JPH11311565A - Load cell balance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily correct a zero point and a span. SOLUTION: The specified value of a zero point corresponding to a dish load and the specified value of a span corresponding to a rated load are stored, and the correction coefficient of the zero point that is the difference between the actual metering value of the zero point being the actual metering value corresponding to the dish load and the stored specified value of the zero point is calculated for storing. Also, according to the ratio of the actual metering value of the span corresponding to the rated load to the specified value of the span being stored, the correction coefficient of the span is calculated for storing. Then, corresponding to the stored correction coefficients of the zero point and the span, the correction voltages of the zero point and span are set in an A/D converter 5, thus allowing the output of a load cell 3 to be subjected to zero-point and span correction according to the set correction voltages of the zero point and span, and hence eliminating special work required for the zero-point and span correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load cell scale.

[0002]

2. Description of the Related Art A schematic structure of a conventional load cell scale is shown in FIG. FIG. 5 is a schematic block diagram of the electrical connection of each unit. First, the load cell scale amplifies the analog output of the load cell 101 by the amplifier 102 and
In step 3, the digital value is converted into a digital value, and the converted digital value is converted into a weight value having a unit such as g by arithmetic processing in a microcomputer 104 (hereinafter, simply referred to as a microcomputer 104), and this is displayed on the display unit 105. It is provided with a schematic structure to perform. That is, the object to be weighed 108 is placed on the pan 107 connected to the load cell 101 and
When a load is applied to the load cell 1
The weighing based on the output of 01 is performed. The microcomputer 1
04 executes various setting processes and the like according to an input operation from the keyboard 109.

Here, since the load cell 101 has an output error based on individual differences, it is necessary to correct such an output error in advance. Alternatively, the load cell 101 may be adapted to meet the specifications of the load cell scales having different characteristics.
It is necessary to adjust the characteristics of the load sensor unit (the load cell 101, the amplifier 102, and the A / D converter 103) including In such a case, zero point correction and span correction are performed. Such a correction process will be described with reference to the graph of FIG. FIG. 4 is a graph showing the relationship between the specified values of the zero point and the span and the actual weighing value.

First, in order to perform the zero point correction and the span correction, a weighing value is obtained when the pan is loaded (W ₀ ), that is, when nothing is placed on the pan 107. In the graph of FIG. 4, A / A based on the output of the load cell 101 with respect to the dish load (W ₀ ).
The digital output of D converter 103 has become a _1. Thus, the actual weight value of the zero point is a _1. Next, a weighed value at the time of the rated load (Wm), that is, when the object 108 having the rated load is placed on the tray 107 is obtained.
In the graph of FIG. 4, the rated load (Wm) + the plate load (W ₀ )
The digital output of the A / D converter 103 based on the output of the load cell 101 has a b ₁ against. Then, the span S ₁ (sensitivity of the scale) at the rated load (Wm) is
b ₁ −a ₁ . Then, in order to perform the zero point correction and the span correction, the zero point and the span at the time of actual weighing are made to match or approximate to the specified values of the zero point and the span of the load cell scale on which the load cell 101 is mounted. That is, in the graph of FIG. 4, since the specified value of the zero point is a ₂ and the specified value of the span is S ₂ , the actual weight value a ₁ at the zero point is changed to the specified value a.
_The zero point correction and the span correction are performed by making the actual measured value S ₁ of the span coincide with or approximate to the specified value S ₂ in FIG. Therefore, conventionally, the actual weighing value a ₁ of the zero point is made to match or approximate the specified value a ₂ by adjusting the zero point setting device 110, and the actual weighing value S ₁ of the span is adjusted by adjusting the sensitivity setting device 111. match or approximate to the specified value S _2, it is common that that.

FIG. 6 shows an example of a conventional structure of the zero point setting device 110 and the span setting device 111. The zero point setting device 110 and the span setting device 111 have a structure in which a plurality of resistors R _{1 to} R ₆ are connected in series so that a plurality of resistors R _{1 to} R ₆ can be short-circuited to the output line of the load cell 101 to which the resistor R ₀ is connected in parallel. is there. That is, when the output voltage Vin of the load cell 101 is taken out as the voltage V ₀ , the resistances R _{1 to} R
_The circuit configuration is such that the value of the voltage V ₀ is adjusted by short-circuiting any of the _six resistors. More specifically, the voltage V ₀ is

[0006]

(Equation 1)

[0007] The resistance R
The value of the voltage V ₀ by shorting any resistance of ₁ to R ₆ is varied.

[0008]

However, when a circuit configuration as illustrated in FIG. 6 is employed as the zero point setting device 110 or the span setting device 111, any _{one of} the resistors R _{1 to} R ₆ is short-circuited. This must be determined based on the intuition of the operator, and the work of short-circuiting the resistor itself is complicated, time-consuming, and time-consuming. Therefore,
The conventional load cell scale has a problem that it is extremely difficult to perform zero point correction and span correction.

An object of the present invention is to facilitate zero point correction and span correction.

[0010]

According to a first aspect of the present invention, a load cell for outputting an analog value according to an applied load, and a zero point correction voltage and a span correction voltage are set and set. An analog-to-digital converter that converts the output of the load cell to a digital value by performing zero-point correction and span correction according to the zero-point correction voltage and span correction voltage, and a zero-point specified value and a rated load, which are specified values corresponding to the plate load A data storage unit for storing a span specified value that is a specified value corresponding to the data, a data storage unit for storing a zero-point actual weighed value that is an actual weighed value corresponding to the pan load output from the analog-digital converter, A zero-point correction coefficient calculating means for calculating a zero-point correction coefficient which is a difference between the zero-point actual weighing value stored in the storage means and the zero-point prescribed value stored in the storage means. And the actual span value obtained by subtracting the actual zero value stored in the data storage means from the actual weight value corresponding to the load obtained by adding the rated load to the pan load output from the analog-digital converter to calculate the actual span value. Value calculation means, span correction coefficient calculation means for calculating a span correction coefficient from a ratio between the actual span value calculated by the actual span value calculation means and the specified span value stored in the storage means, and a zero point correction coefficient. A second data storage unit for storing the zero point correction coefficient calculated by the calculation unit and the span correction coefficient calculated by the span correction coefficient calculation unit; and a zero point correction coefficient stored in the second data storage unit. The analog-to-digital converter includes a correction unit that sets a zero-point correction voltage and a span correction voltage in accordance with the span correction coefficient.

Therefore, the zero point correction coefficient is calculated by the zero point correction coefficient calculation means, the span correction coefficient is calculated by the span correction coefficient calculation means, and the calculated zero point correction coefficient and span correction coefficient are calculated as the second Is stored in the data storage means. Then, the correction means sets the zero point correction voltage and the span correction voltage in the analog-to-digital converter according to the zero point correction coefficient and the span correction coefficient stored in the second data storage means. Accordingly, the analog-to-digital converter converts the output of the load cell to a digital value by performing zero-point correction and span correction according to the set zero-point correction voltage and span correction voltage. Therefore, the zero point correction and the span correction can be executed only by applying the dish load and the rated load to the load cell, and no special operation is required for the zero point correction and the span correction.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to FIGS. Since the graph of FIG. 4 has already been described, the description thereof will be omitted.

FIG. 1 is a schematic block diagram of the electrical connection of each part. First, a load cell 3 to which the tray 2 is connected is provided, and an output of the load cell 3 is supplied to a microcomputer 6 (hereinafter, microcomputer 6) via an amplifier 4 and an analog / digital converter 5 (hereinafter, abbreviated as A / D converter 5). ). The microcomputer 6 includes a display 7, a keyboard 8, and a flash ROM 9. A data register 10 is connected to the microcomputer 6, and the data register 10 is connected to the A / D converter 5 via a zero point setting device 11 and a sensitivity setting device 12. Here, the amplifier 4, the A / D converter 5, the data register 10, the zero point setting device 11, and the sensitivity setting device 12
Is a one-chip unit as a load sensor unit.

The load cell 3 outputs an analog value to the amplifier 4, and the value of the analog output fluctuates when an object 13 including a rated load is placed on the pan 2. The analog output of the load cell 3 that fluctuates in this manner is amplified by the amplifier 4 and is converted into a digital signal by the A / D converter 5. At this time, the A / D converter 5 outputs a zero point correction voltage and a span correction voltage according to the zero point setting voltage and the span setting voltage (sensitivity setting voltage) transmitted and output from the zero point setting device 11 and the sensitivity setting device 12, respectively. Set yourself. That is, the A / D converter 5 has a function of variably setting the zero-point correction voltage and the span correction voltage, and zero-corrects the output of the load cell 3 according to the set zero-point correction voltage and span correction voltage. In addition, the data is converted into a digital value by performing span correction. Then, the microcomputer 6 inputs a digital value corrected and output from the A / D converter 5 according to the zero point correction voltage and the span correction voltage set in the A / D converter 5 as an output value of the load cell 3. Here, the microcomputer 6 has a ROM and a RAM that execute various arithmetic processes and centrally control each unit.
Is a microcomputer connected to the bus (all not shown), executes a predetermined process according to an input from the keyboard 8, and displays the processing result on the display 7. For example, the microcomputer 6 converts the digital value, which is the output value of the load cell 3 corrected and output from the A / D converter 5, into a numerical value in units of g, and displays this on the display 7. Further, the flash ROM9 that the memory is separately connected to the microcomputer 6 the microcomputer 6 is built, the zero point specified value a ₂ is a specified value that corresponds to the dish load (W _0), corresponding to the rated load (Wm) a span specified values S ₁ is a predetermined value that can be stored rewritably. Therefore, the flash ROM 9 functions as storage means. here,
The zero point specified value a ₂ and span specified value S _1, so description thereof will be as already described based on the graph in FIG. 4 will be omitted.

Here, processing for zero point correction and sensitivity correction of the load cell 3 will be described with reference to the flowcharts of FIGS. First, the dish load (W ₀ ) output from the A / D converter 5 when nothing is placed on the tray 2.
Is obtained (step S1) and stored in the flash ROM 9 (expressed as a nonvolatile memory in the flowchart) (step S2). The digital output obtained in step S1 is a ₁ (ct) (FIG. 4).
Graph). Therefore, the flash ROM 9
It functions as data storage means for storing the zero-point actual weighing value, which is the actual weighing value corresponding to the dish load (W ₀ ) output from the A / D converter 5.

Next, when it is determined that the rated load has been applied (step S3), a digital output from the A / D converter 5 when the rated load (Wm) is applied is obtained (step S4). It is stored (step S5). The digital output obtained in step S4 is b ₁ (ct) (see the graph of FIG. 4).
This b ₁ (ct) is, as described above, the rated load (W
m) + Dish load (W ₀ ). Next, the span S _{1 of the} measured data is obtained from the digital outputs a ₁ (ct) and b ₁ (ct) of the A / D converter 5 stored in the flash ROM 9 (step S6), and the flash RO
It is stored in M9 (step S7). In step _{S5, b 1 (ct) -a} 1 a (ct) determining the span S ₁ of the measurement data by calculating the microcomputer 6. Here, the dish load (W ₀ ) output from the A / D converter 5
Of the actual span value calculation means for calculating the actual span value by subtracting the zero actual weight value stored in the flash ROM 9 as the data storage means from the actual weight value corresponding to the load obtained by adding the rated load (Wm) to the actual weight value. The function is performed.

Next, the microcomputer 6 recognizes the numerical value input from the keyboard 8 as the designated value of the zero point (step S8), and confirms that the numerical value is within the proper zero point range (step S9). Is stored in the flash ROM 9 (step S11). If it is determined in step S9 that the input numerical value is not in the zero point range, error processing is performed (step S10). In such a series of processing, the specified value of the zero point is the specified value a ₂ (ct) (see the graph of FIG. 4), whereby the specified zero point value a ₂ (ct) is stored in the flash ROM 9. become.

Next, the microcomputer 6 recognizes the numerical value input from the keyboard 8 as the designated value of the span (step S12), and confirms that the numerical value is within the proper span range (step S13), and then flashes. ROM 9
(Step S15). If it is determined in step S13 that the input numerical value is not in the span range, error processing is performed (step S14). In such a series of processing, the specified value of the span is the specified value S ₂ (ct) (FIG. 4).
, The span specified value S ₂ (ct) is stored in the flash ROM 9.

[0019] Then, the calculation processing of the microcomputer 6, the flash R from the specified value a ₂ of the zero point stored in the flash ROM 9 (ct) in step S ₂ in step S11
The zero-point correction coefficient Kz is obtained by subtracting the zero-point actual weighing value a ₁ (ct) stored in the OM 9 (step S1).
6) The calculated zero point correction coefficient Kz is the flash RO
It is stored in M9 (step S17). Here, the function of the zero-point correction coefficient calculating means for calculating the zero-point correction coefficient Kz, which is the difference between the zero-point actual weighing value a ₁ (ct) and the specified zero-point value a ₂ (ct), is executed. Further, following step S17, the microcomputer 6 determines in step S7 that the flash RO
Span S ₁ and step S of the measurement data stored in M9
Span specified value S stored in flash ROM 9 at 12
₂ , the calculation of S ₂ / S ₁ is executed to determine the span correction coefficient Ks (step S18). Then, the obtained span correction coefficient Ks is stored in the flash ROM 9 (step S19). Here, the span correction coefficient K is calculated based on the ratio between the span actual weighing value S ₁ and the specified span value S _2.
The function of the span correction coefficient calculating means for calculating s is executed.

Next, moving to the flowchart of FIG.
After it is confirmed whether or not the load sensor unit including the amplifier 4, the A / D converter 5, the data register 10, the zero point setting device 11, and the sensitivity setting device 12 which are made into a chip unit is connected to the microcomputer 6 (step S2).
0), the zero point correction coefficient Kz and the span correction coefficient Ks stored in the flash ROM 9 are transmitted and output to the load sensor unit (step S22). At this time, step S
If it is determined at 20 that the load sensor unit is not connected to the microcomputer 6, a load sensor unit non-connection error is output (step S21). Until the load sensor unit replies that transmission is OK (Y in step S23), retry transmission is performed (steps S24 and S22). If retry over is determined (Y in step S24), data transmission NG error output Is performed (step S25).

Here, the load sensor unit formed into one chip has a simple microcomputer configuration and executes various processes by itself. For example, the microcomputer of the load sensor unit transmits a signal serving as a basis for determining whether or not the microcomputer 6 is OK in step S23 to the microcomputer 6, and executes the processing in step S26 and subsequent steps. The processing after step S26 will be described next.

The load sensor unit that has received the transmission output of the zero point correction coefficient Kz and the span correction coefficient Ks from the microcomputer 6 stores the received zero point correction coefficient Kz and span correction coefficient Ks in the data register 10 (step S).
26). Therefore, the data register 10 functions as a second data storage unit that stores the zero point correction coefficient Kz and the span correction coefficient Ks.

Next, the load sensor unit inputs the zero point correction coefficient Kz to the zero point setter 11 (step S).
27). Then, the zero point setter 11 outputs the zero point set voltage Vz to the A / D converter 5 (step S2).
8). The zero point setting voltage Vz at this time is Vz = f (K
z). Thereby, the zero point correction voltage based on the zero point setting voltage Vz is set in the A / D converter 5.
Here, the data register 1 as the second data storage means
The function of the correcting means for setting the zero point correction voltage in the A / D converter 5 according to the zero point correction coefficient Kz stored in 0 is executed.

Next, the load sensor unit inputs the span correction coefficient Ks to the sensitivity setting device 12 (step S2).
9). Then, the sensitivity setting device 12 controls the A / D converter 5
Then, the span setting voltage Vs is output (step S30).
At this time, the span setting voltage Vs is Vs = f (Ks). Thus, a span correction voltage based on the span setting voltage Vs is set in the A / D converter 5. here,
The A / D converter 5 according to the span correction coefficient Ks stored in the data register 10 serving as second data storage means.
The function of the correction means for setting the span correction voltage is executed.

Thus, the zero point correction voltage and the span correction voltage are set in the A / D converter 5. So, A
The / D converter 5 converts the output of the amplifier 4 into a digital signal (step S31), transmits the digital output to the CPU of the microcomputer 6 (step S32), and performs processing for zero point correction and sensitivity correction of the load cell 3. To end.
As described above, in the load cell scale of the present embodiment, the zero point correction and the span correction can be executed only by applying the dish load and the rated load to the load cell 3, and therefore,
No special work is required for the zero point correction and the span correction, which can be facilitated.

When the object 13 is actually weighed, the analog output of the load cell 3 is amplified by the amplifier 4 and converted into a digital value by the A / D converter 5, and the converted digital value is calculated by the microcomputer 6. The weight value is converted into a weight value having a unit such as, and is displayed on the display 7. At this time, A
The / D converter 5 converts the output of the load cell 3 into a digital value by performing zero point correction and span correction according to the set zero point correction voltage and span correction voltage.

[0027]

The present invention is constructed as described above.
The zero point correction and the span correction can be executed only by applying the dish load and the rated load to the load cell. Therefore, no special work is required for the zero point correction and the span correction, which can be facilitated.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram of an electrical connection of each unit according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a flow of processing for zero point correction and span correction of a load cell.

FIG. 3 is a flowchart showing a process following a part A in the flowchart of FIG. 2;

FIG. 4 is a graph showing a relationship between specified values of a zero point and a span and actual measured values.

FIG. 5 is a schematic block diagram of an electrical connection of each unit showing an example of the related art.

FIG. 6 is a circuit diagram showing an example of a conventional structure of a sensitivity setting device and a zero point setting device.

[Explanation of symbols]

Reference Signs List 3 load cell 5 analog / digital converter (A / D converter) 9 data storage means, data storage means (flash ROM) 10 second data storage means (data register) a ₁ zero point actual weighing value a ₂ zero point specified value S ₁ span actual metering value S ₂ span specified value S6 span actual metering value calculating unit S16 zero point error calculating unit S18 span correction factor calculating means S27~S30 correcting means

Claims (1)

[Claims] 1. A load cell that outputs an analog value according to an applied load, a zero point correction voltage and a span correction voltage are set, and a load cell of the load cell is set according to the set zero point correction voltage and span correction voltage. An analog-to-digital converter that converts the output to a digital value by zero-point correction and span correction, and saves a zero-point specified value corresponding to the countersunk load and a span specified value corresponding to the rated load. Data storage means, data storage means for storing a zero-point actual weight value which is an actual weight value corresponding to the pan load output from the analog-digital converter, and the zero-point actual weight value stored in the data storage means Zero-point correction coefficient calculating means for calculating a zero-point correction coefficient that is a difference between the zero-point correction value stored in the storing means and the analog-digital value; Span actual weighing value calculation for subtracting the zero-point actual weighing value stored in the data storage means from the actual weighing value corresponding to the load obtained by adding the rated load to the dish load output from the converter to calculate the span actual weighing value Means, a span correction coefficient calculating means for calculating a span correction coefficient from a ratio between the actual span value calculated by the actual span value calculating means and the specified span value stored in the storage means; Second data storage means for storing the zero point correction coefficient calculated by the point correction coefficient calculation means and the span correction coefficient calculated by the span correction coefficient calculation means, and storage in the second data storage means Setting a zero point correction voltage and a span correction voltage in the analog-to-digital converter according to the zero point correction coefficient and the span correction coefficient thus set. Load cell balance comprising: a positive means.