JP2010122140A - Load-cell-type weighing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology of effectively preventing dew condensation on a load cell without providing a separate heater around the load cell inside a load-cell-type weighing apparatus. <P>SOLUTION: Power is supplied through two paths to strain gauges 32a-32d of the load cell, including a first feed path for supplying electric power to an input terminal of a bridge circuit 30 constituted of the strain gauges 32a-32d and a second feed path for supplying electric power to the respective strain gauges so that the strain gauges 32a-32d are connected with one another in parallel. Feed path changeover switches 33a-33c are operated to select the first feed path during weighing by a desktop digital scale 10a and to select the second feed path as a dew condensation preventive mode in a standby state. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a load cell type weighing device using a load cell as a load converter for converting weight or the like into an electric signal, and more particularly to a load cell type weighing device that can be used in a high humidity environment.

  The load cell used in the load cell type weighing device is generally a strain gauge type load cell, and includes a strain generating body and a strain gauge attached to the strain generating body. The strain body has a movable part configured such that the weight of the object to be weighed is applied as a load. When the weight of the object to be weighed is applied to the movable part as a load, the movable part is displaced as seen from the fixed position of the strain generating body, and the displacement is detected by a strain gauge and converted into an electric signal.

  The load cell type weighing device is used for weighing various kinds of objects to be weighed. Among these, if the objects to be weighed are agricultural and fishery products, fresh foods, etc., these contain a lot of moisture, so that the environment for measurement becomes high humidity. In addition, agricultural and fishery products and fresh foods are relatively susceptible to spoilage compared to processed foods. Therefore, in the environment where these are handled, since high level food hygiene management is required, it is necessary to frequently wash and disinfect equipment and containers related to processing, transportation, and weighing. Of course, it goes without saying that even processed foods may have to be handled in the same manner as described above depending on the type and handling method.

  In this way, particularly when a load cell type weighing device is used for measuring agricultural and fishery products, fresh foods, etc., the load cell type weighing device is required to have waterproofness (or water resistance) that can cope with washing.

  However, even if it is waterproof, the required performance differs depending on the state of exposure to moisture. For example, Patent Document 1 discloses a technique related to a waterproof structure that can cope with cleaning in a combination weighing device using a load cell. In order to clean the combination weighing device from the viewpoint of hygiene or quality control, if the dispersion feeder is covered with a feeder cover and has a waterproof structure, heat is trapped in the waterproof cover and the load cell is adversely affected by the heat. . Therefore, in this technology, a ventilation duct having an intake port and an exhaust port is introduced and disposed in the waterproof portion of the distributed feeder portion that is waterproofed by the feeder cover, and ventilation that performs intake and exhaust from the ventilation duct into the waterproof portion. Means are provided outside the flow path of the object to be weighed. According to the document, the above configuration can prevent heat from being trapped in the waterproof portion.

  Similarly, Patent Document 2 discloses a technique for preventing water from entering a motor even if it is washed immediately after operation in a weighing device having a waterproof motor. In this technique, the waterproof cover of the motor unit and the housing are connected by ventilation with a ventilation pipe. According to this document, even if the motor unit is washed immediately after the apparatus is operated and the motor unit is rapidly cooled, the pressure change can be absorbed on the housing side through the ventilation pipe. It is said that it is possible to prevent inundation from a weakly waterproof portion.

  In addition to the waterproofing technology corresponding to the cleaning, a technology (condensation handling technology) that avoids the influence of condensation occurring in a high humidity environment has also been proposed. For example, Patent Document 3 is not a technique that targets only a load cell type weighing device, but has a configuration including a heater, a fan, and a dew condensation detector provided in a box of the electric device as a dew condensation prevention device for the electric device. It is disclosed. According to this document, for example, even if the heater is operated to prevent dew condensation when the humidity is 95% or higher, the heater operation time becomes longer, so that the effect of reducing power consumption is not obtained so much. . Therefore, in this technique, a heater and a fan are provided in the box, and both are controlled by a dew condensation detector disposed in the box to operate most efficiently, thereby reducing power consumption. In this document, a switchboard is cited as a specific electric device.

  Similarly, Patent Document 4 discloses a technique that targets audio tape recorders and video tape recorders, but discloses a condensation detection apparatus that can more suitably perform the condensation detection operation. This technology aims to solve the problem that if the power is shut off during the condensation detection state, the detection device will not enter the condensation detection state even if the power is turned on again. Even when the power is shut off, this state is stored by the storage means, and when the power is turned on again, the dew condensation detection state is forcibly set for a certain time.

  Patent Document 5 discloses a technique for dealing with condensation related to a weighing device. According to this document, if a force measuring device such as a weighing module is provided with a force measuring cell sealed by a housing, the inspection of the force measuring cell is very expensive and even impossible. . Therefore, parameters of the atmospheric state of the internal space that affect the operating life of the force measurement cell are measured by a sensor disposed in the internal space of the housing and / or a sensor disposed in the housing. For example, a humidity sensor is used as a sensor, and a humidity change in the internal space is detected as a parameter.

  By the way, in the load cell type measuring device, it is known that if the load cell which is a load converter is not in an appropriate state, the measuring accuracy is affected. For example, as disclosed in Patent Document 1, it is known that a load cell is adversely affected by heat. Patent Document 6 discloses the knowledge that weighing accuracy is sacrificed when the load cell resistance value is increased. Specifically, in this document, in a load cell type weighing instrument using a battery as a power source, the problem is that the battery is consumed relatively quickly. One possible countermeasure is a method of decreasing the current value by increasing the resistance value of the resistor or the load cell. However, this method discloses that the weighing accuracy is sacrificed. Therefore, in the technique disclosed in Patent Document 6, the standby power state and the normal power state are switched.

Furthermore, if moisture contacts the load cell or condensation occurs, the load cell may corrode. Such corrosion naturally has a great influence on the weighing accuracy. Thus, for example, Patent Document 7 and Patent Document 8 disclose a technique for coating the surface of a strain generating body constituting the main body of the load cell with a resin or the like to avoid corrosion of the strain generating body. In the technique disclosed in Patent Document 7, the strain-generating body is coated with urethane gel. In the technique disclosed in Patent Document 8, an electrical insulation including a coating layer made of a resin having a glass transition temperature of 40 ° C. or higher. The strain-generating body is covered with a film having properties.
Japanese Patent Laid-Open No. 06-317454 JP 2000-009522 A Japanese Utility Model Publication No. 63-045765 Japanese Patent Laid-Open No. 03-293545 JP 2007-139768 A Japanese Patent No. 2532639 JP 2001-343293 A JP 2002-365146 A

  In recent years, in general processing and production of foods including agricultural and fishery products and fresh foods, more advanced hygiene management is required than before. In view of this, various measures have been taken in load cell type weighing devices having waterproof properties to cope with advanced hygiene management. In particular, in order to enhance the convenience for washing, a stainless steel case is used as the exterior of the load cell type weighing device instead of the resin case. However, since stainless steel has higher thermal conductivity than resin, there is a problem that the inside of the load cell type measuring device is likely to condense.

  As mentioned above, at the site where agricultural and fishery products, fresh foods, etc. are weighed as objects to be weighed, it is set to a lower temperature than the outside air when the humidity is high and the objects to be weighed are likely to rot due to frequent washing. It is often done. Even in such an environment, if the exterior of the load cell type metering device is made of resin, the heat conductivity is low, so that a kind of heat insulating action is generated inside the load cell type metering device. Therefore, in the inside of the load cell type weighing device, normally, condensation is hardly generated inside. On the other hand, if the exterior is made of stainless steel, the exterior is easily cooled because of its high thermal conductivity, and therefore, condensation is likely to occur inside compared to a conventional resin. In particular, if condensation occurs in the load cell, the measurement accuracy is greatly reduced, so internal condensation is a phenomenon that should be avoided.

  Here, the techniques disclosed in Patent Documents 1 and 2 can improve the waterproofness of the load cell type weighing device, but cannot prevent the occurrence of internal condensation. On the other hand, the techniques disclosed in Patent Documents 3 to 5 are configured to include a dew condensation detector and a humidity sensor. In particular, the techniques disclosed in Patent Documents 3 and 4 use a heater to prevent condensation. It is disclosed. Therefore, in order to prevent the occurrence of condensation, it is assumed that a heater is provided inside the load cell type weighing device.

  However, as disclosed in Patent Document 1, it is known that the load cell is adversely affected by heat, and generally, as the temperature rises, the resistance value also increases. Therefore, as disclosed in Patent Document 6, The weighing accuracy of the load cell also decreases. Therefore, it is not realistic to provide a heater near the load cell.

  It is assumed that a heater can be provided in the vicinity of the load cell. Here, since the heater is required to have an output capable of sufficiently warming the inside of the load cell type weighing device to the extent that condensation can be prevented, a large amount of electric power is required to operate the heater. As the power source of the load cell type weighing device, an AC power source and / or a battery can be adopted depending on the type, but if the power source is a battery, the battery is quickly consumed when the heater is operated.

  In addition, the load cell type weighing device having a configuration in which the power source is an AC power source and the weighing unit and the display operation unit are integrated with each other, a configuration that generates heat such as a display panel or a CPU is accommodated around the load cell, Further, since the volume becomes relatively large, it is easy to secure a space around the load cell. Therefore, even if the exterior is made of stainless steel, the surroundings of the load cell are not easily cooled and condensation is not easily generated without providing a separate heater. On the other hand, for example, if the load cell type weighing device is a desktop type or a separate type in which the weighing unit and the display / operation unit are separated, the outer casing is relatively small and the volume is small. If it is made of stainless steel, it is easy to cool and condensation is likely to occur. In addition, if the size is small, it is difficult to secure a space in which the heater is provided around the load cell. In addition, if the power source is a battery, sufficient power for operating the heater cannot be secured.

  Furthermore, even if the surface of the strain generating body is coated, the condensation of the load cell cannot be sufficiently prevented. In general, a silicone resin is often used in coating applications. However, a silicone resin film exhibits a strong water repellency, but also has a high moisture permeability, so that the effect of preventing condensation is insufficient. Further, in the techniques disclosed in Patent Documents 7 and 8, since the strain generating body is covered with urethane gel or a special coating, the strain generating body can be prevented from being corroded, but attached to the strain generating body. It does not lead to corrosion prevention of the strain gauge that is used. When the strain gauge corrodes, resistance change occurs, so that the weight detection accuracy is greatly reduced. Moreover, the corrosion that occurs in the strain gauge causes a resistance change even at a slight level that is difficult to understand with the naked eye. Therefore, even if the strain generating body is coated, the effect of preventing condensation cannot be sufficiently obtained for the entire load cell.

  The present invention has been made to solve the above-described problem, and can effectively avoid the occurrence of dew condensation in the load cell without providing a separate heater in the vicinity of the load cell in the load cell type weighing device. The purpose is to provide.

  As a result of intensive studies in view of the above problems, the present inventor has clearly switched the load cell between a weighing state and a standby state, and in the standby state, the load cell is given a voltage different from the weighing state, It was found that it was possible to effectively avoid the occurrence of dew condensation in the load cell even if it was operated as a heater and no additional heater was provided, and the present invention was completed.

  That is, in order to solve the above-described problem, the load cell type weighing device according to the present invention includes a strain generating body having a movable part that generates a displacement by applying the weight of an object to be weighed as a load, and the strain generating body. A load cell that includes at least a plurality of strain gauges that detect the displacement, and in which the plurality of strain gauges form a bridge circuit, and a power supply path switch that switches a plurality of power supply paths to the load cell The power supply path switching device is connected to each strain gauge so that the plurality of strain gauges are connected in parallel to each other, or a first power supply path that supplies power to the input terminal of the bridge circuit. It is configured to select and switch one of the second power supply paths for supplying power.

  According to the above configuration, if the first power supply path is selected, each strain gauge functions as a bridge circuit, so that the weight of the object to be weighed is output as an electrical signal, while if the second power supply path is selected, Since the power supply voltage is directly applied to each strain gauge, it functions as a heater. In this case, since the load cell itself generates heat, a large dew condensation prevention effect can be obtained with a smaller amount of heat generation than when a separate heater is provided to heat the load cell. Therefore, even if the load cell type weighing device is installed in an environment where condensation is likely to occur, condensation of the load cell, particularly condensation of the strain gauge can be effectively prevented.

  The load cell type weighing device further includes a weight calculator that is connected to an output terminal of the bridge circuit and calculates the weight of the object to be weighed from an output signal of the bridge circuit. It is preferable that the connection between each strain gauge and the weight calculator is further cut off when the second power feeding path is selected.

  The load cell type weighing device further includes a switching driver that drives the power supply path switching device, a humidity detector that detects humidity around the load cell, and a controller, and the controller includes the humidity When the humidity value detected from the detector exceeds a preset upper limit value and the displacement is not detected from the plurality of strain gauges, the power supply path switching unit selects the second power supply path. The switching driver is preferably configured to operate.

  Further, when the displacement is detected from at least one of the plurality of strain gauges in a state where the power supply path switch selects the second power supply path, the controller is configured to supply the power supply path. More preferably, the switching driver is configured to operate so that the switching device selects the first power feeding path. Alternatively, the load cell type weighing device further includes a notification device for notifying a user, and when the humidity value detected from the humidity detector exceeds a preset upper limit value, the controller More preferably, the alarm is operated.

  According to the said structure, since switching from a 1st electric power feeding path | route to a 2nd electric power feeding path | route is performed by a controller, a load cell type | mold weighing device can perform the operation | movement of a dew condensation prevention by automatic control. Moreover, if it is configured to notify the user of the switching of the power feeding path, the user can clearly determine whether or not the load cell type weighing device is in a dew condensation prevention state.

  More preferably, the load cell type weighing device further includes a switching drive operating device that operates the switching drive by an operation by a user. As a result, the load cell type weighing device can be made to perform dew condensation prevention operation at the user's discretion.

  In the load cell type weighing device, if the exterior is made of stainless steel, it has excellent cleaning properties and hygiene, and can also exhibit an effective anti-condensation effect. It can be used suitably.

  In the load cell type weighing device, the power source for supplying the power is not particularly limited, but a battery can be preferably used. As described above, according to the present invention, since the load cell itself generates heat, a large condensation prevention effect can be obtained with a smaller heat generation amount. However, the small heat generation amount requires less power consumption. Therefore, a battery can be suitably used as a power source.

  As described above, the present invention has an effect that it is possible to effectively avoid the occurrence of condensation on the load cell without providing a separate heater in the vicinity of the load cell inside the load cell type weighing device.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, the same or corresponding elements are denoted by the same reference symbols throughout the drawings, and redundant description thereof is omitted.

(Embodiment 1)
[Basic configuration of desktop digital scale]
In the present embodiment, a preferred embodiment of the present invention will be described by taking a desktop digital balance as a representative example of the load cell type weighing device according to the present invention. FIG. 1 is a cross-sectional view showing a configuration of a desktop digital balance 10a according to the present embodiment, and FIG. 2 is a schematic diagram showing a configuration of a load cell 30 provided in the desktop digital balance 10a shown in FIG.

  As shown in FIG. 1, a desktop digital balance 10a according to the present embodiment includes a weighing pan 11, a tray tray 12, a stainless steel case 13, a battery box 14, a bottom lid 15, legs 16a and 16b, a control board 20, An operation input unit 21, a display unit 22, a load cell 30, a humidity sensor 41, and a battery 42 are provided.

  The weighing pan 11 is provided above the desktop digital balance 10a so as to be stacked on the tray holder 12, and places an object to be weighed on the upper surface thereof. In the tray receiver 12, the upper side is a flat surface that receives the weighing pan 11, and the lower side is in contact with the strain body of the load cell 30. Since the weighing pan 11 is provided on the flat surface of the tray receiver 12, the weight of the object to be weighed placed on the weighing pan 11 is added to the strain body of the load cell 30 as a load. The stainless steel case 13 is an exterior of the desktop digital balance 10a and becomes the main body of the desktop digital balance 10a. Inside the stainless steel case 13, a battery box 14, a control board 20, a load cell 30, a humidity sensor 41, and the like are provided. The battery box 14 is provided so as to form an opening below the desktop digital balance 10a, and accommodates the battery 42 therein. The battery box 14 includes an electrode (not shown), and the electrode is connected to a power supply terminal (not shown) of the control board 20 via a wiring (not shown). The bottom lid 15 closes the opening of the battery box 14 on the bottom side of the desktop digital balance 10a. For example, a total of four legs 16a are provided below the desktop digital balance 10a, and all of them can adjust the horizontal position of the desktop digital balance 10a.

  The control board 20 is provided on the front side of the desktop digital balance 10 a in the stainless steel case 13. In front of this, an operation input unit 21 and a display unit 22 are provided, and the control board 20 is located on the back side thereof. The operation input unit 21 and the display unit 22 are provided on the operation display surface 13a which is a single surface inclined upward in front of the desktop digital balance 10a. The operation input unit 21 includes a plurality of keys, switches, and the like (not shown), and inputs operation commands, setting conditions, and the like of the desktop digital balance 10a to the calculator of the control board 20 by operating these keys and switches. The display unit 22 is composed of, for example, a liquid crystal display panel, and is configured to display at least the weight of the object to be weighed under the control of the arithmetic unit of the control board 20. In addition, it may be configured to display operation details and setting condition details. Moreover, the operation input part 21 and the display part 22 may be collectively comprised as one touch panel. The control board 20 will be specifically described together with the control system of the desktop digital balance 10a.

  As shown in FIG. 2, the load cell 30 includes a strain generating body 31 and four strain gauges 32a, 32b, 32c, and 32d. The strain generating body 31 has a movable rigid body portion 311 at one end and a fixed rigid body portion 312 at the other end. The movable rigid body portion 311 and the fixed rigid body portion 312 are two upper and lower beam portions 313 and 314. It is connected with. The strain body 31 is made of, for example, nickel chrome molybdenum steel, stainless steel, aluminum alloy, or the like.

  In the beam portion 313 of the strain generating body 31, a strain measuring portion 315a formed so that the thickness is reduced on the movable rigid portion 311 side and a strain measuring portion formed so that the thickness is reduced on the fixed rigid portion 312 side. 315b is formed. Similarly, the beam portion 314 includes a strain measurement unit 315c formed so that the thickness is reduced on the movable rigid body portion 311 side and a strain measurement unit 315d formed so that the thickness is reduced on the fixed rigid body portion 312 side. Is formed. Strain gauges 32a, 32b, 32c, and 32d are attached to the strain measuring units 315a, 315b, 315c, and 315d, respectively. As will be described later, these four strain gauges 32a, 32b, 32c, and 32d are electrically connected to each other so as to form a Wheatstone bridge, and are added to the movable rigid portion 311 as indicated by arrows in FIG. The degree (displacement) of the strain generated in the strain generating body 31 due to the load is detected as a change in the electric resistance value.

  The humidity sensor 41 is provided in the vicinity of the load cell 30, detects the humidity in the vicinity of the load cell 30, and outputs the detected humidity to a CPU described later. In the present embodiment, as shown in FIG. 1, two pieces are provided so as to be close to the movable rigid body portion 311 and the fixed rigid body portion 312 which are both ends of the strain body 31 (in FIG. 31, reference numerals of the movable rigid body portion 311 and the fixed rigid body portion 312 are not shown). As the humidity sensor 41, for example, an electrical humidity sensor such as a resistance change type humidity sensor or a capacitance change type humidity sensor can be used.

  The battery 42 is a driving power source for the desktop digital balance 10a, and supplies power to the control board 20 through the electrodes, wiring, power supply terminals, and the like as described above while being housed in the battery box 14. As the battery 42, a dry battery or various secondary batteries compatible with the dry battery can be used. Of course, a battery other than the dry battery may be used.

[Control configuration and weighing operation of desktop digital scale]
Next, the control configuration and weighing operation of the desktop digital balance 10a according to the present embodiment will be described with reference to FIG. FIG. 3 is a diagram showing a control system of the desktop digital balance 10a shown in FIG.

  As shown in FIG. 3, the desktop digital balance 10a according to the present embodiment includes a CPU 23 as a controller, an A / D converter 24, a power feeding path switching drive unit 25, power feeding path switching switches 33a, 33b, and 33c, and amplification. A circuit 34 is further provided. The CPU 23 is connected to the operation input unit 21 and the display unit 22, and is connected to the A / D converter 24, the power feeding path switching drive unit 25, and the humidity sensor 41. In addition, an amplifier circuit 34 is connected to the A / D converter 24, and the load cell 30 is connected to the amplifier circuit 34 via power supply path switching switches 33a, 33b, and 33c. Further, a battery 42 is connected to the load cell 30 via a constant voltage circuit 43. The positive electrode of the battery 42 is connected to the constant voltage circuit 43, the negative electrode is grounded, and the constant voltage circuit 43 is also grounded. In the present embodiment, the CPU 23, the A / D converter 24, the power supply path switching drive unit 25, and the amplifier circuit 34 are mounted on the control board 20.

  The CPU 23 receives an operation command and input information from the operation input unit 21, a detected value of the weight of the object to be measured from the A / D converter 24, a detected value of the humidity in the vicinity of the load cell 30 from the humidity sensor 41, and the like. The display unit 22 is configured to display a weight value, operation setting information, or the like, or to operate the power supply path switching drive unit 25 as described later.

  In FIG. 3, the load cell 30 is shown as a Wheatstone bridge circuit composed of four strain gauges 32a, 32b, 32c and 32d shown as resistors. That is, in the load cell 30, the four strain gauges 32a, 32b, 32c, and 32d that detect the strain of the strain generating body 31 form a Wheatstone bridge. In the following description, the load cell 30 is expressed as a “bridge circuit 30” only for the description of the circuit configuration.

  In the bridge circuit 30, a strain gauge 32 a and a strain gauge 32 b are connected in series, and a positive electrode of the battery 42 is connected between these via a power supply path changeover switch 33 a. Further, the strain gauge 32c and the strain gauge 32d are connected in series, and the negative electrode of the battery 42 is connected between them. As described above, one end of the strain gauge 32a is connected to the strain gauge 32b, but the other end is connected to the strain gauge 32c, and the strain gauge 32a and the strain gauge 32c are connected via a power supply path switching switch 33c. The amplifier circuit 34 is connected. Similarly, one end of the strain gauge 32b is connected to the strain gauge 32a, but the other end is connected to the strain gauge 32d, and the strain gauge 32b and the strain gauge 32d are connected via a power supply path switching switch 33b. An amplifier circuit 34 is connected.

For convenience of explanation, in the bridge circuit 30, the strain gauge 32a and the strain gauge 32b point to a connection point to be connected to the feeding path switching switch 33a between (node) P _11, between the strain gauge 32b and strain gauges 32d the connection points for the feeding path switching switch 33b and points (nodes) P ₁₂ in a strain gauge 32a and the strain gauge 32c point to a connection point to be connected to the feeding path switching switch 33c between the (node) P ₁₃ To do. Further, between the strain gauge 32c and strain gauge 32d, point to connection point which is connected to the wiring from the cathode of the battery 42 (node) and P _14. These points P _{11 to} P ₁₄ correspond to input terminals or output terminals of the bridge circuit 30 as described later.

In this embodiment, the amplifier circuit 34 includes at least two operational amplifiers 34a and 34b and three resistors 34c, 34d, and 34e. One input terminal of the operational amplifier 34a via the feeding path switching switch 33b, is connected to the point P ₁₂ of the bridge circuit 30, the output terminal of the operational amplifier 34a is connected to the A / D converter 24, and the branch And connected to the other input terminal via a resistor 34c. Similarly, one input terminal of the operational amplifier 34b via a feed path switching switch 33c, is connected to the point P ₁₃ of the bridge circuit 30, the output terminal of the operational amplifier is connected to the A / D converter 24, It branches and is connected to the other input terminal via a resistor 34d. As described above, the operational amplifiers 34 a and 34 b feed back and amplify the outputs via the resistors 34 c and 34 d, respectively, and output them to the A / D converter 24.

  A resistor 34e is connected between the resistor 34c and the other input terminal of the operational amplifier 34a, and between the resistor 34d and the other input terminal of the operational amplifier 34b. That is, when viewed from the operational amplifier 34a, the resistor 34c and the resistor 34e constitute a voltage dividing circuit of the feedback path of the operational amplifier 34a. From the viewpoint of the operational amplifier 34b, the resistor 34d and the resistor 34e are divided by the feedback path of the operational amplifier 34b. The pressure circuit is configured.

  As will be described later, the power supply path switching switches 33a, 33b, and 33c switch the power supply paths to the strain gauges 32a, 32b, 32c, and 32d that form the bridge circuit 30 according to the state of the desktop digital balance 10a. As the power supply path switching switches 33a, 33b, and 33c, electromagnetic relay switches, semiconductor relay switches, bipolar transistors, MOSFETs, and the like can be used.

  Next, the weighing operation of the desktop digital balance 10a having the above configuration will be described. First, when an object to be weighed is placed on the weighing pan 11 shown in FIG. 1, a load is applied to the load cell 30 via the tray receiver 12. In the load cell 30, as shown in FIG. 2, the weight of the object to be weighed is added as a load to the movable rigid body portion 311 of the strain generating body 31 (arrow in the figure). As a result, strain is generated in the strain generating body 31, and the degree (displacement) of this strain is detected by the four strain gauges 32a, 32b, 32c, and 32d. That is, according to the displacement of the strain generating body 31, the resistance values of the four strain gauges 32a, 32b, 32c, and 32d slightly change.

Here, strain gauges 32a, 32b, 32c, 32d forms a bridge circuit 30 as shown in FIG. 3, between the points P ₁₁ and P ₁₄ of the bridge circuit 30, a DC voltage is applied from the battery 42 It has been. Here, the points P ₁₁ and P ₁₄ correspond to the input terminals of the bridge circuit 30, and the points P ₁₂ and P ₁₃ correspond to the output terminals of the bridge circuit 30. Thus, the bridge circuit 30, an output signal corresponding to the weight value of the objects to be weighed result from the potential difference between the points P ₁₂ and P _13. This output signal is amplified by the amplifier circuit 34, digitally converted by the A / D converter 24, and output to the CPU 23. The CPU 23 calculates the weight of the object to be detected by calculation from the output signal, and causes the display unit 22 to display the weight value.

[Switching power supply path]
In the present embodiment, the power feeding path to the bridge circuit 30 (the strain gauges 32a, 32b, 32c, 32d of the load cell 30) is configured to be switched to two different power feeding paths by the power feeding path changeover switches 33a, 33b, 33c. ing. The switching of the power supply path will be described with reference to FIGS. 3 and 4A and 4B. FIG. 4A is a circuit diagram schematically showing a power supply path to the bridge circuit 30 when the table-type digital balance 10a having the circuit configuration shown in FIG. FIG. 4B is a circuit diagram schematically showing a power feeding path to the bridge circuit 30 when in a standby state. 4A and 4B, the battery 42 is assumed to be connected to the bridge circuit 30 without passing through the constant voltage circuit 43, and the circuit configuration is shown.

In the present embodiment, as shown in FIG. 3, the battery 42 and the bridge circuit 30 switch the positive pole of the battery 42 to points P ₁₂ and P ₁₃ of the bridge circuit 30 by switching the power supply path switching switches 33 b and 33 c. Are configured so that the negative pole of the battery 42 can also be connected to the point P ₁₁ of the bridge circuit 30 by switching the power feeding path selector switch 33a.

The power supply path switching switch 33a has a movable contact Ca0, a first fixed contact Ca1, and a second fixed contact Ca2. The movable contact Ca0 can be switched so as to contact either the first fixed contact Ca1 or the second fixed contact Ca2. Movable contact Ca0 is connected to the point P ₁₁ of the bridge circuit 30, a first fixed contact Ca1 is connected to the positive pole of the battery 42, the second fixed contact Ca2 the battery 42 - are connected to the poles.

Similarly, the power supply path switching switch 33b has a switchable movable contact Cb0, a first fixed contact Cb1, and a second fixed contact Cb2. Movable contact Cb0 is connected to the point P ₁₂ of the bridge circuit 30, a first fixed contact Cb1 is connected to one input terminal of the operational amplifier 34a which constitutes the amplifying circuit 34, the second fixed contact Cb2 is the battery 42 Connected to the + pole.

The power supply path switching switch 33c also includes a switchable movable contact Cc0, a first fixed contact Cc1, and a second fixed contact Cc2. Movable contact Cc0 is connected to the point P ₁₃ of the bridge circuit 30, a first fixed contact Cc1 is connected to one input terminal of the operational amplifier 34b constituting the amplifying circuit 34, the second fixed contact Cc2 is the battery 42 Connected to the + pole.

In the above-described configuration, the positive pole of the battery 42 includes the first fixed contact Ca1 of the power supply path switch 33a, the second fixed contact Cb2 of the power supply path switch 33b, and the second fixed contact Cc2 of the power supply path switch 33c. It is connected. Therefore, in the present embodiment, for convenience of explanation, as shown in FIG. 3, the connection from the + pole of the battery 42 to the power supply path switching switch 33a, and the connection from the same + pole to the power supply path switching switches 33b and 33c, The branch point is a branch point P _01, and the branch point between the connection from the same + pole to the power supply path switch 33 b and the connection to the power supply path switch 33 c is a branch point P ₀₂ .

Similarly, the battery 42 - the electrode, a second fixed contact Ca2 feeding path switching switch 33a, the point P ₁₄ of the bridge circuit 30 is connected. Therefore, in this embodiment, for convenience of explanation, from the feeding path switching switch 33a battery 42 - connection to poles, from the point P ₁₄ the same - the confluence of the connection to the pole, the merging point P ₀₃ .

The desktop digital balance 10a according to the present embodiment is in a state in which a weighing operation can be performed in a normal state. Therefore, the movable contact Ca0 of the power supply path switching switch 33a contacts the first fixed contact Ca1, the movable contact Cb0 of the power supply path switching switch 33b contacts the first fixed contact Cb1, and the movable contact Cc0 of the power supply path switching switch 33c is It contacts the first fixed contact Cc1. In this state, in the circuit configuration shown in FIG. 3, all of the movable contacts Ca0, Cb0, and Cc0 are in a connected state indicated by a solid line in the drawing. More specifically, as shown in FIG. 4A, a DC power source (battery 42) is connected to the point P ₁₁ (and point P ₁₄ ) of the bridge circuit 30, and the point P _{12 of the} bridge circuit 30 and the point P _13, so that the amplifier circuit 34 is connected. In FIGS. 4A and 4B, the power supply path switching switches 33a, 33b, and 33c are simplified as rectangular symbols.

Thus, tabletop digital scale 10a is if the normal state, the feeding path switching switch 33a~33c as a power supply path, supplying power to the point P ₁₁ and point P ₁₄ corresponds to the input terminal of the bridge circuit 30 Select the route to be closed. This power supply path is defined as a first power supply path. When the first power supply path is selected, the strain gauges 32a to 32d form the bridge circuit 30. Therefore, the bridge circuit 30, that is, the load cell 30, converts the load into an electrical signal and outputs it to the CPU 23. Function as.

  On the other hand, in the present embodiment, the power feeding path to the strain gauges 32a to 32d can be switched from the first power feeding path to the second power feeding path by switching the power feeding path switching switches 33a, 33b, and 33c. Specifically, in the power supply path switching switch 33a, the movable contact Ca0 is switched from the first fixed contact Ca1 to contact the second fixed contact Ca2, and in the power supply path switching switch 33b, the movable contact Cb0 is switched to the first fixed contact Cb1. From the first fixed contact Cc1 to the second fixed contact Cc2. In the power supply path switching switch 33c, the movable contact Cc0 is switched from the first fixed contact Cc1 to the second fixed contact Cc2. In this state, in the circuit configuration shown in FIG. 3, all of the movable contacts Ca0, Cb0, and Cc0 are in a connected state indicated by broken lines in the drawing.

Therefore, as shown in FIG. 4B, voltages are applied to the strain gauges 32a, 32b, 32c, and 32d forming the bridge circuit 30 so as to be in parallel with each other. Specifically, via the P ₀₂ from the branch point P _01, + electrode of the battery 42, the strain gauges 32b, is connected to a point P ₁₂ is the midpoint of 32d, the strain gauge 32c, 32a midpoint it is connected to a point P ₁₃ is. On the other hand, strain gauge 32d, 32c, the battery 42 via the confluence point P ₀₃ from the point P ₁₄ - are connected to the poles. Similarly, the strain gauges 32 b, 32a, through the confluence point P ₀₃ from the point P ₁₁ Connected to the same pole.

  As described above, when the desktop digital balance 10a is in the standby state, the power supply path changeover switches 33a to 33c provide power to the strain gauges 32a to 32d so that the strain gauges 32a to 32d are connected in parallel as power supply paths. Select the route that supplies the current and close it. This power feeding path is defined as the second power feeding path.

  Before switching the power feeding path changeover switches 33a to 33c, that is, when the first power feeding path is closed, a voltage value of ½ of the power supply voltage is applied to each strain gauge 32a to 32d. On the other hand, if the power feeding path selector switches 33a to 33c are switched so that the second power feeding path is closed, the power supply voltage is applied to the strain gauges 32a to 32d as they are. Therefore, the parallel circuit formed by the four strain gauges 32a to 32d functions as a heater that generates heat due to its resistance. As a result, the load cell 30 itself can generate heat, so even if the desktop digital balance 10a is installed in an environment where condensation is likely to occur, condensation on the load cell 30 (especially condensation on the strain gauges 32a to 32d) is effectively prevented. can do.

  Note that when the second power feeding path is closed, an operation for preventing condensation is performed instead of performing the weighing operation. Therefore, in the present embodiment, the state in which the second power feeding path is closed is set as a dew condensation prevention mode.

  Further, when the second power supply path is selected as the power supply path, the connection to the amplifier circuit 34 is cut off by the power supply path changeover switches 33b and 33c. As described above, the amplifier circuit 34 is connected to the CPU 23 via the A / D converter 24. The CPU 23 is a controller of the desktop digital balance 10a, and at the same time, the output signal of the load cell 30 is used to determine the object to be weighed. It is also a weight calculator that calculates the weight. Therefore, when the desktop digital balance 10a is in the dew condensation prevention mode, the connection between the strain gauges 32a to 32d and the CPU 23 is cut off. Since a large voltage value is output from the strain gauges 32a to 32d functioning as heaters, an overvoltage is not applied to the CPU 23 by blocking the output path to the CPU 23. Therefore, the desktop digital balance 10a in the dew condensation prevention mode is also configured to avoid the occurrence of failures and abnormalities in the controller and the weight calculator.

  Further, in the present embodiment, the power supply path switching drive unit 25 is operated so as to automatically switch the power supply path switching switches 33a to 33c under the control of the CPU 23 according to the humidity value detected from the humidity sensor 41. As shown in FIG. 3, the power feeding path changeover switches 33a to 33c are driven by the power feeding path switching drive unit 25 to switch the movable contacts Ca0, Cb0, Cc0 to either the first power feeding path or the second power feeding path. Select to close the circuit. As the power feeding path switching drive unit 25, a driving circuit having a configuration corresponding to the type of the power feeding path switching switches 33a to 33c is used.

  For example, based on the specific configuration of the desktop digital balance 10a and the load cell 30, or the installation conditions of the desktop digital balance 10a, an upper limit value of allowable humidity is set in advance, and this upper limit value is stored in the internal memory of the CPU 23, It is stored in a storage device (not shown). When the humidity value detected from the humidity sensor 41 exceeds the upper limit value, the CPU 23 confirms that the desktop digital balance 10a is not in the weighing operation, and switches the power supply path selector switches 33a to 33c to What is necessary is just to select and close a 2 electric power feeding path.

  In addition, when the CPU 23 determines that the desktop digital balance 10a has entered the weighing operation with the second power supply path closed, the CPU 23 switches the power supply path switching switches 33a to 33c to the first power supply path. The power supply path switching drive unit 25 may be configured to operate.

  The determination as to whether or not the desktop digital balance 10a has entered the weighing operation may be based on whether or not a signal is output from the load cell 30. If no displacement is detected by the strain gauges 32a to 32d, since the load is not applied to the load cell 30, it is not in the weighing state and can be determined as the standby state. On the other hand, if a displacement is detected from the strain gauges 32a to 32d, an output signal is output from the load cell 30, so it can be determined that the weighing operation has been started.

[Desktop digital scale exterior and power supply]
The desktop digital balance 10a according to the present embodiment can be used particularly effectively in an environment with a lot of moisture and moisture, but in particular, it is used for measurement in the field of processing and manufacturing food including agricultural and fishery products and fresh food. It can be used suitably. Here, in the desktop digital balance 10a, the exterior may be made of various resins, but the stainless steel case 13 is particularly preferable.

  For example, when measuring marine products, particularly crabs and octopus, mucus tends to adhere to the measuring device. Since the main component of this mucus is protein, it has high affinity with various resins. Therefore, if the exterior of the metering device is a resin case, if this mucus adheres to the surface of the resin case, it is difficult to remove the mucus with a general cleaning method. Further, if the surface of the exterior is rubbed with a hard cleaning tool such as scrubbing to remove mucus, the surface is easily scratched. Therefore, from the viewpoint of cleanability and hygiene, a stainless steel case 13 is preferably used as the exterior.

  However, since the stainless steel case 13 has a high thermal conductivity, the entire desktop digital balance 10a is easily cooled and the inside is likely to condense. In particular, the desktop digital balance 10a may need to be washed with water from the viewpoint of hygiene, and therefore, the inside is more likely to condense.

  On the other hand, in this embodiment, since the desktop digital balance 10a can be in the dew condensation prevention mode, power is supplied to the strain gauges 32a to 32d through the second power supply path by the power supply path changeover switches 33a to 33c. As a result, the strain gauges 32a to 32d constituting the load cell 30 generate heat. Although this heat generation amount is not so large, the member itself that should prevent condensation is heated, so that a large condensation prevention effect can be obtained with a smaller heat generation amount than when the load cell 30 is heated by providing a separate heater.

  In addition, since the amount of heat generated is small, the power consumption can be small, so that the battery 42 can be suitably used as a power source. That is, when the load cell 30 is heated by providing a separate heater, a large amount of power is consumed for the operation of the heater. Therefore, if the battery is used as a power source, the battery is quickly consumed. In addition, since the weighing device whose power source is a battery is often small and the component parts themselves generate little heat, it is particularly easy to cool compared to a weighing device that is large and uses an AC power source. On the other hand, according to the present embodiment, it is not necessary to provide a heater, and sufficient condensation prevention effect can be obtained with low power consumption.

[Modification]
The specific configuration of the desktop digital balance 10a according to the present embodiment is not limited to the above configuration. For example, in addition to the above configuration, a known heater, a dehumidifier, a convection fan, and the like are separately provided to further enhance the dew condensation prevention effect of the load cell 30. An example of the heater is a small lamp. Examples of the dehumidifier include a small dehumidifier using a Peltier element used for a CPU or the like. This small dehumidifier is provided at a position away from the object to prevent condensation (in this embodiment, the load cell 30), and cools the inside of the space to be dehumidified (in this embodiment, inside the stainless steel case 13) to provide moisture. Dehumidify by forcing condensation. Examples of the convection fan include a small fan used in an air cooling device for a CPU. Thereby, the dew condensation prevention effect can be enhanced by circulating the air inside the stainless steel case 13.

  In the present embodiment, the CPU 23 detects the humidity in the vicinity of the load cell 30 with the humidity sensor 41 and determines whether or not to enter the dew condensation prevention mode. However, the present invention is not limited to this. Instead of the humidity sensor 41, a dew condensation sensor that detects that dew condensation has occurred on the surface of the load cell 30 may be used. Examples of the dew condensation sensor include a thin film type sensor that measures the electrical conductivity of the surface.

  Further, the heater, the dehumidifier, and the convection fan may be configured to be controlled by the CPU 23 based on the humidity value detected from the humidity sensor 41, similarly to the heat generation of the load cell 30. Similarly to the above, when the humidity becomes a certain level or higher, the heater, the dehumidifier, or the convection fan may be operated while switching from the first power feeding path to the second power feeding path.

  In the present embodiment, a known coating process may be applied to the strain body 31. That is, in the dew condensation prevention mode, the strain gauges 32a to 32d are heated to prevent dew condensation on the load cell 30, so that the condensation of the strain gauges 32a to 32d can be more effectively prevented. By subjecting the body 31 to a coating treatment, the effect of preventing condensation on the strain generating body 31 can be further improved.

(Embodiment 2)
In the first embodiment, the basic configuration in which the desktop digital balance 10a switches the normal operation mode to the dew condensation prevention mode and generates heat in the load cell 30 under the control of the CPU 23 has been described. However, in this embodiment, it is more preferable. With reference to FIG. 5, a desktop digital scale that can be appropriately selected to switch to the dew condensation prevention mode by an operator's operation will be described. FIG. 5 is a diagram showing a control system and a circuit configuration of the main part of the desktop digital balance 10b according to the present embodiment.

  Specifically, the desktop digital balance 10b according to the present embodiment has the same configuration as that described in the first embodiment, but as shown in FIG. 26 is provided. According to this configuration, when the operator operates the dew condensation prevention mode key 26, the CPU 23 operates the power supply path switching drive unit 25 regardless of the humidity value from the humidity sensor 41. The power feeding path switching drive unit 25 drives the power feeding path switching switches 33a to 33c, and the power feeding path switching switches 33a to 33c select and close the second power feeding path.

  According to the present embodiment, for example, if the desktop digital balance 10b is used in an environment where condensation is particularly likely to occur, the condensation is determined by the operator in addition to the automatic control by the CPU 23 described in the first embodiment. Since it can switch to prevention mode, the effect of prevention of dew condensation can be heightened more.

  In the present embodiment, the dew condensation prevention mode key 26 is included in the operation input unit 21, but the present invention is not limited to this. For example, a dew condensation prevention mode operation switch independent of the operation input unit 21 may be provided, or various keys and switches included in the operation input unit 21 may be provided in a predetermined method and order without providing a separate key or switch. It may be configured to operate a dew condensation prevention mode by operating.

  Furthermore, in the present embodiment, as shown in FIG. 5, it is more preferable to include a notification lamp 27 and a buzzer 28 that notify the operator that the detection result of the humidity sensor 41 has exceeded the allowable humidity range. preferable. According to this configuration, when the humidity value detected from the humidity sensor 41 exceeds the upper limit value, the CPU 23 lights the notification lamp 27 and generates a warning sound from the buzzer 28. Thus, the operator can determine the timing for operating the dew condensation prevention mode manually by operating the dew condensation prevention mode key 26.

  In addition, the specific structure of the notification lamp 27 and the buzzer 28 is not specifically limited, A well-known thing can be used suitably. Moreover, in this Embodiment, although it becomes the structure provided with two types of alerting devices, the alerting lamp 27 and the buzzer 28, it is not limited to this, Either may be sufficient and alerting | reporting different from these may be sufficient It may be a vessel. For example, it may be configured to emit a message such as “humidity is high” by voice, or a warning message or warning image may be displayed on the display screen of the display unit 22 without providing the notification lamp 27 or the buzzer 28. It may be configured to display.

(Embodiment 3)
In the first and second embodiments, the desktop digital balance 10a or 10b using the battery 42 as the power source has been described. However, the present invention is not limited to this, and with reference to FIGS. 6, 7 and 8, The present invention can be applied to other various load cell type weighing devices. FIG. 6 is a diagram showing a control system and a circuit configuration of a main part of the desktop digital balance 10c according to the present embodiment. FIG. 7 is a schematic diagram showing an external configuration of a separate digital balance 50 according to the present embodiment. FIG. 8 is a schematic diagram showing an external configuration of the desktop combination weigher 60 according to the present embodiment.

For example, the power source of the desktop digital balance 10c may be an AC power source instead of a DC power source such as a battery. In this case, as shown in FIG. 6, the desktop digital balance 10 c includes a power supply circuit 44 instead of the battery 42. Then, if the first feed path is selected, the branch point P ₀₁ from the power supply circuit 44 is fed to a point P ₁₁ of the bridge circuit 30 through the feeding path switching switch 33a (the movable contact in FIG Ca0, Cb0, Connection state in which Cc0 is indicated by a solid line). On the other hand, as long switched to a second power supply path, by switching the feeding path switching switch 33a, the point P ₁₁ of the bridge circuit 30 is grounded, the feeding path switching switch 33b, by switching the 33c, it is connected to the amplifier circuit 34 blocking In addition, power is supplied from the power supply circuit 44 to the points P ₁₂ and P ₁₃ of the bridge circuit 30 via the branch points P ₀₁ and P ₀₂ (the connection state in which the movable contacts Ca0, Cb0, and Cc0 are indicated by broken lines in the drawing) ). In the configuration shown in FIG. 6, since the point P ₁₄ of the bridge circuit 30 is grounded, the connection point corresponding to the merging point P ₁₃ is absent.

  As another load cell type weighing device to which the present invention can be applied, for example, as shown in FIG. 7, there is a separate digital balance 50 in which an operation setting display unit 51 and a weighing unit 52 are separated. In this configuration, the load cell 30 and the like are provided in the weighing unit 52, and the operation setting display unit 51 is provided with the operation input unit 21, the display unit 22, the CPU 23, and the like. The operation setting display unit 51 and the weighing unit 52 are connected by a cable 53 and configured to input and output various signals.

  Alternatively, as another load cell type weighing device to which the present invention can be applied, as shown in FIG. 8, an operation setting display unit 61 and a weighing unit 62 are provided, and the weighing unit 62 includes a plurality of weighing units 63 (FIG. 8). Tabletop combination weigher 60 provided with 12 pieces in the example shown in FIG. The desktop combination weigher 60 measures the objects to be weighed having variations in individual weights so that the weights are within an allowable range by performing combination weighing. In the combination weighing, the weights of the objects to be weighed accommodated in the plurality of weighing units 63 are detected by the load cell, and the detected weights of the objects to be weighed are summed for each predetermined number of weighing units 63 to set a preset target. This is a weighing method in which a suitable combination of a predetermined number of weighing units 63 is selected in comparison with the weight.

  Even if it is the separate type digital balance 50 shown in FIG. 7 or the table type combination balance 60 shown in FIG. 8, the weighing unit 52 or 62 and the operation setting display unit 51 or 61 are not combined in one case. Separated. With such a configuration, since the measuring portion 52 or 62 is relatively small, it is easy to be cooled, and therefore, condensation is likely to occur. Further, the operation setting display unit 51 or 61 is provided with many components that are relatively easy to generate heat, such as the display unit 22 and the CPU 23, but the weighing unit 52 or 62 has few such components that easily generate heat. . Therefore, condensation is likely to occur in the load cell as compared to a large digital balance or a large combination balance integrated in one case.

  On the other hand, if the present invention is applied and the power feeding path to the load cell is switched from the first power feeding path to the second power feeding path and the plurality of strain gauges are configured to generate heat, the load cell is placed inside the weighing unit 52 or 62. It is possible to effectively prevent dew condensation.

  Here, in the first and second embodiments and the desktop digital balances 10a to 10c in the present embodiment, the CPU 23 is configured to function as both a controller and a weight calculator, but the present invention is not limited thereto. Instead, the controller and the weight calculator may be constituted by independent CPUs.

  It should be noted that the present invention is not limited to the description of the above-described embodiment, and various modifications are possible within the scope shown in the claims, and are disclosed in different embodiments and a plurality of modifications, respectively. Embodiments obtained by appropriately combining technical means are also included in the technical scope of the present invention.

  The present invention can be used for measuring agricultural products such as cut vegetables, broilers, and other meats, for measuring marine products such as octopus, crab, and fish fillets, and for measuring applications in environments where there are significant temperature differences. It can be widely applied to the load cell type weighing device used.

It is sectional drawing which shows the structure of the desktop digital balance which concerns on Embodiment 1 of this invention. It is a schematic diagram which shows the structure of the load cell with which the desktop digital balance shown in FIG. 1 is provided. It is a figure which shows the circuit structure of the control system and principal part of the desktop digital balance shown in FIG. (A) is a circuit diagram schematically showing a power feeding path to the bridge circuit when in the weighing state in the desktop digital balance shown in FIG. 3, and (b) is a bridge circuit when in the standby state. It is a circuit diagram which shows typically the electric power feeding path | route to. It is a figure which shows the circuit structure of the control system and principal part of the desktop digital balance which concerns on Embodiment 2 of this invention. It is a figure which shows the circuit structure of the control system and principal part of the desktop digital balance which concerns on Embodiment 3 of this invention. It is a schematic diagram which shows the external appearance structure of the separate type digital balance which concerns on Embodiment 3 of this invention. It is a schematic diagram which shows the external appearance structure of the desktop type | mold combination weigher which concerns on Embodiment 3 of this invention.

Explanation of symbols

10a Desktop digital scale (load cell type weighing device)
10b Desktop digital scale (load cell type weighing device)
10c Desktop digital scale (load cell type weighing device)
13 Stainless steel case 23 CPU (weight calculator, controller)
25 Power supply path switching drive unit (switching drive)
26 Condensation prevention mode key (switch drive actuator)
27 Notification lamp (notification device)
28 Buzzer (alarm)
30 Load cell (bridge circuit)
31 Strain bodies 32a, 32b, 32c, 32d Strain gauges 33a, 33b, 33c Feed path switching switch (feed path switch)
41 Humidity sensor (humidity detector)
42 Battery 50 Separate type digital scale (load cell type weighing device)
60 Desktop combination weigher (load cell type weighing device)
311 Movable rigid part (movable part)
P ₁₁ , P ₁₄ points (bridge circuit input terminals)
P _12, P ₁₃ point (the output terminal of the bridge circuit)

Claims (8)

A strain generating body having a movable part that generates a displacement by applying a weight of an object to be weighed as a load, and a plurality of strain gauges attached to the strain generating body and detecting the displacement, and the plurality of strain gauges. A load cell in which the strain gauge forms a bridge circuit;
A power supply path switching device that switches a plurality of power supply paths to the load cell,
The power supply path switch is a first power supply path for supplying power to the input terminal of the bridge circuit, or a second power supply for supplying power to the strain gauges so that the plurality of strain gauges are connected in parallel. A load cell type weighing device configured to select and switch one of power feeding paths. A weight calculator connected to the output terminal of the bridge circuit and calculating the weight of the object to be weighed from an output signal of the bridge circuit;
The load cell type weighing device according to claim 1, wherein when the power feeding path switching unit selects the second power feeding path, the connection between each strain gauge and the weight calculator is further cut off. A switching driver for driving the power supply path switching device;
A humidity detector for detecting the humidity around the load cell;
A controller, and
When the humidity value detected from the humidity detector exceeds a preset upper limit value and the displacement is not detected from the plurality of strain gauges, the controller switches the power supply path switch to the second. The load cell type weighing device according to claim 1 or 2, wherein the switching driver is configured to operate so as to select a power feeding path.   When the displacement is detected from at least one of the plurality of strain gauges in a state where the power supply path switch selects the second power supply path, the controller is configured to switch the power supply path switch The load cell type metering device according to claim 3, wherein the switch driver is configured to operate so as to select the first power feeding path. An alarm device for notifying the user is further provided,
The load cell type according to claim 3 or 4, wherein the controller is configured to operate the alarm when a humidity value detected from the humidity detector exceeds a preset upper limit value. Weighing device.   The load cell type weighing device according to any one of claims 3 to 5, further comprising a switching drive operating device that operates the switching drive device according to an operation by a user.   The load cell type measuring device according to any one of claims 1 to 6, wherein an exterior of the load cell type measuring device is made of stainless steel.   The load cell type weighing device according to any one of claims 1 to 7, wherein the power source for supplying the electric power is a battery.

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