JP2013234949A - Weighing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use one common power source for both measuring a load signal and measuring an insulation resistance value.SOLUTION: Two opposing excitation terminals 20a, 20b of a bridge circuit 18 which is constituted by a plurality of strain gauge 8 for measuring the load provided in a strain inducing portion 6 of a metallic strain inducing body 2 are connected to a common line C and a normal line N of a power source 38. The output voltage between output terminals 20c, 20d of the bridge circuit 18 is changed by the application of the load to the metallic strain inducing body 2. A strain gage 24 for measuring the insulation resistance value is provided so as to apply the same environment load as that of each strain gage 8 for measuring the load to the strain inducing body 2, and a bridge circuit 49 including the strain gage 24 for measuring the insulation resistance value is connected to the common line C and the normal line N of the power source 38. The output voltage of the bridge circuit 49 is changed according to the resistance change of the strain gage 24 for the insulation resistance value.

Description

  The present invention relates to a weighing device, and more particularly, to a weighing device that uses a load cell to estimate and evaluate a decrease in insulation resistance value related to a strain gauge included in the load cell.

  Since the metal resistor constituting the strain gauge is usually covered with an insulating and water-resistant resin such as polyimide, moisture does not easily pass therethrough. In addition, the terminal for wiring connection to the metal resistance wire that constitutes the strain gauge and the relay terminal for taking the cable from the load cell to the outside are all provided on the insulating plate made of resin. Silicon rubber, butyl rubber, etc. Since it is covered with rubber for the cover, moisture does not pass easily.

  However, since the water-resistant resin and the cover rubber are porous, water vapor is basically allowed to pass through. Therefore, depending on the long-term use and usage environment of the load cell, the absorbed water vapor becomes moisture, and the insulation resistance between the strain gauge metal resistor or the strain gauge wiring connection terminal and the metal strain generator to which the strain gauge is attached The insulation resistance value related to the strain gauge, which is the value, may drop, and may affect the zero point or span of the load signal as a measurement error.

  For weighing devices used in harsh environments such as an environment with a large temperature difference, an environment in which the measuring unit is washed daily, or an environment where it is installed outdoors, the insulation resistance value related to the strain gauge cannot be ignored in the load signal. Equipment is provided that measures the magnitude of the insulation resistance value related to the strain gauge, determines the magnitude, and gives an alarm before the load signal cannot be measured with the specified accuracy. Is desirable.

  An example of a technique for measuring the insulation resistance value related to the strain gauge is 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. For this reason, two power supplies for exciting the bridge circuit and for the amplifier are prepared. Further, in order to measure the insulation resistance value of the bridge circuit, it is necessary to switch the excitation power source for the bridge circuit between measurement and measurement of the insulation resistance value.

Japanese Patent Publication No. 61-16006

  As described above, the technique of Patent Document 1 requires two power supplies for exciting a bridge circuit and an amplifier, and there is a problem that the circuit cost increases. Further, in the technique of Patent Document 1, when measuring a load signal and measuring an insulation resistance value, the excitation power supply to be supplied to the bridge circuit must be switched to load signal measurement.

  The present invention enables measurement of an insulation resistance value and a load signal by not switching the power supply of the bridge circuit between the case of measurement of a load signal and the case of measurement of an insulation resistance value. An object of the present invention is to provide a weighing device having a common power source used for measurement of insulation resistance.

  The weighing device of one embodiment of the present invention has a metal strain body. Various metal strain bodies can be used, and for example, a Robertal type or a column type can be used. A load measuring strain gauge is provided in each of the plurality of strain generating portions of the metal strain generating body. These strain gauges are connected to a bridge circuit to constitute a load measuring means. In the load measuring means, two opposing excitation ends of the bridge circuit are connected to the common line and the normal line of the unipolar power supply means or connected between the normal lines of the bipolar power supply means. Yes. The output voltage between the two other opposite output ends of the bridge circuit is changed by applying a load to the metal strain body. The insulation resistance value measuring means includes at least one insulation resistance value measuring element provided so that the same environmental load as the load measuring strain gauge is applied to the strain generating body. The at least one insulation resistance value measuring element constitutes a bridge circuit together with other bridge constituting means, for example, and constitutes the insulation resistance value measuring means. The insulation resistance value measuring means is connected to the common line and the normal line of the unipolar power supply means, or connected between the respective normal lines of the bipolar power supply means. The output voltage of the insulation resistance value measuring means changes according to the resistance change of the insulation resistance value measuring element.

  In the weighing apparatus configured as described above, a common unipolar or bipolar power supply means is used for the insulation resistance value measuring means and the load measuring means. Therefore, since it is not necessary to switch between separate power supply means for the load measurement and the insulation resistance value measurement, both measurements can be performed simultaneously. Further, since a common power source is used by the insulation resistance value measuring means and the load measuring means, it is not necessary to prepare separate power means, and the cost of the weighing device can be reduced.

  The voltage measuring means for the load measuring means to which the output voltage of the load measuring means is supplied, and at the same time when the output voltage of the load measuring means is supplied to the voltage measuring means for the load measuring means, An insulation resistance value measuring means voltage measuring means to which an output voltage is supplied can be provided. In this case, the voltage measuring means for the load measuring means and the voltage measuring means for the insulation resistance value measuring means are connected to a common line and a normal line of the unipolar power supply means, or of the bipolar power supply means. Connected between each normal line.

  If comprised in this way, an insulation resistance value can also be measured in parallel with the measurement of a load signal, without switching a power supply means at the time of the measurement of a load signal, and the measurement of an insulation resistance value. Moreover, a common power supply means can be used for the load measuring means, the voltage measuring means for the load measuring means, the insulation resistance measuring means, and the voltage measuring means for the insulation resistance value measuring means. If the power supply means is switched from the measurement state of the insulation resistance value to the measurement state of the load signal, the load signal output from the bridge means varies at the time of switching. In many cases, the load measuring means voltage measuring means to which the output voltage supplied by the load signal measuring means is supplied and the subsequent processing calculation means are provided with a filter having a large delay for signal smoothing. When the power supply is switched to measure the load signal again from measurement, a waiting time is required until the delayed response of the filter converges, and a weighing device such as a conveyor scale that requires continuous measurement of the load signal Then, when the power supply means is switched to measure the insulation resistance value, the load signal cannot be measured while waiting for the stability of the load signal. Because of such timing delay, even a normal weighing device that does not always measure the load signal continuously cannot switch from the load signal measurement to the insulation resistance value measurement or vice versa at any timing. However, with the configuration described above, there is no need to switch the power supply means, and no standby time is required, and it is necessary to constantly measure the load signal. There is no measurement timing delay, and even a normal weighing device can be switched from measurement of a load signal to measurement of an insulation resistance value or vice versa at an arbitrary timing. Further, since the load measuring means voltage measuring means and the insulation resistance value measuring means voltage measuring means are provided, one voltage measuring means is switched to the load measuring insulation resistance value measuring means by the switching means, and the voltage measuring means. It is not necessary to switch the low-level signal line in the previous stage, and no leakage current flows through the switching means, so that the load signal and the insulation resistance value can be measured with high accuracy.

  Alternatively, it is possible to provide one voltage measuring means for switching and supplying the output voltage of the load measuring means and the output voltage of the voltage measuring means for the insulation resistance value measuring means via the switching means. In this case, the voltage measuring means is connected to the common line and the normal line of the unipolar power supply means, or is connected between the normal lines of the bipolar power supply means. If comprised in this way, since only one voltage measuring means should be prepared, cost reduction can be aimed at.

  The at least one element for measuring and measuring an insulation resistance value can be attached in the same posture as the strain gauge in the vicinity of the strain gauge for load measurement. The at least one insulation resistance value measuring element may have the same properties as the load measuring strain gauge. With this configuration, since a change in the insulation resistance value similar to the change in the insulation resistance value occurring in the strain gauge for load measurement occurs in at least one insulation resistance value measuring element, the insulation resistance value is accurately measured. be able to.

  Alternatively, the at least one insulation resistance value measuring element is subjected to a moisture proof or waterproof measure common to the strain gauge for load measurement on a portion of the strain generating body that is not distorted when a load is applied to the strain generating body. Can be provided. With this configuration, since the change in the insulation resistance value similar to that of the strain gauge for load measurement occurs at least in one insulation resistance measurement element without being affected by the applied load, the insulation resistance value can be accurately determined. Can be measured.

  The insulation resistance value measuring means may be constituted by the at least one insulation resistance value measuring element and a plurality of resistance means. In this case, the change in the resistance value of the at least one insulation resistance element can be measured regardless of the temperature change in the resistance of the wiring connecting them. For example, the technique disclosed in Patent Document 1 discloses that a change amount due to a decrease in the insulation resistance value of an input resistance value is detected as a detection voltage. In a mathematical expression representing this detection voltage, a load cell, a voltage measurement circuit, and the like are disclosed. If the distance between the voltage measurement circuit and the load cell is long and the wiring resistance value increases, the wiring resistance value fluctuates due to changes in temperature, resulting in detection errors. . However, in this aspect, the insulation resistance value can be measured regardless of the temperature change of the resistance of the wiring, and even if the wiring between the voltage measurement circuit and the bridge circuit is long, it is affected by the temperature change of the wiring resistance. Therefore, the insulation resistance value can be measured accurately.

  As described above, according to the present invention, it is possible to use a common power supply means for measuring a load signal and for measuring an insulation resistance value, thereby reducing the cost of the weighing device. Further, according to one aspect of the present invention, there is no need to switch from the insulation resistance value measurement state to the load signal measurement state, and the standby time is unnecessary. Moreover, in another aspect, since only one voltage measuring means needs to be provided, the cost can be further reduced. According to another aspect, the insulation resistance value can be measured with high accuracy, and the influence of the wiring resistance can be removed.

FIG. 2 is a circuit diagram of a part of the weighing device according to the first embodiment of the present invention. It is the front view and top view of the weighing | measuring apparatus of FIG. FIG. 2 is a block diagram of the weighing device in FIG. 1. FIG. 2 is an equivalent circuit diagram of a part of the circuit of FIG. 1. It is a circuit diagram of a part of the weighing device according to the second embodiment of the present invention. It is a partial circuit diagram of the weighing | measuring apparatus of the 3rd Embodiment of this invention. It is a partial circuit diagram of the weighing | measuring apparatus of the 4th Embodiment of this invention. FIG. 8 is an equivalent circuit diagram of a part of the circuit of FIG. 7. It is a partial circuit diagram of the weighing | measuring apparatus of the 5th Embodiment of this invention.

  The weighing device according to the first embodiment of the present invention includes a load cell 1 as shown in FIGS. 2 (a) and 2 (b). The load cell 1 has a metal strain body 2. This metal strain body 2 is a parallelogram type of Robertal type, and a plurality of, for example, two strain portions 6 are formed on each of two beam portions 4 positioned in parallel with a space in the vertical direction. Has been. A plurality of, for example, four load measuring strain gauges 8 are attached to the upper strain generating portion 6. A fixed portion 10 is formed across one end side of the two beam portions 4, and a load applying portion 12 is formed across the other end side. The fixing unit 10 is fixed to the support unit 14, and a mounting table 16 is attached to the load application unit 12.

  As shown in FIG. 1, the four load measuring strain gauges 8 are connected to form a bridge circuit, for example, a Wheatstone bridge circuit 18. The Wheatstone bridge circuit 18 has power supply excitation ends 20a and 20b facing each other and output ends 20c and 20d facing each other, and these are wiring lines provided in the fixed portion 10 as shown in FIG. The plates 22 are connected to terminals 22a to 22d, respectively. That is, as shown in FIG. 1, the power excitation end 20a is connected to the terminal 22a, the power excitation end 20b is connected to the terminal 22b, the output end 20c is connected to the terminal 22c, and the output terminal 20d is connected to the terminal 22d.

  As shown in FIGS. 2 (a) and 2 (b), a position in the metal strain body 2 that is not strained by application of a load and is as close to the load measuring strain gauge 8 as possible, for example, the upper beam. An insulation resistance value measuring element, for example, an insulation resistance value measuring strain gauge 24 is attached to the center of the length direction of the portion 4. This insulation resistance value measuring strain gauge 24 has the same properties as the load measuring strain gauge 8. That is, the insulation resistance value measuring strain gauge 24 has substantially the same environmental conditions as the load measuring strain gauge 8, and the specification of the insulation resistance value measuring strain gauge 24 is the same as that of the load measuring strain gauge 8. It is the same as the specification. As shown in FIG. 1, one end of the insulation gauge measuring strain gauge 24 is connected to the terminals 22e and 22f of the wiring board 22, and the other end is connected to the power excitation end 20b of the Wheatstone bridge circuit 18. It is connected to the terminal 22b. Although not shown, the load signal measurement strain gauge 8, the insulation resistance value measurement strain gauge 24, and the terminal board 22 are coated with an organic material such as butyl rubber, and are provided with common waterproof and moisture-proof measures. .

  Each terminal 22a thru | or 22f of the wiring board 22 is connected to the indicator 26 shown in FIG. 3 via the cable which is not shown in figure. The indicator 26 has a voltage measurement circuit 28, an arithmetic circuit 30, an operation setting switch 32, and a display unit 34. The arithmetic circuit 30 includes a CPU, an input / output circuit, and a memory. The operation setting switch 32 sets data used in the arithmetic circuit 30 and gives an operation instruction such as calculation start. Displays warning characters for weight display value and insulation resistance drop. In this embodiment, a part of the voltage measuring circuit 28 and the arithmetic circuit 30 constitute a load measuring means voltage measuring means and an insulation resistance measuring means voltage measuring means. In addition, an alarm buzzer is also provided (not shown) for notifying the decrease of the insulation resistance value by voice.

  As shown in FIG. 1, the voltage measurement circuit 28 also has a wiring board 36. The wiring board 36 has terminals 36a to 36f connected to the terminals 22a to 22f of the wiring board 22 by cables, respectively. That is, the terminal 36a is connected to the terminal 22a, the terminal 36b is connected to the terminal 22b, the terminal 36c is connected to the terminal 22c, the terminal 36d is connected to the terminal 22d, the terminal 36e is connected to the terminal 22e, and the terminal 36f is connected to the terminal 22f. In addition, what is shown by the code | symbol r in FIG. 1 is the resistance part of the cable which connects between each terminal.

  The terminal 36 a is connected to a unipolar power supply means, for example, the normal line N of the power supply 38, and the terminal 36 b is connected to the common line C of the power supply 38. Therefore, the normal line N of the power source 38 is connected to the power source excitation end 20a of the Wheatstone bridge circuit 18 through the terminals 36a and 22a, and the common line C of the power source 38 is connected to the Wheatstone bridge circuit 18 through the terminals 36b and 22b. Is connected to the excitation power supply terminal 20b. As a result, the voltage of the power supply 38 is supplied between the excitation power supply terminals 20 a and 20 b of the Wheatstone bridge circuit 18.

  The terminals 36c and 36d are connected to two input terminals of the operational amplifier 40 via an input circuit (not shown). Therefore, the output voltage between the output terminals 20c and 20d of the Wheatstone bridge circuit 18 is supplied to both input terminals of the operational amplifier 40 via the terminals 36c, 22c, 36d and 22d, and this is the voltage measurement for the load signal measuring means. It is amplified by an operational amplifier 40 that forms part of the means. The operational amplifier 40 has one power supply terminal connected to the normal line N of the power supply 38 and the other power supply terminal connected to the common line C of the power supply 38. As a result, an operating voltage is supplied from the power source 38 to the operational amplifier 40. The output voltage of the operational amplifier 40 is digitized by A / D conversion means, for example, an A / D converter 42, and supplied to the arithmetic circuit 30 shown in FIG. Note that the positive power supply terminal of the A / D converter 42 is connected to the normal line N of the power supply 38, and the negative power supply terminal is connected to the common line C of the power supply 38, so that an operating voltage is supplied from the power supply 38. Therefore, when a load is applied to the load application unit 12 of the metal strain body 2, the output voltage between the output ends 20 c and 20 d changes, and the changed output voltage is amplified by the operational amplifier 40 and A / D converted. It is digitized by the device 42, supplied to the arithmetic circuit 30, subjected to arithmetic processing, and the load value is displayed on the display unit 34.

  In the voltage measurement circuit 28, reference resistors 44 and 46 are connected in series between the terminals 36a and 36b, that is, between the normal line N and the common line C of the power source 38 at the interconnection point 37a. The reference resistors 44 and 46 have substantially the same resistance value and are stable against temperature changes. A reference resistor 48 is also connected between the terminals 36a and 36e. The reference resistor 48 has substantially the same resistance value as the insulation resistance value measuring strain gauge 24 and is stable with respect to a temperature change. The reference resistors 44, 46, and 48 and the insulation resistance value measuring strain gauge 24 constitute an insulation resistance value measuring means, for example, a bridge circuit, specifically, a Wheatstone bridge circuit 49. In the bridge circuit 49, the terminals 36 a and 36 b serve as excitation power supply terminals, and these are connected to the normal line N and the common line C of the power supply 38. Therefore, the power source of the bridge circuit 49 serving as the insulation resistance measuring means is common to the Wheatstone bridge circuit 18 serving as the load signal measuring means.

  An interconnection point 37a of the reference resistors 44 and 46 is connected to one input terminal of an operational amplifier 50 forming a part of the voltage measuring means for insulation resistance measuring means via an input circuit (not shown), and the other input terminal is The terminal 36f is connected via an input circuit (not shown). Since the terminal 36f is connected to the terminal 22f, between the input terminals of the operational amplifier 50, the terminal 22f that is the output terminal of the bridge circuit 49 and the interconnection point 37a of the reference resistors 44 and 46 are connected. Output voltage is supplied. The normal line N of the power supply 38 is connected to the positive power supply terminal of the operational amplifier 50, the common line C of the power supply 38 is connected to the negative power supply terminal, and an operating voltage is supplied from the power supply 38 to the operational amplifier 50. . The output voltage of the operational amplifier 50 is digitized by A / D conversion means, for example, an A / D converter 52, and supplied to the arithmetic circuit 30 shown in FIG. One power supply terminal of the A / D converter 52 is connected to the normal line N of the power supply 38, and the other power supply terminal is connected to the common line C of the power supply 38, and the operating voltage is supplied from the power supply 38. .

  FIG. 4 is an equivalent circuit diagram of the bridge circuit 49 in FIG. 1. The resistance r of the cable between the terminals 36e and 22e and the resistance r of the cable between the terminals 36b and 22b are the reference resistor 48 and the insulation resistance value, respectively. A measuring strain gauge 24 is connected in series. The resistance of the cable between the terminal 22f and the terminal 36f is connected to the other input terminal of the operational amplifier 50. The input resistance value at the other input terminal is a large value that can ignore the change in the resistance r. In this way, an input circuit (not shown) is configured.

  As described above, the load signal measuring strain gauge 8, the insulation resistance measuring strain gauge 24, and the terminal board 22 are coated with an organic material such as butyl rubber, and are provided with common waterproof and moisture-proof measures. When 1 is placed in an environment where water vapor is contained and the temperature changes drastically, the water vapor absorbed by the porous organic material is moistureated, and the resistance value of the strain gauge 8 for measuring each load signal of the bridge circuit 18. Changes, and the insulation resistance value between each load signal measuring strain gauge 8 and the metal strain body 2 decreases. At this time, the same resistance change as that of the load signal measuring strain gauge 8 occurs in the insulation resistance measuring strain gauge 24 which is placed in the same environment as the load signal measuring strain gauge 8 and uses the same material and the same coating agent. . Utilizing this point, by measuring the decrease in the insulation resistance value of the insulation resistance value measuring strain gauge 24, the arithmetic circuit 30 estimates and evaluates the decrease in the insulation resistance value in the load signal measuring strain gauge 8. .

  That is, the reference resistors 44, 46, and 48 in FIG. 1 have stable performance against temperature changes as described above, and even if the resistance r of the cable changes in temperature, the equivalent circuit in FIG. As shown, the resistance r of the cable is connected in series to the reference resistor 48 and the strain gauge 24 for measuring the insulation resistance value. The reference resistor 48 is the same type as the insulation resistance value measuring strain gauge 24 and is attached to a plate of the same material as the metal strain body 2 on the side where the voltage measuring circuit 28 is accommodated. It is appropriate to do. In this state, if the load resistance measuring strain gauge 8 and the insulation resistance value measuring strain gauge 24 have high insulation resistance values with respect to the strain generating body 2 and the insulation resistance values between the terminals of the strain gauges 8 and 24 are also high. For example, even if the ambient temperature changes, the potential at one end of the insulation resistance value measuring strain gauge 24 connected to the terminals 22e and 22f and the potential at the interconnection point 37a of the reference resistors 44 and 46, that is, the bridge The potential at each output terminal of the circuit 49 does not change. As shown in FIG. 1, an insulation resistance value re1 is generated between the strain gauge 24 for measuring the insulation resistance value and the metal strain body 2, and the terminal on the wiring board 22 and the metal strain body 2 are connected to each other. An insulation resistance value re2 is generated between the two ends of the insulation resistance measuring strain gauge 24 in series with the insulation resistance value re1. Similarly, an insulation resistance value re3 is generated between the terminals of the insulation resistance value measuring strain gauge 24 and the wiring board 22 and is connected between both ends of the insulation resistance value measuring strain gauge 24. Even when these values are extremely high, resistances that are sufficiently smaller than the resistance values of the reference resistors 44 and 48 and stable with respect to temperature so that the polarity of the output voltage of the operational amplifier 50 is positive. The values of the reference resistors 44, 46 and 48 are set by connecting the resistors in series. When one of the insulation resistance values re1, re2, and re3 is lowered due to the influence of moisture or the like from the state in which the insulation resistance values re1, re2, and re3 are all high, the insulation resistance value is equivalently measured. The resistance value of the strain gauge 24 decreases, and the output voltage of the operational amplifier 50 varies. Based on this variation, the arithmetic circuit 30 estimates and evaluates the reduced state of the insulation resistance value of the load signal measuring strain gauge 8. Note that, regardless of whether the output voltage of the operational amplifier 50 decreases or increases due to a change in the insulation resistance value, the output voltage of the operational amplifier 50 is always positive within the range that can be evaluated.

  The digital value E0 of the output voltage of the operational amplifier 50 is read as an initial value into the arithmetic circuit 30 at the time when the load cell 1 is used because the insulation resistance value of the load cell 1 is high and normal, for example, when the load cell 1 is adjusted. The data is stored in the memory in the arithmetic circuit 30 by operating the setting switch 32. In the use state of the load cell 1, the digital value Ex of the output voltage of the operational amplifier 50 is read into the arithmetic circuit 30, and the arithmetic circuit 30 obtains the fluctuation value Edx from the initial value as Ex-E0.

  Edx at a level that gives an error to the load signal is determined in advance as an allowable value Ee and stored in the arithmetic circuit 30. When the arithmetic circuit 30 determines that Edx> Ee is satisfied, the insulation resistance value for the strain gauge for load signal measurement is determined. Is estimated to be lower than the allowable value, and a warning character is displayed on the display unit 30 or a specially provided electronic buzzer is operated to notify the decrease in the insulation resistance value. .

  In the weighing device according to the first embodiment, since the strain gauge 8 for measuring the load signal and the strain gauge 24 for measuring the insulation resistance value are excited by the common power source 38, the circuit configuration is simplified. Further, since the load signal measurement and the insulation resistance value measurement can be simultaneously performed in parallel, the load signal can be continuously measured without waiting time. That is, when one voltage measurement circuit is used for measuring the insulation resistance value and the load signal, the output voltage of the bridge circuit 18 and the output voltage of the bridge circuit 49 are used for one voltage measurement. In particular, when the output voltage of the bridge circuit 18 is switched from the state where the output voltage of the bridge circuit 49 is supplied to the state where the output voltage of the bridge circuit 18 is supplied, the operation amplifier is in a standby state where the output voltage is stabilized. Although the load cannot be measured until the passage of time, in this embodiment, since the load signal measurement and the insulation resistance value measurement can be performed simultaneously in parallel, there is no waiting time. In addition, when the output voltage of the bridge circuit 18 and the output voltage of the bridge circuit 49 are switched and supplied to a single operational amplifier for voltage measurement, if an analog switch is used as the switching means, a leakage current flows to the analog switch. If a relay switch is used, the thermoelectromotive force generated at the contact point of the relay becomes an error factor. However, in this embodiment, switching is not necessary, and the above-described error does not occur. . Further, a bridge circuit that supplies an evaluation to the operational amplifier with respect to the insulation resistance value between both terminals of the load signal measuring strain gauge 8 and the insulation resistance value between both terminals of the strain gauge 8 and the metal strain body 2. Can be performed without switching. Further, since the bridge circuit 49 is configured as shown by an equivalent circuit in FIG. 4, even if the distance between the load cell 1 and the voltage measurement circuit 28 is long, the temperature change in the resistance value of the cable connecting the two is insulated. Does not affect the resistance measurement.

  A weighing device according to a second embodiment of the present invention is shown in FIG. In this embodiment, the strain body 2 and the indicator 26 are arranged at a short distance, and the resistance value of the cable and the temperature change thereof can be ignored. The terminals 22e and 36e are removed, the terminals 36a, A reference resistor 48 is connected between 36 f, and an end of the reference resistor 48 on the terminal 36 f side is connected to the other input terminal of the operational amplifier 50. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted.

  A weighing device according to a third embodiment of the present invention is shown in FIG. The weighing device according to this embodiment simplifies the circuit configuration when an analog switch is inserted in the low-level signal line in the previous stage of the voltage measuring means and the leakage current of the analog switch does not affect the measurement accuracy. Therefore, the operational amplifier is only the operational amplifier 50, and switching means, for example, analog switches 54 and 56 are provided. One of the output terminal 20 c of the bridge circuit 18 and the interconnection point of the reference resistors 44 and 46, which are one output terminal of the bridge circuit 49, is connected to one input terminal of the operational amplifier 50 via the analog switch 54. The other input terminal of the operational amplifier 50 is connected to one of the output terminal 20d of the bridge circuit 18 and the terminal 36 which is the other output terminal of the bridge circuit 49. The analog switches 54 and 56 are controlled by the arithmetic circuit 30. The control is performed when the output terminal 20c of the bridge circuit 18 is connected to one input terminal of the operational amplifier 50 and the output terminal 20d of the bridge circuit 18 is connected to the other input terminal. When the interconnection point of the reference resistors 44 and 46, which is one output terminal of the bridge circuit 49, is connected to one input terminal, the other output terminal is connected to the other output terminal of the bridge circuit 49. It is performed so that one of the states in which a certain terminal 36f is connected is selected. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted.

  A weighing device according to a fourth embodiment of the present invention is shown in FIGS. In the weighing device of this embodiment, two insulation resistance value measuring strain gauges 24a and 24b are used. These strain gauges 24a and 24b are provided on the metal strain body 2 in the same manner as the strain gauge 24 of the first embodiment. The terminals of the wiring boards 22 and 36 are two more than in the first embodiment, and terminals 22a to 22h and 36a to 36h are provided. The terminals 36a and 36b are connected to the normal line N and the common line C of the power supply 38 as in the first embodiment, and the terminals 36a and 36b are connected to the terminals 22a and 22b via cables. Thus, the power supply excitation ends 18a and 18b of the bridge circuit 18 are connected. Similarly to the first embodiment, the output ends 20c and 20d of the bridge circuit 18 are connected to the terminals 22c and 22d via cables, and are connected to the terminals 36c and 36d.

  A reference resistor 44 is connected between the terminals 36a and 36e, the terminal 36e is connected to the terminal 22e via a cable, and the terminal 22e is connected to the terminal 22b via an insulation resistance measuring strain gauge 24b. . One end of the insulation resistance value measuring strain gauge 24a is connected to the terminal 22a, and the other end is connected to the terminals 22f and 22g. The terminals 22f and 22g are connected to the terminals 36f and 36g via cables, and the terminal 36g is connected to the terminal 36b via a reference resistor 46. Accordingly, the reference resistors 44 and 46 and the insulation resistance value measuring strain gauges 24a and 24b constitute a bridge circuit 49a. A terminal 22f, which is one of the two output ends of the bridge circuit 49a, is connected to a terminal 36f via a cable, and the terminal 36f is connected to one input terminal of the operational amplifier 50. The other output terminal 22h of the bridge circuit 49a is connected to the terminal 36h via a cable, and the terminal 36h is connected to the other input terminal of the operational amplifier 50. Therefore, the output voltage of the bridge circuit 49a is supplied to the operational amplifier 50. FIG. 8 is an equivalent circuit of FIG. 7, in which the resistance of the cable is connected in series to the reference resistors 44 and 46 and the strain gauges 24a and 24b for measuring the insulation resistance value, and the resistance of the cable is the same as in the first embodiment. Unaffected by temperature changes in minutes. As in the first embodiment, the input resistance value of both input terminals of the operational amplifier 50 is set to a large value so that the change in resistance of the connected cable can be ignored. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted.

  In this configuration, the same effects as those of the first embodiment are obtained, and the two insulation resistance value measuring strain gauges 24a and 24b are used. Therefore, when these insulation resistance values are reduced, the first A change in the insulation resistance value can be detected with higher sensitivity than in the embodiment.

  A metering device according to a fifth embodiment of the present invention is shown in FIG. The weighing device of this embodiment uses bipolar power supply means, for example, a positive power source 38p and a negative power source 38n, instead of the unipolar power source 38 of the weighing device of the first embodiment. The bridge circuit 18, the operational amplifier 50, and the A / D converter 52 are connected to the normal line Np of the voltage + V and the normal line Nn of the voltage −V by the positive and negative power supplies 38p and 38n. When the reference resistor 48 and the insulation resistance value measuring strain gauge 24 are selected in the same manner as in the first embodiment, the voltage at the terminal 22f is substantially equal to the voltage at the common line C. Are connected to a common line C. Since other configurations are the same as those of the first embodiment, detailed description thereof is omitted. Also in this weighing device, the insulation resistance values re1, re2, and re3 are generated as in the first embodiment. When any one of the insulation resistance values re1, re2, re3 is lowered due to the influence of moisture or the like from a state in which the insulation resistance values re1, re2, re3 are all high, the resistance value of the strain gauge 24 for measuring the insulation resistance value is equivalent. Decreases, and the output voltage of the operational amplifier 50 fluctuates. Based on this variation, the arithmetic circuit 30 estimates and evaluates the reduced state of the insulation resistance value of the load signal measuring strain gauge 8.

  Even in the case where both the positive and negative power supplies 38p and 38n are provided, the insulation resistance value measuring strain gauge 24 is provided between the normal line Np and the common line C of the positive power supply 38p as in the first embodiment. The reference resistors 44, 46, 48, the operational amplifier 50, and the A / D converter 52 can be connected.

  In each of the above embodiments, the metal strain body 2 is a parallelogram type, but is not limited to this, and a column type can also be used. In order to save power consumption in the first embodiment, a resistor may be connected in series with each of the reference resistor 48 and the insulation resistance value measuring strain gauge 24. However, the resistor connected in series to the strain gauge 24 for measuring the insulation resistance value is connected on the metal strain body 2.

  In the weighing devices of the second to fourth embodiments, as in the weighing device of the fifth embodiment, bipolar power supply means, for example, the positive power supply 38p and the negative power supply 38n can be used. In any of the fourth embodiments, the bridge circuit 18, the operational amplifier 50, and the A / D converter 52 are connected to the normal line Np of the voltage + V and the normal line Nn of the voltage −V by the positive and negative power supplies 38p and 38n. Is done. In the second embodiment, as in the fifth embodiment, one terminal of the operational amplifier 50 is connected to the terminal 22f via the terminal 36f, the other terminal is connected to the common line C, and the reference resistor 44 and 46 are removed. In the third embodiment, one input terminal of the operational amplifier 50 is connected to one of the terminal 22f and the output terminal 20d of the bridge circuit 18 via the analog switch 56 and the terminal 36f, and the other terminal of the operational amplifier 50 is connected. Is connected to one of the common line C and the output end 20 c of the bridge circuit 18 via an analog switch 54 that is switched in synchronization with the analog switch 56. The reference resistors 44 and 46 are removed. In the fourth embodiment, the connection to the two input terminals of the operational amplifier 50 is not changed.

2 Metal strain body 8 Load measurement strain gauge 18 Wheatstone bridge circuit 22a to 22f Terminal 24 Insulation resistance value measurement strain gauge 28 Voltage measurement circuit (voltage measurement means for load signal measurement means, voltage for insulation resistance value measurement means Measuring means)
30 arithmetic circuit (voltage measurement means for load signal measurement means, voltage measurement means for insulation resistance value measurement means)
38 Unipolar power supply (Unipolar power supply means)
38p 38n Positive and negative power supply (bipolar power supply means)

Claims (6)

A metal strain body,
A bridge circuit composed of a plurality of load measuring strain gauges provided in a strain generating portion of the metal strain generating body, and two exciting ends facing each other are connected to a common line of a unipolar power source means Are connected between the normal lines of the bipolar power supply means, and an output voltage between two other opposite output terminals of the bridge circuit is supplied to the metal strain body. Load measuring means that changes by applying the load,
Including at least one insulation resistance value measuring element provided so that the same environmental load as the strain gauge for each load measurement is applied to the strain generating body, and connected to the common line and the normal line of the unipolar power supply means Or insulation resistance value measuring means connected between the respective normal lines of the bipolar power supply means, wherein the output voltage changes according to the resistance change of the insulation resistance value measuring element,
Weighing device to have.   2. The weighing device according to claim 1, wherein the voltage measuring means for load measuring means to which the output voltage of the load measuring means is supplied, and the output voltage of the load measuring means is supplied to the voltage measuring means for the load measuring means. Voltage measurement means for insulation resistance value measurement means to which the output voltage of the insulation resistance value measurement means is supplied at the same time, the voltage measurement means for load measurement means and the voltage measurement means for insulation resistance value measurement means, Is a weighing device connected to the common line and the normal line of the unipolar power supply means or connected between the normal lines of the bipolar power supply means.   2. The measuring device according to claim 1, wherein the output voltage of the load measuring means and the output voltage of the voltage measuring means for the insulation resistance value measuring means are supplied by being switched via the switching means. And the voltage measuring means is connected to the common line and the normal line of the unipolar power supply means, or connected between the normal lines of the bipolar power supply means.   4. The weighing device according to claim 1, wherein the at least one insulation resistance value measuring element is a strain gauge having the same property as the load measuring strain gauge.   4. The weighing device according to claim 1, wherein the at least one insulation resistance value measuring element is provided at the portion of the strain generating body where no strain is generated when a load is applied to the strain generating body. Weighing device provided with moisture or waterproof measures common to strain gauges.   6. The measuring device according to claim 1, wherein the insulation resistance value measuring means includes the at least one insulation resistance value measuring element and a plurality of resistance means, and a temperature change in resistance of a wiring connecting them. A measuring device configured to be able to measure a change in resistance value of the at least one insulation resistance element irrespective of the above.

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