JPH102784A - Weighing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the load of a microprocessor or a memory by providing a drift correction circuit, delivering a corrected signal to an A/D converter. SOLUTION: A drift correction circuit 5 holds a drift signal outputted from an amplifier circuit 2, when the input terminals thereof are short-circuited in drift correction mode. When short circuit is released in the weighing mode, the drift signal is subtracted from an amplified analog weight signal, and a corrected signal is delivered to an A/D converter 6. Since the corrected signal is delivered to the A/D 6 by simply switching the mode through the mode- switching means 9 of a CPU 8, drift of the circuit 2 can be corrected, without requiring any processing through the CPU 8, and the load of the processor of the memory can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for amplifying an analog weight signal obtained by detecting the weight of an object to be weighed,
The present invention relates to a weighing device for generating a digital weighing signal for indicating the weight, and more particularly to drift correction of the amplifier circuit.

[0002]

2. Description of the Related Art A weighing device such as an electronic weigher or a combination weighing device amplifies an analog weight signal obtained by detecting the weight of an object to be weighed by an amplifier circuit and then displays a digital weighing signal (for displaying the weight). Metric value). In this type of weighing device, it is known that a drift occurs in an analog signal processing circuit such as the amplifier circuit due to a change in power supply voltage or a change in temperature. Since such a drift appears as an error in the measured value, it is necessary to perform drift correction to ensure the accuracy of the measured value.

FIG. 8 shows a conventional weighing device for correcting this drift. In the drift correction mode, as shown in FIG.
When W1 is turned off and SW2 is turned on, the input terminals of the amplifier circuit 2 are short-circuited, and an offset voltage of the amplifier circuit 2 appears at the output terminal. This voltage is applied to the anti-alias filter 3
Is converted to digital by the A / D converter 6 via the DSP (D
After the digital filtering processing by the digital signal processor 7, the processing result is stored in the memory 11.

In the weighing mode, as shown in FIG. 8B, under the control of the CPU 8, SW1 is turned on and SW2 is turned on.
Is turned off, a differential voltage proportional to the weight of the object detected by the weight sensor 1 is input to the differential input terminal of the amplifier circuit 2. Therefore, the voltage at its output is
The sum of the voltage obtained by amplifying the differential voltage and the offset voltage of the amplifier circuit 2 is obtained.

This voltage is converted into a digital signal by an A / D converter 6 through an anti-alias filter 3 and a digital filtering process is performed by a DSP 7. The DSP 7 subtracts the offset voltage processing result stored in the memory 11 in the drift correction mode from the addition processing result of the amplified differential voltage and the offset voltage from the amplifier circuit 2 stored in the memory 11 in the drift correction mode, and Is sent to the CPU 8 as the weight data. It should be noted that the subtraction processing is performed not by DSP7 but by C
It may be performed by the PU8. As such a weighing device,
For example, one disclosed in Japanese Patent Publication No. 5-69173 by the present applicant is known.

[0006]

However, the drift correction in the conventional apparatus is a correction based on the arithmetic processing of the microprocessor, and therefore largely depends on the capabilities of the DSP 7 and the CPU 8. In particular, in a high-speed weighing device, the arithmetic processing load of the microprocessor is large, and it has been difficult to perform drift correction. There is also a problem that a load on a memory capacity for performing drift correction is large.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and enables drift correction of an amplifier circuit independent of the performance of a microprocessor, thereby reducing the processing load on the microprocessor and the load on the memory capacity related to drift correction. It is an object of the present invention to provide a weighing device that can perform measurement.

[0008]

In order to achieve the above object, a weighing device according to the present invention detects weight of the object to be weighed and outputs an analog weight signal; An amplifier circuit that amplifies the signal, holds a signal corresponding to a drift signal output from the amplifier circuit when the input terminals of the amplifier circuit are short-circuited, and outputs the signal from the amplifier circuit when the short circuit is released. A drift correction circuit that outputs a drift-corrected signal from which the drift signal has been subtracted; and an A / D converter that converts the drift-corrected signal into a digital signal. According to the above configuration, since the drift corrected signal corrected by the drift correction circuit is output to the A / D converter, drift correction of the amplifier circuit can be performed without performing arithmetic processing in the CPU.

According to a second aspect of the present invention, in the weighing device according to the first aspect, switching between the first connection for inputting the analog weight signal to the amplifier circuit and the second connection for short-circuiting between input terminals of the amplifier circuit. A first switch means for performing the above operation, a first connection for inputting the amplified analog weight signal to the drift correction circuit and setting a weighing mode, and inputting a drift signal output from the amplification circuit to the drift correction circuit. And second switching means for switching to a second connection for setting the drift correction mode, and further, by switching the first and second switching means to the first connection at a first timing. The weighing mode is set, and the drift correction mode is set by switching the first and second switch means to the second connection at a second timing. And a over de switching means. According to the above configuration, a drift-corrected signal corrected by the drift correction circuit can be obtained only by switching between the measurement mode and the drift correction mode by the mode switching unit.

According to a third aspect of the present invention, in the weighing device according to the first or second aspect, the drift correction circuit is connected to, for example, an operational amplifier including a negative feedback amplifier circuit and a positive input terminal of the operational amplifier. A holding circuit that generates a drift-corresponding voltage corresponding to the drift signal in the drift correction mode and holds the drift-corresponding voltage in the weighing mode; A distribution circuit that removes the drift signal from the output signal of the operational amplifier by distributing and inputting the output signal of the amplifier circuit and the output signal of the operational amplifier at a predetermined ratio to the maintained negative input terminal; It consists of.

According to a fourth aspect of the present invention, in the weighing device according to any one of the first to third aspects, the input of the analog weight signal to the amplifier circuit is cut off, and a reference voltage is input to the amplifier circuit. A self-diagnosis circuit for outputting a signal corresponding to the span amount of the weight detecting means from the A / D converter is provided. Therefore, diagnosis of the signal processing circuit can be easily performed.

According to a fifth aspect of the present invention, in the weighing device according to the second or third aspect, an analog filter for reducing a high-frequency component of the amplified analog weight signal and a first connection for exhibiting a filter function of the analog filter. And a third switch means for switching between a second connection and a second connection functioning as a buffer function. The mode switching means further switches the third switch means to the first connection in the weighing mode, Further, the third switch means is switched to the second connection. According to the above configuration, even in the weighing device including the analog filter for reducing the high frequency component of the analog weight signal, the CP
Drift correction of the amplifier circuit can be performed without performing arithmetic processing in U.

In a weighing device according to a sixth aspect of the present invention, in any one of the first to fifth aspects, the A / D converter is configured as a delta-sigma type. Therefore, a weighing device having high resolution, that is, high accuracy and excellent responsiveness can be obtained.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a weighing device according to an embodiment of the present invention. This weighing device weighs an object to be weighed, performs digital filtering processing, and generates a digital weight signal for displaying the weight thereof. A weight sensor (weight detecting means) 1 having a strain gauge attached thereto, a first switch means S1, a second switch means S2, an amplifier circuit 2, an anti-alias filter 3,
Drift correction circuit 5, A / D converter 6, DSP (Digital
A signal processor 7 and a CPU 8 including a mode switching means 9. This weighing device is applied to, for example, a combination weighing device that selects a combination of weighing hoppers close to a target value within a certain allowable range based on a weight signal of each weight sensor connected to a plurality of weighing hoppers.

The weight sensor 1 detects the weight of an object to be weighed and outputs an analog weight signal. The amplifier circuit 2 amplifies the analog weight signal. First switch means S1 is interposed between the weight sensor 1 and the amplifier circuit 2,
The first switch means S1 includes a switch SW1 and a switch SW2 for switching between a first connection for inputting an analog weight signal from the weight sensor 1 to the amplifier circuit 2 and a second connection for short-circuiting between input terminals of the amplifier circuit 2. It has. The anti-alias filter 3 prevents aliasing due to a signal in a frequency band equal to or more than の of the sampling frequency of the A / D converter 6. Therefore, the anti-alias filter 3 may be connected between the drift correction circuit 5 and the A / D converter 6.

The drift correction circuit 5 holds a signal corresponding to the drift signal output from the amplifier circuit 2 when the input terminals of the amplifier circuit 2 are short-circuited, and is amplified when the short circuit is released. A drift corrected signal obtained by subtracting the drift signal from the analog weight signal is output.

The drift correction circuit 5 has an input terminal 3
1 has an operational amplifier (op-amp) OP composed of a negative feedback amplifier circuit that receives an output signal of the amplifier circuit 2 that has passed through the anti-alias filter 3, performs a predetermined operation on the output signal, and outputs a signal to an output terminal 32. doing. This operational amplifier OP
A holding circuit 12 composed of a kind of integrating circuit is interposed between the non-inverting (positive) input terminal of the first embodiment and the input terminal 31. The holding circuit 12 includes resistors R3 and R4 connected in series between the input terminal 31 and the ground, and a capacitor C connected between the connection point of the resistors R3 and R4 and the ground. It is interposed between the inverting input terminal and ground.
A second switch means S2 is interposed between the resistor R4 and the capacitor C of the holding circuit 12. Input terminal 31
The output terminal 32 is connected to the distribution circuit 14 composed of a series circuit of the resistors R1 and R2, and the connection point of the resistors R1 and R2 is connected to the inverted (negative) input terminal of the operational amplifier OP.

The second circuit provided in the drift correction circuit 5
The switch means S2 inputs the amplified analog weight signal to the drift correction circuit 5 and sets the first connection (ON) to set the weighing mode, and the drift signal output from the amplifier circuit 2 having the input terminals short-circuited. Is input to the drift correction circuit 5 and a switch SW3 for switching to the second connection (off) for setting the drift correction mode is provided.

The A / D converter 6 converts the drift corrected signal output from the drift correction circuit 5 at a first timing set according to the measurement timing into a digital signal.

The DSP 7 performs a digital filtering process on the drift-corrected signal digitally converted by the A / D converter 6.

The mode switching means 9 in the CPU 8 controls the first and second modes in the weighing mode by the control signal c1.
Switch means S1, S2 of the A / D converter 6
The first connection is switched to the first connection at the timing of the first and second switching means S1, S in the drift correction mode.
2 is switched to the second connection at the second timing. The second timing may be the same timing as the first timing, or may be one for a plurality of times of the first timing.

Next, the operation of the present weighing device will be described with reference to FIG. FIG. 3A shows the circuit connection in the drift correction mode, and FIG. 3B shows the circuit connection in the weighing mode. Hereinafter, the drift correction mode and the weighing mode that are switched by the mode switching means 9 will be described separately.

(A) Drift correction mode First, in the drift correction mode, in FIG.
The first switch means S1 is switched to the second connection by the control signal c1 from the mode switching means 9 of the CPU 8, and
By turning off the switch SW1 and turning on the switch SW2, the input terminals of the amplifier circuit 2 are short-circuited, and the output terminal thereof becomes the offset voltage of the amplifier circuit 2. Also, the second switch means S2 provided in the drift correction circuit 5 is switched to the second connection by the control signal c2, and the switch SW3
Is turned on.

Assume that the output of the amplifier circuit 2 (offset voltage of the amplifier circuit 2) is VE, the non-inverting (positive) input terminal voltage of the operational amplifier OP of the drift correction circuit 5 is V1, and S = j.
When Kirchhoff's law is applied to the non-inverting input terminal point at ω, the following equation is established.

[0025]

(Equation 1)

When formula (1) is subjected to inverse Laplace transform,

[0027]

(Equation 2)

In the equation (2), when a sufficient time has elapsed, the non-inverting input terminal voltage V1 becomes V1Ｒ (R4 / (R3 + R4)) · VE (3) (drift-corresponding voltage).

(B) Weighing Mode Next, in FIG. 2B, in the normal weighing mode,
The first switch means S1 is switched to the first connection by the control signal c1 from the mode switching means 9 of the CPU 8, and
The switch SW1 is turned on and the switch SW2 is turned off, so that the analog weight signal from the weight sensor 1 is input to the amplifier circuit 2. Further, the second switch means S2 of the drift correction circuit 5 is switched to the first connection by the control signal c2, and the switch SW3 is turned off.

Therefore, the output terminal of the amplification circuit 2 is connected to the voltage obtained by amplifying the differential voltage from the weight sensor 1 and the amplification circuit 2
Is the voltage obtained by adding the offset voltage. That is, the output of the amplifier circuit 2 is the differential voltage output of the weight sensor 1 as VIN,
Assuming that the amplification factor is G, G · VIN + VE. And
By turning off SW3, the non-inverting input terminal voltage of the operational amplifier in the drift correction circuit 5 becomes (R4 / (R3 + R
4)) • Held at VE. In an ideal operational amplifier, the impedance between the input terminals is infinite and no current flows, so the inverted (negative) input terminal voltage is the same (drift) as (R4 / (R3 + R4)) · VE of the non-inverted input terminal voltage. Corresponding voltage). In this state, when Kirchhoff's law is applied to the inverting input terminal point in FIG. 2B, the following equation is established, and the output VO of the drift correction circuit 5 is obtained.

[0031]

(Equation 3)

By substituting equation (3) into equation (4), the following equation (5) is obtained.

[0033]

(Equation 4)

To eliminate the effect of the offset voltage VE,
Since it is only necessary that the value in the second term parenthesis on the right side of the equation (5) is 0, if this is arranged, ((R1 + R2) / R2) · (R4 / (R3 + R4))
= 1 The above equation is satisfied when R1 = R2 and R3 = R4, or when R1 = R3 and R2 = R4. At this time, VO =-(R2 / R1) .G.VIN (6) Therefore, the differential voltage output VIN of the weight sensor 1
Is output from the drift correction circuit 5, and the drift-corrected signal is output to the A / D converter 6. The A / D converter 6 converts the drift-corrected signal into a digital signal, and the DSP 7 performs digital filtering. The processing result is sent to the CPU 8 as true weight data.

As described above, the drift correction circuit 5 holds the drift signal output from the amplifier circuit 2 when the input terminals of the amplifier circuit 2 are short-circuited in the drift correction mode, and the short circuit is released in the measurement mode. Then, the drift signal is subtracted from the amplified analog weight signal and the drift corrected signal is output to the A / D converter 6.

In FIG. 2, R1 = R2 = R3 =
When R4 = R, the above equation (3) becomes V1 = １ ／ · VE, and the above equation (6) becomes VO = −G · VIN.

Since the time required for drift correction is determined by the values of the resistor R and the capacitor C in the drift correction circuit 5, the drift correction time is shortened when the values of R and C are reduced. In other words, in high-speed weighing equipment,
By reducing the values of R and C to some extent, drift correction corresponding to this can be performed.

As described above, in this apparatus, the drift-corrected signal is output to the A / D converter only by switching the mode by the mode switching means 9 of the CPU.
Thus, the drift correction of the amplifier circuit 2 can be performed without performing the arithmetic processing, so that the processing load on the microprocessor and the load on the memory capacity can be reduced.

Next, the description will proceed to the second embodiment. This circuit can be applied to a general-purpose electronic balance, a weight sorter, a circuit that does not use a DSP even in combination weighing, and the like. FIG.
5 to 5 show circuit diagrams of the weighing device according to the second embodiment. This weighing device is a general-purpose electronic balance here, weighs an object to be weighed, and filters out noise (high-frequency) components included in the input signal by an analog filter (secondary active low-pass filter) 4 in FIG. It attenuates and generates a digital weight signal for indicating the weight. The self-diagnosis circuit 16 diagnoses the signal processing circuit.

This weighing device comprises a weight sensor (weight detecting means) 1, a first switch means S1, a second switch means S2, a third switch means S3, and a fourth switch means S.
4, a differential amplifier circuit 2a, 2b, an analog filter 4, a drift correction circuit (sample and hold circuit) 5, a delta-sigma A / D converter 6, a CPU 8 including a mode switching means 9, and a self-diagnosis circuit 16. Have. In the drift correction mode, the differential amplifier circuits 2a and 2b are short-circuited by the control signal c1 from the mode switching means 9 and the drift signal is output to the analog filter 4.

The analog filter 4 includes a buffer amplifier OP composed of a negative feedback amplifier, an RC integrator having two resistors R5 and R6 and a capacitor Cb connected in series to its non-inverting input terminal, Two resistors R
5, a capacitor Cd inserted between the midpoint of R6 and the negative feedback terminal of the buffer amplifier OP.

The third filter provided in the analog filter 4
The switch means S3 switches SW4a and SW4b for switching between the first connection for performing the filter function of the analog filter 4 and the second connection for performing the buffer function.
It has. Further, the mode switching means 9 outputs the control signal c
3, the third switch means S3 in the weighing mode
Is switched to the first connection, and the third switch means S3 is switched to the second connection in the drift correction mode. In other words, in the weighing mode, the analog filter 4 is switched to the low-pass filter function to attenuate the high-frequency noise component included in the input signal. The signal passes through the filter 4 and is input to the drift correction circuit 5.

A grounded capacitor Ca is interposed between the weight sensor 1 and the amplifier circuit 2a. This is because if there is a high-frequency component in the output of the weight sensor 1, the time required for the analog filter 4 to stabilize at the time of filter switching becomes very long. Therefore, the high-frequency component is attenuated by the capacitor Ca to improve the weighing accuracy. That's why.

The fourth switch means S4 provided in the self-diagnosis circuit 16 is connected to a first connection for inputting a reference (bias) voltage to the amplifier circuit 2 by a control signal c4 from the mode switching means 9. SW5a and SW5b for switching between the first connection and the second connection which does not input this. The self-diagnosis circuit 16 switches the switch SW by the control signal c1.
1 is switched to the second connection so that the input of the analog weight signal to the amplifier circuit 2 is cut off, and a reference voltage corresponding to the weight of the reference weight is input to the amplifier circuit 2 and the A / D converter 6
A signal corresponding to the span amount of the weight sensor 1 is output from the controller to diagnose the signal processing circuit. The other configuration is almost the same as that of the first embodiment, and a detailed description will be omitted.

FIG. 6 shows a time chart of the weighing device. (A) shows the operation timing (first timing) of the sampling / conversion (hold) of the A / D converter 6;
(B) shows the operation timing (second timing) of the charge and hold of the capacitor C in the drift correction circuit 5, and (c) shows the alternating operation timing of the buffer filter of the analog filter 4. (A) conversion (hold) timing, (b) charging timing,
Although the respective buffer timings shown in (c) are substantially simultaneous, strictly, with a slight time difference, the conversion and the conversion shown in (a) are performed.
The buffer of (c) and the charging of (b) are started in this order.

The A / D converter 6 converts the drift corrected signal output from the drift correction circuit 5 at a first timing set according to the measurement timing into a digital signal. On the other hand, in the drift correction mode of FIG. 3, in this example, the mode switching means 9 includes the A / D converter 6
When the conversion (hold) timing rises, the first
The mode is switched from the weighing mode to the drift correction mode at a second timing substantially at the same time as the timing. At this time, as in the first embodiment, the mode switch 9 turns off the switch SW1 of the first switch S1 and the switch SW2.
Is turned on, and the switch SW3 of the second switch means S2 of the drift correction circuit 5 is turned on to charge the capacitor C with the drift signal voltage. Further, the third switch means S3 of the analog filter 4 is switched to the second connection by the control signal c3 of the mode switching means 9, and the switch SW4 is turned off, so that the analog filter 4 exhibits a buffer function.

At this time, the A / D converter 6 captures and stores the drift-corrected signal voltage at the rise of the conversion (hold), and then A / D converts this voltage. Therefore, the stabilization time of the analog filter 4 can be increased, and the measurement error can be reduced, so that stable measurement can be performed.

In the weighing mode shown in FIG. 4, the mode switch 9 switches the switch SW1 of the first switch S1.
Is turned on, SW2 is turned off, and the second
The switch SW3 of the switch means S2 is turned off, and the switch SW4 of the analog filter 4 is turned off, thereby exhibiting a low-pass filter function. Thus, a signal in which the noise (high frequency) component included in the input signal is attenuated and the drift is corrected is output to the A / D converter 6.

During the above-mentioned mode time, the weighing mode occupies the majority and the drift correction mode is instantaneous (0.1 to 1 ms), so that the continuity of the analog weight signal is maintained and the weighing is stable.

In the above example, the mode switching means 9 switches between the first timing for setting the weighing mode and the second timing for setting the drift correction mode at a rate of one conversion time. As a result, the drift correction accuracy is improved and a rapid temperature change can be followed. Further, since the voltage holding time by the capacitor C can be shortened, there is an effect that the capacity of the capacitor C of the drift correction circuit 5 can be reduced. The drift correction mode may be set once for a plurality of A / D conversions instead of 1: 1 depending on the weighing conditions.

In this way, the present weighing device attenuates the noise (high frequency) component included in the input signal and, as in the first embodiment, outputs the drift corrected signal from the drift correction circuit (sample and hold circuit) 5 to A / A. The signal is output to the D converter 6 and is not processed by the CPU 8.
And drift correction of the analog filter 4 can be performed.

FIG. 7 shows the operation (d) of the self-diagnosis circuit 16.
3 shows a time chart to which "" is added. As shown in FIG.
In the self-diagnosis mode of FIG. 5, the input of the analog weight signal is cut off by the control signals c1 to c4 of the mode switching means 9, and the reference (bias) voltage BV is applied to the amplifier circuit 2, whereby the reference weight is applied to the balance. The state becomes the same as that of loading, and the signal processing circuit can be diagnosed as needed even during weighing. In this case, since the capacitor C is charged at the beginning of the A / D conversion, it is possible to gain time until the reference voltage signal for the self-diagnosis applied subsequently stabilizes, and to perform the self-diagnosis reliably. it can.

In the second embodiment, a digital filter is not provided. However, a DSP for performing digital filtering may be additionally provided after the A / D converter 6.

[0054]

As described above, according to the present invention, the drift corrected signal corrected by the drift correction circuit is A
Since the output is output to the / D converter, drift correction of the amplifier circuit can be performed without performing arithmetic processing in the CPU. As a result, the processing load on the microprocessor and the load on the memory capacity for drift correction can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a weighing device according to an embodiment of the present invention.

2A is a circuit diagram showing a drift correction mode, and FIG. 2B is a circuit diagram showing a weighing mode.

FIG. 3 is a circuit diagram illustrating a weighing device according to a second embodiment.

FIG. 4 is a circuit diagram illustrating a weighing device according to a second embodiment.

FIG. 5 is a circuit diagram illustrating a weighing device according to a second embodiment.

FIG. 6 is a timing chart showing the operation of the weighing device.

FIG. 7 is a timing chart illustrating an operation of the weighing device.

FIG. 8A is a circuit diagram showing a drift correction mode of the conventional weighing device, and FIG. 8B is a circuit diagram showing the weighing mode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Weight detection means, 2 ... Amplifier circuit, 3 ... Anti-alias filter, 4 ... Analog filter, 5 ... Drift correction circuit, 6 ... A / D converter, 7 ... DSP, 8 ... CPU, 9
... mode switching means, 12 ... holding circuit, 14 ... distribution circuit,
16: Self-diagnosis circuit, OP: Operational amplifier, S1: First
Switch means, S2... Second switch means.

Claims (6)

[Claims] 1. A weighing device for weighing an object to be weighed and generating a digital weight signal for displaying the weight of the object, detecting a weight of the object to be weighed and outputting an analog weight signal. Detecting means, an amplifier circuit for amplifying the analog weight signal, and a signal corresponding to a drift signal output from the amplifier circuit when an input terminal of the amplifier circuit is short-circuited;
A drift correction circuit that outputs a drift corrected signal obtained by subtracting the drift signal from the output signal of the amplifier circuit when the short circuit is released; and A that converts the drift corrected signal into a digital signal.
/ D converter and a weighing device. 2. The switch according to claim 1, wherein the first switch means switches between a first connection for inputting the analog weight signal to the amplifier circuit and a second connection for short-circuiting between input terminals of the amplifier circuit. A first connection for inputting the amplified analog weight signal to the drift correction circuit and setting a weighing mode, and a second connection for inputting the drift signal output from the amplification circuit to the drift correction circuit and setting the drift correction mode Second switch means for switching between the two connections is provided, and the first and second switch means are switched to the first connection at a first timing to set the weighing mode, A weighing device comprising mode switching means for setting the drift correction mode by switching the first and second switch means to the second connection at a second timing. apparatus. 3. The drift correction circuit according to claim 1, wherein the drift correction circuit is connected to a positive input terminal of the operational amplifier, and the drift correction circuit is connected to a positive input terminal of the operation amplifier. A holding circuit that generates a drift-corresponding voltage corresponding to the signal and holds the drift-corresponding voltage in the measurement mode; and a negative input terminal maintained in the drift-corresponding voltage in the measurement mode. A weighing device comprising: a distribution circuit that removes the drift signal from the output signal of the operational amplifier by dividing and inputting an output signal of the circuit and an output signal of the operational amplifier at a predetermined ratio. 4. The analog-to-digital converter according to claim 1, wherein input of said analog weight signal to said amplifier circuit is cut off, a reference voltage is input to said amplifier circuit,
A weighing device having a self-diagnosis circuit for outputting a signal corresponding to the span amount of the weight detecting means from the converter. 5. The analog filter according to claim 2, wherein the analog filter reduces a high-frequency component of the amplified analog weight signal, and a first filter function of the analog filter.
A third switch for switching between a connection and a second connection for exhibiting a buffer function, wherein the mode switching means further switches the third switch to the first connection in the weighing mode, and performs the correction. In the mode, the third switch means is further switched to the second switch means.
A weighing device that switches to a connection. 6. The weighing device according to claim 1, wherein the A / D converter is a delta-sigma type.