JP2005210202A - Offset adjustment method of operational amplifier for power measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an offset adjustment method of operational amplifiers for power measurement, capable of easily matching the offset voltages of a plurality of operational amplifiers with each other. <P>SOLUTION: The operational amplifiers OP1, OP2, OP3 of an amplifier section 43 are formed on the same chip and contained in the same package, each resistance of resistors Rc1, Rc2, Rc3 is set so as to minimize each offset current of the operational amplifiers OP1, OP2, OP3, and even the offset voltage of the operational amplifiers OP1, OP2 whose amplification factor is smaller than that of the operational amplifier OP3 is adjusted to a prescribed value, by adjusting the resistance of a variable resistor VR, while the output of the operational amplifier OP3, whose amplification factor is highest is monitored, to adjust the offset voltage of the output of the operational amplifier OP3 to a prescribed value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an offset adjustment method for a plurality of power measurement operational amplifiers.

  FIG. 2 shows the internal configuration of the residential distribution board A. The external power lines L1, L2 and the neutral line N are first connected to the primary side of the current limiter 1, and the current limiter 2 The secondary side is connected to the primary side of the main earth leakage breaker 2. The secondary side of main leakage breaker 2 is connected to each primary side of a plurality of branch breakers 3, and is connected from the secondary side of each branch breaker 3 to a subsequent circuit.

  Further, in the residential distribution board A, there is housed a power meter 4 for measuring the power consumed by the two systems of the power line L1 and the power line L2. The power measuring instrument 4 is connected to the secondary side of the main earth leakage breaker 2 through the power supply terminal 5 to measure the voltage between the power line L1 and the neutral line N and the voltage between the power line L2 and the neutral line N, respectively. The currents flowing through the power lines L1 and L2 are measured using the current detection signals of the current transformers CT1 and CT2 inserted through the power lines L1 and L2 on the primary side of the main earth leakage breaker 2, respectively. Then, the power consumed in the system of the power line L1 is calculated from the voltage between the power line L1 and the neutral line N and the current flowing through the power line L1, and from the voltage between the power line L2 and the neutral line N and the current flowing through the power line L2. The power consumed in the system of the power line L2 is calculated, and the measurement result of power in each system is displayed on the power display unit, and the measurement result of power in each system is output from the monitor display terminal 4a to the outside.

  Since such a power measuring device 4 amplifies each current detection signal from the current transformers CT1 and CT2, as shown in FIG. 3, an operational amplifier OP for power measurement having a non-inverting input terminal connected to the ground level, One end is connected to the inverting input terminal of the operational amplifier OP, the resistor Ra is connected to the other end of the current detection signal from the current transformer, and the resistor Rb is connected between the inverting input terminal and the output terminal of the operational amplifier OP. An inverting amplifier circuit is provided for each current transformer, and the amplification factor is represented by -Rb / Ra. Further, as shown in FIG. 4, a resistor Rc may be provided between the non-inverting input terminal of the operational amplifier OP and the ground level.

  Furthermore, the power measuring device 4 includes a plurality of inverting amplifier circuits having different amplification factors with respect to the current detection signal from one current transformer in order to widen the input range of the current detection signal from the current transformer. For example, as shown in FIG. 5, one end is connected to each of the operational amplifiers OP1, OP2, and OP3 for power measurement, and the inverting input terminals of the operational amplifiers OP1, OP2, and OP3. Resistors Ra1, Ra2, Ra3 connected to the other ends of the current detection signals from the amplifiers, resistors Rb1, Rb2, Rb3 connected between the inverting input terminals and the output terminals of the operational amplifiers OP1, OP2, OP3, and operational amplifiers OP1, Resistors Rc1, Rc2, and Rc3 having one ends connected to the non-inverting input terminals of OP2 and OP3, one ends connected to the other ends of the resistors Rc1, Rc2, and Rc3, and the other ends to the ground level Between the connected resistors Rd1, Rd2, Rd3, resistors Re1, Re2, Re3 each having one end connected to each other end of the resistors Rc1, Rc2, Rc3, and the positive voltage source + Vcc and the negative voltage source −Vcc Some have three inverting amplifier circuits each composed of variable resistors VR1, VR2 and VR3 having both ends connected and movable terminals connected to the other ends of the resistors Re1, Re2 and Re3. The amplification factors of these three inverting amplification circuits are different from each other, the amplification factor (−Rb1 / Ra1) = 30 of the operational amplifier OP1, the amplification factor (−Rb2 / Ra3) = 100 of the operational amplifier OP2, and the amplification factor (− Rb3 / Ra3) = 300.

  And each output of operational amplifier OP1, OP2, OP3 is connected to the electric power calculating part comprised with a microcomputer. However, the upper and lower limits of the voltage range that can be taken in by the microcomputer are determined. It was necessary to set each offset voltage to the upper and lower center voltages of the voltage range that the microcomputer can capture. For example, as shown in FIG. 6, when the voltage range that the microcomputer can capture is 0 mV to 5000 mV, if each offset voltage of the operational amplifiers OP1, OP2, and OP3 is 2500 mV, the output of the operational amplifier has an offset voltage of 2500 mV as shown in the waveform S1. The allowable range of the positive amplitude and the negative amplitude of the output of the operational amplifier can be provided by 2500 mV. However, when the offset voltages of the operational amplifiers OP1, OP2, and OP3 are shifted to 3500 mV, the output of the operational amplifier changes around the offset voltage 3500 mV as shown in the waveform S2, and the allowable range of the positive amplitude of the operational amplifier is 1500 mV, the negative amplitude. The allowable range is 3500 mV, and the allowable ranges of the positive amplitude and the negative amplitude are different from each other.

  Therefore, conventionally, with respect to a plurality of operational amplifiers, a variable resistor is provided for each operational amplifier, and the offset voltage is adjusted for each operational amplifier by adjusting the resistance values of the plurality of variable resistors. (For example, refer to Patent Document 1). For example, in FIG. 5, the offset voltage of the operational amplifier OP1 is adjusted by adjusting the resistance value of the variable resistor VR1, the offset voltage of the operational amplifier OP2 is adjusted by adjusting the resistance value of the variable resistor VR2, and the resistance of the variable resistor VR3. The offset voltage of the operational amplifier OP3 was adjusted by adjusting the value.

The power measuring instrument 4 shown in FIG. 2 includes two circuits shown in any of FIGS. 3 to 5, and the current values of the power lines L1 and L2 are calculated from the current detection signals from the current transformers CT1 and CT2. Each output.
JP-A-5-203918 (paragraph number [0013], FIG. 2)

  However, in the above conventional example, offset voltage adjusting means comprising resistors Rd1 to Rd3, Re1 to Re3 and variable resistors VR1 to VR3 are connected to each of the operational amplifiers OP1 to OP3 constituting the inverting amplifier circuit, and the offset voltage of each operational amplifier. Therefore, there is a problem that the offset voltages of the operational amplifiers OP1 to OP3 do not match each other due to temperature variation between the resistors and between the variable resistors.

  The present invention has been made in view of the above reasons, and an object of the present invention is to provide an offset adjustment method for an operational amplifier for power measurement that can easily combine offset voltages of a plurality of operational amplifiers.

  The invention of claim 1 is a plurality of operational amplifiers formed on the same chip and housed in the same package, and a plurality of operational amplifiers connected at one end to the inverting input terminals of the respective operational amplifiers and connected at the other end to the same measurement signal. One end of each of the first resistors, a plurality of second resistors connected between the inverting input terminal and the output terminal of each operational amplifier, and a non-inverting input terminal of each operational amplifier. A plurality of third resistors each having a resistance value at which the offset current of each operational amplifier is minimized, and one variable resistor that varies the voltage at the connection point of each other end of the plurality of third resistors. Offset voltage adjusting means having the variable resistor, and adjusting the offset value of the output of the operational amplifier having the highest amplification factor to a predetermined value by adjusting the resistance value of the variable resistor, so that each offset voltage of the plurality of operational amplifiers is predetermined. And adjusting the.

  According to the present invention, the offset voltages of a plurality of operational amplifiers can be easily combined with each other.

  As described above, in the present invention, a plurality of operational amplifiers formed on the same chip and housed in the same package are used to adjust each offset voltage of the plurality of operational amplifiers with one variable resistor, thereby There is an effect that the offset voltages of the operational amplifier can be easily matched with each other.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment)
In the present embodiment, the configuration of the residential distribution board A is shown in FIG. 2 as in the conventional example, and the electric power stored in the residential distribution board A and consumed by the two systems of the power line L1 and the power line L2 is measured. The configuration of the power measuring instrument 4 is shown in FIG. FIG. 1 shows a configuration corresponding to the measurement of one power line, and the actual power measuring instrument 4 has two circuits as shown in FIG. 1 so as to correspond to each measurement of the power lines L1 and L2 in FIG. It has a circuit.

  The power meter 4 includes a filter unit 40 that reduces noise from the detection signal of the power line voltage, an amplifier unit 41 that amplifies the voltage detection signal that has passed through the filter unit 40, a current transformer that detects a current flowing through the power line, and the like. The filter unit 42 reduces noise from the current detection signal from the current detection unit CT, the amplification unit 43 amplifies the current detection signal that has passed through the filter unit 42, the voltage detection signal output from the amplification unit 41, and the amplification unit 43. Is provided with a power calculation unit 44 that calculates the power of each system from the current detection signal output from the power and a power display unit 45 that displays the measurement result of the power in each system.

  The amplifier 43 has three operational amplifiers OP1, OP2, and OP3 for power measurement, and one end connected to each inverting input terminal of the operational amplifiers OP1, OP2, and OP3, and receives a current detection signal (measurement signal) from the filter unit 42. Resistors Ra1, Ra2, and Ra3 connected to the other ends, resistors Rb1, Rb2, and Rb3 connected between the inverting input terminals and the output terminals of the operational amplifiers OP1, OP2, and OP3, and the non-inverting terminals of the operational amplifiers OP1, OP2, and OP3, respectively. Resistors Rc1, Rc2, and Rc3 each having one end connected to the input terminal, a resistor Rd having one end connected to the connection point of each other end of the resistors Rc1, Rc2, and Rc3, and the other end connected to the ground level, and a resistor Rc1, Both ends are connected between a resistor Re having one end connected to the connection point of each other end of Rc2 and Rc3, and a positive voltage source + Vcc and a negative voltage source −Vcc, and the movable terminal is connected to the resistor. And a variable resistor VR connected to the other end of Re, constituting three of the inverting amplifier circuit consisting of an operational amplifier OP1, OP2, OP3. The amplification factors of these three inverting amplifier circuits are different from each other. The amplification factor (−Rb1 / Ra1) = 30 of the operational amplifier OP1, the amplification factor (−Rb2 / Ra2) = 100 of the operational amplifier OP2, and the amplification factor (− Rb3 / Ra3) = 300. The power calculation unit 44 obtains power using the output of the operational amplifier OP1, OP2, and OP3 that has a large amplification factor and whose output is not saturated.

  The values of the resistors Rc1, Rc2, and Rc3 are set for each inverting amplifier circuit. For example, in the operational amplifier OP1, the offset current of the operational amplifier OP1 is set by setting Rc1 = Ra1 · Rb1 / (Ra1 + Rb1). The effect of offset current is minimized by setting the minimum value. In the operational amplifiers OP2 and OP3, the values of the resistors Rc2 and Rc3 are set in the same manner as described above. Furthermore, the operational amplifiers OP1, OP2, and OP3 are formed on the same chip, which is formed on the same chip obtained by dividing the wafer, among the plurality of operational amplifiers formed on the same wafer, and is formed on the same chip. The operational amplifiers OP1, OP2, and OP3 housed in the same package have substantially the same temperature characteristics, and the offset voltage of the output of each operational amplifier similarly changes with respect to the temperature change, and each offset for each operational amplifier. The voltage is almost the same value. Therefore, even if the offset adjustment voltages of the operational amplifiers OP1, OP2, and OP3 are supplied via one variable resistor VR, the offset voltages of the outputs of the operational amplifiers OP1, OP2, and OP3 are substantially the same. Thus, by making the offset current of each operational amplifier the minimum value and making the offset voltage of each operational amplifier substantially the same, the amplification unit 43 reduces the difference between the offset voltages of a plurality of operational amplifiers.

  In such an amplifying unit 43, by adjusting the resistance value of one variable resistor VR, the voltage at the connection point between the resistors Rc1, Rc2, Rc3 and the resistor Re can be varied, and each of the operational amplifiers OP1, OP2, OP3. Adjust the output offset voltage. Specifically, the resistance value of the variable resistor VR is adjusted while monitoring the output of the operational amplifier OP3 having the largest amplification factor, and the offset voltage of the output of the operational amplifier OP3 is adjusted to a predetermined value (2500 mV in FIG. 6). Since the difference between the offset voltages of the operational amplifiers OP1, OP2, and OP3 is small as described above, the amplification factor is smaller than that of the operational amplifier OP3 by adjusting the offset voltage of the operational amplifier OP3 having the largest amplification factor to a predetermined value. The offset voltages of the operational amplifiers OP1 and OP2 are also adjusted to a predetermined value.

  In other words, the variable voltage resistors and resistors for adjusting the offset voltage are connected to the respective operational amplifiers as in the prior art, depending on the temperature variation between the variable resistors and between the resistors, and the temperature characteristics of the operational amplifiers. Although the offset voltages do not match each other, in the present embodiment, one variable resistor VR, one resistor Rd, 1 are formed using a plurality of operational amplifiers OP1, OP2, OP3 formed on the same chip and housed in the same package. By adjusting each offset voltage of a plurality of operational amplifiers with an offset voltage adjusting means comprising two resistors Re, the offset voltages of the respective operational amplifiers can be easily matched to each other.

  An operational amplifier with a small offset voltage and offset current is generally expensive, but the amplifying unit 43 can be configured using an operational amplifier with a large offset voltage and offset current.

It is a figure which shows the circuit structure of the amplification part using the operational amplifier for electric power measurement accommodated in the residential distribution board of embodiment of this invention. It is a figure which shows the external appearance structure of a housing distribution board same as the above. It is a figure which shows the 1st structure of the amplification part using the operational amplifier for the conventional power measurement. It is a figure which shows the 2nd structure of the amplification part using the operational amplifier for the conventional power measurement. It is a figure which shows the 3rd structure of the amplification part using the operational amplifier for the conventional power measurement. It is a figure which shows the offset voltage adjustment of the operational amplifier for electric power measurement.

Explanation of symbols

Reference Signs List 4 Power measuring device 40 Filter unit 41 Amplifying unit 42 Filter unit 43 Amplifying unit 44 Power calculating unit 45 Power display unit CT Current detecting unit OP1, OP2, OP3 Op-amp Ra1, Ra2, Ra3 resistor Rb1, Rb2, Rb3 resistor Rc1, Rc2, Rc3 resistance Rd, Re resistance VR Variable resistance

Claims (1)

A plurality of operational amplifiers formed on the same chip and housed in the same package, a plurality of first resistors each having one end connected to the inverting input terminal of each operational amplifier and the same measurement signal connected to the other end; A plurality of second resistors connected between the inverting input terminal and the output terminal of each operational amplifier, one end connected to each non-inverting input terminal of each operational amplifier, and the other end connected to each other, A plurality of third resistors each having a resistance value that minimizes the offset current; and an offset voltage adjusting means having one variable resistor that varies the voltage at the connection point of each other end of the plurality of third resistors. And adjusting each offset voltage of a plurality of operational amplifiers to a predetermined value by adjusting a resistance value of the variable resistor and adjusting an offset voltage of an operational amplifier having the largest amplification factor to a predetermined value. Offset adjustment method for power measurement operational amplifier to symptoms.

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