JP2013170954A - Explosion-proof load cell device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an explosion-proof load cell device capable of reducing a manufacturing cost more than load cell devices of a pressure-resistant and explosion-proof structure and an intrinsically safe explosion-proof type, miniaturizing the device more than the load cell device of pressure-resistance and explosion-proof type structure, and surely preventing intrusion of explosive gas and the like into a strain gauge adhesion part and an arrangement part of an electronic component connected to a strain gauge.SOLUTION: The explosion-proof load cell device includes: a strain generator 1; a strain gauge 2 closely stuck to the strain generator; an electric circuit 3 connected to the strain gauge 2 and mounted on the strain generator 1; a resin part 4 for covering the strain gauge 2 and the electric circuit 3 in a closely sealed state; and a power-limiting circuit 5 that limits a power to be supplied to the electric circuit 3 and the strain gauge 2 such that, even when the strain generator 1 and the strain gauge 2 are short-circuited, a heat generating temperature of the electric circuit 3 becomes lower than or equal to a heatproof temperature of the resin part 4.

Description

  The present invention relates to an explosion-proof load cell device.

  A load cell device in which a strain gauge is attached to a metal strain body is already widely known. This load cell device is also used in an environment where explosive gas is handled. In this case, conventionally, a load cell device having a pressure-proof explosion-proof structure and a load cell device having an intrinsically safe explosion-proof structure are used.

  The explosion-proof explosion-proof load cell device is disclosed in, for example, Patent Document 1 and the like. The load cell is covered with a strong metal box such as a casting from the surroundings, and even if it is ignited internally, It is configured so that no flame escape occurs.

  A load cell device having an intrinsically safe explosion-proof structure is disclosed in, for example, Patent Document 2 and the like, and a controller having a barrier (safety holder) for limiting voltage or the like is disposed in a safe place so that the load cell does not ignite. It is configured as follows.

JP 60-11127 A JP-A-9-236480

  However, the explosion-proof load cell device requires a metal box or the like that covers the load cell from the surroundings, so that the manufacturing cost is greatly increased and the size of the box is increased due to the box.

  In addition, in the intrinsically safe explosion-proof load cell device, a controller having a barrier (safety holder) or the like must be provided, and in this case, the manufacturing cost is greatly increased. In addition, since very little power can be used in the load cell, it is necessary to place a controller with a barrier (safety retainer) in a safe place, as a general rule, which limits the usage and usage. There are drawbacks.

  As a method to remedy these disadvantages, cover the load gauge strain gauge affixed part or the circuit board connected to the strain gauge with resin, and then use the explosive gas to the strain gage affixed part or the circuit board placement part. It is conceivable to prevent such intrusion. With this configuration, the structure can be simplified, the manufacturing cost can be reduced, and a metal box such as a pressure-proof explosion-proof load cell device need not be provided. It is also possible to reduce the size. Insulating the electrical component with resin, if the minimum thickness of the solid insulation is 0.1 mm, that is, if the thickness of the resin at the location to be insulated is 0.1 mm or more, the dielectric strength IEC (International Electro technical Commission: International Electro Technical Commission) International Standard “600079-18 (Electrical equipment for detecting flammable gases Part 18: Encapsulated“ m ”structure of protective electrical equipment ”Test and marking)” in “7.2.3.2 Distance in solid insulation”.

  However, in the strain gauge attachment part, the sensitivity is lowered unless the strain gauge is closely attached to the metal strain body. Therefore, when trying to obtain a certain degree of sensitivity, the strain gauge is closely attached with a size smaller than 0.1 mm. In other words, a thick resin layer of 0.1 mm or more cannot be interposed between the strain gauge and the strain generating body. Therefore, when the strain gauge and strain body are short-circuited or failed, the strain gauge or electrical components connected to the strain gauge generate heat, and the temperature rises to a temperature that exceeds the heat-resistant temperature. As a result, the resin near the heat generating part may be softened or melted out, and in this case, in the worst case, explosive gas may generate heat from the short-circuited parts or electrical parts through the resin-melted space. There is a possibility of exploding by invading parts.

  The present invention solves the above-mentioned problems, and can reduce the manufacturing cost as compared with a load cell device having a pressure-proof explosion-proof structure or an intrinsically safe explosion-proof structure, and can be made smaller than a load cell device having a pressure-proof explosion-proof structure. The purpose of this invention is to provide an explosion-proof load cell device that can reliably prevent the explosive gas and the like from entering the strain gauge adhering part and the arrangement part of the electrical parts connected to the strain gauge. is there.

  In order to solve the above problems, an explosion-proof load cell device according to the present invention includes a strain generating body, a strain gauge attached in close contact with the strain generating body, and the strain generating body connected to the strain gauge. An electric circuit mounted on the resin, a resin portion covering the strain gauge and the electric circuit in a sealed state, the strain generating body and the strain gauge are short-circuited, or the electric component and wiring connected to the electric component Even if the part comes into contact with the strain body or the electric part fails, the electric circuit and the strain gauge are arranged so that the heat generation temperature of the electric circuit and the strain gauge is lower than the heat resistance temperature of the resin part. And a power limiting circuit that limits power to be supplied.

  This configuration restricts the power supplied to the strain gauge and the electrical circuit by the power limiting circuit, so that in the unlikely event that the strain-generating body and the strain gauge are short-circuited or connected to the terminal of the electrical component or this electrical component Even when the wiring part thus contacted with the strain generating body or an electrical component fails, the heat generation temperature by the electric circuit or the strain gauge becomes lower than the heat resistance temperature of the resin part. Therefore, the resin part covering the electric circuit or the strain gauge is prevented from being softened or melted beyond the heat-resistant temperature, and as a result, explosive gas can pass through the space where the resin part is melted and It is possible to prevent an explosion from entering the heat generating part of the circuit.

  In addition, the present invention is characterized in that the power limiting circuit includes a current direction limiting element that limits a current direction in one direction. With this configuration, for example, when there is a possibility that both a positive voltage and a negative voltage are added to the circuit up to the power limiting circuit, the strain-generating body and the strain gauge are short-circuited, Even if the terminal or wiring part of a component comes into contact with a strain generating body or an electrical component breaks down, the current direction is limited to one side, so only a positive or negative voltage can be applied. Only can suppress the calorific value of electrical circuits and strain gauges.

  The power limiting circuit preferably includes two current direction limiting elements and a current amount limiting element for limiting the amount of current. According to this configuration, the current direction and the current Since the amount can be satisfactorily limited, the electric power flowing through the electrical component and the strain gauge can be satisfactorily limited.

  In addition, as the electrical circuit, an analog signal processing circuit that processes an analog signal output from a bridge circuit composed of a plurality of strain gauges, an A / D converter, and a digital signal output from the A / D converter are processed. And a digital signal processing circuit. With this configuration, even when the power limiting circuit has a current amount limiting element such as a resistor, the signal output from the bridge circuit can be satisfactorily processed.

  It is preferable to provide a protective cover that covers and protects the resin portion. With this configuration, the resin part is protected by the protective cover, so that when the explosion-proof load cell device is installed, something hits the resin part and the thickness of the resin part covering the electric circuit or the strain gauge becomes small. It is possible to prevent the occurrence of defects and improve the reliability.

  Further, the present invention provides a conductive wire exposed portion excluding a covering portion on a plurality of wires arranged in an electric wire connected to the power limiting circuit, and a resin portion is filled around the conductive wire exposed portion. In addition, a conductive wire guide portion for preventing the conductive wire exposed portions of the wiring from contacting each other is provided. With this configuration, even if an explosion-proof gas enters from the outside through the space between the coating part and the conductor part of the wiring, the resin part filled around the exposed part of the wiring leads to the inside. It is possible to prevent the explosion-proof gas from entering. In addition, since the conductive wire guide portion prevents the conductive wire exposed portions of the wiring from contacting each other, the reliability is improved.

  In addition, it is preferable to attach a flat plate-shaped fixture that prevents the electric wire from coming out of the strain generating body, or to form a bubble removal hole at the upper portion of the portion where the resin portion is filled. When the air bubble removing hole is formed, it is possible to prevent air bubbles from remaining inside when filling the resin, and the reliability is improved.

  According to the present invention, when the strain body and the strain gauge are short-circuited, or when the terminal of the electrical component or the wiring part connected to the electrical component is in contact with the strain body or the electrical component fails However, by providing a power limiting circuit that limits the power supplied to the electrical circuit and strain gauge so that the heat generation temperature of the electrical circuit and strain gauge is lower than the heat resistance temperature of the resin part, Even when the gauge is short-circuited, or when the terminal of the electrical component or the wiring part connected to the electrical component comes into contact with the strain generating body or the electrical component fails, the temperature generated by the electrical circuit or the strain gauge is increased. It becomes below the heat resistant temperature of the resin part. Therefore, the resin part covering the electric circuit or the strain gauge is prevented from being softened or melted beyond the heat-resistant temperature, and as a result, explosive gas can pass through the space where the resin part is melted and It is possible to prevent an explosion from entering the heat generating part of the circuit, and the reliability is improved.

  In addition, since it is a relatively simple configuration that simply covers the electrical circuit and strain gauge with a resin part and provides a power limiting circuit, the manufacturing cost can be reduced compared to a load cell device with a pressure-proof explosion-proof structure or an intrinsically safe explosion-proof structure. And can be made smaller than a load cell device having a flameproof structure.

  In addition, by providing a current direction limiting element that limits the current direction to one direction as the power limiting circuit, the current direction is limited to one side, so that the amount of heat generated in the electric circuit or the strain gauge can be suppressed.

(A), (b) and (c) are the top view, front view, and bottom view of an explosion-proof load cell device according to an embodiment of the present invention. (A) is a left side view of the explosion-proof load cell device, and (b) is a vertical right side view of the explosion-proof load cell device (a cross-sectional side view taken along line IIb-IIb in FIG. 1 (b)). FIG. 3 is a longitudinal front view of the explosion-proof load cell device (a cross-sectional front view taken along line III-III in FIG. 1A). It is a cross-sectional top view (IV-IV arrow directional cross-sectional top view of FIG.1 (b)) of the explosion-proof load cell apparatus. It is a transverse bottom view of the explosion-proof load cell device (a sectional bottom view taken along line VV in FIG. 1B). It is a plane sectional view of a part in which a holding frame and a power limiting circuit of the explosion-proof load cell device are provided. (A) is a schematic circuit diagram of the explosion-proof load cell device, and (b) is a schematic circuit diagram showing a modification of the explosion-proof load cell device.

  Hereinafter, an explosion-proof load cell device according to an embodiment of the present invention will be described with reference to the drawings. In addition, embodiment shown here is an example to the last, Comprising: It is not necessarily limited to this embodiment.

  1A, 1B, and 1C show a plan view, a front view, and a bottom view of an explosion-proof load cell device according to an embodiment of the present invention, and FIG. 2A shows the explosion-proof type. The left side view of the load cell device, FIG. 2B is a vertical right side view of the explosion-proof load cell device (cross-sectional side view taken along the line IIb-IIb in FIG. 1B), and FIG. 3 is the explosion-proof load cell device. Longitudinal front view (cross-sectional front view taken along line III-III in FIG. 1 (a)), FIG. 4 is a cross-sectional plan view of the explosion-proof load cell device (cross-sectional plan view taken along line IV-IV in FIG. 1 (b)) 5 is a transverse bottom view of the explosion-proof load cell device (a cross-sectional bottom view taken along line VV in FIG. 1B), and FIG. 6 is provided with a holding frame and a power limiting circuit of the explosion-proof load cell device. FIG.

  As shown in FIGS. 1 to 5, the explosion-proof load cell device according to the embodiment of the present invention is made of a metal strain generating body (load cell main body) 1 and attached to the strain generating body 1 in close contact with each other. A plurality of strain gauges 2, an electric circuit 3 including a plurality of circuit boards 3 A and 3 B attached to the strain generating body 1 while being connected to the strain gauges 2, and the strain gauges 2 and the electric circuit 3 are sealed. A resin portion 4 covered with a power, a power limiting circuit 5 for limiting power supplied to the electric circuit 3 and the strain gauge 2, an electric wire 6 connected to the power limiting circuit 5, and a resin portion 4 covered from the outside for protection. The protective cover 7 (7A, 7B) made of metal is used.

  The strain body 1 includes a support fixing portion 1a supported (fixed) at a predetermined position, a load loading portion 1b to which a load is applied, and a thin portion formed between the support fixing portion 1a and the load loading portion 1b. 1c is formed, and the strain gauge 2 (that is, the four strain gauges 2) paired on the upper surface and the lower surface of the thin portion 1c is extremely thin (thickness smaller than 0.1 mm) insulating film (not shown) Z)). In addition, the strain body 1 has a substantially rectangular parallelepiped shape, and the thin portion 1c includes a recess portion 1d that is recessed downward from the upper surface of the strain body 1, and a recess portion 1e that is recessed upward from the lower surface of the strain body 1. Are formed between these depressions 1d and 1e, but as shown in FIGS. 4 and 5, the left and right portions of the upper and lower depressions 1d and 1e (see FIGS. In the paper surface of FIG. 5, through portions 1f and 1g penetrating vertically are also formed on the upper and lower portions.

  The lower part of the support fixing part 1a of the strain body 1 is formed with depressions 1h and 1i that are recessed upward from the lower surface, and the electric circuit 3 (circuit boards 3A and 3B) is disposed in these depressions 1h and 1i. Has been. In this embodiment, the circuit board 3A is attached to the bottom surface of the recess 1h on the surface of the single-sided board on which the metal pattern is not formed, and the circuit board 3B is fixed via the boss-like spacer 11. However, the circuit board 3A and the circuit board 3B may be attached via an insulating film thicker than 0.1 mm or the like.

  Above the support fixing portion 1 a of the strain generating body 1, the power limiting circuit 5 is fixed with a screw or the like through a boss-like spacer 12 and is arranged in a state of being separated from the upper surface of the strain generating body 1. Yes. Further, above the support fixing portion 1a of the strain generating body 1, a thin plate-like packing 13 (see FIG. 3) in a posture extending upward in a state of surrounding the power limiting circuit 5 from four sides (front and rear, left and right) in plan view. ) Through which the holding frame 14 is mounted.

  Further, as shown in FIG. 3 and the like, a hole 1j is formed so as to extend in the lateral direction from the end of the support fixing portion 1a of the strain body 1 to the inside, and the tip of the electric wire 6 is formed in the hole 1j. The part has been rushed. The electric wire 6 includes four wires 6a and shield wires 6b (see FIGS. 7A and 7B) covered with a covering portion 6c, and a cylindrical packing 15 is provided at the end of the covering portion 6c. The end of the electric wire 6 is attached in a state in which the shield wire 6b is externally fitted and the shield wire 6b is in contact with the metal strain body 1. The electric wire 6 is assembled with an electric wire holder (so-called retainer) 16 and an electric wire holding attachment (so-called adapter) 17 for securely attaching the electric wire 6 so as not to be detached from the strain body (load cell main body) 1. It has been. In this embodiment, as shown in FIG. 4, a substantially annular electric wire holding / attaching body 17 is assembled to the strain generating body 1 with fixing screws 18, and is formed at the center of the electric wire holding / attaching body 17. The electric wire holding body 16 is fixed to the electric wire holding attachment body 17 in a state in which the thin male screw portion 16a protruding from the large diameter portion 16a of the electric wire holding body 16 is inserted into the female screw portion 17a and screwed.

  Furthermore, as shown in FIG. 4, FIG. 5, etc., the notch part 16c notched from the outer peripheral surface to the location where the electric wire 6 was let through is formed in a part of the large diameter part 16a of the electric wire holder 16. The notch portion 16c has a flat plate-like locking plate (an example of a fixture) 16d for holding the electric wire 6 so as to prevent the end portion of the electric wire 6 from coming out of the strain generating body 1. 20 is attached.

  The support fixing portion 1a of the strain generating body 1 has an inner space of the holding frame 14 in which the inner space of the hole 1j and the power limiting circuit 5 are disposed following the hole 1j through which the electric wire 6 passes. A wiring communication hole 1k for communicating with the holding frame inner region 14a) is formed, and the wiring 6a of the electric wire 6 is passed through the holding frame inner region 14a via the wiring communication hole 1k. Then, the conductor exposed portion 6aa excluding the coating of each wiring 6a is connected to the input terminal portion of the power limiting circuit 5 (specifically, the input terminal portion of the circuit board 5a on which the power limiting circuit 5 is provided). . Here, the conductive wire exposed portion 6aa of the wiring 6a is stripped with a longer covering portion 6ab (for example, a length of about 5 mm or more). Further, an insulating conductor guide portion 21 is attached with a screw 22 (see FIG. 3) in the vicinity of the portion of the holding frame inner region 14a that communicates with the wiring communication hole 1k. As shown in FIG. In the guide portion 21, four groove portions 21a for individually guiding the end portions of the covering portions 6ab of the four wirings 6a and the conductive wire exposed portions 6aa following the end portions are formed at positions separated from each other in the lateral direction. . The insulating wire guide portion 21 is connected to the input terminal portion of the power limiting circuit 5 in a state in which the wire exposed portions 6aa are prevented from contacting each other.

  In addition, the inner regions of the recesses 1h and 1i in which the electric circuit 3 (circuit boards 3A and 3B) is disposed and the holding frame inner region 14a in which the power limiting circuit 5 is disposed are vertically extended. It communicates also with the common holes 1m and 1n.

  In the strain body 1, recessed dents 1 d and 1 e in which the strain gauge 2 is provided, through-holes 1 f and 1 g that pass through and communicate with the dents 1 h and 1 i, and an electric circuit 3 (circuit Indented portions 1h, 1i in which the substrates 3A, 3B) are disposed, a holding frame internal region 14a in which the power limiting circuit 5 is disposed, a wiring communication hole 1k, the recessed portions 1h, 1i, and the retaining frame The communication holes 1m and 1n that communicate with the internal region 14a are all filled with resin. The resin gauge 4 filled with the resin covers the strain gauge 2, the electric circuit 3 (circuit boards 3A and 3B) and the power limiting circuit 5 in a sealed state. In addition, an opening hole (an example of a bubble removal hole) 14b that opens widely is formed in the upper part of the holding frame 14, and this opening hole 14b confirms the filling amount of the resin when filling the resin. It also functions as a confirmation hole.

  Moreover, the surface in which the resin part 4 in the strain body 1 is exposed to the outside (that is, the upper surface of the resin part 4 filled in the depression part 1d, the lower surface of the resin part 4 filled in the depression part 1e, and the depression The lower surface of the resin portion 4 filled in the portions 1h and 1i) and the upper surface where the resin portion 4 in the holding frame inner region 14a of the holding frame 14 is exposed to the outside are a metal protective cover 7 (7A, 7B). Thus, it is covered and protected from the outside with a gap.

  FIG. 7A shows a schematic circuit diagram of the explosion-proof load cell device. As described above, all the strain gauges 2, the electric circuits 3 (circuit boards 3A and 3B), and the power limiting circuit 5 are covered with the resin portion 4. For example, the circuit board 3A is a connection circuit that connects the strain gauges 2 so as to form a bridge circuit. The circuit board 3B includes a circuit that processes the analog signal output from the bridge circuit, an A / D converter that converts the signal from the circuit into a digital signal, a signal processing circuit that processes the digital signal, and the signal. And a communication circuit for transmission. These circuits, the plurality of strain gauges 2, the strain generating body 1, and the like constitute a digital load cell unit.

  The power limiting circuit 5 includes, for example, two current direction limiting elements 5b made of diodes that limit the current direction in one direction, and three current amount limiting elements 5c made of resistors that limit the amount of current. That is, in the power limiting circuit 5, currents are respectively supplied to a place where the wiring 6 a-1 supplying power toward the strain gauge 2 side is connected and a place where the wiring 6 a-4 serving as the ground line is connected. The direction limiting element 5b is provided. As a result, in the power limiting circuit 5, only when the positive voltage is applied from the wiring 6a-1 and the wiring 6a-4 is grounded, the electric circuits 3, 3A, 3B, Electric power is supplied to the strain gauge 2. Further, in the power limiting circuit 5, there are connected to the wiring 6a-1 for supplying power toward the strain gauge 2 side, and wirings 6a-2 and 6a-3 for transmitting signals from the strain gauge 2 side. A current amount limiting element 5c made of a resistor is disposed at each connected location. In the unlikely event that the strain gauge 2 comes into contact with the strain generating body 1 and is short-circuited, the terminals of the electrical components disposed in the electrical circuits 3, 3A, 3B and the wiring portions connected to the electrical components are strained. Even when electrical leakage occurs from the electrical circuits 3, 3 </ b> A, 3 </ b> B due to contact with the body or failure of the electrical component, the heat generation temperature of the electrical circuits 3, 3 </ b> A, 3 </ b> B and the strain gauge 2 remains The electric power supplied to the electric circuits 3, 3 </ b> A, 3 </ b> B and the strain gauge 2 is limited so as to be equal to or lower than the temperature. As shown in FIG. 7 (b), a fuse or the like is used instead of the current amount limiting element 5c made of a resistor in the power limiting circuit 5 where the power supply wiring 6a-1 is connected. The current amount limiting element 5d may be provided, and the maximum current can also be limited by this.

  According to the above configuration, the electric power supplied to the strain gauge 2 and the electric circuits 3, 3A, 3B is limited by the power limiting circuit 5, so that the strain body 1 and the strain gauge 2 may short-circuit, Even when electric leakage occurs from the electric circuits 3, 3 A, 3 B, the heat generation temperature by the electric circuits 3, 3 A, 3 B and the strain gauge 2 is lower than the heat resistance temperature of the resin part 4. Therefore, the resin part 4 covering the electric circuits 3, 3A, 3B and the strain gauge 2 is prevented from being softened or melted beyond the heat resistance temperature. As a result, the explosive gas is melted by the resin part 4. It is possible to prevent an explosion due to intrusion into the short-circuited portion or the heat generating portion of the electric circuits 3, 3A, 3B through the open space, and the reliability is improved.

  In addition, since the power limiting circuit 5 includes two current direction limiting elements 5b that limit the current direction to one direction, for example, the circuit up to the power limiting circuit 5 has both positive and negative voltages. In the unlikely event that the strain generating body 1 and the strain gauge 2 are short-circuited, the terminals or wiring portions of the electric circuits 3, 3A, 3B are in contact with the strain generating body 1 or the like. Even in the case of failure or failure, the current direction is limited to one side. Thereby, in this embodiment, only a positive voltage (or a negative voltage depending on the circuit) can be applied, and the amount of heat generated by the electrical circuits 3, 3A, 3B and the strain gauge 2 can be suppressed accordingly. Further, the reliability is improved.

  In addition, since the electric circuit 3, 3A, 3B and the strain gauge 2 are covered with the resin portion 4 and the power limiting circuit 5 is provided, the load cell device has a pressure-proof explosion-proof structure or an intrinsically safe explosion-proof structure. The manufacturing cost can be reduced more than the load cell device having the explosion-proof type structure.

  In other words, the explosion-proof explosion-proof load cell device requires an extremely robust metal box that covers the load cell from the surroundings, which significantly increases the manufacturing cost and the intrinsically safe explosion-proof load cell device. In this case, the manufacturing cost is greatly increased because a controller having a safety retainer) must be provided. On the other hand, in the explosion-proof load cell device filled with resin as in the present embodiment, the electric circuit 3, 3A, 3B and the strain gauge 2 are covered by the resin portion 4 and only the power limiting circuit 5 is provided. Therefore, the manufacturing cost can be significantly reduced as compared with the case of the explosion-proof explosion-proof load cell device and the intrinsically safe explosion-proof load cell device.

  Intrinsically safe explosion-proof load cell devices can use only very small power, so there are disadvantages that limit the usage and method of use, and in principle, a controller with a barrier (safety cage) can be used in a safe place. However, in the explosion-proof load cell device according to the present embodiment, the heat generation temperature by the electric circuits 3, 3A, 3B and the strain gauge 2 is lower than the heat resistance temperature of the resin part 4. Since it is possible to handle electric power, that is, relatively large electric power as compared with an intrinsically safe explosion-proof load cell device, restrictions on use and usage are greatly relaxed as compared with an intrinsically safe explosion-proof load cell device. In addition, by covering the power limiting circuit 5 with the resin portion 4, it is possible to install the entire load cell device in a dangerous place.

  Moreover, in the said embodiment, since the protective cover 7 (7A, 7B) which covers and protects the resin part 4 is provided, and the resin part 4 is protected by the protective cover 7 (7A, 7B), the said explosion-proof type When the load cell device is installed, it can be prevented that something hits the resin part 4 and the resin part covering the electric circuits 3, 3A, 3B or the strain gauge 2 becomes thin. Even reliability improves. That is, in the load cell device having a pressure-proof explosion-proof structure, it is necessary to cover a very strong box or the like so that the fire does not escape to the outside even if it explodes inside. Since the protective cover 7 (7A, 7B) for preventing the thickness of the resin part 4 from decreasing due to contact, etc. may be used, the structure can be simplified and the thickness can be reduced. Therefore, it can be made smaller than a load cell device having a flameproof structure.

  In addition, since the explosion-proof load cell device of the present embodiment is configured by a digital load cell unit including an A / D converter, the power limiting circuit 5 has a current amount limiting element such as a resistor. Even in this case, the signal output from the bridge circuit can be processed satisfactorily. In other words, in a load cell device that processes analog signals, if a resistor is added to a bridge circuit or the like, the balance of the bridge circuit is lost, causing a problem that accurate measurement cannot be performed, but the explosion-proof load cell device of the present embodiment is Since it is a digital load cell, it can be measured well even if a current amount limiting element such as a resistor is provided.

  In addition, according to the above-described embodiment, the conductive wire exposed portion 6aa excluding the covering portion 6c is provided in the wiring 6a of the electric wire 6, and the resin portion 4 is also filled around the conductive wire exposed portion 6aa. Even if an explosion-proof gas enters from the outside through the space between the covering portion 6c and the conductor portion of the wiring 6a, the resin portion 4 filled around the conductor exposed portion 6aa of the wiring 6a Further, the explosion-proof gas can be prevented from entering inside. As a result, the explosion-proof gas can be prevented from entering the power limiting circuit 5 and exploding. The conductive wire exposed portion 6aa is preferably provided with a resin explosion-proof specified dimension (for example, 5 mm) or more. Further, since the conductive wire guide portion 21 prevents the conductive wire exposed portions 6aa of the wiring 6a from contacting each other, it is possible to prevent explosion due to the contact of the conductive wire exposed portions 6aa of the wiring 6a with each other. Will improve.

  Further, a flat locking plate 16 d that holds the electric wire 6 and holds the electric wire 6 so that the end of the electric wire 6 does not come out of the strain generating body 1 is attached to the electric wire holding body 16 with a fixing screw 20. Therefore, it can prevent reliably that the edge part of the electric wire 6 slips out from the strain body 1, and reliability improves also by this. In addition, since the locking plate 16d as an example of the fixture has a flat plate shape, the electric wire 6 having a substantially round cross section can be favorably pressed. In addition, by making the shape of the locking plate 16d substantially rectangular and curving the corners thereof (see FIG. 1B), there is also an advantage that the electric wire 6 can be prevented from being damaged when the locking plate 16d is assembled. .

  In addition, since the opening hole 14b that opens widely is formed in the upper part of the holding frame 14 corresponding to the upper part of the load cell device that fills the resin portion 4, after the resin is injected into the load cell device, the internal bubbles are passed through the opening hole 14b. Can be prevented from being discharged to the outside and bubbles remaining inside, which also improves reliability. Moreover, since this opening hole 14b functions also as a confirmation hole part for confirming the filling amount of the resin when filling the resin, while filling the resin, while confirming the resin amount in the opening hole 14b, Resin can be satisfactorily filled and workability is also improved.

  In the above-described embodiment, the case where the strain body 1 is an explosion-proof load cell device having a substantially rectangular parallelepiped shape is described, but the present invention is not limited to such a type of load cell device. That is, not only the cantilever type load cell device in which the strain generating body is a rectangular parallelepiped shape as described above, but also the both ends fixed beam type load cell device in which the strain generating body is a rectangular parallelepiped shape or the cantilever having a cylindrical shape in the strain generating body. The configuration of the present invention can be applied to almost all types of load cell devices, such as a load cell device having a mold, a both-end fixed beam type or a column shape, and a load cell device having a diaphragm or ring shape.

1 Strain body (load cell body)
2 Strain gauge 3 Electric circuit 4 Resin part 5 Power limiting circuit 5b Current direction limiting element 5c, 5d Current amount limiting element 6 Electric wire 6a Wiring 6aa Conducting wire exposed part 6ab Covering part 7 (7A, 7B) Protective cover 14 Holding frame 14b Opening hole (Bubble release hole)
16 Wire holder 17 Wire holder 21 Conductor guide

In order to solve the above problems, an explosion-proof load cell device according to the present invention includes a strain generating body, a strain gauge attached in close contact with the strain generating body, and the strain generating body connected to the strain gauge. An electric circuit mounted on the resin, a resin part covering the strain gauge and the electric circuit in a sealed state, and the strain body and the strain gauge are short-circuited, or the electric circuit and wiring connected to the electric circuit Even if the part contacts the strain generating body or the electric circuit breaks down, the electric circuit and the strain gauge are arranged so that the heat generation temperature of the electric circuit and the strain gauge is lower than the heat resistant temperature of the resin part. And a power limiting circuit that limits power to be supplied.

With this configuration, since the electric power supplied to the strain gauges and the electrical circuit is limited by the power limiting circuit, the unlikely event that the strain generating body and a strain gage is shorted or connected to the terminal and the electric circuit of the electric circuit Even when the wiring portion thus contacted with the strain generating body or the electric circuit fails, the heat generation temperature by the electric circuit or the strain gauge becomes lower than the heat resistant temperature of the resin portion. Therefore, the resin part covering the electric circuit or the strain gauge is prevented from being softened or melted beyond the heat-resistant temperature, and as a result, explosive gas can pass through the space where the resin part is melted and It is possible to prevent an explosion from entering the heat generating part of the circuit.

According to the present invention, if the strain generating body and the strain gauge is shorted, or the case where wiring portions connected terminals and to the electric circuit of the electric circuit is the electric circuit or in contact with the strain body has or failure However, by providing a power limiting circuit that limits the power supplied to the electrical circuit and strain gauge so that the heat generation temperature of the electrical circuit and strain gauge is lower than the heat resistance temperature of the resin part, If the gauge is shorted, or the wiring part connected terminals and to the electric circuit of the electric circuit even if the electric circuit or in contact with the strain body has or failure, due to heat generation temperature electrical circuits and strain gauges It becomes below the heat resistant temperature of the resin part. Therefore, the resin part covering the electric circuit and the strain gauge is prevented from being softened or melted beyond the heat resistance temperature. It is possible to prevent an explosion from entering the heat generating part of the circuit, and the reliability is improved.

Claims (8)

A strain body,
A strain gauge adhered in close contact with the strain body,
An electrical circuit connected to the strain gauge and attached to the strain body;
A resin part covering the strain gauge and the electric circuit in a sealed state;
Even when the strain body and the strain gauge are short-circuited, or when a terminal of the electrical component or a wiring part connected to the electrical component comes into contact with the strain body or the electrical component fails, the electrical component A power limiting circuit that limits power supplied to the electrical circuit and the strain gauge so that the heat generation temperature of the circuit and the strain gauge is equal to or lower than the heat-resistant temperature of the resin portion;
An explosion-proof load cell device comprising:   The explosion-proof load cell device according to claim 1, wherein the power limiting circuit includes a current direction limiting element that limits a current direction to one direction.   3. The explosion-proof load cell device according to claim 2, wherein the power limiting circuit includes two current direction limiting elements and a current amount limiting element that limits a current amount. 4. As the electrical circuit, an analog signal processing circuit that processes an analog signal output from a bridge circuit composed of a plurality of strain gauges, an A / D converter, and a digital that processes a digital signal output from the A / D converter The explosion-proof load cell device according to claim 1, further comprising a signal processing circuit.   The explosion-proof load cell device according to any one of claims 1 to 4, further comprising a protective cover that covers and protects the resin portion.   A plurality of wires arranged in the electric wire connected to the power limiting circuit are provided with a conductor exposed portion excluding the covering portion, and a resin portion is filled around the conductor exposed portion, and the wiring The explosion-proof load cell device according to any one of claims 1 to 5, further comprising a conductive wire guide portion for preventing the conductive wire exposed portions from contacting each other.   The explosion-proof load cell device according to any one of claims 1 to 4, further comprising a plate-like fixture that prevents the electric wire from coming out of the strain generating body. The explosion-proof load cell device according to any one of claims 1 to 6, wherein a bubble removing hole is formed in an upper portion of a portion where the resin portion is filled.

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