JP2007078374A - Dc current measurement device and method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem all at once that the temperature dependency of the Hall element constituting the current sensor, and the generation of offset voltage caused by the temperature drift of the DC amplifier and moreover to simplify the design and implementation. <P>SOLUTION: The current sensor 1 measures the DC large current of the primary conductor 2 with a Hall element, the output voltage of this Hall element is amplified by the DC amplifier, then a current measurement signal is derived. The signal process circuit 3 obtains the current measurement signal by converting the output of the current sensor by A/D converter 3A into the digital value. The false current sensor 4 is constituted of circuit constitution and structure same as the current sensor, and arranged in the almost same circumference temperature and not interlinked with the primary conductor. The subtractor 3D in the signal process circuit derives the current measurement signal by subtracting the output of false current sensor from the current measurement signal derived by the current sensor by canceling the offset voltage. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a direct current measuring device and a measuring method for measuring a large direct current.

  When measuring a large DC current, a large current cannot be taken directly into the measuring terminal, so in general, a voltage converted to a minute voltage or current of 0 to 5 V, 4 to 20 mA, etc. using a shunt and a transducer. The measurement information is taken into a monitoring device or the like. However, it is necessary to consider the countermeasures for the heat generated by the shunt when a large current is passed to the shunt and transducer, and when trying to manufacture a measuring terminal with a combination of shunt and transducer, It becomes difficult to produce a small and lightweight measuring instrument.

  Therefore, there is a device that realizes miniaturization of a direct current measuring instrument by applying a current sensor using a Hall element instead of a shunt or a transducer (see, for example, Patent Document 1).

  A current sensor using a Hall element is an external view shown in FIG. The opening 1A provided at the center of the current sensor 1 is provided with a donut-shaped core having an air gap (air gap) inside, and a Hall element disposed in the air gap, and the output voltage of the Hall element is further increased. A DC amplifier (AMP, an analog amplifier made into IC) for amplification is provided. The primary side conductor 2 is passed through the opening of the current sensor 1 and a constant current is passed from the external power source to the hall element, so that the primary side conductor 2 is connected to the secondary side output of the current sensor 1 (output of the DC amplifier). A measurement voltage (or measurement current) proportional to the current value of is obtained.

As shown in FIG. 3, the configuration of the measuring device from the primary side conductor 2 to the measurement terminal (signal processing circuit) converts the secondary output value of the current sensor 1 into an A / D converter in the measurement signal processing circuit 3. The digital value is converted by 3A, and this data is taken into the DC voltage measuring unit 3B.
JP-A-1-105177

  A current sensor using a Hall element is smaller and lighter than a shunt or transducer, but has a problem that it is vulnerable to temperature changes.

  FIG. 4 shows an example of offset voltage-temperature characteristics for three current sensors. A DC output due to an offset appears on the secondary side of the sensor due to a change in ambient temperature. In the configuration of the measuring apparatus as shown in FIG. Errors due to changes in ambient temperature are included, and stable measurement is not possible.

  The generation of the offset voltage is caused by the temperature dependency of the Hall element. This temperature dependency is caused by the basic characteristics of the Hall element and cannot be eliminated directly. Therefore, as a method of compensating for the output fluctuation of the sensor due to the temperature of the Hall element, in Patent Document 1 described above, a temperature compensation circuit including a temperature sensor and an impedance conversion circuit is added to the drive circuit for flowing a constant current through the Hall element. It is proposed to provide. This compensation method requires the design and addition of a compensation circuit for each Hall element, such as adjusting the drive voltage of the Hall element based on the temperature detection value, and also requires the selection of circuit elements and circuit constant adjustment during mounting. , Requires a lot of hassle and time.

  Another factor for the generation of the offset voltage is a temperature drift of the DC amplifier. To eliminate this temperature drift, it is conceivable to attach a temperature sensing element and variable resistance circuit to the bias circuit of the DC amplifier, or to form a part in the IC amplifier, but the circuit configuration is complicated. Become expensive.

  An object of the present invention is to provide a DC current measuring device and a measuring method that can eliminate the temperature dependency of the Hall element and the generation of the offset voltage due to the temperature drift of the DC amplifier at once, and that can be easily designed and mounted.

  In order to solve the above problems, the present invention provides a simulated current sensor having a circuit configuration and structure identical to that of the current sensor and electromagnetically decoupled from the primary conductor in addition to the current sensor having a primary circuit. By taking the difference between the measured value obtained from the current sensor having the primary side circuit and the output of the simulated current sensor, the current measurement signal canceling the offset voltage (measurement error) is obtained. It is characterized by the configuration of

(1) A current sensor that obtains an output voltage corresponding to a large DC current of the primary conductor in a Hall element, amplifies the output voltage of the Hall element with a DC amplifier, and obtains a current measurement signal, and outputs the current sensor digitally In a direct current measuring device comprising a signal processing circuit for obtaining a current measurement signal converted into a value,
A simulated current sensor having the same circuit configuration and structure as the current sensor, an arrangement in which the ambient temperature is substantially the same as that of the current sensor, and electromagnetically decoupled from the primary conductor;
The signal processing circuit includes a subtractor that obtains a current measurement signal obtained by subtracting an output of the simulated current sensor from a current measurement signal obtained by the current sensor to cancel an offset voltage.

(2) The current sensor obtains an output voltage corresponding to the direct current large current of the primary conductor to the Hall element, amplifies the output voltage of the Hall element with a DC amplifier to obtain a current measurement signal, and the signal processing circuit In a direct current measurement method for obtaining a current measurement signal obtained by converting the output of a current sensor into a digital value,
The circuit has the same circuit configuration and structure as the current sensor, an arrangement in which the ambient temperature is substantially the same as that of the current sensor, and a simulated current sensor that is electromagnetically uncoupled from the primary conductor is provided.
The signal processing circuit is characterized in that an output of the simulated current sensor is subtracted from a current measurement signal obtained from the current sensor to obtain a current measurement signal in which an offset voltage is canceled.

  As described above, according to the present invention, in addition to a current sensor having a primary circuit, a simulated current sensor having the same circuit configuration and structure as the current sensor and electromagnetically decoupled from the primary conductor is provided. By taking the difference between the measured value obtained from the current sensor with the side circuit and the output of the simulated current sensor, the current measurement signal that canceled the offset voltage (measurement error) was obtained, so the temperature dependence of the Hall element And offset voltage generation due to temperature drift of the DC amplifier can be eliminated all at once, and stable DC current measurement can always be performed without being affected by ambient temperature.

  In addition, it is only necessary to provide a simulated current sensor and a subtracting unit. The current sensor and the simulated current sensor need not have a conventional drive circuit or bias circuit, or can be simply configured, and the design and mounting thereof can be simplified.

  FIG. 1 is a configuration diagram of a direct current measuring apparatus showing an embodiment of the present invention, and parts equivalent to those in FIG. 3 are denoted by the same reference numerals.

  In FIG. 1, a simulated current sensor 4 has the same circuit configuration and structure as the current sensor 1, and is arranged so that the temporary conductor 2 does not penetrate through the opening (1A in FIG. 2) (that is, the primary conductor is electromagnetic Implementation).

  The signal processing circuit 3 includes an A / D converter 3C that converts the output of the simulated current sensor 4 into a digital value, and a subtractor that subtracts the output A2 of the A / D converter 3C from the output A1 of the A / D converter 3A. It is set as the structure which added 3D.

  As described above, the present embodiment is obtained from the current sensor 1 in which the simulated current sensor 4 that is electromagnetically uncoupled from the primary conductor is provided separately from the current sensor 1 and actually takes in the primary current. The difference from the measured value is taken as the DC current measured value.

  Here, if the current sensor 1 and the simulated current sensor 4 are installed close to each other or installed integrally in one case, their ambient temperatures can be made substantially the same. Therefore, since the offset voltage of the current sensor 1 and the simulated current sensor 4 is always substantially the same value, the measurement error due to the change of the ambient temperature can be canceled by taking the difference between the outputs of both sensors by the subtractor 3D.

  Accordingly, the current sensor 1 and the simulated current sensor 4 may have a configuration in which a conventional driving circuit and a bias adjustment circuit for compensating for the offset voltage are unnecessary or simplified.

  For example, the simulated current sensor 4 is prepared as a spare part when the current sensor 1 is manufactured, so that the temperature and electrical performance of both the sensors 1 and 4, particularly the temperature characteristics of the offset voltage. The equivalent can be secured.

  Further, the signal processing circuit 3 can be appropriately changed in design to obtain the same effect. For example, the A / D converter 3A can be configured to switch and input the outputs of the current sensors 1 and 4 with a multiplexer, temporarily hold these inputs on the DC current measuring unit 3B side, and perform a difference calculation thereof. .

The block diagram of the current measuring device which shows embodiment of this invention. The external view of a current sensor. The block diagram of a direct current measuring device (conventional). An example of offset voltage-temperature characteristics of a current sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Current sensor 2 Primary side conductor 3 Signal processing circuit 4 Simulated current sensor 3A, 3C A / D converter 3B DC current measurement part 3D subtractor

Claims (2)

A current sensor that obtains the output voltage corresponding to the large DC current of the primary conductor to the Hall element, amplifies the output voltage of the Hall element with a DC amplifier, and obtains a current measurement signal, and converts the output of this current sensor into a digital value In a direct current measuring device provided with a signal processing circuit for obtaining a current measurement signal,
A simulated current sensor having the same circuit configuration and structure as the current sensor, an arrangement in which the ambient temperature is substantially the same as that of the current sensor, and electromagnetically decoupled from the primary conductor;
The DC current measuring apparatus, wherein the signal processing circuit includes a subtractor that obtains a current measurement signal obtained by subtracting an output of the simulated current sensor from a current measurement signal obtained by the current sensor to cancel an offset voltage. The current sensor obtains an output voltage corresponding to the DC large current of the primary side conductor in the Hall element, amplifies the output voltage of the Hall element with a DC amplifier to obtain a current measurement signal, and the signal processing circuit In a DC current measurement method for obtaining a current measurement signal obtained by converting an output into a digital value,
The circuit has the same circuit configuration and structure as the current sensor, an arrangement in which the ambient temperature is substantially the same as that of the current sensor, and a simulated current sensor that is electromagnetically uncoupled from the primary conductor is provided.
The signal processing circuit obtains a current measurement signal obtained by subtracting the output of the simulated current sensor from a current measurement signal obtained by the current sensor to cancel an offset voltage.

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