JPH0219883B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gain drift correction circuit suitable for use in electronic scales and the like.

Generally, electronic scales use elements such as load cells that convert weight into electrical signals, and electronic circuits such as amplifiers that amplify the signals obtained by the load cells.The gain of electronic circuits varies depending on temperature conditions. Electronic scales that require high accuracy due to fluctuations must be corrected by some method. In this case, if the drift characteristic is linear, it can be easily corrected using a thermistor, but in the case of electronic scales installed in the middle of automatic filling lines, etc., filter circuits and analog-to-digital conversion circuits are required. Since a large number of circuits are used, the gain drifts generated in each circuit may influence each other, resulting in complex characteristics such as a quadratic curve or a cubic curve. Correction of such gain drift can be done using software using a microcomputer, but in this case, a certain amount of processing time is required. It is not suitable for electronic scales where instantaneous measurement is required, and there are other problems such as the need for specialized software for each electronic scale.

The present invention has been made in view of the above points, and includes a temperature detection element provided near the circuit that causes gain drift, and a detection signal obtained by this detection element determined in advance. The gain of the amplifier is adjusted by an analog switch selected by the correction amount program circuit,
The resistance value of the analog switch circuit is set so that the gain fluctuation rate due to ON/OFF operation of each analog switch changes in a geometric series with a common ratio of 2, and the time required for correction operation is extremely small. However, it is an object of the present invention to provide a gain drift correction circuit that can correct complicated drift characteristics with high precision and over a wide range.

Next, the present invention will be described with reference to illustrated embodiments.

FIG. 1 is a side view of an electronic balance using a circuit according to the present invention, and FIG. 2 is a block diagram showing the electrical configuration thereof.

In the figure, 1 is a weighing conveyor provided in the middle of an automatic filling line, etc., and this weighing conveyor 1 is placed on an electronic scale 3 together with a drive motor 2.
This electronic scale 3 uses a load cell 4 as a weight change-electrical signal conversion element that receives the load of the weighing conveyor 1, and electronic circuit boards 5, 6, and 7 are placed close to each other near the load cell 4. attached. Therefore, the electronic circuit boards 5, 6, 7 and the load cell 4 are housed in the same outer casing 3a, so that each of the electronic circuit boards 5, 6, 7
7 and the load cell 4 are placed under substantially the same temperature conditions.

Next, an outline of the electrical configuration of the electronic scale 3 will be explained with reference to FIG.

A DC power supply 8 is connected to the load cell 4,
A current/voltage change that changes depending on the load applied to the load cell 4 is output as a detected value of the load cell 4. The output of the load cell 4 is applied to an amplifier circuit 9, and the signal amplified by the amplifier circuit 9 is applied to a low-pass filter 10 to eliminate the effects of harmful mechanical vibrations, electrically induced noise, etc. on the load cell 4. is reduced. The low-pass filter 10 is composed of multiple stages of active filters connected in series using operational amplifiers, and the output of the low-pass filter 10 is applied to a voltage-frequency converter 11, where it is converted into a frequency value. The resulting signal is taken out as an output of the electronic balance 3. The signal outputted from the electronic balance 3 is applied to the counter circuit 12, the pulses per unit time are counted, and the pulses are applied to the arithmetic circuit 13. The numerical value obtained by the arithmetic circuit 13 is applied to a control device 14 and used for, for example, feedback control or feedforward control of an automatic filling line, and is also applied to a display device 15 for display.

The amplifier circuit 9, low-pass filter 10, and voltage-frequency converter 11 are attached to the electronic circuit boards 5 and 7 shown in FIG. A temperature detection element 16, a correction amount program circuit 17, and an analog switch circuit 18 are provided. The temperature detection element 16, the correction amount program circuit 17, and the analog switch circuit 18 have a detailed circuit configuration shown in FIG. 3, and a thermistor is used as the temperature detection element 16. The potential across both ends of this temperature detection element 16 is applied to comparison circuits 19 and 20. The comparison circuits 19 and 20 are composed of a large number of comparators C, and the reference input side terminals of each comparator are connected to each other via a resistor RS, and each of the voltages at both ends of the resistor RS is set to a constant value. There is. The comparison input terminals of each comparator C are all connected in common, and the temperature detection element 1
The output from 6 is connected.

The output of each comparator C is set to be in an ON state when the comparison voltage exceeds the respective reference voltage. Comparator C above
are used in this embodiment, but they are determined by the temperature range to be corrected and the resolution required within that temperature range, and each output terminal of this comparator C is gated by an exclusive OR circuit. It is connected to circuit 22. This gate circuit 22 takes the exclusive OR of the adjacent outputs of the comparator C, and inverts the inverter 23 for each one.
We are getting output terminals _O2 ~ _O20 through. Output terminal O ₁
obtains the output _I1 of the comparator C via a two-stage inverter 23. Output terminal O ₂₁ is
The output of the exclusive OR of the output I ₂₀ of the comparator C and the ground potential (zero volts) is obtained via the inverter 23.

In this way, the above-mentioned output terminals O ₁ and O ₂₁ are configured such that even if the ambient temperature deviates from the temperature detection range, one of the output terminals is turned ON. In other words, as shown in Figure 3, even if the temperature deviates toward a relatively high temperature, the output signal of the output _O21 will not be eliminated and the output will continue; conversely, even if the temperature deviates toward a relatively low temperature, the output The output signal of _O1 continues to be output without disappearing.

These output terminals O ₁ to O ₂₁ are configured to output bar graph changes applied to the input side as line graph changes. That is, the input terminals I ₁ to I ₂₀ of this gate circuit 22 have, for example, input terminals I ₁ , I ₂ , and I ₃ in the ON state, and other input terminals I ₄ to I 20 .
I ₂₀ is set to OFF state, and a signal is applied so that adjacent points of ON state and OFF state are bordered so that one is all ON and the other is all OFF, and output terminals O ₂ to O ₂₁ is on the input terminal side.
Only one terminal corresponding to the boundary between the ON state and the OFF state is turned ON. Above output terminal O ₁ ~
Each of O ₂₁ is the correction amount program circuit 17
This correction amount program circuit 1
7, a diode matrix circuit is used. The horizontal direction of this diode matrix circuit is the output terminal row of the gate circuit 22, and the vertical direction is the drive terminal row of the analog switch circuit 18. 18
It is composed of analog switches based on f, and the gate of the amplifier circuit 9 is controlled by the combination of ON and OFF of each switch. That is, the amplifier circuit 9 uses an operational amplifier OP,
The gain is controlled by changing the resistance values of the input side resistors R ₁ , R ₂ , and R ₃ of this operational amplifier OP.
When the resistance value between the resistors R ₁ , R ₂ , and R ₃ decreases, the gain increases, and conversely, when the resistance value increases, the gain decreases. Alternatively, the gain may be controlled by changing the resistance value of the feedback resistor _R4 of the operational amplifier OP.
As the resistance value of _R4 decreases, the gain decreases, and as the resistance value increases, the gain increases. Therefore, the combination of the analog switch circuits 18 may be set to increase or decrease the resistance value in the opposite manner.

Six multiplexers 18a to 18f are used in the analog switch circuit 18, and the first multiplexer 18a is used to switch the correction amount between the positive and negative directions, and normally +4e is added in advance. It is being Other five second to sixth multiplexers 18
b to 18f are for reducing the resistance values of the input side resistors R ₁ , R ₂ , R ₃ by a combination of ON/OFF operations, and varying the gain of the amplifier 9 by the correction amount. In this embodiment, the accuracy of the electronic scale 3 is reduced to 1/
Since the circuit according to the present invention is used to make the number 2000 or less, each of the second to second multiplexers 18b to 18f is
The gain fluctuation rate in the ON state is set, and when the first multiplexer 18a is turned OFF, the gain changes by -4e, and the second multiplexer 18a changes by -4e.
When b is turned on, the gain is set to change by +4e, and similarly, the third multiplexer 18c changes to +4e.
2e, the fourth multiplexer 18d is +1e, the fifth multiplexer 18e is +1/2e, and the sixth multiplexer 18f is +1/4e. Each set value is determined by the internal resistance of each multiplexer 18a to 18f and each externally connected resistor _R5 to _R10 , and in this way, each set value is configured to take a double value. With each combination, a wide range of corrections can be made precisely in 1/4e steps.

In the case where the drift characteristic shown in FIG. 4A is obtained, the gate circuit 22 as shown in FIG.
A diode D is connected at a predetermined location between each output terminal of the analog switch circuit 18 and each drive terminal of the analog switch circuit 18.

With the above-described configuration, the pre-correction characteristic G ₁ shown in FIG. 4A has a step-shaped correction amount G ₂ shown in FIG. 4B.
is added, and the corrected characteristic _G3 shown in FIG. 4C is obtained. With this, for example, the temperature detection element 16
If 31°C is detected at , gate circuit 2
2 is output from output terminal _O15 . This output terminal O ₁₅
are connected to the fourth and fifth multiplexers 18d and 18e by a diode D, and the third and fifth multiplexers 18d and 18e are
The fourth multiplexers 18d and 18e correspond to gain fluctuations of 1/2e and 1e, respectively, so the temperature is 31°C.
A correction G ₂ X of 1+4/1e is added to the pre-correction characteristic _G 1

Therefore, the temperature correction range is set as 0°C to 40°C, and the range is divided into 20 equal parts, and the slope of the curve before correction is 2°C per 2°C.
If it is within 1/4e, the corrected characteristic G ₃ X is located within the range of ±1/4e. In this way, the characteristics after correction
G ₃ is located within the range of ±1/4e, which allows for extremely high-precision correction, and the gain fluctuation rate for ON-OFF of each multiplexer 18b to 18g is expressed as a geometric series with a common ratio of 2. Since the values are set to change, a wide range of corrections can be made by combining each of them.

In the above-mentioned embodiment, the analog-to-digital converter is performed by voltage-frequency conversion.
This may be a commonly known A/D converter, and although a diode matrix circuit is used as the correction amount program circuit 17, a memory element such as a PROM may be used instead of the diode matrix circuit.

As explained above, according to the present invention, a temperature detection element is provided near a circuit that causes gain drift, and an analog switch selected based on a detection signal obtained from this detection element and a correction amount program circuit , a configuration in which the gain of the amplifier is adjusted, and the resistance value of the analog switch circuit is set so that the gain fluctuation rate due to ON/OFF operation of each analog switch changes in a geometric series with a common ratio of 2. Therefore, there is an effect that complex drift characteristics like a quadratic curve or a cubic curve can be corrected with high accuracy and over a wide range. However, since the correction is performed electronically, it has the effect of being instantaneously accomplished, and there is no problem in using it in an electronic scale of an automatic filling line. Furthermore, according to the present invention, even if the correction target is changed, it can be used simply by adjusting the correction amount program circuit.
There is no need to replace other parts, and it has the effect of being able to easily handle small-volume, high-mix products, and also being able to easily deal with changes in draft characteristics due to aging.

[Brief explanation of drawings]

Fig. 1 is a side view of an electronic scale in which the circuit according to the present invention is used, Fig. 2 is a block diagram showing the electrical configuration of the same, Fig. 3 is a circuit diagram showing the main parts of the present invention, and Fig. 4 is the drift characteristic corrected by the same circuit,
FIG. 3 is a graph diagram showing a correction amount and characteristics after correction. 9... Amplifier circuit, 16... Temperature detection element, 17... Correction amount program circuit, 18... Analog switch circuit, 18a to 18f... Multiplexer as analog switch, 19, 20... Comparison circuit, 22...
Gate circuit, R ₁ , R ₂ , R ₃ ... input side resistance, R ₄ ... feedback resistance, OP ... operational amplifier.

Claims (1)

[Claims] 1 A temperature detection element installed near the circuit that causes gain drift, a plurality of comparison circuits to which the detection signal obtained from this temperature detection element is added and generates an output each time a predetermined temperature is reached, and this A gate circuit that selects one of the outputs of a plurality of comparison circuits, a correction amount program circuit that generates a preprogrammed signal based on the output of the gate circuit, and an ON/OFF operation based on the output signal of this correction amount program circuit. The analog switch circuit comprises an analog switch circuit and an amplifier circuit comprising an operational amplifier whose resistance value of at least one of the input side resistance and the feedback resistance is changed by the analog switch circuit. It is composed of a plurality of analog switches and a resistor connected in series to each analog switch, and the resistance value of each analog switch and resistor is equal to the gain fluctuation rate of the operational amplifier in the ON state of each analog switch. A gain drift correction circuit characterized in that the gain drift correction circuit is set to vary in a geometric series with a common ratio of 2.