according to Patent Document 1, the two half-bridge circuits have different gain coefficients related to the respective load output voltages. For this reason, the magnitude of the output voltage change with respect to the same load is different. Therefore, when setting an allowable value for the outputs of both half-bridge circuits, an allowable value for an output change corresponding to the same load load should be set. Setting is difficult for users of measuring instruments who are not aware of this.

  In short, the failure diagnosis apparatus according to Patent Document 1 has a problem that the failure of the load sensor may not be accurately detected depending on the weighing conditions such as the type of weighing instrument and whether or not the weighing operation is being performed. .

The present invention has been made in view of the above-described problems, and can accurately detect a failure of a load sensor regardless of weighing conditions such as the type of weighing instrument and whether or not weighing is being performed. It is an object of the present invention to provide a failure diagnostic apparatus for a strain gauge type load cell .

In order to achieve the above object, a strain gauge type load cell failure diagnosis apparatus according to the present invention comprises:
A full bridge circuit is constituted by two sets of half-bridge circuits, and an output of the two sets of half-bridge circuits is obtained for each half-bridge circuit, thereby providing a weighing platform supported by the strain gauge load cell. A strain gauge type load cell fault diagnosis device comprising weighted object weight value calculating means for calculating a weight value of a placed object to be weighed for each output of each half bridge circuit,
Storage means for storing an allowable value determined based on a predetermined weighing accuracy or a predetermined rated load;
When the force or load of an arbitrary magnitude is loaded on the weighing platform, the operating zero point fluctuation component included in each output signal is removed from the output signals of the two sets of half bridge circuits . Comparing and determining means for comparing weight values calculated from the output signals and determining whether or not the comparison result exceeds the allowable value (first invention).

In the present invention, in a state where the objects to be weighed of the weighing sample on the platform is not a state or any existing loads are present, the weight value calculated from an output signal of said two sets of half-bridge circuit by said comparison determination means It is preferable that alarm means for issuing an alarm when it is determined that the comparison result exceeds the allowable value is provided (second invention).

In the present invention, the respective weight values calculated from the output signals of the two sets of half-bridge circuit, to execute the objects to be weighed weight values become such processing of the same size with respect to the applied load of the same magnitude It is preferable that a load signal calculation means is provided (third invention).

In the present invention, in the state where the object to be weighed does not exist on the weighing table or the object to be weighed having a known weight value is placed, it is selected which of the two sets of half bridge circuits is in failure. It is preferable to provide a selection determining means for determining (fourth invention).

In the present invention, when one of the two sets of half-bridge circuits is selected and determined by the selection determining means, the other output signal of the two sets of half-bridge circuits is sent to the weighing target on the weighing table. It is preferable to provide a conversion means for converting to a weight measurement value as an output signal for weight measurement of an object (fifth invention).

  In the present invention, it is preferable to use a load signal calculation formula including a memorized value of the zero point variation obtained by manual zero point adjustment and / or automatic zero point tracking in the calculation processing by the load signal calculating means (sixth invention). .

In the present invention, there is provided error compensation means for compensating an output error corresponding to the load load for each of the weight values calculated from the output signals of the two sets of half-bridge circuits obtained through the arithmetic processing by the load signal calculation means. (7th invention) is preferable.

According to the present invention, when detecting a failure of the strain gauge type load cell, when in the state in which an arbitrary amount of force or load to the strain gauge type load cell is loaded, from the output signals of the two sets of half-bridge circuit The calculated weight value is compared, and it is determined whether the comparison result exceeds an allowable value determined based on a predetermined weighing accuracy or a predetermined rated load. Regardless of the weighing condition such as whether or not the weighing operation is in progress, the failure of the load sensor can be accurately detected.

In use state view of the strain gauge type load cell failure diagnosis apparatus of the strain gauge type load cell is applied according to a first embodiment of the present invention, the state diagram used to compress load cell (a) and the dual beam load cell Used state diagram (b) 1 is a schematic system configuration diagram of a strain gauge type load cell failure diagnosis apparatus according to a first embodiment of the present invention. Functional block diagram of the central processing unit Strain gauge load cell full bridge circuit output voltage diagram Hysteresis characteristics of strain gauge load cell output Error relationship diagram for weighing signal Schematic system configuration diagram of a strain gauge type load cell failure diagnosis apparatus according to a second embodiment of the present invention Illustration for explaining the problems of the prior art

Next, a specific embodiment of a strain gauge type load cell failure diagnosis apparatus (hereinafter simply referred to as “failure diagnosis apparatus”) according to the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a use state diagram of a strain gauge type load cell to which the failure diagnosis apparatus of the present embodiment is applied, a state diagram (a) used for a compression type load cell and a state diagram (b) used for a double beam type load cell. ) Are shown respectively.

<Overview of compression load cell>
In the compression load cell 1 shown in FIG. 1A, a strain generating portion 3 is provided on a support portion 2, and a force receiving portion 4 is provided above the strain generating portion 3. The strain generating portion 3 is compressed when the impact receiving portion 4 receives a force. The strain gauges 11 a and 13 a are attached to the strain generating part 3 in parallel to the axial direction of the strain generating part 3, and the strain gauges 12 a and 14 a are attached to the strain generating part 3 at right angles to the axial direction of the strain generating part 3. . The strain gauges 11a and 13a detect compressive force, and the strain gauges 12a and 14a detect tensile force.

<Overview of double beam load cell>
In the double beam type load cell 5 shown in FIG. 1B, a strain generating portion 8 is formed so as to constitute two beams (beams) 6 and 7. In the strain generating portion 8, strain gauges 11b and 12b are attached to the beam 6, and strain gauges 13b and 14b are attached to the beam 7 along the longitudinal direction of the beam. When an object to be weighed is placed on the weighing table 9 coupled to the strain generating part 8, a load corresponding to the weight of the object to be weighed acts on the strain generating part 8, and the strain gauges 12b and 14b have gauge adhesive surfaces. The strain gauges 11b and 13b receive a bending stress in a direction in which the gauge bonding surface contracts.

<Explanation of the generic names of strain gauge symbols>
In the following description, the strain gauges 11a and 11b are collectively referred to as the strain gauge 11, the strain gauges 12a and 12b are collectively referred to as the strain gauge 12, and the strain gauges 13a and 13b are collectively referred to as the strain gauge 13. The strain gauges 14a and 14b are collectively referred to as a strain gauge 14.

<Description of full bridge circuit>
As shown in FIG. 2, the strain gauges 11, 12, 13, and 14 are connected to each other so as to constitute a full bridge circuit 15. Here, in the full bridge circuit 15, if both the strain gauges 12 and 14 constituting the opposite sides are tensile forces, the tensile force is obtained, and both the strain gauges 11 and 13 constituting the opposite sides are both compressive forces. Then, it is wired to receive the same type of force as compression force.

<Description of full bridge circuit>
In the full bridge circuit 15, a DC voltage for excitation is applied to two opposing connection points 16 and 17, and force or load is detected from the connection points 18 and 19 positioned at right angles to these connection points 16 and 17. The voltage is taken out.

  Next, a specific configuration of the failure diagnosis apparatus of the present embodiment will be described below using the schematic system configuration diagram of FIG.

<Outline of fault diagnosis device>
As shown in FIG. 2, the failure diagnosis apparatus 20 of the present embodiment includes two voltage reference fixed resistors 21 and 22 provided for the above-described full bridge circuit 15, an analog adder circuit 23, Two analog-digital converters (hereinafter referred to as “A / D converters”) 24 and 25 and an arithmetic circuit 26 are provided.

<Description of fixed resistor for voltage reference>
The two fixed resistors 21 and 22 for voltage reference are connected in series with each other. These fixed resistors 21 and 22 are connected to connection points 16 and 17 of the full bridge circuit 15.

<Description of half-bridge circuit>
Here, the half bridge circuit 15 a is formed by the fixed resistors 21 and 22 and the strain gauges 12 and 13. Further, a half bridge circuit 15 b is formed by the fixed resistors 21 and 22 and the strain gauges 11 and 14.

<Description of analog adder circuit>
The analog adder circuit 23 includes a first operational amplifier 31, a second operational amplifier 32, a third operational amplifier 33, and a fourth operational amplifier 34.
In the first operational amplifier 31, the input positive terminal 31 a is connected to the connection point 18 of the full bridge circuit 15, the input negative terminal 31 b is connected to the output terminal 31 c, and the output terminal 31 c is connected to the resistor 40.
In the second operational amplifier 32, the input positive terminal 32a is connected to the connection point 41 of the two fixed resistors 21 and 22, the input negative terminal 32b is connected to the output terminal 32c, and the output terminal 32c is connected to the resistors 42 and 43. It is connected.
In the third operational amplifier 33, the input positive terminal 33a is connected to the circuit ground 44, the input negative terminal 33b is connected to the resistors 40 and 42, and is connected to the output terminal 33c via the resistor 45, The output terminal 33c is connected to the A / D converter 24.
In the fourth operational amplifier 34, the input positive terminal 34 a is connected to the connection point 19 of the full bridge circuit 15, and the input negative terminal 34 b is connected to the resistor 43 and connected to the output terminal 34 c via the resistor 46. The output terminal 34 c is connected to the A / D converter 25.

<Description of analog-digital converter>
The A / D converters 24 and 25 convert the analog load signal from the analog adder circuit 23 into a digital load signal. Digital load signals from the A / D converters 24 and 25 are output to the arithmetic circuit.

<Description of hardware configuration of arithmetic circuit>
The arithmetic circuit 26 includes an input / output circuit (I / O) 51, a central processing unit (CPU) 52, and a memory block (MEM) 53.
In the arithmetic circuit 26, output signals of the A / D converters 24 and 25 are read from the input / output circuit 51 into the memory block 53 via the central processing unit 52.
The memory block 53 is composed of a storage element (semiconductor element) such as a RAM that primarily stores data for input, output, and computation, an EEPROM that continuously stores setting data, and a PROM that continuously stores predetermined programs.
Calculation formulas such as Wan, Wbn, and D, which will be described later, are stored in the PROM, and Es and Wabs values for calculating the value of the span allowable error Er described later are set in the EEPROM.
A display device (DIS) 54, a key switch (KEY) 55, an alarm device (ALARM), and the like are connected to the arithmetic circuit 26. The values of Wan and Wbn, which will be described later, are displayed on the display device 54, and data setting is performed. Operations such as zero point adjustment and the like are performed by the key switch 55, and an alarm for notifying the failure is issued from the alarm device 56.

<Description of functions of central processing unit>
In the central processing unit 52, by executing a predetermined program stored in the memory block 53, a filter processing unit 52a, a load signal calculation unit 52b, a comparison determination unit 52c, an alarm as shown in FIG. The functions of the signal generation unit 52d, the selection determination unit 52e, the conversion unit 52f, the error compensation unit 52g, and the display signal generation unit 52h are realized.

<Description of Filter Processing Unit>
The filter processing unit 52a performs a predetermined filtering process on the digital load signals from the A / D converters 24 and 25.

<Description of load signal calculation unit>
The load signal calculation unit 52b performs arithmetic processing such that each digital load signal from the A / D converter 24 and the A / D converter 25 becomes an output signal having the same magnitude with respect to the load having the same magnitude. Execute.

<Description of the comparison determination unit>
When the compression load cell 1 or the double beam load cell 5 is in a state where a force or a load of an arbitrary magnitude is applied, the comparison / determination unit 52c receives the digital load signal from the A / D converter 24 and The digital load signal from the A / D converter 25 is compared, and it is determined whether or not the comparison result exceeds an allowable value determined based on a predetermined weighing accuracy or a predetermined rated load.

<Description of alarm signal output unit>
The alarm signal generation unit 52d is determined by the comparison determination unit 52c that the comparison result between the digital load signal from the A / D converter 24 and the digital load signal from the A / D converter 25 exceeds the allowable value. Sometimes, an alarm signal for generating an alarm in the alarm device 56 is generated.

<Description of the selection determination unit>
Based on the digital load signal from the A / D converter 24 and the digital load signal from the A / D converter 25 obtained through the arithmetic processing by the load signal calculation unit 52b, the selection determination unit 52e has two sets of half. It is selected and determined which of the bridge circuits 15a and 15b is faulty.

<Description of conversion unit>
The conversion unit 52f corresponds to the other circuit of the two sets of half bridge circuits 15a and 15b when the selection determination unit 52e selects and determines that one of the two sets of half bridge circuits 15a and 15b is faulty. Convert the digital load signal into an output signal for weight measurement.

<Description of error compensation unit>
The error compensator 52g compensates for an output error corresponding to the load load for each of the digital load signals of the two sets of half-bridge circuits 15a and 15b obtained through the arithmetic processing by the load signal calculator 52b.

<Description of display signal output unit>
The display signal generation unit 52h generates a display signal for causing the display device 54 to display values of Wan and Wbn, which will be described later.

<Explanation of load signal processing flow>
In the failure diagnosis apparatus 20 having the configuration described above, the analog load signals eoa and eob output from the two sets of half-bridge circuits 15a and 15b are converted into analog signals via an analog adder circuit 23 as shown in FIG. The load signals are eoa ′ and eob ′. These analog load signals eoa ′ and eob ′ are converted into digital load signals Wa and Wb by A / D converters 24 and 25, respectively. These digital load signals Wa and Wb are taken into the arithmetic circuit 26, and as shown in FIG. 3, a predetermined filtering process is performed in the filter processing unit 52a to obtain digital load signals Wax and Wbx.

  Next, the contents of the arithmetic processing based on the digital load signals Wax and Wbx in the arithmetic circuit 26 will be described below by taking as an example a measuring instrument in which the double beam type load cell 5 is equipped with the measuring table 9.

<Description of initial load storage operation>
At the time of adjustment of the weighing device, when a power is applied to the double beam type load cell 5 without placing an object to be weighed on the weighing table 9 (which may be a weighing container such as a weighing hopper), two sets of half bridge circuits 15a and 15b. Outputs analog load signals eoa and eob to which an unbalanced component of bridge resistance and a tare load are added. These analog load signals eoa and eob are converted into digital load signals Wax and Wbx via the analog adder circuit 23, A / D converters 24 and 25, and the filter processing unit 52a. Assume that Wax = Wai and Wbx = Wbi are obtained as the digital load signals Wax and Wbx at this time. The values of Wai and Wbi are stored in the memory block 53 as an initial load by operating the initial load storage key switch in the key switch 55.

<Explanation of load signal calculation formula definition>
The load Wan on the half bridge circuit 15a side is defined by the following equation (1).
Wan = ka · (Wax-Wai) (1)
Similarly, the load Wbn on the half bridge circuit 15b side is defined by the following equation (2).
Wbn = kb · (Wbx−Wbi) (2)
At this time, ka and kb are set to 1 as temporary values.
Since Wax = Wai and Wbx = Wbi when the initial load values Wai and Wbi are stored in the initial load memory, Wan = Wbn = 0 for any numerical value of ka and kb which is not zero.

<Explanation of definition of span coefficient>
Next, the span coefficients ka and kb are determined so that the value of Wan and the value of Wbn each represent the value of Ws / 2 when the rated load Ws (the value of Ws is known) is placed. Thus, Wan and Wbn change by the same amount for the same load change.

<Explanation of discriminant definition>
After setting the mathematical formula as described above, the value of the discriminant D defined by the following formula (3) is obtained for an arbitrary load.
D = Wan-Wbn (3)
If the load signal is not vibrational and stable, the measurement is performed for a load of an arbitrary magnitude on the weighing platform 9.

<Description of relationship between change in tare load and value of discriminant D>
The measuring table 9 of the measuring instrument receives foreign matter such as moisture, mud, and dust from the object to be measured during use. These are the zero point drift factors due to the change in the tare load of the weighing table 9 that the half bridge circuits 15a and 15b receive in common, and Wan and Wbn fluctuate by the same magnitude with respect to the same load change on the weighing table 9. This variation is not a failure of the full bridge circuit 15.
In this case, even if the change in the tare load is received, since Wan = Wbn, the discriminant D = 0, and it is not affected by the gain difference between the half-full bridge circuits 15a and 15b.

<Explanation of relationship between failure effect and discriminant D value>
On the other hand, when one of the strain gauges 12, 13; 11, 14 in both the half bridge circuits 15 a, 15 b is wet or corroded, the strain gauge resistance value changes or the resistance change rate with respect to the load changes. If the size varies, a failure peculiar to each of the half-bridge circuits 15a and 15b occurs.
Since a change amount different from the other appears in either Wan or Wbn, the discriminant D is not affected by the gain difference between the respective half bridge circuits 15a and 15b, and is not affected by the drift common to both. A value corresponding to a change caused by a failure peculiar to any of the half bridge circuits 15a and 15b appears, and error information of discriminant D = ΔE appears.

<Description of allowable values>
Here, an allowable value Et is set based on a predetermined weighing accuracy or a predetermined rated load as the measuring device, and the allowable value Et is stored in the memory block 53 in advance.

<Description of the operation of the comparison judgment unit>
The comparison determination unit 52c compares Wan and Wbn, and determines whether the following expression (4) is established based on the discriminant D.
D = | ΔE |> Et (4)

<Operation explanation of alarm signal output unit>
When the comparison / determination unit 52c determines that the above equation (4) is established, the alarm signal generation unit 52d generates and outputs an alarm signal for causing the alarm device 56 to generate an alarm in response to this determination. As a result, an alarm indicating that there is a failure is issued from the alarm device 56.
In this way, it is possible to accurately detect a failure of one of the half bridge circuits 15a and 15b with respect to an arbitrary load. Of course, the operator does not have to operate the zero adjustment device, and it is not necessary to detect the presence of the object to be weighed on the weighing table 9 by an article sensor or the like.

By the way, zero points and span drifts (failures) due to factors such as moisture absorption and corrosion of the strain gauges 11 to 14 occur gradually (by a small amount), so that even if there is a failure, the automatic zero point tracking function operates. Therefore, if the weight display value is continuously displayed as zero when the weighing instrument is used by the automatic zero tracking function, the operator operates the zero adjustment device, specifically, the zero adjustment key on the key switch 55 is pressed. There is no operation.
As shown in FIG. 4, the output voltage of the full bridge circuit 50 is the zero point of the measuring instrument at the point where the tare load is applied. Therefore, as shown in FIG. 4, the span coefficient k varies to k ′. However, at the zero point of the weighing instrument (when there is no object to be weighed on the weighing table 9), it can be detected only as the zero point fluctuation amount.
If the zero point fluctuation is caused by span fluctuation, even if the zero point is corrected by Δe by the automatic zero tracking device, Δe ≠ Δe ′ at the load of any object to be measured. Measurement values cannot be taken.
Then, only when the operator operates the zero adjustment device as in the conventional case, the failure determination is performed on the outputs of the half bridge circuits 15a and 15b. Will result in incorrect weighing.
Further, even if the span change rate exceeds the allowable accuracy, if the zero point change amount in the state where there is no object to be weighed on the weighing table 9 is small, a failure may not be detected and the zero point adjustment may be performed.

<Explanation of definition of load signal calculation formula including stored value of zero variation>
Therefore, the mathematical formula for obtaining the weight measurement value including the zero adjustment function is also applied to the output load signals of the respective half bridge circuits 15a and 15b.
The zero point memory Wza is prepared in the above equation (1) and the zero point memory Wzb is prepared in the above equation (2), and the following equations (5) and (6) are defined.
Wan = ka. (Wax-Wai) -Wza (5)
Wbn = kb · (Wbx−Wbi) −Wzb (6)
Each zero point adjusting device (zero point adjusting key switch) may be specially provided. However, the zero point adjusting device for displaying a weight measurement value as a measuring instrument is also used for operation and function.
Furthermore, both of the drift memories Wda and Wdb are prepared (or Wza and Wzb may also serve as their respective roles), and the following expressions (7) and (8) are defined.
Wan = ka. (Wax-Wai) -Wza-Wda (7)
Wbn = kb · (Wbx−Wbi) −Wzb−Wdb (8)

<Description of Operation of Comparison Determination Unit Based on Load Signal Calculation Formula Including Memory Value of Zero Point Variation>
A new discriminant D represented by the following formula (9) based on the above formulas (7) and (8) is defined.
D = | Wan−Wbn | (9)
Automatic zero point tracking is also activated for the output signals of both half bridge circuits 15a and 15b. In this case, if the measuring instrument is used with zero adjustment properly or automatic zero tracking performed, and both the half bridge circuits 15a and 15b do not fail at the same time, the above equation (9) is obtained. The value of the discriminant D represents the amount of fluctuation due to the failure of one of the two half-bridge circuits 15a and 15b when an object with an arbitrary weight is loaded (see the specific example below). ), The span failure can be evaluated and determined by the value of the discriminant D.

<Description of specific examples of span failure evaluation / determination>
For example,
Normal amount of zero change due to dust adhering to the weighing platform 9 = 10
Zero change amount due to failure inherent in half-bridge circuit 15b = 5
Span change amount due to failure inherent in half-bridge circuit 15b = 3 (however, span error is 3 for 1000 loads)
Wza = Wzb = 0
And
If there is no object to be weighed on the weighing platform 9 and the zero adjustment operation is not performed,
Wan = 10-0 = 10
Wbn = 15-0 = 15
It becomes.
(1) Perform zero adjustment. (10 is stored in Wza and 15 is stored in Wzb)
(Or automatic zero tracking is working)
Wan = 10-10 = 0
Wbn = 15-15 = 0
(2) Place the load on the weighing platform.
Wan = 1010−10 = 1000
Wbn = 1015 + 3-15 = 1003
And the value of discriminant D based on said Formula (9) is calculated | required as follows.
D = | Wan−Wbn | = 3
Thus, the span error is extracted even when the zero adjustment operation is performed.
(3) Place the load on the weighing platform without adjusting the zero point.
Wan = 1010-0 = 01010
Wbn = 1015 + 3-0 = 1018
And the value of discriminant D based on said Formula (9) is calculated | required as follows.
D = | Wan−Wbn | = 8
Thus, when the zero adjustment operation is not performed, the span error and the zero error are extracted by mixing.

<Another example of discriminant D>
The discriminant D can also be defined by a ratio calculation formula like the following formula (3) ′.
D = Wan / Wbn (3) ′
Then, it may be evaluated how far away from a value larger or smaller than D = 1.

<Explanation of relationship between influence of span fluctuation and discriminant D value>
When the measuring instrument is used in a state in which the zero point adjustment is not properly performed, a value obtained by adding a variation due to the span abnormality to a variation due to the zero abnormality appears as the value of the discriminant D.
In the case of a measuring instrument such as a platform scale or a fee scale, which is often used in a state where there is no object to be weighed on the weighing platform 9, the span variation is evaluated.
Assuming that the error tolerance derived from the measurement accuracy with respect to the span variation amount is Er, the comparison / determination unit 52c determines that a span failure has occurred if the following equation (10) holds.
D> Er (10)
When the comparison / determination unit 52c determines that the above expression (10) is established, the alarm signal generation unit 52d generates and outputs an alarm signal for causing the alarm device 56 to generate an alarm in response to this determination. As a result, an alarm indicating that a span failure has occurred is issued from the alarm device 56.
By the way, the amount of error generated due to span variation differs depending on the magnitude of the load of the object to be weighed. Therefore, the allowable value Er must be different depending on the magnitude of the load on the object to be weighed.
Therefore, the allowable error Er related to the span at an arbitrary load is set to Es + Wabs at the time of adjustment, where Wan + Wbn = Wabs when the rated load is applied and Es is the allowable span error at the rated load. The span allowable error Er at a load of 1 is defined as in the following equation (11).
Er = Es · {(Wan + Wbn) / Wabs} (11)

<Description of the relationship between the influence of span fluctuation and the value of discriminant D (in the case of ratio)>
When the value of the discriminant D is expressed as a ratio, if the allowable accuracy at the rated load is Rs (%),
D <1- (Rs / 100)
Or
D> 1+ (Rs / 100)
If so, the comparison / determination unit 52c determines that there is a span failure, and upon receiving this determination, the alarm signal generation unit 52d outputs an alarm signal.

<Explanation of the relationship between the influence of zero point fluctuation due to abnormal factors and the value of discriminant D>
On the other hand, in the case of a measuring instrument used without returning to the zero point for a long period of time such as a conveyor scale, the fluctuation due to the zero point abnormality is not corrected and is included in Wan and Wbn. Is preferably set to a value Er + Ez that allows for an allowable value Ez for the zero point variation due to an abnormal factor.
And
D> Er + Ez
The failure is determined by the following formula.
Here, Ez is preset to a value of what percentage of the rated load.

<Explanation of the effect of span error evaluation / determination>
As described above, Wan and Wbn are set as in the above formulas (5), (6) or the above formulas (7), (8), and zero adjustment for Wan and Wbn is performed automatically or manually appropriately. For example, the span error can be evaluated and determined in a state where an object to be weighed having an arbitrary weight is loaded.
In the case of a failure due to the zero point fluctuation of the half bridge circuits 15a and 15b, if the fluctuation is within a range where the zero point adjustment is possible, it is possible to continue using the measuring instrument for the time being by performing the zero point adjustment operation. If the fluctuation exceeds the allowable value, the meter cannot continue to be used.

<Explanation as to which side of the half-bridge circuit has a span fluctuation due to a failure>
The failure diagnosis apparatus 20 of the present embodiment operates the key switch 55 to operate the display device 54 by converting the values of Wan and Wbn, or values obtained by converting them into weight display values WDa and WDb as shown in Table 1 below. Can be displayed.

<Description of weight display value>
The value of Wnx (Wax, Wbx) is called an internal count value, and the analog load signal corresponding to one count is set to a size of at least 1/4 or less of the minimum display amount of the display weight value by the measurement method. Yes. Conversely, for the same analog load voltage, the internal count corresponding to one count of the minimum display amount of the display weight value is set to have a value that is four times or more.
For example, as shown in Table 1, it is configured to represent one count of the minimum display amount of the display weight value WD (WDa, WDb) with an analog load signal corresponding to four counts of the internal count value Wnx.
One count of WD (WDa, WDb) is, for example, the minimum display amount 0, 5, 0, 5..., 0, 2, 4, 6. -Corresponds to (g).

<Description of automatic zero correction by automatic zero tracking>
Automatic zero point correction by automatic zero point tracking means that a drift memory Wd is provided for an expression (for example, Wnx = k · (Wox−Wi) −Wz) representing Wnx, and Wnx is
Wnx = k · (Wox−Wi) −Wz−Wd
And the value of Wnx when the display weight value WD is 0 (the range indicated as 0 of the display value in Table 1 above), and if the value of Wnx is −1 or 1, Wnx = 0. By automatically adding +1 or -1 to the drift memory Wd in a certain direction, correction is made so as to enter the true zero (referred to as center zero) in Table 1 where Wnx = 0. Note that the zero point memory Wz and the drift memory Wd may be one common memory.
The weighing instrument configured in accordance with the weighing law automatically performs the above zero tracking operation when the object to be weighed is removed from the weighing table 9 and the load signal is stabilized and the weight display value becomes zero. Is done.

<Explanation on which side of the half-bridge circuit is broken>
When the display of the display device 56 is not zero, the zero point adjustment key in the key switch 55 is pressed to adjust the zero points of Wan and Wbn, and an object to be weighed (for example, a weight) having a known weight value is placed on the weighing table 9 and Wna. , Wbn or these values are converted into display weight values WDa, WDb for display.
The operator can easily determine which side of the half-bridge circuits 15a and 15b has failed by comparing the displayed weight values with known weight values.
If there is an abnormality in the half-bridge circuit 15a, the operator also gives a display switching command to display the weight measurement value as a weighing instrument with the output of the half-bridge circuit 15b by operating the key switch 55. The conversion unit 52f handles 2 · Wbn as a weight measurement value. Needless to say, when the half-bridge circuit 15b fails, the converter 52f handles 2 · Wan as a weight measurement value based on the output of the half-bridge circuit 15a.

<Explanation as to which side of the half-bridge circuit is fluctuating due to failure>
For zero point failure, only Wan, Wbn according to the above formulas (1) and (2) or the values of ka · (Wax−Wai) and kb · (Wbx−Wbi) in the above formulas (5) to (8), or These values can be converted into WDa ′ and WDb ′ and displayed as display weight values for the zero point variation.
When the operator operates the key switch 55 for displaying the zero variation, the values of the equations (1) and (2) that do not involve the manual and automatic correction amounts for the zero variation are displayed on the equation. To do.
These values include the zero fluctuation due to factors common to both the half-bridge circuits 15a and 15b, such as dust adhering to the weighing table 9, and the span fluctuation at the zero. Is small, compare the magnitude of the deviation from the zero value of both displayed values in the zero point state (a specific state in the conventional case), that is, without placing the object to be weighed on the weighing table 9. For example, the zero point abnormality and the degree of the half bridge circuit 15a, 15b which shows a value far away from the zero point in the plus or minus direction are found.
Even when the zero point abnormality is automatically determined, since the two sets of half bridge circuits 15 and 15b are previously adjusted in span so as to change the display amount of the same magnitude with respect to the same load change, The allowable range of fluctuation can be set to the same allowable value, such as A% of the rated load. The allowable value determined in this way and the values of the equations (1) and (2) at the zero point are respectively set. In comparison, if the display weight value for the zero point fluctuation amount exceeds the set allowable value, an abnormality alarm is given and either of the malfunctioning sides is displayed.

<Explanation of more accurate span error determination and error compensation in case of failure>
In order to determine the span error more accurately and to output the weight measurement of the object to be measured more accurately at the time of failure, prepare at the time of adjustment as follows.
In general, load sensors applied to the compression load cell 1 and the double beam load cell 5 have non-linearity and hysteresis characteristics. Therefore, a load that outputs Wan = WA when a weight value Ws is loaded after zero adjustment is performed. Even if an arbitrary load Wx is applied to the sensor, the output on the straight line determined by the following equation (12) is not obtained, and a hysteresis curve is applied as shown in FIG. 5 for gradually increasing and decreasing loads of Wx to Ws. Draw.
Wan = (WA / Ws) · Wx (12)
That is, as shown in FIG. 5, an error of ex occurs when the load gradually increases and ex ′ when the load gradually decreases, with respect to an arbitrary load.

<Explanation of more accurate span error determination and error compensation in case of failure>
Therefore, a plurality of different objects to be weighed with a weight value between 0 and Ws are loaded onto the weighing table 9, and the wan at each load is measured. For example, as shown in FIG. 5, the weight values Wx1, Wx2 Assuming that the error when loading an object to be measured is ea1 and ea2 when the load is gradually increased, and ea1 ′ and ea2 ′ when the load is gradually decreased,
As an average value when the load increases or decreases,
At Wx1 load, measured value = (WA1 + WA1 ′) / 2 = WA1a
Error = (ea1 + ea1 ′) / 2 = ea1a,
At the time of Wx2 load, measured value = (WA2 + WA2 ′) / 2 = WA2a
Error = (ea2 + ea2 ′) / 2 = ea2a,
As shown in FIG. 6, the error-measurement signal Wan is replaced with the coordinates, and the measurement values shown in FIG. 5 are plotted at the coordinates shown in FIG. The function represented by the following formula (13) representing the error is determined, and the error compensation unit 52g obtains ex for the value of Wan, and corrects Wan as represented by the following formula (14).
ex = f (Wan) (13)
Wan + ex (14)
The same applies to Wbn.
Since the value of the discriminant D is expressed more accurately by correcting the output signals of the half-bridge circuits 15a and 15b in this way, the failure determination can be performed more accurately.
Further, an accurate value can be given even when the output of one of the two sets of half-bridge circuits 15a and 15b is replaced with a weight measurement value as a measuring instrument due to a span failure.

<Explanation of correspondence relationship of words with the present invention>
The load signal calculation unit 52b corresponds to the “object weight value calculation unit” and the “load signal calculation unit” of the present invention.
The comparison determination unit 52c corresponds to the “comparison determination unit” of the present invention.
The configuration including the alarm signal generation unit 52d and the alarm device 56 corresponds to the “alarm unit” of the present invention.
The selection determination unit 52e corresponds to the “selection determination unit” of the present invention.
The converter 52f corresponds to the “converter” of the present invention.
The error compensator 52g corresponds to the “error compensator” of the present invention.
The memory block 53 corresponds to “storage means” of the present invention.

[Second Embodiment]
FIG. 7 shows a schematic system configuration diagram of a failure diagnosis apparatus according to the second embodiment of the present invention. Note that the same or similar parts as those of the failure diagnosis apparatus 20 of the previous embodiment are given the same reference numerals in the drawing, and detailed description thereof is omitted, and in the following, the failure diagnosis apparatus 20 of the previous embodiment and The explanation will focus on the differences.

The failure diagnosis apparatus 20A of the present embodiment includes an analog adder circuit 57, an A / D converter 58, and an arithmetic circuit 26 that are provided for the full bridge circuit 15.
Here, the full bridge circuit 15 and the arithmetic circuit 26 are the same as those used in the failure diagnosis apparatus 20 of the previous embodiment.
In the failure diagnosis apparatus 20 of the previous embodiment, two A / D converters 24 and 25 are used, but in the failure diagnosis apparatus 20A of this embodiment, one A / D converter 58 is used.
In the fault diagnosis apparatus 20 of the previous embodiment, a DC voltage is applied in which the potential at the connection point 16 in the full bridge circuit 15 is + V and the potential at the connection point 17 is zero. A DC voltage is applied such that the potential at the connection point 16 is + V and the potential at the connection point 17 is −V. In this case, the half-bridge circuits 15a and 15b using the voltage reference fixed resistors 21 and 22 that are required in the failure diagnosis apparatus 20 of the previous embodiment are not necessary.

The analog adder circuit 57 includes a first operational amplifier 61, a second operational amplifier 62, a third operational amplifier 63, a fourth operational amplifier 64, and a fifth operational amplifier 65.
In the first operational amplifier 61, the input positive terminal 61a is connected to the connection point 18 of the full bridge circuit 15, the input negative terminal 61b is connected to the output terminal 61c, and the output terminal 61c is connected to the resistors 66 and 67. .
In the second operational amplifier 62, the input positive terminal 62 a is connected to the connection point 19 of the full bridge circuit 15, the input negative terminal 62 b is connected to the output terminal 62 c, and the output terminal 62 c is the resistor 68 and the fourth operational amplifier 64. Each is connected to the input positive terminal 64a.
In the third operational amplifier 63, the input positive terminal 63a is connected to the resistor 68, and is connected to the circuit ground 70 via the resistor 69, and the input negative terminal 63b is connected to the resistor 66. The output terminal 63 c is connected to the A / D converter 58 via the analog switch 72.
In the fourth operational amplifier 64, the input positive terminal 64a is connected to the output terminal 62c of the second operational amplifier 62 and the resistor 68, respectively, and the input negative terminal 64b is connected to the circuit ground 70 via the resistor 73. At the same time, the resistor 74 is connected to the output terminal 64 c, and the output terminal 64 c is connected to the A / D converter 58 via the analog switch 75.
In the fifth operational amplifier 65, the input positive terminal 65 a is connected to the circuit ground 70 via a resistor 76, and the input negative terminal 65 b is connected to a resistor 67, and is also connected to a output terminal 65 c via a resistor 77. The output terminal 65 c is connected to the A / D converter 58 via the analog switch 78.

In the failure diagnosis apparatus 20A of the present embodiment, the analog load signal for the weighing instrument is synthesized by the third operational amplifier 63.
The output load signal of the half-bridge circuit 15a on the connection point 18 side is eoa, the load signal of the half-bridge circuit 15b on the connection point 19 side is eob, and only one A / D converter 58 is used for all signals. The input is switched by analog switches 72, 75, 78. Thus, the number of A / D converters used may be selected as appropriate.

The strain gauge type load cell failure diagnosis apparatus of the present invention has been described based on a plurality of embodiments. However, the present invention is not limited to the configuration described in the above embodiments, and is described in each embodiment. The configuration can be changed as appropriate within a range not departing from the gist, such as appropriately combining the configurations.

The strain gauge load cell failure diagnosis device of the present invention has the characteristic that it can accurately detect a strain gauge load cell failure regardless of the weighing conditions such as the type of weighing instrument and whether or not the weighing operation is in progress. Therefore, it can be suitably used for fault diagnosis of strain gauge type load cells used in measuring instruments such as conveyor scales, hopper scales, track scales, platform scales, and fee scales.

DESCRIPTION OF SYMBOLS 1 Compression type load cell 5 Double beam type load cell 9 Weighing table 15a Half bridge circuit 15b Half bridge circuit 20 Failure diagnosis device (first embodiment)
20A Fault diagnosis device (second embodiment)
52b Load signal calculation unit (load signal calculation means)
52c Comparison determination unit (comparison determination means)
52d Alarm signal generator (alarm means)
52e Selection discrimination unit (selection discrimination means)
52f Conversion unit (conversion means)
52g Error compensator (error compensation means)
53 Memory block (storage means)
56 Alarm (alarm means)

Claims (7)

A full bridge circuit is constituted by two sets of half-bridge circuits, and an output of the two sets of half-bridge circuits is obtained for each half-bridge circuit, thereby providing a weighing platform supported by the strain gauge load cell. A strain gauge type load cell fault diagnosis device comprising weighted object weight value calculating means for calculating a weight value of a placed object to be weighed for each output of each half bridge circuit,
Storage means for storing an allowable value determined based on a predetermined weighing accuracy or a predetermined rated load;
When the force or load of an arbitrary magnitude is loaded on the weighing platform, the operating zero point fluctuation component included in each output signal is removed from the output signals of the two sets of half bridge circuits . A strain gauge type load cell fault diagnosis apparatus comprising: a comparison determination unit that compares weight values calculated from output signals and determines whether the comparison result exceeds the allowable value.   In a state where an object to be weighed does not exist on the weighing table or an object to be weighed of an arbitrary load exists, the comparison result of the weight value calculated from the output signals of the two sets of half bridge circuits by the comparison determination unit is The strain gauge type load cell failure diagnosis apparatus according to claim 1, further comprising an alarm unit that issues an alarm when it is determined that the allowable value is exceeded.   Load signal calculation means for executing calculation processing such that each of the weight values calculated from the output signals of the two sets of half-bridge circuits has the same weight value for the load to be measured. The fault diagnostic apparatus for a strain gauge type load cell according to claim 1 or 2, wherein:   Selection determination for selecting and determining which of the two sets of half-bridge circuits is faulty in a state where an object to be weighed does not exist on the weighing platform or a object to be weighed having a known weight value is placed 4. The strain gauge type load cell failure diagnosis apparatus according to claim 3, wherein a means is provided.   When the selection determining means selects and determines that one of the two sets of half-bridge circuits is faulty, the other output signal of the two sets of half-bridge circuits is used to measure the weight of an object to be weighed on the weighing platform. 5. A strain gauge type load cell fault diagnosis apparatus according to claim 4, wherein conversion means for converting the weight measurement value into an output signal for use is provided.   4. The failure of the strain gauge load cell according to claim 3, wherein a load signal calculation formula including a stored value of a zero fluctuation amount obtained by manual zero adjustment and / or automatic zero tracking is used in the calculation processing by the load signal calculation means. Diagnostic device.   The error compensation means for compensating the output error corresponding to the load load for each of the weight values calculated from the output signals of the two sets of half-bridge circuits obtained through the arithmetic processing by the load signal calculation means is provided. The strain gauge type load cell failure diagnosis apparatus described.

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