JP2008151596A - Load cell and mass meter - Google Patents

Abstract

A cost reduction of a load cell is realized.
A load cell includes a strain generating body whose strain amount changes according to a load, a bridge circuit 100, and a peripheral circuit 100P. The bridge circuit 100 includes terminals 102 to 105, strain gauges G1 to G4, a zero balance adjustment circuit 20, and a zero point temperature compensation circuit 30, and the peripheral circuit 100P includes a span temperature compensation circuit 10. The span temperature compensation circuit 10 uses a thermistor TH1 and resistors R11 to R13 to compensate the temperature characteristics of the strain amount of the strain generating body. Further, a chip resistor R21 is used for the zero balance adjustment circuit 20, and a thermistor TH2 and chip resistors R31 and R32 are used for the zero point temperature compensation circuit 30.
[Selection] Figure 1

Description

  The present invention relates to a load cell and a mass meter that output an electrical signal corresponding to a change in resistance value of a strain gauge.

A strain gauge is an element whose resistance value changes according to the amount of strain generated by a load on a strain generating body. A load cell for measuring a force (load) acting on an elastic body by attaching the strain gauge to the elastic body (strain body) is widely used. The load cell outputs a voltage corresponding to the resistance value of the strain gauge as an electric signal. For example, Patent Document 1 describes a load cell having a bridge circuit A as shown in FIG. As shown in FIG. 9, the bridge circuit A includes four terminals a to d and four strain gauges 1 to 4, and the strain gauges 1 to 4 are between the terminal a and the terminal b and between the terminal b and the terminal. c, between terminal c and terminal d, and between terminal d and terminal a. The bridge circuit A is set so that the potential difference taken out from the terminal b and the terminal d becomes zero when the load on the strain generating body is zero.
JP-A-8-159984

  By the way, the Young's modulus (elastic modulus) of the strain body varies depending on the temperature. For this reason, conventionally, a resistance temperature sensor such as a platinum temperature sensor has been provided in the bridge circuit in order to compensate for the temperature characteristics of the strain amount of the strain generating body. However, since this platinum temperature sensor uses platinum as a material, the price thereof is very high, which hinders cost reduction of the load cell.

  In the bridge circuit A described above, the resistance values of the strain gauges 1 to 4 may vary. In order to absorb this variation, a zero balance adjustment circuit may be provided so that the potential difference extracted from the terminal b and the terminal d becomes zero at a predetermined temperature. Although it is conceivable to use a constantan wire having a low temperature coefficient as the zero balance adjustment circuit, the constantan wire has a large variation in resistance value with respect to a predetermined length due to its composition. For this reason, in order to perform compensation using a constantan line, it is necessary to repeat measurement and fine adjustment a plurality of times, which causes an increase in the number of compensation steps.

In addition, the strain gauges 1 to 4 themselves of the bridge circuit A also have a temperature characteristic that the resistance value increases as the temperature rises. In order to compensate the temperature characteristics of the strain gauges 1 to 4, a zero point temperature compensation circuit may be provided in the bridge circuit A. Although it is conceivable to use a copper wire as the zero point temperature compensation circuit, in that case, the compensation cannot be completed in a single compensation step, as in the case of the constantan wire described above. Further, there is a problem of processing error such as part of the copper wire being melted when soldering the copper wire, and the compensation may not be partitioned even if the compensation is repeated. For this reason, the resistor replaced with a copper wire was calculated | required.
This invention is made | formed in view of the situation mentioned above, and makes it a solution subject to provide the load cell and mass meter which the temperature characteristic is compensated reliably, suppressing cost.

  A load cell according to the present invention includes a strain-generating body whose amount of strain changes according to a load, a span temperature compensation circuit that compensates a temperature characteristic of the strain amount of the strain-generating body, and a predetermined temperature via the span temperature compensation circuit. And a bridge circuit for extracting a potential difference corresponding to the amount of strain of the strain generating body, and the span temperature compensation circuit includes a thermistor and a resistor connected in parallel to the thermistor. In the load cell of the present invention, a thermistor is used for the span temperature compensation circuit. Since the thermistor is cheaper than the conventional platinum temperature sensor, the cost of the load cell can be reduced. The thermistor has a characteristic that the resistance value exponentially changes according to the temperature. By connecting the resistor in parallel with the thermistor, a desired temperature characteristic can be obtained by the combined resistance of the thermistor and the resistor. . This makes it possible to correct the temperature characteristics of the strain amount of the strain generating body.

  Another load cell of the present invention is a load cell including a strain generating body whose amount of strain changes according to a load and a bridge circuit, wherein the bridge circuit includes a first terminal to which a predetermined voltage is applied and a third terminal. The resistance value changes according to the amount of strain of the terminal, the second terminal and the fourth terminal for extracting the potential difference according to the strain amount, and the strain amount of the strain generating body, and between the first terminal and the second terminal. , First to fourth provided between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal, respectively. The strain gauge, between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the fourth terminal, and the fourth terminal Provided in at least one of the first terminal and the front when the load is zero at a predetermined temperature And zero balance adjustment circuit having a chip resistor to a potential difference is taken out from said second terminal fourth terminal to zero comprises. The chip resistance is inexpensive and its resistance value is known, and there is little variation in the material. Therefore, it is possible to easily perform compensation by simply disposing a chip resistor having an appropriate value on the circuit that is appropriately adjusted without repeatedly performing measurement and fine adjustment. As the chip resistor, it is preferable to use a film resistance such as a carbon film resistor, a metal film resistor, and a metal oxide film resistor.

Another load cell of the present invention is a load cell including a strain generating body whose amount of strain changes according to a load and a bridge circuit, wherein the bridge circuit includes a first terminal to which a predetermined voltage is applied and a third terminal. The resistance value changes according to the amount of strain of the terminal, the second terminal and the fourth terminal for extracting the potential difference according to the strain amount, and the strain amount of the strain generating body, and between the first terminal and the second terminal. , First to fourth provided between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal, respectively. The strain gauge, between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the fourth terminal, and the fourth terminal Provided in at least one of the first terminals and within a predetermined temperature range centered on a predetermined temperature. The load is a zero-point temperature compensation circuit having a thermistor in order to compensate for the temperature characteristic to the zero potential difference is taken out from said second terminal at zero and the fourth terminal comprises. According to this aspect, since the temperature characteristic can be given by the thermistor, it is possible to compensate for the temperature without repeating measurement and fine adjustment by appropriately adjusting the resistance value on the circuit. Therefore, temperature compensation can be performed simply and with a small number of steps.
Preferably, the zero point temperature compensation circuit is provided between the first terminal and the second terminal, between the third terminal and the fourth terminal, and between the second terminal and the third terminal. And any one of the fourth terminal and the first terminal. Thereby, since the balance in the bridge circuit is ensured, it becomes possible to perform the zero point temperature compensation more reliably.

  Furthermore, this invention is grasped | ascertained also as a mass meter provided with the load cell mentioned above. This mass meter includes the load cell described above and a signal generation unit (for example, 40 and 50 shown in FIG. 7) that generates a signal indicating mass based on a potential difference extracted from the bridge circuit.

Embodiments according to the present invention will be described below with reference to the accompanying drawings. In the drawings, the ratio of dimensions of each part is appropriately changed from the actual one.
<A: Bridge circuit>
FIG. 1 shows a circuit configuration of a bridge circuit 100 and its peripheral circuit 100P according to an embodiment of the present invention. As shown in FIG. 1, the bridge circuit 100 includes a terminal 102 (first terminal), a terminal 103 (third terminal), a terminal 104 (fourth terminal), and a terminal 105 (second terminal). 4 strain gauges G (G1, G2, G3, G4). The strain gauge G 1 is provided between the terminal 102 and the terminal 105, and the strain gauge G 2 is provided between the terminal 103 and the terminal 105. The strain gauge G3 is provided between the terminal 103 and the terminal 104, and the strain gauge G4 is provided between the terminal 102 and the terminal 104. Each strain gauge G is a resistor whose resistance value changes in accordance with the amount of strain. For example, when used by being attached to an elastic body having elasticity such as aluminum, iron, and stainless steel, the resistance value of the strain gauge Based on the change, it is possible to measure the amount of load on the elastic body (hereinafter referred to as “strain body”).

  A peripheral circuit 100 </ b> P is connected to the terminal 102 of the bridge circuit 100. The peripheral circuit 100P includes a terminal 101 and a span temperature compensation circuit 10 described later. The bridge circuit 100 and the peripheral circuit 100P of this embodiment are used in a load cell (for example, FIG. 5) that is attached to a strain generating body and detects a load on the strain generating body.

The power supply potential V _DD is supplied to the terminal 101 of the peripheral circuit 100P, and the reference potential V _SS is supplied to the terminal 103 of the bridge circuit 100. In other words, a predetermined voltage is applied to the bridge circuit 100 via the span temperature compensation circuit 10. The bridge circuit 100 has a design value (ideal value) in which each of the above-described strain gauges G has the same potential output from each of the terminal 104 and the terminal 105 when the load on the strain generating body is zero. Each resistance value is set.
However, in reality, the metal that is a strain generating body has temperature characteristics. That is, the amount of strain changes with temperature. The resistance value of the strain gauge G also has temperature characteristics. Specifically, the resistance value increases as the temperature increases. In order to compensate for the temperature characteristics of the strain generating body and the strain gauge G, the bridge circuit 100 includes a zero balance adjustment circuit 20A, a terminal 103, and a terminal between the terminal 102 and the terminal 104 in addition to the above-described elements. A zero balance adjustment circuit 20B is provided between the terminal 104 and the terminal 105, a zero point temperature compensation circuit 30A between the terminal 102 and the terminal 105, and a zero point temperature compensation circuit 30B between the terminal 103 and the terminal 105. Is provided. Further, the span temperature compensation circuit 10 is provided between the terminals 101 and 102 in the peripheral circuit 100P.
Hereinafter, each of the span temperature compensation circuit 10, the zero balance adjustment circuit 20 (20A, 20B), and the zero point temperature compensation circuit 30 (30A, 30B) will be described in detail.

As shown in FIG. 1, the span temperature compensation circuit 10 includes a thermistor TH1. The thermistor TH1 is a temperature measuring element (NTC thermistor: Negative Temperature Coefficient Thermistor) having a negative temperature coefficient, and its resistance value varies exponentially with temperature. The change in resistance value of the thermistor is expressed by the following equation.
Ra = Rb · exp {B (1 / Ta−1 / Tb)}
here,
Ra: Zero load resistance value (Ω) at absolute temperature Ta (K)
Rb: Zero load resistance value (Ω) at the absolute temperature Tb (K)
B: B constant (K)

  A chip resistor R11 is connected in parallel to the thermistor TH1, and a chip resistor R12 is connected in series to the thermistor TH1 and the chip resistor R11. In addition, a chip resistor R13 is connected in parallel to the combined resistor of the thermistor TH1, the chip resistor R11, and the chip resistor R12, and a chip resistor R14 is further connected in series. Of these chip resistors, the chip resistors R12, R13, and R14 function as fine adjustment resistors. As the chip resistor, any one of film resistors such as a carbon film resistor, a metal film resistor, and a metal oxide film resistor can be used. Further, any of the chip resistors R11 to R14 has a positive temperature coefficient. That is, as the temperature rises, the resistance value increases. The resistance values of the chip resistors R11 to R14 are adjusted so that the combined resistance with the thermistor TH1 cancels the temperature characteristics of the strain generating body. Details are described below.

  FIG. 2 is a graph showing an example of a change in the combined resistance of the span temperature compensation circuit 10. Although the change in the resistance value of the thermistor TH1 is exponential when used alone, it is converted into a linear change by connecting the resistors R11 to R14 in parallel. Although the thermistor TH1 has a negative temperature coefficient, the span temperature compensation circuit 10 is set to have a positive temperature coefficient as a whole by combining with the resistance values of the chip resistors R11 to R14. The strain generating body of the present embodiment has a temperature characteristic that when the temperature rises, the strain amount with respect to the same load increases (that is, the slope of the change in strain amount with respect to the load increases). As a result, the output span (maximum output value) of the load cell increases. For this reason, the input voltage applied between the terminal 102 and the terminal 103 is suppressed by increasing the resistance value of the span temperature compensation circuit 10 in accordance with an increase in the strain amount of the strain generating body. The temperature characteristic of the voltage output from 100 is compensated.

  Next, the zero balance adjustment circuit 20 (20A, 20B) will be described. Each zero balance adjustment circuit 20 has a chip resistor R21 (R21a, R21b). Since the resistor R21 only needs to be able to absorb mainly variations in the resistance value of each strain gauge G, the resistance value of the chip resistor R21 (R21a, R21b) is lower than the resistance value of each strain gauge G. As the chip resistor, for example, any of a carbon film resistor, a metal film resistor, and a metal oxide film resistor can be used. The zero balance adjustment circuit 20 is a circuit for setting the potential difference taken out from the terminal 104 and the terminal 105 to zero when the load on the strain generating body is zero at a predetermined temperature (20 ° C. in the present embodiment). The chip resistor has a temperature characteristic with a positive temperature coefficient, but the resistance value corresponding to each temperature is known. For this reason, if the zero point temperature compensation circuit 30 described later is provided with a temperature sensitive resistor so that the temperature compensation of the chip resistor R21 is performed, there is an advantage that the zero balance at a predetermined temperature can be easily adjusted.

  Next, the zero point temperature compensation circuit 30 will be described. As shown in FIG. 1, each zero point temperature compensation circuit 30 (30A, 30B) includes a thermistor TH2 (TH2a, TH2b) and a low resistance chip resistor R31 (R31a, R31b) connected in series to each thermistor TH2. ) And chip resistors R32 (R32a, R32b) connected in parallel to the combined resistance of the thermistor TH2 and the chip resistor R31. The thermistor TH2 is an NTC thermistor having a negative temperature coefficient, and has the same temperature characteristics as the above-described thermistor TH1. On the other hand, the chip resistors R31 to R32 have a positive temperature coefficient. Any of a carbon film resistor, a metal film resistor, and a metal oxide film resistor can be used as the chip resistor.

  The chip resistor R31 connected in series with the thermistor TH2 has a function of controlling the current flowing through the thermistor TH2. When the resistance value of the chip resistor R32 is fixed and the resistance value of the chip resistor R31 is increased, the current flowing through the thermistor TH2 is decreased. On the other hand, when the resistance value is decreased, the current flowing through the thermistor TH2 is increased. The chip resistor R31 has a function of finely adjusting the current flowing through the thermistor TH2. Increasing the resistance value of the chip resistor R31 increases the current flowing through the thermistor TH2, and decreasing the resistance value of the chip resistor R31 decreases the current flowing through the thermistor TH2. That is, when there is the chip resistor R31, the current flowing through the thermistor TH2 is limited. Further, since the resistance values of the chip resistor R31 and the thermistor TH2 only have to compensate for the temperature characteristics of the strain gauges G1 to G4, their resistance values may be very small.

  FIG. 3 shows an example of a change in the combined resistance of the zero point temperature compensation circuit 30. As understood from FIG. 3, the zero-point temperature compensation circuit 30 functions as a temperature sensitive resistor having a negative temperature coefficient as a whole, thereby compensating for the temperature characteristics of the strain gauges G1 to G4 and the above-described temperature characteristics. The temperature characteristic of each chip resistor R21 in the zero balance adjustment circuit 20 is compensated. Specifically, since each temperature characteristic of the strain gauge G and the chip resistor R21 has a positive temperature coefficient, the thermistor of the zero point temperature compensation circuit 30 and the zero point temperature compensation circuit 30 have a negative temperature coefficient as a whole. By adjusting the resistance value of each chip resistor, the temperature characteristics of the zero point temperature compensation circuit 30 can be canceled. As a result, even when the temperature is changed, the terminal 102 and the terminal 105 are connected, the terminal 105 and the terminal 103 are connected, the terminal 103 and the terminal 104 are connected, and the terminal 104 and the terminal 102 are connected in a state where the strain generating body is not loaded. It becomes possible to keep the bridge circuit in a balanced state. In other words, the zero point temperature compensation circuit 30 has a potential difference taken out from the terminal 104 and the terminal 105 when the load on the strain generating body is zero in a predetermined temperature range centered on a predetermined temperature (for example, 20 ° C.). This is a circuit for setting zero to zero.

  FIG. 4 shows a bridge circuit B and its peripheral circuit BP as a comparative example of the present embodiment. As shown in FIG. 4, the peripheral circuit BP of this comparative example includes a span temperature compensation circuit B <b> 1 instead of the span temperature compensation circuit 10, and the bridge circuit B includes a zero balance adjustment circuit instead of the zero balance adjustment circuit 20. B2 (B2a, B2b) is provided, and a zero point temperature compensation circuit B3 (B3a, B3b) is provided instead of the zero point temperature compensation circuit 30. Except for these points, the bridge circuit B and the peripheral circuit BP have the same configuration as the bridge circuit 100 and the peripheral circuit 100P described above. For this reason, about the same component, the same code | symbol is used and the description is abbreviate | omitted.

  As shown in FIG. 4, in this peripheral circuit BP, the span temperature compensation circuit B1 has a platinum temperature sensor B11 and two resistors B12 and B13 connected in parallel to the platinum temperature sensor B11. In the bridge circuit B, each zero balance adjustment circuit B2 includes a resistor B21 (B21a, B21b) made of a constantan wire (copper nickel alloy wire), and each zero point temperature adjustment unit B3 has a resistance made of a copper wire. A body B31 (B31a, B31b) is provided.

  Incidentally, the platinum temperature sensor B11 used in the span temperature compensation circuit B1 of the peripheral circuit BP is expensive because it uses a platinum wire as a material. On the other hand, in the peripheral circuit 100P of the present embodiment, an inexpensive thermistor TH1 is used as the temperature sensitive resistor used in the span temperature compensation circuit 10. As described above, the exponential temperature characteristic of the thermistor is converted into a linear change, and the negative temperature coefficient of the thermistor is changed to a positive temperature coefficient (that is, the synthesis in the span temperature compensation circuit 10). The resistance values of the resistors R11 to R14 connected in parallel with the thermistor TH1 are adjusted so that the temperature characteristics of the resistance cancel the temperature characteristics of the strain-generating body. As described above, according to the load cell including the peripheral circuit 100P of the present embodiment, the temperature characteristics of the strain generating body can be reliably compensated even using an inexpensive thermistor. In comparison, the cost of the apparatus can be reduced without impairing the function of the span temperature compensation circuit.

  In the zero balance adjustment circuit B2 of the bridge circuit B, a constantan line is used as the resistor B21. Since the constantan line has a low temperature coefficient (that is, the resistance value is almost constant even when the temperature changes), it can be said that its temperature characteristic is suitable for adjusting the zero balance at a predetermined temperature. However, the constantan wire generally has a large variation in resistance value with respect to a predetermined length due to its composition. For this reason, when compensating using a constantan line, even if a line of a corresponding length is inserted after measuring the characteristics and calculating the applicable value, it can be completely compensated with a single compensation. Therefore, it was necessary to repeat measurement and fine adjustment several times. As a result, it was a factor in increasing the number of compensation man-hours. On the other hand, in the zero balance adjustment circuit 20 of the present embodiment, a chip resistor R21 whose resistance value is known is used instead of the constantan line. Thereby, it is not necessary to repeat measurement and fine adjustment, compensation can be performed, and work man-hours are reduced. As a result, the manufacturing is simplified and the cost of the apparatus is reduced.

  In addition, a copper wire is used as the resistor B31 in the zero point temperature compensation circuit B3 of the bridge circuit B. However, in the compensation using the copper wire, the compensation cannot be completed in a single compensation step, like the constantan wire described above. Specifically, in compensation using a copper wire, first, the temperature characteristics of the bridge circuit B, that is, characteristics in a temperature load (high temperature region and low temperature region) are measured, and a compensation value is determined according to the result. Insert the required amount of copper wire. Then, the temperature load is performed again, and the characteristics of the bridge circuit B are confirmed. However, there is a problem of processing error such as part of the copper wire being melted when the copper wire is soldered, and compensation may not be partitioned even if measurement and confirmation are repeated. On the other hand, in the zero point temperature compensation circuit 30 of the present embodiment, the thermistor TH2 is used as the temperature sensitive resistor to perform the zero point temperature compensation. Then, chip resistors R31 and R32 having a known resistance value are connected in parallel to the thermistor TH2. For this reason, the adjustment required when using a copper wire becomes unnecessary, and a compensation man-hour is reduced.

  Therefore, in the bridge circuit 100 of the present embodiment, a chip resistor is used for the zero balance adjustment circuit 20 and a thermistor and a chip resistor are used for the zero point temperature compensation circuit 30. Therefore, compensation is performed by simulating appropriate values on the circuit. The process can be completed once. In particular, it is preferable to use a film resistor having a low cost and a known temperature characteristic and resistance value as the chip resistor.

  As described above, according to the bridge circuit 100 of the present embodiment, the peripheral circuit 100P is provided on the terminal 102 side to which the voltage is input, and an inexpensive thermistor is used for span temperature compensation in the peripheral circuit 100P. Reduction is possible. Furthermore, since the zero point temperature compensation and the zero balance adjustment are performed using the thermistor and the chip resistor, the compensation process is completed at a time by selecting an appropriate value by simulation. Therefore, according to the load cell including the bridge circuit 100 of the present embodiment, a highly accurate load cell can be easily manufactured at a lower cost.

<B: Load cell>
FIG. 5 is a perspective view showing the load cell 200 including the bridge circuit 100A and the peripheral circuit 100AP. FIG. 6 shows the arrangement of the elements of the bridge circuit 100A and the peripheral circuit 100AP arranged on the surface of the flexible substrate 400. FIG. As shown in FIG. 5, the load cell 200 includes a strain generating body 300, a bridge circuit 100A, and a peripheral circuit 100AP. As understood from FIGS. 5 and 6, the bridge circuit 100 </ b> A and the peripheral circuit 100 </ b> AP are disposed on the surface of the flexible substrate 400, and the flexible substrate 400 is bent along the V line and the V ′ line, respectively. Affixed to the surface of the body 300. Specifically, as shown in FIG. 6, the flexible substrate 400 includes a region 400C that is a region sandwiched between the V line and the V ′ line, a region 400L that is a region on the left side of the V line, It is divided into a region 400R, which is a region on the right side in the drawing with respect to the V ′ line. As shown in FIG. 5, the flexible substrate 400 has a region 400 </ b> L attached to the upper surface portion of the strain generating body 300 in the drawing, and a region 400 </ b> R attached to the lower surface portion of the strain generating body 300 in the drawing. Is attached to the back surface portion of the strain generating body 300 in the drawing. The strain generating body 300 is an elastic body such as a metal and has a property of being deformed by a load from the direction of the arrow A. The load cell 200 can detect the amount of the load applied to the strain generating body 300 by a strain gauge attached to the strain generating body 300.

FIG. 7 is a circuit diagram showing an electrical configuration of the load cell 200 including the bridge circuit 100A and the peripheral circuit 100AP. As shown in FIG. 7, the load cell 200 includes a bridge circuit 100A, a peripheral circuit 100AP, an operational amplifier 40 that amplifies and outputs an electric signal input from the bridge circuit 100A, and an analog signal input from the operational amplifier 40. And an A / D converter 50 that converts the digital signal and outputs the digital signal. The digital signal output from the A / D converter 50 is supplied to a control unit of a device (for example, a mass meter) provided with the load cell 200 and subjected to predetermined processing, and then a display device (for example, a mass meter). Used in peripheral devices such as a display (not shown).
5 to 7, the same components as those of the above-described bridge circuit 100 are denoted by the same reference numerals, and the description thereof is omitted as appropriate.

  As shown in FIG. 7, the bridge circuit 100A is the bridge circuit described above except that the span temperature compensation circuit 10A of the peripheral circuit 100AP has only the thermistor TH1 and one chip resistor R11 connected in parallel to the thermistor TH1. The configuration is similar to that of the circuit 100 and the peripheral circuit 100P. In the span temperature compensation circuit 10A, the characteristics and resistance of the thermistor TH1 and the chip resistor R11 can be compensated by using only the thermistor TH1 and the chip resistor R11 so that the same compensation as the span temperature compensation circuit 10 of the peripheral circuit 100P can be performed. The value is set appropriately. That is, in the span temperature compensation circuit 10 described above, if the resistance value of the chip resistor R13 is ∞ (infinite) and the resistance values of the chip resistors R12 and R14 are zero, the span temperature compensation circuit 10A includes the thermistor TH1 and the chip resistor. Only R11.

  As shown in FIG. 6, each of the terminals 101, 103, 104, 105, the strain gauges G1 to G4, the span temperature compensation circuit 10A, the zero balance adjustment circuits 20A, 20B, and the zero point temperature compensation circuits 30A, 30B. The element is disposed on the surface of the flexible substrate 400. Specifically, the terminals 101, 103, 104, and 105 are arranged in the region 400C, and the strain gauges G1 and G4, the span temperature compensation circuit 10A, the zero balance adjustment circuit 20A, and the zero point temperature compensation circuit 30A are in the region 400R. Be placed. Strain gauges G2 and G3, zero balance adjustment circuit 20B and zero point temperature compensation circuit 30B are arranged in region 400L. The region 60 in the region 400L is a portion corresponding to the span temperature compensation circuit 10A in the region 400R, but the region 60 is provided with a jumper line for short-circuiting the land.

  As described above, since the region 400L is attached to the upper surface portion of the strain body 300 and the region 400R is attached to the lower surface portion of the strain body 300, when the strain body 300 is deformed by a load from the L direction, A load (amount of strain) applied to the strain generating body 300 is detected by strain gauges G1 to G4 attached to the upper surface portion and the lower surface portion of the strain generating body 300.

  According to the bridge circuit 100A and the peripheral circuit 100AP described above, the same effects as those of the bridge circuit 100 and the peripheral circuit 100P described above can be obtained. Therefore, the same effect can be obtained by the load cell 200 including the bridge circuit 100A and the peripheral circuit 100AP.

<C: Modification>
(1) In the above-described embodiment, the aspect in which the thermistor TH2 and the resistors R31 and R32 are used as the zero point temperature compensation circuit 30 has been described. Instead, as shown in FIG. 8, a copper wire is used as the resistor. It is good also as an aspect. Also according to this aspect, it is possible to obtain the same effect as in the above embodiment.
(2) In the above embodiment, the peripheral circuit 100P including the span temperature compensation circuit 10,10A between the terminal 101 and the bridge circuit 100,100A that V _DD is applied has been described for the case where providing the 100AP, V Peripheral circuits 100P and 100AP including the span temperature compensation circuits 10 and 10A may be provided between the _SS and the terminal 103. The same effect can be obtained by this configuration.
(3) In the embodiment described above, in the zero balance adjustment circuit 20, the zero balance adjustment circuit 20 </ b> A is provided between the terminal 102 and the terminal 104, and the zero balance adjustment circuit 20 </ b> B is provided between the terminal 103 and the terminal 104. However, only one of the zero balance adjustment circuit 20A and the zero balance adjustment circuit 20B may be provided. Similarly, when the temperature characteristics of the strain gauges G1 to G4 and the chip resistance R21 (R21a and / or R21b) of the zero balance adjustment circuit can be compensated by one zero point temperature compensation circuit 30, the zero point temperature compensation circuit 30A. Alternatively, any one of the zero point temperature compensation circuits 30B may be provided.
(4) In the embodiment described above, the zero balance adjustment circuit 20 is provided on the right side of the bridge circuits 100 and 100A, and the zero point temperature compensation circuit 30 is provided on the left side (FIGS. 1 and 7). The adjustment circuit 20 and the zero point temperature compensation circuit 30 may be provided on either the left or right side. Therefore, for example, both the zero balance adjustment circuit 20 and the zero point temperature compensation circuit 30 may be provided on the left side.
That is, the zero balance adjustment circuit 20 and the zero point temperature compensation circuit 30 are provided in at least one of the terminals 102 and 104, the terminals 104 and 103, and the terminals 103 and 105. Just do it.
(5) In the above-described embodiment, a mode in which the temperature compensation and zero balance adjustment of the strain generating body and the bridge circuit are performed using all of the span temperature compensation circuit 10, the zero balance adjustment circuit 20, and the zero point temperature compensation circuit 30 will be described. However, only the span temperature compensation circuit 10, only the zero balance adjustment circuit 20, or only the zero point temperature compensation circuit 30 may be appropriately provided.

FIG. 3 is a circuit diagram showing configurations of a bridge circuit 100 and a peripheral circuit 100P according to an embodiment of the present invention. It is a graph which shows the temperature characteristic of the synthetic resistance of a span temperature compensation circuit. It is a graph which shows the temperature characteristic of the synthetic | combination resistance of a zero point temperature compensation circuit. It is a circuit diagram which shows the structure of the bridge circuit B and the peripheral circuit BP as a comparative example. It is a perspective view showing the appearance of load cell 200 concerning one embodiment of the present invention. 4 is a plan view showing the arrangement of elements of a bridge circuit 100A and a peripheral circuit 100AP used in the load cell 200. FIG. It is a circuit diagram showing the configuration of a bridge circuit 100A and a peripheral circuit 100AP. It is a circuit diagram which shows the structure of the span temperature compensation circuit which concerns on a modification. It is a circuit diagram which shows the structure of the conventional bridge circuit.

Explanation of symbols

  10, 10A ... Span temperature compensation circuit, 20 (20A, 20B) ... Zero balance adjustment circuit, 30 (30A, 30B) ... Zero point temperature compensation circuit, 40 ... Operational amplifier, 50 ... A / D converter, 100, 100A ... Bridge Circuit, 100P, 100AP ... Peripheral circuit, 101-105 ... Terminal, 200 ... Load cell, 300 ... Strain body, 400 ... Flexible substrate, G1-G4 ... Strain gauge, TH1, TH2a, TH2b ... Thermistor, R11-R14, R21a , R21b, R31a, R31b, R32a, R32b... Chip resistors.

Claims (4)

A strain body in which the amount of strain changes according to the load;
A span temperature compensation circuit for compensating the temperature characteristics of the strain amount of the strain generating body;
A predetermined voltage is supplied via the span temperature compensation circuit, and a bridge circuit that extracts a potential difference according to the strain amount of the strain generating body is provided.
The span temperature compensation circuit includes a thermistor and a resistor connected in parallel to the thermistor.
Load cell provided. A load cell including a strain generating body and a bridge circuit whose strain amount changes according to a load,
The bridge circuit is
A first terminal and a third terminal to which a predetermined voltage is applied;
A second terminal and a fourth terminal for extracting a potential difference according to the amount of strain;
The resistance value changes in accordance with the strain amount of the strain generating body, between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the second terminal. First to fourth strain gauges each provided between the four terminals and between the fourth terminal and the first terminal;
Between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal, A zero balance adjustment circuit provided with a chip resistor so that a potential difference taken out from the second terminal and the fourth terminal is zero when the load is zero at a predetermined temperature. And
Load cell provided. A load cell including a strain generating body and a bridge circuit whose strain amount changes according to a load,
The bridge circuit is
A first terminal and a third terminal to which a predetermined voltage is applied;
A second terminal and a fourth terminal for extracting a potential difference according to the amount of strain;
The resistance value changes in accordance with the strain amount of the strain generating body, between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the second terminal. First to fourth strain gauges each provided between the four terminals and between the fourth terminal and the first terminal;
Between the first terminal and the second terminal, between the second terminal and the third terminal, between the third terminal and the fourth terminal, and between the fourth terminal and the first terminal, The potential difference taken out from the second terminal and the fourth terminal is set to zero when the load is zero in a predetermined temperature range centered on the predetermined temperature. A zero point temperature compensation circuit with a thermistor to compensate for temperature characteristics,
Load cell provided. The load cell according to any one of claims 1 to 3,
A signal generator that generates a signal indicating mass based on a potential difference extracted from the bridge circuit;
Mass meter provided.

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