JPH1038664A - Weighing device with temperature sensitivity compensation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of the temperature-sensitive resistors used for compensating the temperature sensitivity of a plurality of weight detectors in a multichannel weighing device with temperature sensitivity compensation. SOLUTION: Weight detecting signals from a plurality of weight detectors 11 -1n are inputted to a common A/D converter 4 while the signals are successively switched to each other by means of a multiplexer 5. The changes of the signals caused by the temperature variation of the detectors 11 -1n are compensated by changing the reference voltage of the A/D converter 4 by means of a temperature-sensitive resistor TR provided in a reference voltage generating circuit 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a weighing device having a plurality of weight detectors, such as a combination weighing device,
The present invention relates to a temperature sensitivity compensation circuit that prevents a change in an output signal from a weight detector due to a temperature change from affecting a weighing value.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram of a weighing apparatus using a weight detector with temperature sensitivity compensation according to a first conventional example. and Ibitsutai (not shown), has a bridge circuit 11 made up of the strain gauge 10 for detecting the amount of strain of the strain body, and the ground side power source V _ex side of the bridge circuit 11, respectively Temperature sensitive resistors TR ₁ and TR ₂ for temperature sensitivity compensation are inserted. The temperature-sensitive resistors TR ₁ and TR ₂ compensate for an increase in the level of the weight detection signal because the Young's modulus of the flexure element decreases with an increase in temperature and the amount of distortion increases, and the resistance value thereof is increased. Increases and decreases as the temperature of the load cell 1 rises and falls, and the voltage VI applied to the bridge circuit 11 of the load cell 1 is adjusted. It does not happen. Reference numeral 2 denotes an amplifier for amplifying the input analog weight detection signal, reference numeral 3 denotes a low-pass filter (hereinafter, referred to as "LPF") for removing a noise component of the input analog weight detection signal, and reference numeral 4 denotes an input analog weight detection signal. A / D to convert to digital data
It is a converter.

FIG. 6 shows the weight detection signals of _n load cells ₁₁ to 1 _n with temperature sensitivity compensation according to a second conventional example.
One of the A / D converter 4 in the block diagram of a multi-channel temperature sensitivity compensation with metering device configured to convert A / D, the weight detection signal of the load cell 1 ₁ to 1 _n are each amplifier 2 ₁ to 2 _n and LPF 3 ₁ through to 3 _n multiplexer (hereinafter, referred to as "MUX") is inputted to 5 M
The signals are switched by the UX 5 and sequentially input to the A / D converter 4 to be A / D converted.

The load cells with temperature sensitivity compensation shown in FIGS. 5 and 6 each have two temperature-sensitive resistors.
Since a temperature-sensitive resistor twice as many as the number of load cells is required, the configuration becomes complicated, which contributes to an increase in cost.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a multi-channel temperature-sensitivity-compensated weighing device configured to sequentially convert the weight detection signals of a plurality of load cells by a common A / D converter. An object of the present invention is to realize simplification of the configuration and cost reduction by compensating the temperature sensitivities of a plurality of load cells with one temperature-sensitive resistor.

[0006]

In order to achieve the above object, a weighing device according to the present invention comprises a plurality of weight detectors for detecting the weight of an object to be weighed, and an analog weight detector from these weight detectors. A common A / D converter for A / D converting a signal, switching means for sequentially switching the plurality of analog weight detection signals and inputting the signals to the A / D converter, and supplying a reference voltage to the A / D converter. A reference voltage generating circuit to be applied, wherein the reference voltage generating circuit is provided with a temperature-sensitive resistor for preventing a level change of the analog weight detection signal due to a temperature change from appearing in an output level of the A / D converter. It is a thing.

According to the above configuration, the reference voltage of the A / D converter is changed by the temperature-sensitive resistor provided in the reference voltage generating circuit, and the level change of the weight detection signal accompanying the temperature change of the weight detector is detected. It works so that the compensated and output digital data does not change.

In one embodiment of the present invention,
The reference voltage generating circuit has a voltage dividing circuit that divides a power supply voltage to generate a reference voltage, and the temperature-sensitive resistor is connected in series to one of the voltage dividing resistors.

According to the above configuration, the reference voltage value increases as the temperature of the temperature-sensitive resistor increases, and the reference voltage value decreases as the temperature decreases.

In one embodiment of the present invention,
The voltage-dividing circuit has a first voltage-dividing resistor and a temperature-sensitive resistor in series on the ground side of the voltage-dividing point, and a second voltage-dividing resistor on the power supply side. vessels of primary temperature sensitivity coefficient f, the resistance value R ₁ of the first minute piezoresistor, the resistance value R ₂ of the second minute piezoresistor, the resistance value r ₀ when the reference temperature T ₀ of the temperature sensitive resistor , And the primary temperature coefficient α of the temperature-sensitive resistor is f = [{r ₀ / (R ₁ + r ₀ )} − {r ₀ / (R ₁ + R
₂ + r ₀ )｝] α.

According to the above configuration, the reference voltage of the A / D converter changes in accordance with the temperature change so as to compensate for the change in the weight detection signal caused by the temperature change of the weight detector.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a weighing device with temperature sensitivity compensation according to an embodiment of the present invention. This weighing device includes, for example, a plurality of weighing hoppers, combines the weighing values in each weighing hopper, selects a combination within an allowable range, and discharges an object to be weighed from the weighing hopper to thereby obtain a product having a desired weight. A combination weighing device that obtains, or a weighing table on which a heavy object to be weighed is placed is supported by a plurality of weight detectors, and a weighing device that obtains the weight of the object to be weighed from the sum of the weighing values of these weight detectors is there.

This weighing device includes a plurality of load cells ₁₁ to 1 _n which are an example of a weight detector. The load cell 1 is incorporated in, for example, an individual electronic balance, and includes a strain-generating body that generates a strain by receiving a load from the weighing platform, and a strain gauge 10 that detects the amount of the strain. And outputs a weight detection signal from the bridge circuit 11 including.

[0014] The weight detection signals from the load cell ₁ 1 to 1 _n are each amplifier 2 ₁ to 2 _n and LPF 3 ₁ to 3 _n
, And is input to the MUX 5, selected by the MUX 5 and sequentially input to the common A / D converter 4.
_Is subjected to A / D conversion based on the reference voltage V _REF input from the reference voltage generation circuit 6. This reference voltage V _REF and A /
When the input analog voltages to the D converter 4 are equal, the maximum number of bits is given to the output of the A / D converter 4 which digitizes the analog input voltage. The digital weight signal output from the A / D converter 4 is subjected to, for example, digital filtering and zero point correction by a signal processing circuit (not shown) at a subsequent stage.

The reference voltage generating circuit 6 is constituted by a second partial piezoresistor DR ₂ and series body in which the first partial piezoresistor DR ₁ and the temperature-sensitive resistor TR is connected in this order, the second voltage V _ex is applied to a separatory piezoresistor DR ₂ side is grounded the temperature-sensitive resistor TR side and a second partial piezoresistor DR ₂ first minute piezoresistor D
The reference voltage V _REF is extracted from the connection point of R ₁ .

Next, the operation of compensating for the temperature sensitivity of the load cell in this embodiment will be described with reference to FIGS. Now, t the temperature sensitivity of the load cell f, when the load signal voltage output from the load cell with respect to the load G at the reference temperature T ₀ and v _0, as shown in FIG. 2, from T ₀
The load signal voltage v at the temperature T that is only higher is v = v ₀ {1 + f (T−T ₀ )} = v ₀ (1 + ft) (1)

Next, the reference voltage V _REF output from the reference voltage generating circuit 6 shown in FIG.
R _{1 1} of the resistance value and the second frequency圧抵resistance antibody DR ₂ R _2, the resistance of the temperature sensitive resistive element TR and _{r, V REF = (R 1} + r) / (R 1 + R given by _{2 + r) V ex ···· (} 2).

Next, assuming that the resistance value of the temperature-sensitive resistor TR at the reference temperature T ₀ is r ₀ and the primary temperature coefficient (TCR) is α, the resistance value r of the temperature-sensitive resistor TR at the temperature T is r = R ₀ (1 + αt) (3)

Therefore, the reference voltage V _REF of the reference voltage generating circuit 6 is obtained by substituting equation (3) into equation (2).

[0020]

(Equation 1)

## EQU1 ## From the above, in order for the relationship between the load signal voltage v and the reference voltage V _{REF at} the temperature T to be constant, the coefficient f of the equation (1) and the coefficient part of the equation (4) are the same, that is,

[0022]

(Equation 2)

It suffices to select r ₀ and α of the temperature-sensitive resistor TR and the resistance values of the first and second resistors DR ₁ and DR ₂ so as to satisfy the relationship of: Thus, the resistance value r (Equation (3)) of the temperature-sensitive resistor TR increases due to the temperature rise, the reference voltage V _REF increases, and the load signal voltage V
The rise due to the temperature of (Expression (1)) is canceled. As a result, the output level of the A / D converter 4 does not change due to the temperature, so that an accurate measurement value can be obtained.

Examples of the resistor having such a primary temperature coefficient α include nickel, copper, platinum and the like. Although the number of the temperature-sensitive resistors TR may be one, two or more resistors having different temperature characteristics may be used to have a temperature characteristic more closely matching the temperature characteristic of the load cell.

FIG. 4 is a block diagram of a weighing device with multi-channel temperature sensitivity compensation according to another embodiment of the present invention.
There are provided m scales having n load cells, and the A / D converter 4 converts the weight detection signals of the n × m load cells ₁₁ to 1 _{m + n} by one A / D converter 4. It is what was constituted. In the figure, the load cell _{1 1 ~1 m + n}
Are switched by the MUXs 5 _{1 to} 5 _m of the first stage, and the amplifiers 2 ₁ to 5 which configure the lines _{1 to m} , respectively.
MUX5 of the second stage through 2 _m and LPF3 _{1-3 m
The} reference voltage V _REF is input to the _{m + 1} , is switched, is sequentially input to the A / D converter 4, and is A / D converted based on the reference voltage V _REF input from the reference voltage generation circuit 6.

Also in this embodiment, the temperature sensitivity compensation of the weight detection signals of the n × m load cells can be performed by one temperature sensitive resistor.

[0027]

As described above, according to the present invention, the temperature sensitive resistor disposed in the reference voltage generating circuit allows the A
Since the reference voltage applied to the / D converter changes so as to cancel out the variation of the weight detection signal due to the temperature change, a plurality of weights can be obtained by a simple and inexpensive configuration in which a temperature-sensitive resistor is provided in the reference voltage generation circuit. A metering device is provided which compensates for the temperature sensitivity of the detector.

[Brief description of the drawings]

FIG. 1 is a block diagram of a weighing device with multi-channel temperature sensitivity compensation according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a compensation principle of the embodiment.

FIG. 3 is a circuit diagram for explaining the operation of the reference voltage generation circuit of the embodiment.

FIG. 4 is a block diagram of a weighing device with multi-channel temperature sensitivity compensation according to another embodiment of the present invention.

FIG. 5 is a block diagram showing a first conventional example.

FIG. 6 is a block diagram showing a second conventional example.

[Explanation of symbols]

1 ₁ to 1 _n ... load cell (weight detector), 2 ₁ to 2 _n ...
Amplifiers, 3 _{1 to} 3 _n ... LPFs, 4 ... A / D converters, 5 ...
Multiplexer, 6 ... reference voltage generating circuit, TR ... temperature sensitive resistors, DR _1, DR ₂ ... min piezoresistor, V _REF ... reference voltage.

Claims (3)

[Claims] 1. A plurality of weight detectors for detecting the weight of an object to be weighed, and an analog weight detection signal from these weight detectors being A / A
A common A / D converter for performing D conversion, switching means for sequentially switching the plurality of analog weight detection signals and inputting the signals to the A / D converter, and a reference voltage for applying a reference voltage to the A / D converter A temperature generator having a temperature-sensitive resistor for preventing a level change of the analog weight detection signal due to a temperature change from appearing in an output level of the A / D converter. Weighing device with sensitivity compensation. 2. The reference voltage generating circuit according to claim 1, further comprising a voltage dividing circuit for dividing a power supply voltage to generate a reference voltage, wherein the temperature-sensitive resistor is connected in series with one of the voltage dividing resistors. Measuring device with temperature sensitivity compensation connected to. 3. The voltage-dividing circuit according to claim 2, wherein the voltage-dividing circuit includes a series circuit of a first voltage-dividing resistor and a temperature-sensitive resistor on the ground side and a second voltage-dividing circuit on the power supply side. Each of which has a resistor, a temperature sensitivity coefficient f of the weight detector, a resistance value R _{1 of} a _first voltage-dividing resistor, a resistance value R _{2 of} a _second voltage-dividing resistor, and a reference temperature of the temperature-sensitive resistor. The resistance value r _{0 at} T ₀ and the temperature coefficient α of the temperature-sensitive resistor are given by f = [{r ₀ / (R ₁ + r ₀ )} − {r ₀ / (R ₁ + R)
₂ + r ₀ )｝] A weighing device with temperature sensitivity compensation set so as to satisfy the relationship α.