JP4333278B2 - measuring device - Google Patents

Description

  The present invention relates to a measuring apparatus, and more particularly to correction of instrument loss inside the apparatus.

Patent Document 1 discloses an isolation technique using a current transformer for expanding a frequency band, for example, for a broadband wattmeter.

  However, in Patent Document 1, there is no mention regarding correction of instrument loss inside the apparatus which is the object of the present invention.

JP 2002-271153 A

  In measuring devices with current measuring functions such as wattmeters, ammeters, and digital multimeters, the voltage drop at the current sensor or its surroundings is added to the voltage drop at the measurement target, and the current sensor is not connected. It is difficult to measure the current flowing through the measurement object in the same state as the actual use state.

  For this reason, in this type of measuring device, parameters for correcting voltage drop in such devices have been conventionally expressed as input impedance such as □ Ω, □□ H, □□ F, etc. as “instrument loss”. Has been done.

  In addition, the measurement device is physically and electrically connected to ensure the safety of operation, countermeasures against the effects of noise generated by various devices on the measurement device, and the physical size and measurement location of the measurement target device. However, it is inevitable that it will become a certain size. Therefore, in power measurement, power including the instrument loss and the measurement line loss is measured as load power consumption.

  FIG. 8 is a configuration block diagram showing an example of such a conventional measuring apparatus, and shows an example in which a wattmeter is connected via VI. In the figure, an amplifier 13 is connected to the high voltage terminal 11 of the voltage input unit 10 via a resistor 12. A resistor 14 is connected between the input terminal and the output terminal of the amplifier 13. The low voltage terminal 15 is connected to a common potential point.

  The terminals a and b of the four-terminal current sensor 23 are connected to the current terminal 21 and the common terminal 22 of the current input unit 20. The amplifier 24 is connected to the terminal c of the current sensor 23, and the terminal d is connected to the common potential point. As the current sensor 23, a resistor, a current transformer or a Hall element is used.

  One end of the power source 30 is connected to the high voltage terminal 11 of the voltage input unit 10 and one end of the load 40, and the other end of the power source 30 is connected to the low voltage terminal 15 of the voltage input unit 10 and the common terminal 22 of the current input unit 20. . The other end of the load 40 is connected to the current terminal 21 of the current input unit 20.

  An amplifier 13 is connected via a resistor 12. A resistor 14 is connected between the input terminal and the output terminal of the amplifier 13. The low voltage terminal 15 is connected to a common potential point.

  According to such a V-I connection configuration, the current flowing through the load 40 also flows through the current sensor 23. When the current sensor 23 is a shunt, the current value is measured based on the voltage drop of the current sensor 23. When the current sensor 23 is a CT (current transformer), the measurement current is changed to an appropriate current value (transformed), and then converted into a voltage to measure the current value.

  However, in the V-I connection configuration, since the current input unit 20 is connected in series with the load 40, the voltage drop in the current sensor 23 is also added to the voltage drop of the load 40 and is measured and becomes an error factor. Yes. Further, the impedances Z1 and Z2 cannot be made zero as long as the wiring for guiding the current from the load 40 to the current sensor 23 has a physical size. Therefore, the wiring also consumes power, and these are also regarded as the power consumption of the load 40. As a result, the measured power value W is

It becomes. Note that the second term of equation (1) is an error (T is a period).

  FIG. 9 shows an example in which a conventional power meter is IV connected. In the figure, one end of the power supply 30 is connected to the current terminal 21 of the current input unit 20. The other end of the power supply 30 is connected to the low voltage terminal 15 of the voltage input unit 10, and is connected to the high voltage terminal 11 of the voltage input unit 10 and the common terminal 22 of the current input unit 20 via the load 40.

  According to such an IV connection configuration, the loss of the current sensor 23 does not affect the power consumption of the load 40.

  However, a part of the current that should flow to the load 40 also flows to the voltage input unit 10, and this current becomes an error with respect to the power consumption of the load 40 to be measured. As a result, the measured power value W is

Next, the minute error due to i _V (2) below.

  In order to accurately measure the voltage drop of the load 40, it is necessary to correct errors in the current input unit 20 system including the voltage drop in the current sensor 23 described above. The drop is generally described as “instrument loss” in one item of the rated specification, and it is difficult to describe individual values for each device because the measurement conditions cannot be specified.

  Further, in order to widen the current measurement range, a plurality of current sensors are incorporated and switched, but in this case, the loss of the changeover switch cannot be ignored. The loss of the changeover switch currently depends on the manufacturer's specifications of the changeover switch, and the actual loss cannot be grasped. For this reason, there is a problem that the measurement accuracy must be lowered according to the specifications of each device, and the loss of each device cannot be confirmed.

  Further, the connection of the measuring device itself causes an error in the power consumption measurement of the load 40, and the error varies depending on the measurement target (measurement waveform) and the wiring method (VI connection or IV connection). Therefore, it is not easy to obtain the measurement error.

  That is, at present, it is difficult to accurately grasp the loss of the measurement system including the meter loss. For example, in the case of the wattmeter, the power measurement value that does not vary to some extent is based on the specifications of the wattmeter. The user can only calculate an approximate value.

  The present invention solves such a conventional problem, and an object of the present invention is to provide a measuring apparatus capable of measuring instrument loss of a current sensor or a peripheral portion thereof and performing highly accurate measurement.

The problem to be solved by the present invention is to provide a means for measuring instrument loss and wiring loss of a current sensor and a voltage input unit,
1) Clarification of instrument loss in measurement equipment specifications
2) Measurement of individual losses during adjustment
3) Understanding the connection status inside the measuring device
4) Measuring instrument loss in use
5) Measurement circuit error measurement in use
6) To realize a measuring device that enables high-precision measurement based on loss correction.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In a measuring device using at least one of a current input unit and a voltage input unit,
The current input unit includes a current sensor, an amplifier, a current terminal, a common terminal, and two loss measurement terminals, and the voltage input unit includes a high voltage terminal, a low voltage terminal, a first amplifier, and a second amplifier. A loss measurement terminal is provided,
One loss measurement terminal of the current input unit is connected to the amplifier, and the other loss measurement terminal is connected to a common potential point equal to an external common potential. Measure the loss
The loss measurement terminal of the voltage input unit is connected to the voltage measurement system of the first amplifier via the second amplifier to correct the instrument loss in real time.

The invention according to claim 2 is the measuring apparatus according to claim 1,
The output terminals of the first amplifier and the second amplifier in the voltage input unit are connected in common via the first switch and the second switch, respectively.
Depending on the on / off combination of these switches,
A measurement mode for measuring a measurement signal, a loss measurement mode for measuring a voltage drop in a peripheral portion including the current sensor and a voltage input unit or a measurement circuit, and loss compensation for the measurement result of the measurement mode based on the measurement result of the loss measurement mode One of the loss compensation modes for performing the above is selectively set .

The invention according to claim 3 is the measuring apparatus according to claim 1 or 2,
The voltage sensor includes a changeover switch connected to switch between a voltage on the measurement terminal side and a voltage on the output terminal side of the current sensor as a voltage input to the amplifier of the current input unit .

The invention according to claim 4 is the measuring apparatus according to any one of claims 1 to 3,
The current sensor is characterized in that a low current measurement sensor and a high current measurement sensor are connected in series between measurement terminals including the current terminal and the common terminal .

The invention according to claim 5 is the measuring apparatus according to any one of claims 1 to 3,
The current sensor is characterized in that a low-current measurement sensor and a high-current measurement sensor are connected in parallel between measurement terminals including the current terminal and the common terminal .

A sixth aspect of the present invention is the measuring apparatus according to any one of the first to fifth aspects, wherein the current sensor is any one of a resistor, a current transformer, and a Hall element.

The invention according to claim 7 is the measuring apparatus according to claim 1 or 2,
By connecting the loss measurement terminal of the voltage input unit to the voltage measurement system of the first amplifier via the second amplifier, the potential at the common potential point equal to the external common potential in the voltage input unit is corrected. And a change-over switch for selecting whether or not to perform the potential correction of the common potential point based on the measurement mode.

The invention according to claim 8 is the measuring apparatus according to any one of claims 1 to 7,
The measuring device is any one of a wattmeter , an ammeter, and a digital multimeter .

The invention described in claim 9 is the measuring apparatus according to any one of claims 1 to 8 ,
The output system of the voltage input unit is connected to an A / D converter and a DSP that performs arithmetic processing including power calculation based on output data of the A / D converter.

According to the present invention, the following effects can be obtained.
First, it is possible to grasp the state of the changeover switch used as the instrument loss measuring means, prevent and prevent malfunctions and measurement due to deterioration of the changeover switch, etc., and measure an accurate power value and the like.

  And since the instrument loss of a measuring device can be evaluated in advance in an actual connection state, it becomes easy to eliminate instability of measurement values that often arise from wiring before measurement.

  Moreover, not only can the instrument loss in the connected state be measured, but also correction by an instantaneous value is possible, so that measurement with higher accuracy is possible.

  Further, when it is impossible to determine whether the connection is IV connection or VI connection, assistance for the determination can be obtained.

  Furthermore, the instrument loss that becomes a problem due to the load can be corrected from the instantaneous value, and the troublesomeness of having to change the connection due to the load can be eliminated.

  Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the main part of one embodiment of the present invention in a V-I connection configuration, and the same reference numerals are given to portions common to FIG.

  In FIG. 1, one end of a load 40 is connected to a loss measurement terminal SVH provided in the voltage input unit 10 and a loss measurement terminal SAH provided in the current input unit 20. The loss measurement terminal SVH is connected to the output terminal of the amplifier 13 through an amplifier 50 that functions as a loss measurement circuit. A loss measurement terminal SAL provided in the current input unit 20 is connected to the other end of the power supply 30.

  The amplifier 50 connected to the loss measurement terminal SVH has a high input impedance, and the gain has a phase opposite to that of the amplifier 13. For example, when the amplifier 13 is an inverting amplifier, the first stage of the amplifier 50 is a non-inverting amplifier, so that an opposite polarity output with respect to the amplifier 13 can be obtained with high impedance.

  The loss measurement by the loss measurement terminal SAH-SAL in the current input unit 20 can mainly evaluate the loss of the measurement line and the instrument when measuring power from DC to low frequency.

When correcting the loss in real time, the SVH terminal provided in the voltage input unit 10 is used at the time of VI connection. I-V when connected, by obtaining i _V from the resistor 14 of the amplifier 13 at the voltage input 10 of FIG. 2, it is possible to correct instrument loss.

  An explanation will be given of the loss evaluation of the measurement line and the instrument in the case of measuring the low frequency power from DC. FIG. 3 and FIG. 4 are structural block diagrams of the main part showing an example of the embodiment of the present invention, and the same reference numerals are given to the parts common to FIG. FIG. 3 shows an example in which a current sensor 25 for low current and a current sensor 26 for large current are connected in series, and FIG. 4 shows that a current sensor 25 for low current and a current sensor 26 for large current are connected in parallel. It is an example, By these, the electric current of a wider range can be measured than the case where there is one current sensor.

  In FIG. 3, one end of the current sensor 25 is connected to the current terminal 21 and connected to one fixed contact a of the changeover switch SW1, and the other end is connected to one end of the current sensor 26 and the movable contact of the changeover switch SW1. The output terminal of the current sensor 25 is connected to the fixed contact b of the changeover switch SW2.

  The other end of the current sensor 26 is connected to the common terminal 22 and connected to the fixed contact b of the changeover switch SW3, and the output terminal of the current sensor 26 is connected to the fixed contact c of the changeover switch SW2.

  The fixed contact b of the changeover switch SW1 is opened. The fixed contact a of the changeover switch SW2 is connected to the loss measurement terminal SAH and the movable contact d is connected to the amplifier 24. The fixed contact a of the changeover switch SW3 is connected to the loss measurement terminal SAL and the movable contact c is set to the common potential point. It is connected.

  The movable contacts of the change-over switches SW1 to SW3 are switched and driven in conjunction with each other as follows according to the measurement object.

<Low current measurement>
Changeover switch SW1 → Fixed contact b
Changeover switch SW2 → fixed contact b
Changeover switch SW3 → fixed contact b
As a result, the measurement current flows through the current sensor 25 and the current sensor 26 connected in series between the current terminal 21 and the common terminal 22, and a low current can be measured.

<Large current measurement>
Changeover switch SW1 → Fixed contact a
Changeover switch SW2 → fixed contact c
Changeover switch SW3 → fixed contact b
As a result, the measurement current flows only through the current sensor 26 among the current sensor 25 and the current sensor 26 connected in series between the current terminal 21 and the common terminal 22, and a large current can be measured.

<Loss measurement during low current measurement>
Changeover switch SW1 → Fixed contact b
Changeover switch SW2 → Fixed contact a
Changeover switch SW3 → fixed contact a
Thereby, the loss resulting from the current sensor 25 and the current sensor 26 connected in series can be measured while the measurement current flows through the current sensor 25 and the current sensor 26 connected in series between the current terminal 21 and the common terminal 22. When instrument loss occurs, connect SAH to A and SAL to ±. When including the current line from the load, connect SAH and SAL between the load and the power supply.

< Loss measurement during large current measurement>
Changeover switch SW1 → Fixed contact a
Changeover switch SW2 → Fixed contact a
Changeover switch SW3 → fixed contact a
As a result, the loss caused by the current sensor 26 can be measured in a state where only the current sensor 26 flows between the current sensor 25 and the current sensor 26 connected in series between the current terminal 21 and the common terminal 22.

  In FIG. 4, the current terminal 21 is connected to the movable contact c of the changeover switch SW1.

  One end of the current sensor 25 is connected to one fixed contact a of the changeover switch SW1, the other end of the current sensor 25 is connected to the common terminal 22 and the fixed contact b of the changeover switch SW3, and the output terminal of the current sensor 25 is the changeover switch. It is connected to the fixed contact b of SW2.

  One end of the current sensor 26 is connected to the other fixed contact b of the changeover switch SW1, the other end of the current sensor 26 is connected to the common terminal 22 and the fixed contact b of the changeover switch SW3, and the output terminal of the current sensor 26 is the changeover switch. It is connected to the fixed contact c of SW2.

  The fixed contact a of the changeover switch SW2 is connected to the loss measurement terminal SAH and the movable contact d is connected to the amplifier 24. The fixed contact a of the changeover switch SW3 is connected to the loss measurement terminal SAL and the movable contact c is set to the common potential point. It is connected.

  The movable contacts of the change-over switches SW1 to SW3 are switched and driven in conjunction with each other as follows according to the measurement object.

<Low current measurement>
Changeover switch SW1 → Fixed contact a
Changeover switch SW2 → fixed contact b
Changeover switch SW3 → fixed contact b
As a result, the measurement current flows through the current sensor 25 of the current sensor 25 and the current sensor 26 connected in parallel between the current terminal 21 and the common terminal 22, and a low current can be measured.

<Large current measurement>
Changeover switch SW1 → Fixed contact b
Changeover switch SW2 → fixed contact c
Changeover switch SW3 → fixed contact b
As a result, the measurement current flows through the current sensor 26 of the current sensor 25 and the current sensor 26 connected in parallel between the current terminal 21 and the common terminal 22, so that a large current can be measured.

< Loss measurement during low current measurement>
Changeover switch SW1 → Fixed contact a
Changeover switch SW2 → Fixed contact a
Changeover switch SW3 → fixed contact a
Thereby, the loss resulting from the current sensor 25 can be measured in a state where the measurement current flows through the current sensor 25 of the current sensor 25 and the current sensor 26 connected in parallel between the current terminal 21 and the common terminal 22.

<Loss measurement during large current measurement>
Changeover switch SW1 → Fixed contact b
Changeover switch SW2 → Fixed contact a
Changeover switch SW3 → fixed contact a
As a result, the loss caused by the current sensor 26 can be measured in a state where the measurement current flows through the current sensor 26 of the current sensor 25 and the current sensor 26 connected in parallel between the current terminal 21 and the common terminal 22.

The voltage value in the normal measurement is V1, the current value is A1, the power value is W1, the voltage value in the instrument loss measurement is V2, the current value is A2, and the power value is W2.
Also, assuming that the impedance of the current sensor is Zs, the phase is δs, the combined impedance of Z1 and Z2 is Zw, the phase is δw, the combined impedance of Zs and Zw is Zr, the phase is δr, and the load phase is θ,
W1 ＝ V1 × A1 × cos （θ + δs） (3)
W2 ＝ V2 × A2 × cos （θ + δr） (4)
It is.

When this is converted into normalization processing inside the circuit, Equation (3) and Equation (4) are respectively
KwW1 = (Kv × V1) × (Ka × I1 × Zs) × cos (θ + δs) (5)
KwW2 = (Kv × V2) × (Ka × I2 × Zr) × cos (θ + δr) (6)
It becomes. Kw, Kv, Ka are circuit coefficients, and I1, I2 are current values actually flowing.
Zr and Δr can be expressed by equation (7).

On the other hand, the phase angle measurement values deg1 and deg2 of the voltage and current are θ + δs and θ + δr, respectively, and since δs can be regarded as zero at a low frequency from DC, the phase δr of the impedance Zr that causes loss is
δr ＝ deg2−deg1 (8)
Can be obtained from

  In addition, the currents I1 and I2 that are actually flowing can be regarded as equal by performing normal measurement and loss measurement in a short time, or by carrying out mutual averaging and taking the average, so that Zr can be expressed by equation (9). it can.

  Thus, the loss Wr can be expressed by Expression (10) when the voltage value is V, the current value is A, and the phase angle is θ.

Further, the voltage V _L applied to the load can be expressed by Expression (11).

  Next, real-time loss measurement and compensation for all frequency bands at the time of VI connection will be described with reference to block diagrams showing specific examples of the voltage input unit 10 in FIGS. 5 and 6. The switch SW1V in FIGS. 5 and 6 is for changing the operation mode, and includes two switching contacts 1A and 1B.

  In FIG. 5, an amplifier 50 functioning as a loss measurement circuit is connected to the output terminal of the amplifier 13. The switching contact 1 A of the switch SW 1 V is connected between the amplifier 13 and the amplifier 60, and the switching contact 1 B is connected to the amplifier 50. It is connected between the amplifiers 60.

  On the other hand, in FIG. 6, the amplifier 50 functioning as a loss measurement circuit is connected to the non-inverting input terminal of the amplifier 13, and the switch contact 1A of the switch SW1V is between the resistor 12 and the inverting input terminal of the amplifier 13. The switching contact 1B is connected between the amplifier 50 and the non-inverting input terminal of the amplifier 13.

In these configurations, the operation mode can be switched by ON / OFF control of the switching contacts 1A and 1B of the switch SW1V as follows.
a) Normal measurement: 1A → on, 1B → off b) Loss measurement: 1A → off, 1B → on c) Loss compensation: 1A, 1B → on

By inverting the polarity of the signal waveform input from the loss measurement terminal SVH and adding it to the signal waveform V _V between VH and VL, the voltage V _r (= V _Z1 + V _C + V _Z2 ) generated by the loss is a voltage waveform. The voltage V _L (= V _V −V _r ) applied to the load to be measured can be obtained.

  Then, by multiplying the voltage waveform obtained in this way by a current waveform so as to perform normal power measurement, a power value with corrected loss is obtained as shown in Equation (12). Can do.

The full frequency band real-time loss measurement and compensation at the time of IV connection will be described. As shown in FIG. 2, since there is a current i _V that flows through the voltage input unit 10, the current i _L that actually flows through the load 40 is i _L = i−i _V. Since the current input unit 20 measures i, a power measurement error occurs.

On the other hand, the resistance Rf of the first-stage amplifier 13 of the voltage input section 10, the same current flows i _V. As a result, V _O is generated in the resistor Rf and the voltage can be measured. That voltage measurements are i _V unique to loss. Therefore, since i _L = i− (V _O / Rf), k × (V _O / Rf) is subtracted from the current waveform normalized to the voltage by the current input unit 20. The subtraction method can be either analog or digital. Note that k is a constant depending on the gain.

FIG. 7 is a block diagram illustrating an example of a voltage input unit and a power calculation unit using a digital sampling method.
In FIG. 7, the input voltage is V, the output voltage of the first-stage amplifier 13 is V _O , the output voltage of the normalizing amplifier 60 is V _AD , the rating code of the A / D converter 70 is V _rng , and the A / D converter 70 When the rated voltage is V _FS , the instantaneous voltage value is V _D , the instantaneous current value is i _D , and the gain after the first stage is A, the load current i _L is calculated from i _L = i− (V _O / Rf), i _L = i− (V _AD / A / Rf), and the corrected current instantaneous value i _DL becomes i _DL = i _D − (V _D / V _rng / A / Rf). The DSP 80 executes a series of calculation processes including power calculation.

  Further, according to the present invention, it is possible not only to accurately measure the current value flowing through the load, but also to accurately measure the load fluctuation characteristic on the power generation side by knowing the loss of the wiring and the meter. For example, in the case of current generators, fluctuations are hardly visible because they are controlled by current including loss, but there is an upper limit on the output voltage, so it is easy to check whether the upper limit has been reached and to measure the efficiency of the entire system. Is more accurate.

It is a block diagram which shows the principal part of one Example of this invention. It is a block diagram which shows the principal part of the other Example of this invention. It is a block diagram of the main part showing an example of an embodiment of the present invention. It is a structure block diagram of the principal part which shows the other example of embodiment of this invention. 3 is a block diagram illustrating a specific example of a voltage input unit 10. FIG. 6 is a block diagram illustrating another specific example of the voltage input unit 10. FIG. It is a block diagram which shows an example of the voltage input part and electric power calculating part which used the digital sampling system. It is a block diagram which shows the example which connected the conventional wattmeter to VI. It is a block diagram which shows the example which connected IV of the conventional wattmeter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Voltage input part 20 Current input part 30 Power supply 40 Load 50, 60 Amplifier 70 A / D converter 80 DSP
SW1-SW3 selector switch

Claims (9)

In a measuring device using at least one of a current input unit and a voltage input unit,
The current input unit includes a current sensor, an amplifier, a current terminal, a common terminal, and two loss measurement terminals, and the voltage input unit includes a high voltage terminal, a low voltage terminal, a first amplifier, and a second amplifier. A loss measurement terminal is provided,
One loss measurement terminal of the current input unit is connected to the amplifier, and the other loss measurement terminal is connected to a common potential point equal to an external common potential. Measure the loss
A measuring apparatus for correcting instrument loss in real time by connecting a loss measuring terminal of the voltage input unit to the voltage measuring system of the first amplifier via the second amplifier. The output terminals of the first amplifier and the second amplifier in the voltage input unit are connected in common via the first switch and the second switch, respectively.
Depending on the on / off combination of these switches,
A measurement mode for measuring a measurement signal, a loss measurement mode for measuring a voltage drop in a peripheral portion including the current sensor and a voltage input unit or a measurement circuit, and loss compensation for the measurement result of the measurement mode based on the measurement result of the loss measurement mode The measurement apparatus according to claim 1, wherein any one of the loss compensation modes for performing is selectively set. 2. The switch according to claim 1, further comprising a changeover switch connected to switch between a voltage on the measurement terminal side and a voltage on the output terminal side of the current sensor as a voltage input to the amplifier of the current input unit. 2. The measuring device according to 2.   4. The current sensor, wherein a low current measurement sensor and a high current measurement sensor are connected in series between measurement terminals including the current terminal and the common terminal. The measuring apparatus in any one of.   4. The current sensor, wherein a low current measurement sensor and a large current measurement sensor are connected in parallel between a measurement terminal including the current terminal and the common terminal. The measuring apparatus in any one of.   The measuring apparatus according to claim 1, wherein the current sensor is any one of a resistor, a current transformer, and a Hall element. By connecting the loss measurement terminal of the voltage input unit to the voltage measurement system of the first amplifier via the second amplifier, the potential at the common potential point equal to the external common potential in the voltage input unit is corrected. 3. The measuring apparatus according to claim 1, further comprising a selector switch for selecting whether or not to perform potential correction of the common potential point based on a measurement mode.   The measurement apparatus according to claim 1, wherein the measurement apparatus is a wattmeter, an ammeter, or a digital multimeter.   2. The output system of the voltage input unit is connected to an A / D converter and a DSP that performs arithmetic processing including power calculation based on output data of the A / D converter. The measuring apparatus according to claim 8.

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