JP2014016270A - Weighing instruments - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable measurement of insulation resistance using a common power supply for load signal measurement and insulation resistance measurement in the middle of operation time even when the operation time is long.SOLUTION: Power is supplied by a power supply 40, via two power supply excitation terminals 32, 34, to two power supply excitation ends 10a, 10b of a bridge circuit 10 in which strain gauges 6 attached to a metallic strain element 2 are connected to each other, and measurement terminals 36, 38 are connected to two output ends 10c, 10d of the bridge circuit 10. One terminal of a reference resistor 50 is connected to the metallic strain element 2 or a conductor 2a in contact with the strain element 2, and a current flow path is formed so that a current from the power supply 40 is made to flow through the reference resistor 50 via an insulation resistance components present between the strain gauges 10, the power supply excitation ends 10a, 10b and the output ends 10c, 10d and the metallic strain element 2 or the conductor 2a and return to the power supply 40, and voltage produced between both ends of the reference resistor 50 is measured by an operational amplifier 64.

Description

  The present invention relates to a weighing device, and more particularly to measurement of an insulation resistance value in a weighing device using a load cell.

  Some load cells have a strain gauge attached to a strain-generating portion of a metal strain-generating body. Since the strain gauge is usually covered with an insulating and water-resistant resin such as polyimide, moisture does not easily pass therethrough. In addition, a terminal for wiring to the metal resistance wire, which is a component of the strain gauge, and a terminal for relaying the cable from the load cell to the outside are also provided on the resin insulating plate, and together with the strain gauge, silicon rubber or butyl rubber Because it is covered by, etc., moisture does not pass easily.

  However, since these resins and rubber agents are porous, they basically pass water vapor. Therefore, the absorbed water vapor becomes moisture due to long-term use of the load cell or depending on the usage environment, and the insulation resistance value between the strain gauge and the metal straining body to which the strain gauge is attached is lowered, and the output of the load cell is reduced. It affects the zero point and span of the load signal based on it as a measurement error.

  In particular, weighing devices used in harsh environments, such as weighing devices used in locations with large temperature differences and where condensation is likely to occur, weighing devices that require daily washing of the weighing unit, and weighing devices installed outdoors, are used as load signals. There is a high possibility that the insulation resistance value decreases as an error that cannot be ignored is given. Therefore, it is desirable to provide a means for determining the magnitude of the insulation resistance value and notifying the decrease in the insulation resistance value before the measuring device cannot be used with a predetermined accuracy.

  As a technique for measuring an insulation resistance value in a load cell, there is one disclosed in FIG. In this technique, the load cell is provided with a bridge circuit composed of a strain gauge, and at the time of weighing, a power supply for measurement is connected between two power source excitation ends of the bridge circuit, and a voltage between the two output ends of the bridge circuit is measured. . When measuring an insulation resistance value, one end of a series circuit of a power supply for measurement and a reference resistor is connected to one of two power source excitation ends, and the other end of the series circuit is connected to the ground via an extension cable. . The other of the two power source excitation ends is an empty terminal. Since an insulation resistance exists between the load cell and the ground, a current flows from the measurement power source to the strain gauge, insulation resistance, ground, extension cable, reference resistance, and measurement power source, and a voltage is generated in the reference resistance. This voltage is amplified by an amplifier, digitized by an A / D converter, supplied to an arithmetic and determination circuit, and an insulation resistance value is measured. The power source for measuring the insulation resistance value is a power source having a common line different from that of a power source such as an amplifier used for load measurement in the bridge circuit. Therefore, the power supplied to the bridge circuit is switched by the switching circuit when the load signal is measured and when the insulation resistance value is measured.

Japanese Patent Publication No. 61-16005

  According to the technique of Patent Document 1, the switching resistance circuit switches between an insulation resistance value measuring operation and a load signal measuring operation. Therefore, since the insulation resistance value cannot be measured while the load signal of the object to be measured is being measured continuously or at short time intervals during the operation operation, the insulation resistance value can be increased if the operation operation time is long. There is a possibility that a lot of measurement errors may occur due to a delay in the detection timing of the abnormality. Further, since the power supply means different from the voltage measuring means is used for measuring the insulation resistance value, the cost of the measuring device is high.

  The present invention uses a common power source that does not need to switch the power source for both the load signal measurement and the insulation resistance value measurement, and measures the insulation resistance value in the middle even if the operation time is long. It is an object of the present invention to provide a weighing device that can reduce the cost.

  The weighing device according to an aspect of the present invention includes a metal strain body, and a plurality of strain gauges are attached thereto. The metal strain body can be a column type or a Robert type. The plurality of strain gauges are connected to each other to form a bridge means. Two opposing connection ends of the strain gauges of the bridge means are power source excitation ends, and two other opposing connection ends are two output ends. Two power source excitation terminals are connected to the two power source excitation ends via connection lines, respectively. The power supply means supplies power to the two power excitation terminals. As the power supply means, a unipolar one can be used, or a bipolar one can be used. Two measurement terminals are connected to the two output terminals via connection lines, respectively, and a voltage between the two output terminals is measured as a load signal by voltage measuring means. One terminal of a reference resistance means is connected to the metal strain body or a conductor in contact with the metal strain body. A current flowing from the power supply means via the insulation resistance component existing between the plurality of strain gauges, the two power source excitation ends and the two output ends, and the metal strain body or the conductor is A current path is formed to flow to the reference resistance means and return to the power supply means. For example, when a unipolar power supply means is used, the current flowing from one terminal of the power supply means returns to the other terminal of the power supply means via the insulation resistance component and the reference resistance means, When the power supply means is used, the current flowing from one polarity of the power supply means returns to the other polarity of the power supply means via the insulation resistance component and the reference resistance means. The voltage measuring means measures a voltage generated between both ends of the reference resistance means and indicating an index of the magnitude of the insulation resistance value of the insulation resistance component. The power supply means used for measuring the load signal when measuring the insulation resistance value is used as it is.

  In this measuring device, the voltage across the reference resistance means is measured in a reference state where the insulation resistance value is large, and the voltage across the reference resistance means is measured when the insulation resistance value is measured. It is determined whether or not the insulation resistance value is reduced by comparing the two voltages or by obtaining the difference between the two and comparing the difference with a predetermined allowable value. Even at the time of measurement of the insulation resistance value, in the reference state, the power supply means is in the same state as that at the time of measurement of the load signal, and the power supply means is not switched. Therefore, the measurement of the load signal and the measurement of the insulation resistance value can be performed simultaneously.

  As described above, the insulation resistance value is measured in the first measurement mode, and in addition to this measurement mode, the reference resistance means is used as the first reference resistance means in series with the first reference resistance means. Two reference resistance means are connected, the series circuit is connected between the two power supply excitation terminals, and the third and fourth reference resistance means are connected in series between the two power supply excitation terminals. The voltage between the connection point of the second reference resistance means and the connection point of the third and fourth reference resistance means is measured by the voltage measurement means at the reference state and the measurement point of the insulation resistance. It is also possible to provide a second measurement mode for determining whether or not the insulation resistance value is reduced by comparing the voltages of the two or by obtaining the difference between the two and comparing the difference with a predetermined allowable value. it can.

  When the second measurement mode is provided in this way, the insulation resistance value in the first measurement mode is lowered near one of the two power source excitation terminals, and the current flowing through the first reference resistance means is small. Even if the decrease in the insulation resistance value cannot be detected only in the measurement mode, the decrease in the insulation resistance value can be measured.

  In the first measurement mode, a current flows from the first reference resistance means to the lower one of the two power source excitation terminals via the insulation resistance component. In the second measurement mode, It can also be configured such that the current flows from the higher one of the two power source excitation terminals via the second reference resistance means and the insulation resistance component from the higher potential.

  Even in the above two cases using the first and second measurement modes, the power supply means is not switched when measuring the insulation resistance value. Further, the insulation resistance value can be measured while the load signal is continuously measured.

  As described above, according to the present invention, the load is continuously measured by using one common power source that does not need to switch the power source for both the load signal measurement and the insulation resistance value measurement. Even if the operation operation time is long, it is possible to measure the insulation resistance value in the middle of the operation. Therefore, even when the operation operation continues for a long time, an alarm can be given if the insulation resistance value decreases and an abnormality occurs in the load signal. Since only one type of power supply means is used, the cost can be reduced.

1 is a block diagram of a load cell and a voltage measurement circuit of a weighing device according to a first embodiment of the present invention. It is a longitudinal cross-sectional view of the weighing device of FIG. FIG. 2 is a block diagram of the weighing device in FIG. 1. It is an operation | movement flowchart of the weighing | measuring apparatus of FIG. It is a block diagram of the load cell and voltage measurement circuit of the weighing | measuring apparatus of the 2nd Embodiment of this invention. It is a block diagram of the load cell and voltage measurement circuit of the weighing | measuring apparatus of the 3rd Embodiment of this invention. It is a block diagram of a load cell and a voltage measurement circuit of a measuring device of a 4th embodiment of the present invention, and its equivalent circuit diagram.

  The weighing device according to the first embodiment of the present invention has a load cell 1 as shown in FIG. The load cell 1 has a column-type metal strain body 2, for example. A plurality of, for example, four strain gauges 6 are attached to the strain-generating portion 4 formed on the metal strain-generating body 2. Since the column-type metal strain body 2 and the technique for attaching the strain gauge 6 thereto are well known, a detailed description thereof will be omitted.

  The metal strain body 2 is accommodated in the case 8. The case 8 has a base 8a made of metal, for example, and the strain generating body 2 is disposed on the base 8, and the body 8b of the case 8 surrounds the periphery of the strain generating body 2, and a lid portion is provided on the top of the body 8b. 8c is attached. A portion protruding from the lid 8c of the metal strain body 2 is coupled to a weighing unit (not shown), for example, a conveyor for a conveyor scale or coupled to a weighing hopper of a hopper scale. The load cell 1 measures the load due to the applied article.

  Each strain gauge 6 constitutes a bridge means, for example, a Wheatstone bridge circuit 10 as shown in FIG. Although the Wheatstone bridge circuit 10 may include a resistor other than the strain gauge 6 for temperature compensation or the like, this embodiment shows a Wheatstone bridge circuit that does not include a resistor other than the strain gauge 6. ing. The Wheatstone bridge circuit 10 has two power source excitation terminals 10a and 10b facing each other and two output terminals 10c and 10d facing each other. The power excitation end 10a is connected to a power excitation terminal 14 on the terminal board 12 shown in FIG. The power source excitation end 10b is also connected to the power source excitation terminal 16 on the terminal board 12 through wiring. Similarly, the output end 10 c is connected to the measurement terminal 18 on the terminal plate 12, and the output end 10 d is connected to the measurement terminal 20 on the terminal plate 12. As shown in FIG. 2, the terminal plate 12 is attached to the body portion 8 b of the case 8.

  The load cell 1 is connected to an indicator 22 as shown in FIG. The indicator 22 includes voltage measuring means, for example, a voltage measuring circuit 24, and further includes an arithmetic circuit 26, an operation / setting switch 28, and a display unit 30.

  As shown in FIG. 1, the terminal plate 13 is attached to the voltage measurement circuit 24, and the voltage measurement circuit 24 has power source excitation terminals 32 and 34 and measurement terminals 36, 38, and 48 on the terminal plate 13. The power excitation terminal 32 is connected to the power excitation terminal 14 of the load cell 1 via a cable, and the power excitation terminal 34 is connected to the power excitation terminal 16 of the load cell 1 via a cable. The measurement terminal 36 is connected to the measurement terminal 18 of the load cell 1 via a cable, and the measurement terminal 38 is connected to the measurement terminal 20 of the load cell 1 via a cable. The measurement terminal 48 is connected to the measurement terminal 47 of the load cell 1 on the terminal plate 12 via a cable.

  The power excitation terminal 32 is connected to a normal power source means, for example, a unipolar power source 40 via a normal line N. The power source excitation terminal 34 is connected to the common of the power source 40 via the common line C.

  The measurement terminals 36 and 38 are connected to the input side of an amplification means, for example, an operational amplifier 42. The output is supplied to an A / D conversion means, for example, an A / D converter 44, digitized, and the arithmetic circuit 26. To be supplied. The operational amplifier 42 and the A / D converter 44 constitute a load signal measuring voltage measuring means. The circuits provided on the input side, output side, and feedback loop of the operational amplifier 42 are not shown. The power supply terminals of the operational amplifier 42 and the A / D converter 44 are connected to the normal line N and the common line C of the power supply 40, respectively.

  An insulation resistance value measurement point 46 is provided at an arbitrary position of the metal strain body 2 or an arbitrary position of a conductor in contact with the metal strain body 2, for example, a metal base 8 a of the case 8. The value measuring point 46 is connected to an insulation resistance value measuring terminal 47 on the terminal board 12.

  Between the insulation resistance value measurement terminal 48 connected to the insulation resistance value measurement terminal 47 and the common line C, first reference resistance means, for example, a reference resistor 50 is connected. The insulation resistance value measuring terminal 48 is connected to switching means, for example, a contact 52 a of the analog switch 52. The analog switch 52 also has a contact 52b, and this contact 52b is an empty contact. The contact 52c of the analog switch 52 that contacts either the contact 52a or 52b is connected to the normal line N via a second reference resistance means, for example, a reference resistor 54.

  Between the normal line N and the common line C, third and fourth reference resistance means, for example, reference resistors 56 and 58 are connected in series. The reference resistors 50, 54, 56, and 58 all have stable resistance values with respect to temperature changes, or changes in the resistance value ratio between the reference resistors 50 and 54 and the reference resistors 56 and 58. The change in the resistance value ratio is small.

  A connection point 60 of the reference resistors 56 and 58 is connected to switching means, for example, a contact 62 a of an analog switch 62. Another contact 62 b of the analog switch 62 is connected to the insulation resistance value measuring terminal 48. A contact 62c of the analog switch 62 connected to one of the contacts 62a and 62b is connected to one input side of an amplification means, for example, an operational amplifier 64. The other input side of the operational amplifier 64 is connected to switching means, for example, a contact 66c of an analog switch 66. The contact 66c can contact either of the contacts 66a and 66b, and the contact 66a has an insulation resistance value. Connected to the measurement terminal 48, the contact 66 b is connected to the common line C.

  The analog switches 52, 62, 66 are controlled by the arithmetic circuit 26. When the contact 52c of the analog switch 52 is in contact with the contact 52a, the contact 62c of the analog switch 62 is in contact with the contact 62a, and the analog switch A contact 66c of 66 is in contact with the contact 66a. Hereinafter, the state of the analog switches 52, 62, and 64 is referred to as a first measurement mode, for example, a measurement mode. When the contact 52c of the analog switch 52 is in contact with the contact 52b, the contact 62c of the analog switch 62 is in contact with the contact 62b, and the contact 66c of the analog switch 66 is in contact with the contact 66b. Hereinafter, the state of the analog switches 52, 62, and 64 is referred to as a second measurement mode, for example, the b measurement mode. When the insulation resistance value is normal, that is, when the insulation resistance value is sufficiently larger than the resistance value of the reference resistor 50, the voltage across the reference resistor 50 is intermediate between the normal line N and the common line C. The values of the reference resistors 50 and 54 are set so as to be the potential, and similarly, the reference resistor is set so that the voltage across the reference resistor 58 becomes an intermediate potential between the normal line N and the common line C. The values of the devices 56 and 58 are set.

  In the b measurement mode, the operational amplifier 64 outputs the amplified voltage across the reference resistor 50. In the b measurement mode, a current path through which a current flows is formed between both ends of the reference resistor 50 via an insulation resistance component. In the a measurement mode, the amplified output of the bridge circuit constituted by the reference resistors 50, 54, 56, 58 (the difference between the voltage across the reference resistor 50 and the voltage across the reference resistor 58) is calculated. Output from the amplifier 64. In the operational amplifier 64, the circuits provided on the input side and the output side are not shown.

  The output of the operational amplifier 64 is digitized by A / D conversion means, for example, an A / D converter 68 and supplied to the arithmetic circuit 26. These reference resistors 50, 54, 56, 58, analog switches 52, 62, 66, operational amplifier 64 and A / D converter 68 constitute voltage measuring means for measuring an insulation resistance value. The power supply terminals of the operational amplifier 64 and the A / D converter 68 are connected to the normal line N and the common line C of the power supply 40, respectively. That is, the voltage measuring means for measuring the insulation resistance value and the voltage measuring means for measuring the load signal are operated by the same power source.

  At the time of adjustment of this measuring device, when the insulation resistance component of the load cell 1 is normal and the insulation resistance value is sufficiently large, the voltage across the reference resistor 50 is set as the insulation resistance value index voltage Ebo in the normal state by the b measurement mode. It is stored in the memory of the arithmetic circuit 26. Similarly, at the same time, the voltage difference between both ends of the reference resistors 50 and 58 is measured as the normal insulation resistance value index voltage Eao by the a measurement mode and stored in the memory of the arithmetic circuit 26.

  In the b measurement mode, when the insulation resistance component between each strain gauge 6 of the bridge circuit 10 and the insulation resistance value measurement point 46 is sufficiently large, the current from the power supply 40 via the normal line N at the power supply excitation end 10a. Flows from the power excitation end 10b to the common line C, almost no current flows between both ends of the reference resistor 50, and the potential of the insulation resistance value measuring terminal 48 (voltage across the reference resistor 50) is almost equal. This is the voltage of the common line C. This voltage is stored in the memory of the arithmetic circuit 26 as a normal insulation resistance value index voltage Ebo.

  During the operation of the load cell 1, the a measurement mode and the b measurement are performed in order to appropriately measure the insulation resistance value while the load signal is continuously measured using the operational amplifier 42 and the A / D converter 44. For measuring the insulation resistance value during a short period of time while the article is being supplied to the weighing unit such as the weighing hopper or the article is being discharged from the weighing unit. The a measurement mode and the b measurement mode are performed.

  After using the load cell 1 for a long period of time, the insulation resistance value between each strain gauge 6 of the bridge circuit 10 and the insulation resistance value measurement point 46 may decrease. In this case, when the b measurement mode is performed, in the normal state, as described above, the current that should flow from the power supply excitation end 10a to the power supply excitation end 10b flows from the reference resistor 50 to the common line C through the reduced insulation resistance. The voltage across the reference resistor 50 at that time is measured as the insulation resistance value index voltage Ebx and stored in the memory of the arithmetic circuit 26. If Ebx-Ebo is larger than a predetermined allowable value Ebr, the arithmetic circuit 26 determines that the insulation resistance value is abnormally small, and displays a warning to that effect on the display unit 30, for example. To do. Of course, if Ebx-Ebo is equal to or less than Ebr, since the insulation resistance value can be considered normal, no alarm is given.

  However, in the case of only the b measurement mode, even if the insulation resistance value between the vicinity of the power source excitation end 10b and the insulation resistance value measurement point 46 decreases, the potential near the power source excitation end 10b is originally set to the potential of the common line C. Since it is close, the current flowing to the reference resistor 50 is very small, the value of the insulation resistance value index voltage Ebx is very close to the voltage of the common line C, Ebx-Ebo is smaller than the allowable value Ebr, and a decrease in insulation resistance value is detected. It may not be possible.

  Therefore, the a measurement mode is performed following the b measurement mode. Since the values of the reference resistors 50, 54, 56, and 58 are set as described above at the adjustment time described above, the insulation resistance value index voltage Eao is substantially zero. The input circuit whose operational amplifier 64 is not shown is configured such that its input resistance value is sufficiently larger than that of the reference resistors 50, 54, 56 and 58. It is more preferable to incorporate a buffer amplifier in the operational amplifier 64.

  In the b measurement mode described above, in a state where Ebx−Ebo is smaller than the allowable value Ebr, the insulation resistance value index voltage Eax is measured by the a measurement mode and stored in the memory of the arithmetic circuit 26. If the insulation resistance value between the power supply excitation end 10b and the insulation resistance measurement point 46 decreases, the current flowing through the reference resistor 54 not only flows through the reference resistor 50, It flows to the strain gauge 6 near the power source excitation end 10b through the insulation resistance value measurement terminal 48, the insulation resistance value measurement point 46, and the lowered insulation resistance. As a result, the voltage across the reference resistor 50 is smaller than the voltage across the reference resistor 58, and the insulation resistance value index voltage Eax is the insulation resistance value index voltage Eao when the insulation resistance value is normal. Bigger than. Here, the arithmetic circuit 26 determines whether Eax-Eao is larger than a predetermined allowable value Ear, and if it is larger, an alarm is given in the same manner as described above as an abnormality in the insulation resistance value.

  FIG. 4 is a flowchart showing the operation of the weighing device described above. FIG. 4A is an operation flowchart at the time of adjustment, and FIG. 4B is an operation flowchart during operation. At the time of adjustment, the insulation resistance value index voltage Eao is measured in the a measurement mode and stored in the memory of the arithmetic circuit 26, and the insulation resistance value index voltage Ebo is measured and stored in the memory of the arithmetic circuit 26 in the b measurement mode. (Step S2). The insulation resistance value index voltage Ebx is measured in the b measurement mode as appropriate at the time of operation or during article supply or discharge, and is stored in the memory of the arithmetic circuit 26 (step S4), and Ebx-Ebo is greater than the allowable value Ebr. If the answer is yes, an abnormal alarm is generated (step S8). If the answer to the determination in step S6 is no, the insulation resistance value index voltage Eax is measured in the a measurement mode and stored in the memory of the arithmetic circuit 26 (step S10). Next, it is determined whether Eax-Eao is greater than the allowable value Ear (step S12). If the answer to the determination is yes, step S8 is executed to alert. If the answer to the determination in step S12 is yes, the insulation resistance value is normal, and thus this process ends.

  The a and b measurement modes can be carried out while the excitation power source from the power source 40 is connected to the strain gauge 6 of the bridge circuit 10, so that the operational amplifier 42 and the A / D converter 44 are used, for example, like a conveyor scale. It can be carried out while continuously measuring the load signal, ie weighing. In addition, the a and b measurement modes can be implemented even in a short time during which an article is supplied to or discharged from a hopper scale or a weighing hopper of a combination weigher. Also, when measuring the insulation resistance value, the power supply common to the operational amplifier 42 and the A / D converter 44 for load measurement can be used for the operational amplifier 64 and the A / D converter 68 for measuring the insulation resistance value. There is no need to prepare a power supply for measuring the insulation resistance value.

  Further, it is not necessary to insert an analog switch or a relay contact between the operational amplifier 42 for measuring the load and the bridge circuit 10. When the signal from the bridge circuit 10 input to the operational amplifier 42 is a low level voltage and high precision measurement is required, the leakage current of the analog switch and the thermoelectromotive force of the relay contact are bridged. Although it becomes an error factor with respect to the signal from the circuit 10, there is no problem in the weighing device of this embodiment.

  In the first embodiment, the potential of the insulation resistance value measurement terminal 48 and the connection point 60 in the a measurement mode is an intermediate potential between the normal line N and the common line C. Any voltage between them can also be used.

  A weighing device according to a second embodiment of the present invention is shown in FIG. The weighing device of this embodiment includes a positive power source 40P that outputs + V volts between the normal line N1 and the common line C, and a negative power source that outputs −V volts between the normal line N2 and the common line C. This is a dual power supply type using 40N. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In this embodiment, when the insulation resistance value between the strain gate 6 of the bridge circuit 10 and the metal strain body 2 is large, the potentials of the insulation resistance value measuring terminal 48 and the connection point 60 are both normal lines, for example. The resistance values of the reference resistors 50, 54, 56, and 58 are set so as to be an intermediate potential + V / 2 between N1 and the common line C. It is also possible to set to other values. The weighing device of this embodiment also operates in the same manner as the weighing device of the first embodiment.

  A weighing device according to a third embodiment of the present invention is shown in FIG. In the weighing device of this embodiment, the load signal is also measured using the operational amplifier 64 and the A / D converter 68. Therefore, contacts 52d, 62d, 66d are added to the analog switches 52, 62, 66. Since the load signal generated at the measurement terminals 36 and 38 vibrates according to the load applied to the measuring unit, the input of the filter 70 having a large time constant such as a low-pass filter for removing the vibration is used. The measuring terminals 36 and 38 are connected to the side, and the output of the filter 70 is supplied to the contacts 62d and 66d.

  When the weighing device is in the load signal measurement mode, the contact 52c is connected to the contact 52d, the contact 62c is connected to the contact 62d, and the contact 66c is connected to the contact 66d in order to measure the load signal.

  When the weighing device is in a non-weighing state, for example, when the article is supplied to the weighing hopper of the weighing unit, or when the article is discharged from the weighing hopper, the a measurement mode and the b measurement mode described above are performed. When these measurements are completed, the load signal measurement mode is switched again.

  Unless the excitation power supply to the bridge circuit 10 is switched, the current load signal state is continuously stored in the filter 70 because the filter 70 is a filter having a large time constant even during the a and b measurement modes. As soon as the load signal measurement mode is entered, the current stable load signal can be measured. Therefore, this weighing device is suitable for a weighing device that measures the load of an article in a short time cycle.

  FIG. 7A shows a weighing device according to a fourth embodiment of the present invention. In this weighing device, the contact 52c of the analog switch 52 is connected to the insulation resistance value measuring terminal 48, and the contact 52a is connected to the other end of the reference resistor 50 whose one end is connected to the common line C. The contact 52 b is connected to the other end of the reference resistor 54 whose one end is connected to the normal line N. The contacts 62c and 66c of the analog switches 62 and 66 are connected to the input side of the operational amplifier 64. However, the contact 62a of the analog switch 62 is connected to the insulation resistance value measuring terminal 48, and the contact 62b has one end. The other end of the resistor 56a connected to the normal line N is connected. One end of the contact 66 a of the analog switch 66 is connected to the other end of the resistor 58 b connected to the common line C, and the contact 66 b is connected to the insulation resistance value measuring terminal 48. Since other configurations are the same as those of the weighing device of the first embodiment, detailed description thereof is omitted.

  In this measuring device, in the a measurement mode, the contacts 52c, 62c and 66c of the analog switches 52, 62 and 66 are connected to the contacts 52a, 62a and 66a, and in the b measurement mode, the contacts 52c, 62c and 66c are connected to the contact 52b. , 62b, 66b.

  As a measurement mode at the time of adjustment, the voltage across the reference resistor 50 is measured as an insulation resistance value index voltage Eao and stored in the memory of the arithmetic circuit 26 as shown in FIG. At the adjustment time point when the insulation resistance value is large, the insulation resistance value index voltage Eao is approximately the voltage of the common line C. The a measurement mode is set during operation, and the insulation resistance value index voltage Eax is measured and stored in the memory of the arithmetic circuit 26. At this time, if the insulation resistance value is reduced, a current flows from the power supply excitation end 10a to the reference resistor 50 via the insulation resistance. With this current, the voltage across both ends of the reference resistor 50 (insulation resistance value index voltage Eax) becomes larger than the adjustment time. Therefore, as in the first embodiment, it can be determined whether or not the insulation resistance value is reduced by determining whether or not Eax-Eao is greater than the allowable value Ear.

  However, similarly to the weighing device of the first embodiment, when the insulation resistance value between the vicinity of the power source excitation end 10b and the insulation resistance value measurement point 46 is lowered, there is a possibility that a decrease in the insulation resistance value cannot be detected. Therefore, the b measurement mode is performed at the adjustment time and the operation time. When the b measurement mode is set as shown in FIG. 5C at the adjustment time when the insulation resistance value is large, the voltage across the reference resistor 54 is substantially the voltage of the normal line N. This is measured as an insulation resistance value index voltage Ebx and stored in the memory of the arithmetic circuit 26. The b measurement mode is set during operation, and the insulation resistance value index voltage Ebx, which is the voltage across the reference resistor 54, is measured and stored in the memory of the arithmetic circuit 26. At this time, if the insulation resistance value between the vicinity of the power source excitation end 10b and the insulation resistance value measurement point 46 is reduced, a current flows from the reference resistor 54 to the common line C via the insulation resistance. With this current, the voltage across both ends of the reference resistor 54 (insulation resistance value index voltage Ebx) becomes smaller than the adjustment time. Therefore, it is determined whether Ebo-Ebx is greater than the allowable value Ebr. If it is greater, it can be determined that the insulation resistance value has decreased.

  The reference resistors 50 and 54 need to be stable with respect to temperature as in the first embodiment, but the resistors 56a and 58a have meaning as protective resistors for the operational amplifier 64. Therefore, the stability of the reference resistors 50 and 54 is not necessary.

  In each of the above embodiments, a column-type metal strainer is used, but a Robertal-type metal strainer can also be used. In each of the above embodiments, the a measurement mode and the b measurement mode are executed, but only one of them can be executed. Although the a measurement mode is executed during operation and the b measurement mode is set after that, the b measurement mode may be executed first and then the a measurement mode may be executed. Although not shown in each of the above embodiments, for example, an analog switch is provided between the reference resistor 54 and the normal line N or N1, and between the reference resistor 50 and the common line or normal line N2, respectively. Only when the resistance value is measured, these analog switches are closed, and the voltage of the insulation resistance value measuring terminal 48, that is, the voltage of the metal strain body 2 is not determined during the measurement of the load signal. Even if the insulation resistance value of a part of the bridge circuit 10 starts to decrease during use, the current is prevented from flowing to the metal strain body 2 from the portion where the insulation resistance value has decreased during the load signal measurement. You can also. In the first and third embodiments, the potential of the insulation resistance value measurement terminal 48 and the connection point 60 is set to the intermediate potential between the normal line N and the common line C in the b measurement mode. It can also be any voltage between C.

DESCRIPTION OF SYMBOLS 1 Load cell 2 Metal strain body 6 Load measuring strain gauge 10 Wheatstone bridge circuit 10a, 10b Power supply excitation terminal 14 16 Power supply excitation terminal 18 20 Measurement terminal 32 34 Power supply excitation terminal 36 38 Measurement terminal 40 Power supply 50 Reference resistance 64 Operational amplifier (voltage measuring means)
68 A / D converter (voltage measuring means)

Claims (2)

A metal strain body with a plurality of strain gauges attached thereto;
Bridge means including the plurality of strain gauges, and having two power source excitation ends and two output ends of the connection ends connecting the plurality of strain gauges to each other;
Two power excitation terminals respectively connected to the two power excitation ends via connection lines;
Power supply means for supplying power to the two power excitation terminals;
Two measuring terminals respectively connected to the two output ends via a connecting line, and a voltage between the two output ends being measured as a load signal;
Reference resistance means in which one terminal is connected to the metal strain body or a conductor in contact with the metal strain body, and
A current flowing from the power supply means through the insulation resistance component existing between the plurality of strain gauges, the two power source excitation ends and the two output ends, and the metal strain body or the conductor is the reference resistance. A current path configured to flow through the means and back to the power supply means;
Voltage measuring means for measuring a voltage generated between both ends of the reference resistance means and representing an index of the magnitude of the insulation resistance value of the insulation resistance component;
A weighing apparatus comprising the power supply means used for measuring the load signal when measuring the insulation resistance value.   2. The measuring device according to claim 1, wherein the voltage of the other terminal opposite to the one terminal of the reference resistance means is between the two power excitation terminals in a state where the insulation resistance value is high. A weighing device having a certain value or a value equal to one of the voltages of the two power source excitation terminals.

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