JPH11108741A - Temperature zero point correcting device for amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the necessity of measuring the temperature characteristics of a temperature sensor and an amplifier by removing a zero point changing amount from the measuring signal of the amplifier by a correcting means. SOLUTION: When the driving power supply voltage of a bridge circuit 5 is in a high voltage Vs state and a count value indicating a digital signal for measuring is stable, this count value is stored in a storage section 24. Then, by turning OFF switches SW1 and SW2, the driving voltage is changed to a lower voltage Vs /2, a count value indicating a digital signal for correction is stored in the storage section 24, and then the switches SW1 and SW2 are turned ON. Then, by using both count values, a zero point changing amount is calculated based on a specified expression, and the previously stored zero point changing amount is stored so as to be changed to the zero point changing amount obtained by the current calculation. Since the zero point changing amount is calculated, a newest zero point changing amount stored in the storage section 24 is subtracted from the count value indicating the digital signal for measuring, the zero point changing amount based on the temperature change of an amplifier is removed, and a measuring digital signal which is corrected for a zero point changing amount by removing the zero point changing amount is displayed on a display section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for correcting a zero point fluctuation based on a temperature change of an amplifier provided in an electronic device.

[0002]

2. Description of the Related Art A conventional weighing apparatus to which the above-described apparatus is applied includes a load cell having a strain body and a bridge circuit formed of a strain gauge provided on the strain body, and driving the bridge circuit. A power supply unit, an amplifier that amplifies an output signal of the bridge circuit and outputs an analog weighing signal, and an analog-to-digital conversion circuit (A) that converts the analog weighing signal output from the amplifier into a digital weighing signal and outputs the digital weighing signal
/ D conversion circuit).

A conventional temperature zero correction device for correcting the temperature of an amplifier provided in the weighing device includes a temperature sensor for detecting the temperature of the amplifier and a correction device. The correction device calculates a zero-point change amount of the amplifier based on the temperature change using the temperature detected by the temperature sensor,
The corrected digital weighing signal can be output by subtracting the calculated zero change amount from the digital weighing signal.

[0004]

However, the above-mentioned conventional temperature zero correction device requires a temperature sensor, and has a problem that the structure becomes complicated and the cost increases accordingly.
Then, it is necessary to measure and store in advance the relationship between each temperature of the amplifier and the amount of change in the zero point at each temperature (temperature characteristics of the amplifier). It is extremely difficult to measure accurately and there is a problem that it takes time and effort.

It is an object of the present invention to provide an amplifier temperature zero correction device which does not require a temperature sensor and does not need to measure the temperature characteristics of the amplifier in advance.

[0006]

According to a first aspect of the present invention, there is provided a temperature zero correction apparatus for an amplifier, a bridge circuit including a resistor, a power supply for driving the bridge circuit, and an output signal of the bridge circuit. An amplifier that amplifies the signal and outputs a signal, wherein the power supply voltage for driving the bridge circuit is in a high voltage state and the bridge circuit is driven when the measurement signal output by the amplifier is substantially stable. Voltage changing means capable of changing a power supply voltage to be changed from a high voltage to a low voltage, a measuring signal output by the amplifier when the power supply voltage is high, and the amplifier when the power supply voltage is low. A correction signal to be output, and a zero-point change amount calculating means for calculating a zero-point change amount of the measurement signal based on a temperature change of the amplifier using a ratio of both the high voltage and the low voltage; It is characterized in that it comprises serial and correcting means for removing the metering signal the zero point variation from the.

A temperature zero correction apparatus for an amplifier according to a second aspect of the present invention is a bridge circuit comprising a resistor, a power supply unit for driving the bridge circuit, and an analog signal obtained by amplifying an output signal of the bridge circuit. And an analog-to-digital conversion circuit that converts the analog signal to a digital signal and outputs the digital signal, wherein the power supply voltage for driving the bridge circuit is high and the analog-to-digital conversion is performed. Voltage changing means for changing a power supply voltage for driving the bridge circuit from a high voltage to a low voltage when the digital signal for measurement output by the circuit is substantially stable; and The digital signal for measurement output by the digital conversion circuit, the analog signal when the power supply voltage is low.
Zero-point change amount calculating means for calculating a zero-point change amount of the measurement digital signal based on a temperature change of the amplifier using a correction digital signal output by a digital conversion circuit and a ratio of both the high voltage and the low voltage. And correction means for removing the zero-point change amount from the digital signal for measurement.

According to a third aspect of the present invention, there is provided an amplifier temperature zero correction apparatus including a load cell including a flexure element and a bridge circuit formed of a strain gauge provided in the flexure element, and a power supply for driving the bridge circuit. Unit, an amplifier that amplifies the output signal of the bridge circuit and outputs an analog signal, and an analog-digital conversion circuit that converts the analog signal into a digital signal and outputs the digital signal,
The power supply voltage for driving the bridge circuit can be changed from a high voltage to a low voltage when the digital signal for measurement output from the analog-to-digital conversion circuit is substantially stable while the power supply voltage for driving the bridge circuit is high. Voltage changing means, a digital signal for measurement output by the analog / digital conversion circuit when the power supply voltage is high, and a correction output by the analog / digital conversion circuit when the power supply voltage is low. Zero point change amount calculating means for calculating a zero point change amount of the weighing digital signal based on a temperature change of the amplifier using a ratio of both the high voltage and the low voltage, and the weighing digital signal. And a correcting means for removing the zero-point change amount from the above.

A temperature zero correction device for an amplifier according to the present invention is an electronic device that amplifies an output signal of a bridge circuit driven by a power supply voltage of a power supply unit by an amplifier and outputs a signal. By calculating the amount, the calculated zero-point change amount can be removed from the output signal of the amplifier. That is, when the metering signal output by the amplifier is substantially stable when the power supply voltage is at a high voltage, the voltage changing unit changes the power supply voltage from the high voltage to the low voltage,
The amplifier uses the weighing signal output by the amplifier when the power supply voltage is high, the correction signal output by the amplifier when the power supply voltage is low, and the ratio of both high voltage and low voltage. The zero-point change amount of the measurement signal is calculated by the zero-point change amount calculating means based on the temperature change. Then, the correction means removes the zero point change amount from the weighing signal of the amplifier. Thereby, a zero point error based on a temperature change of the amplifier can be removed from the weighing signal.

A temperature zero correction apparatus for an amplifier according to a second aspect of the present invention is an electronic apparatus provided with an analog / digital conversion circuit for converting an analog output signal of the amplifier into a digital output signal and outputting the digital output signal. This is a device for performing a correction for removing a zero-point change generated based on a change from a digital signal for measurement. The zero-point change amount calculating means calculates a zero-point change amount of the digital signal for measurement based on a temperature change of the amplifier using the digital signal for measurement, the digital signal for correction, and the ratio of both the high voltage and the low voltage. The correction means can remove the zero point change amount from the digital signal for measurement.

A temperature zero correction apparatus for an amplifier according to a third aspect of the present invention is an electronic apparatus provided with a load cell and an analog / digital conversion circuit for converting an analog output signal of the amplifier into a digital output signal and outputting the digital output signal. In a certain weighing device, the correction device removes a zero point change generated based on a temperature change of the amplifier from a digital signal for weighing. The zero point change amount calculating means and the correcting means operate in the same manner as in the second invention.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment in which a temperature zero correction device for an amplifier according to the present invention (hereinafter referred to as "temperature zero correction device") is applied to a weighing device will be described with reference to FIGS. . 1 is a load cell, 2 is an amplifier, 3 is an analog / digital conversion circuit (A / D conversion circuit), and 4 is a power supply unit. The load cell 1 includes a conventionally known flexure element (not shown) and a bridge circuit 5 shown in FIG. The bridge circuit 5 includes, for example, four strain gauges G (G1
~ G4). Output signals generated at both output terminals 6 and 7 of the bridge circuit 5 are amplified by the amplifier 2, and the amplified analog signal for measurement or the analog signal for correction is supplied to the A / D conversion circuit via the switch SW3. 3
Is converted into a digital signal for measurement or a digital signal for correction by the A / D conversion circuit 3 and input to a central processing unit (CPU) 8. The CPU 8 has a storage unit 2
4 are connected.

The amplifier 2 is a generally known operational amplifier. As shown in FIG. 1, an inverting input terminal and a non-inverting input terminal are connected to output terminals 6 and 7 of a bridge circuit 5, respectively. A feedback resistor 9 is connected between the output terminal of the amplifier 2 and the inverting input terminal, and the non-inverting input terminal is grounded via a resistor 10.

The A / D conversion circuit 3 is a conventionally known double integration type A / D conversion circuit, and includes an integration circuit 11 and a comparator 12. The integrating circuit 11 includes an operational amplifier 15, an integrating resistor R, and an integrating capacitor C. The operational amplifier 15 has an inverting input terminal of an integrating resistor R.
, Input changeover switches SW3, SW4, SW5 are connected in parallel, and the non-inverting input terminal is grounded. The output terminal of the operational amplifier 15 is connected to the inverting input terminal via the integration capacitor C. Comparator 12
Has an inverting input terminal connected to the output terminal of the operational amplifier 15 and a non-inverting input terminal grounded. The output terminal of the comparator 12 is connected to the CPU.

The power supply unit 4 has one terminal 16 connected to the switch S
Connected to the input terminal 17 of the bridge circuit 5 via W1,
The other terminal 19 is connected to the input terminal 18 of the bridge circuit 5 via the switch SW2. The terminals 16 and 19 of the power supply unit 4 are connected to resistors R1, RA1, RA2, RA2.
3, RA4, and R2. Further, a connection line 20 connecting the resistors R1 and RA1 is connected to the input terminal 17 of the bridge circuit 5, and a connection line 21 connecting the resistors RA4 and R2 is connected to the input terminal 1 of the bridge circuit 5.
8 is connected. The connection line 22 connecting the resistors RA2 and RA3 is connected to the switch SW4, and the connection line 23 connecting the resistors RA3 and RA4 is connected to the switch SW5. The connection line 22 is grounded.

The resistance values of the resistors R1 and R2 are equal and the same. The total resistance of the resistors R1 and R2 is determined to be equal to the total resistance of the total resistance of the four resistors RA1 to RA4 and the composite resistance of the bridge circuit 5 connected in parallel thereto. is there. Therefore,
When the switches SW1 and SW2 are ON, the high voltage V _S is applied to the input terminal of the bridge circuit 5, and in this state, A
The count value K _out1 representing the digital signal (weighing digital signal) of the object output from the / D conversion circuit 3 can be obtained. Then, the switches SW1 and SW2 are turned off.
In the state of F, the low voltage V _{S is} applied to the input terminal of the bridge circuit 5.
/ 2 is applied, and in this state, a count value K _out2 representing the correction digital signal output from the A / D conversion circuit 3 can be obtained. However, the four resistors RA1 to RA4 of this embodiment have the same resistance value, but need not be limited thereto.

Next, a description will be given of the voltage changing means, the zero point change amount calculating means, and the correcting means which constitute the temperature zero point correcting apparatus which is a feature of the present invention. These voltage changing means, zero point change amount calculating means, and correcting means are constituted by the CPU 8 and a program shown in the flowchart of FIG. The program shown in the flowchart of FIG. 3 is stored in the storage unit 24 connected to the CPU 8. The voltage changing means is
The switches SW1 and SW2 are turned on and the power supply voltage for driving the bridge circuit 5 is set to the high voltage V _S every time, for example, two minutes elapse of the preset zero point change amount calculation time interval.
, The count value K _out1 representing the digital signal for measurement
It is determined whether or not is stable, and when it is determined that it is stable, the count value K _out1 is read and stored in the storage unit 2.
4 to store, then load on the load cell 1 is in the OFF switch SW1,2 in the same state, to change the power supply voltage for driving the bridge circuit 5 to the low voltage V _S / 2, the low voltage V _S This is a means for reading the count value K _out2 representing the digital signal for correction in the state of / 2, storing it in the storage unit 24, and then turning on the switches SW1 and SW2.

The zero-point change amount calculating means is used when the power supply voltage is at the high voltage V _S , when the digital signal for measurement output from the A / D conversion circuit 3 and when the power supply voltage is at the low voltage V _S / 2. , The correction digital signal output from the A / D conversion circuit 3, and the ratio x between both the high voltage V _S and the low voltage V _S / 2.
(= 2) is a means for calculating a zero-point change amount of the digital signal for measurement based on a temperature change of the amplifier 2. Note that the zero-point change amount calculating means determines whether the switches SW1, SW2 are in the state where the weight of the object to be weighed is applied to the load cell 1 or the state where the weight of the object to be weighed is not applied.
Is ON, the zero point change amount can be calculated. However, when a constant load is applied to the load cell 1, the zero point change amount can be accurately determined by using the stable weighing digital signal and the stable correction digital signal output from the A / D conversion circuit 3. Can be calculated. The correction unit is a unit that removes the zero-point change amount from the weighing digital signal and outputs a zero-point change amount-corrected weighing digital signal. The currently calculated zero point change amount is stored in the storage unit 24 until the next time the zero point change amount is calculated.
To memorize it.

Next, the theory that the zero change amount calculating means calculates the zero change amount of the digital signal for measurement based on the temperature change of the amplifier 2 and the correcting means can remove the zero change amount from the digital signal for measurement. Will be described. FIG. 2 shows A / D
FIG. 3 is a diagram illustrating an operation principle of the conversion circuit 3. As shown in this figure, first, in the reset period, the CPU 8 turns on the switch SW4 shown in FIG. 1 (SW3, 5 are OFF),
The charge of the integration capacitor C is discharged. At this time, the output voltage of the integrating circuit 11 is 0.

During the input voltage integration period, the switch SW3 is turned on (SW4 and SW5 are turned off), and the load cell 1 is weighted by the object to be weighed. _A + _Vofs ) or the analog signal for correction ( _VA / 2 + _Vofs ) is integrated for a certain period of time. This integration time is measured by counting the number of clock pulses by the counter of the CPU 8, and when the count reaches a predetermined count N, the operation shifts to the next reference voltage integration period. However, metering analog signal (V _A + V _ofs) is a state where the high voltage V _S is applied to the bridge circuit 5 (the switch SW
1 and 2 are ON), and the analog signal for correction (V _A / 2 + V _ofs ) is a bridge circuit 5.
To which a low voltage V _S / 2 is applied (switches SW1,
2 is OFF).

V _ofs is a zero-point change amount of the measuring analog signal of the amplifier 2 based on a temperature change of the amplifier 2, that is, a total voltage of an offset voltage of the amplifier 2 and a temperature drift of the offset voltage. This zero point change amount V
_ofs, even when the power supply voltage is a high voltage V _S, the low voltage V
_The same applies when _S / 2. Further, assuming that the number of clock pulses in the input voltage integration period is N, the period of the clock pulse is T, the capacitance of the integration capacitor C is C, and the resistance value of the integration resistor R is R, The output voltages V _out1 and V _out2 of the integrating circuit 11 are as follows: V _out1 = − (V _A + V _ofs ) · N · T / (C · R) (1) V _out2 = − ((V _A / 2) + V _ofs ) · N · T / (C · R) (2) However, although the low voltage is V _S / 2, V _S / x
Then, V _out2 = − ((V _A / x) + V _ofs ) · N · T / (C · R) (3) x is the ratio of high voltage to low voltage, and in this embodiment x = 2.

In the reference voltage integration period, the switch SW5 is turned on (SW3 and SW4 are off), and the reference voltage -V _ref or -V of the polarity opposite to the input voltage such as the analog signal for measurement (V _A + V _ofs ). V _ref / 2 is integrated until the output voltage V _out1 or V _out2 of the integration circuit 11 becomes zero. here,
Number of clock pulses K _out1 and K during reference voltage integration period
_out2 is: K _out1 = (V _A + V _ofs ) · N / V _ref (4) K _out2 = ((V _A / 2) + V _ofs ) · N / (V _ref / 2) (5), and can be converted metering analog signal (V _a + V _ofs), or correcting the analog signal _{(V a / 2 + V ofs} ) metering digital signal K _out1, or to the correction digital signal K _out2. When the ratio between the high voltage and the low voltage is x, _Kout2 = (( _VA / x) + _Vofs ) _.N / ( _Vref / x) (6)

Thus, the A / D conversion is completed and the next A / D conversion can be started. For this purpose, the counter is reset and counting is started again, but the metering digital signal K _out1 or the correction digital signal K _out2 obtained this time until the A / D conversion is completed is stored in the storage unit. 24
To be kept.

Next, when the zero point change amount V _ofs (analog amount) is obtained from the expressions (4) and (5), V _ofs = [(K _out2 −K _out1 ) / (x−1)] · (V _ref / N)... (7) When this V _ofs is converted to the zero-point change amount K _ofs of the digital quantity, K _ofs = V _{ofs .N} / V _ref . Where (x−1) and (V _ref / x) are constants,
x is 2, N is 5000, V _ref is V _S / 4, the value of each is stored in the storage unit 24. Therefore, the zero point change amount K _ofs (digital value) can be calculated by substituting the digital signal for measurement K _out1 and the digital signal for correction K _out2 into the equation (7) and calculating the equation (8). . The zero point change amount calculating means calculates the zero point change amount K _ofs by performing the calculations of the expressions (7) and (8).

The correction means subtracts the zero point change amount K _ofs from the weighing digital signal K _out1 to calculate and output a corrected weighing digital signal in which the zero point change based on the temperature change of the amplifier 2 is removed. Therefore, the weight of the object can be accurately output.

Next, the above theory will be described with specific numerical values. The output of the load cell 1 per 1 volt of the power supply voltage is 2 mV / V, the gain of the amplifier 2 is 100 times, the power supply voltage is 10 V at the high voltage V _S , the power supply voltage is 5 V at the low voltage V _S / 2, and the unknown zero. The change amount V _ofs is 1 mV, and the reference voltage V _ref is _10/4 = 2.5 V. The analog signal for measurement (V _A + V _ofs ) output from the amplifier 2 when the high voltage V _A = 10 V is applied to the bridge circuit 5 is (V _A + V _ofs ) = ((2 mV / V) × 10 V + 1 mV) × 100 × = 2.1 V (9), and the analog signal for measurement output by the amplifier 2 in the state where the low voltage V _A = 5 V is applied to the bridge circuit 5 ((V
_(A / 2) + _Vofs ) is as follows: ( _VA / 2) + _Vofs = ((2 mV / V) × 10 V / 2 + 1 mV) × 100 times = 1.1 V (10)

However, the zero point variation V _ofs of the amplifier 2 is
Independent of power supply voltage. By substituting the values of the equations (9) and (10) into the equations (4) and (5), the digital signal for measurement K _out1 and the digital signal for correction K _{out2 become} K _out1 = (V _A + V _ofs ) · N / V _ref = 2.1 · 5000 / 2.5 = 4200 (count) (11) K _out2 = ((V _A / 2) + V _ofs ) · N / (V _ref / 2) = 1. 1.5000 / 1.25 = 4400 (count) (12) These K _out1 and K _out2 are input to the CPU 8.
When the CPU 8 substitutes the values of the equations (11) and (12) into the equation (7), V _ofs = [(K _out2 −K _out1 ) / (x−1)] · (V _ref / N) = [( (4400-4200) / (2-1)] · (2.5 / 5000) = 0.1 (V) (13), and the voltage 0 that is 100 times the gain of 1 mV of the zero-point change amount V _ofs .1 (V). Then, when this V _ofs is converted into the zero-point change amount K _ofs of the digital quantity by the equation (8), K _ofs = V _ofs · N / V _ref = 0.1 · 5000 / 2.5 = 200 (count) .. (14), and the zero point change amount K _ofs = 200 (count) is obtained. Therefore, the correction means of the CPU 8 calculates the zero point change amount K from 4200 (count) of the digital signal for measurement K _out1.
By subtracting 200 (count) of _ofs , it is possible to calculate and output 4000 (count) of the corrected weighing digital signal from which the zero point change based on the temperature change of the amplifier 2 has been removed.

Next, the operation procedure of the temperature zero correction apparatus for the amplifier 2 configured as described above will be described with reference to the flowchart shown in FIG. First, the switches SW1 and SW2 are
N, whether or not a predetermined time interval of zero point change amount calculation, such as 2 minutes, has elapsed since the power of the weighing device was turned on or from the last time the zero point change amount was calculated. A determination is made (S100). And after 2 minutes, Y
When it is determined as ES, the switches SW1 and SW2 are ON and the power supply voltage for driving the bridge circuit 5 is the high voltage V _S
, The count value K _out1 representing the digital signal for measurement
It is determined whether (the count value counted by the CPU 8) is stable (S102). And the count value K
_{When out1} is stable and the determination is YES, the count value _Kout1 at this time is read and stored in the storage unit 24 (S104). However, if the count value K _out1 is not stable and is determined to be NO, the process waits until it is determined to be stable.
Next, the switch SW1,2 to OFF in the state in which the same load cell 1 is applied, to change the power supply voltage for driving the bridge circuit 5 to the low voltage V _S / 2, the low voltage V _S Count value K _out2 representing the correction digital signal in the state of / 2 (count value counted by CPU 8)
Is read and stored in the storage unit 24, and then the switches SW1 and SW2 are changed to ON (S106). Next, the count value _Kout1 and the count value _Kout2 are substituted into the equation (7), and the zero point change amount K _ofs is calculated by the equation (8). Zero change K
_Ofs is stored so as to be changed to the zero-point change amount K _ofs calculated this time (S108). This gives the zero point variation K
_{Since ofs} has been calculated, the latest zero-point change amount K _ofs stored in the storage unit 24 is subtracted from the count value K _out1 representing the digital signal for measurement, and the zero-point change amount based on the temperature change of the amplifier 2 is removed. Then, the display unit (not shown) displays the weighing digital signal with the zero-point change corrected and the zero-point change corrected (S114). However,
When the count values K _out1 and K _out2 are in a state where the weight of the weighing object is loaded on the load cell 1, the weight of the weighing object from which the zero point variation is removed is displayed on the display unit. When the weight of the weighed object is not loaded on the load cell 1, 0 is displayed on the display unit after removing the zero point change amount.

In step 100, when the time interval for calculating the zero-point change amount has not elapsed for 2 minutes and the determination is NO, the count value K representing the digital signal for measurement is obtained.
_out1 is read (S110), and the zero change amount K _ofs stored in the storage unit 24 is subtracted from the read count value K _out1 to remove the zero change amount based on the temperature change of the amplifier 2 (S112). The display unit (not shown) displays the digital signal for weighing with the zero-point change corrected and the zero-point change corrected (S114).

As described above, according to the temperature zero correction device of the amplifier according to the above embodiment, unlike the conventional temperature zero correction device, a temperature sensor is not required, so that the structure is simple and the cost is reduced accordingly. Can be reduced. Then, it is not necessary to measure the temperature characteristic of the amplifier 2 representing the relationship between each temperature of the amplifier 2 and the amount of change in the zero point at each temperature in advance and store it in the storage unit 24.

In the above embodiment, the time interval for calculating the zero-point change amount is set to 2 minutes. However, the zero-point change amount may be calculated at other time intervals, or the weight of the object may be weighed. The zero point change amount may be calculated each time. In the above-described embodiment, the weighing analog signal amplified and output by the amplifier 2 shown in FIG. 1 is processed by a conventionally-known secondary low-pass filter 25 shown in FIG. Is stabilized, when the switches SW1 and SW2 are turned off and the correction analog signal passes through the low-pass filter 25, a time delay occurs, and the time required to calculate the zero-point change amount K _{ofs is} thereby reduced. It will take a long time. Then, in order to eliminate this time delay, the switches SW1, 2
When the analog signal for correction is read by turning OFF, the FET (switch) 26 shown in FIG. 4 is turned ON, and the signal is input to the A / D conversion circuit 3 without using the filter. When the switches SW1 and SW2 are turned on to stabilize the analog signal for measurement, the FET 26 may be turned off and a filter may be activated to input the signal to the A / D conversion circuit 3. Incidentally, the low-pass filter 25 is provided between the output terminal and the switch SW3 of the amplifier 2 shown in FIG. 1, the resistor r ₁ to be connected to FET26 and series, a non-inverting input terminal and the amplifier 2 the output of the operational amplifier 27 It is provided between terminals.

In the above embodiment, the A / D conversion circuit 3 is a conventionally known double integration type A / D conversion circuit. However, an A / D conversion circuit of another type may be used. Good. Further, in the above embodiment, the ratio x between the high voltage and the low voltage is set to 2, but other than 2, 1.5, 2.5, or 3,
.. May be adjusted. For example, when the ratio x = 3, when the switches SW1 and SW2 are ON,
When the high voltage V _S is applied to the input terminal of the bridge circuit 5 and the switches SW1 and SW2 are OFF, the low voltage V _S / 3 is applied to the input terminal of the bridge circuit 5 such that
The total resistance value of the resistors R1 and R2, and the four resistors RA1 to RA1
It is necessary to determine the total resistance value of RA4 and the combined resistance value of bridge circuit 5. In the above-described embodiment, an example in which the temperature zero correction device for an amplifier according to the present invention is applied to a weighing device has been described. .

[0033]

According to the temperature zero correction device for an amplifier according to the present invention, unlike the conventional temperature zero correction device, a temperature sensor is not required, so that the structure is correspondingly simple.
Costs can be reduced. Since there is no need to measure and store in advance the relationship between each temperature of the amplifier and the amount of change in the zero point at each temperature (temperature characteristics of the amplifier),
As in the prior art, it is not necessary to perform a difficult measurement operation of placing the amplifier in a temperature chamber and accurately measuring the temperature characteristics of the amplifier, and therefore, the labor and time required for the measurement can be reduced. Can be manufactured simply and in a relatively short time than before.

[Brief description of the drawings]

FIG. 1 is an electric circuit diagram of an embodiment in which a temperature zero correction device for an amplifier according to the present invention is applied to a weighing device.

FIG. 2 shows an A / D provided in the weighing device of the embodiment.
FIG. 5 is an operation waveform diagram of the conversion circuit.

FIG. 3 is a flowchart showing a correction procedure of the temperature zero correction apparatus according to the embodiment.

FIG. 4 is a circuit diagram of a low-pass filter used in the embodiment.

[Explanation of symbols]

 Reference Signs List 1 load cell 2 amplifier 3 A / D conversion circuit 4 power supply unit 5 bridge circuit 8 CPU 24 storage unit

Claims (3)

[Claims] A bridge circuit comprising a resistor; a power supply unit for driving the bridge circuit; an amplifier for amplifying an output signal of the bridge circuit to output a signal;
In the electronic device comprising: the power supply voltage for driving the bridge circuit is changed from a high voltage to a low voltage when the measurement signal output from the amplifier is substantially stabilized in a state where the power supply voltage for driving the bridge circuit is high voltage. Possible voltage changing means, a measuring signal output by the amplifier when the power supply voltage is high, a correction signal output by the amplifier when the power supply voltage is low, and the high voltage. Zero-point change amount calculating means for calculating a zero-point change amount of the signal for measurement based on a temperature change of the amplifier using a ratio of both low voltages; and a correcting means for removing the zero-point change amount from the signal for measurement. And a temperature zero correction device for the amplifier. 2. A bridge circuit comprising a resistor, a power supply unit for driving the bridge circuit, an amplifier for amplifying an output signal of the bridge circuit to output an analog signal, and a digital signal for converting the analog signal to a digital signal. And an analog-to-digital conversion circuit that converts and outputs the digital signal for measurement, wherein the digital signal for measurement output by the analog-to-digital conversion circuit when the power supply voltage for driving the bridge circuit is high is substantially stable. A voltage changing means for changing a power supply voltage for driving the bridge circuit from a high voltage to a low voltage, and a digital signal for measurement output by the analog / digital conversion circuit when the power supply voltage is a high voltage; A correction digital signal output by the analog / digital conversion circuit when the power supply voltage is low; Zero-point change amount calculating means for calculating a zero-point change amount of the digital signal for measurement based on a temperature change of the amplifier using a ratio of both voltages, and correcting means for removing the zero-point change amount from the digital signal for measurement And a temperature zero correction device for an amplifier. 3. A load cell comprising: a flexure element; and a bridge circuit comprising a strain gauge provided on the flexure element,
An electronic device comprising: a power supply unit that drives the bridge circuit; an amplifier that amplifies an output signal of the bridge circuit and outputs an analog signal; and an analog-to-digital conversion circuit that converts the analog signal into a digital signal and outputs the digital signal. In a device, the power supply voltage for driving the bridge circuit is changed from a high voltage to a low voltage when the digital signal for measurement output from the analog / digital conversion circuit is substantially stable in a state where the power supply voltage for driving the bridge circuit is high. A voltage changing means that can be changed to a digital signal for measurement output by the analog / digital conversion circuit when the power supply voltage is a high voltage, and the analog / digital conversion circuit when the power supply voltage is a low voltage. The correction digital signal to be output and the ratio between the high voltage and the low voltage are used to determine the temperature change of the amplifier. Temperature zero correction of an amplifier, comprising: a zero change amount calculating means for calculating a zero change amount of the digital signal for measurement; and a correcting means for removing the zero change amount from the digital signal for measurement. apparatus.