JPS6359111B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power meter that generates pulses with a frequency proportional to electric power and counts the pulses with a counter or a measuring device to measure the amount of electric power.

As this type of watt-hour meter, one is known that is configured to detect power by multiplying a load voltage and a load current, and convert the detected power into a pulse having a frequency proportional to the power. However, in an electronic watt-hour meter configured in this way, there is no effect of friction like in an inductive watt-hour meter, so the characteristics at light loads are very good, but conversely, when the load is 0, Easily causes output or voltage creep. However, while inductive watt-hour meters prevent the aforementioned voltage creep by providing a creep hole in the rotating disk, electronic watt-hour meters prevent aging of circuit components (particularly the offset of the operational amplifier). Voltage creep occurs due to changes in Therefore, in the past, it has been known to set the light load characteristics to a negative state so that voltage creep does not occur even if the offset of the operational amplifier changes over time, but in this case, the characteristics However, there was a problem that the load characteristics deteriorated.

Further, electronic watt-hour meters generally provide an operation indication by blinking a light emitting diode or rotating a step motor at a frequency proportional to the load power. On the other hand, inductive watt-hour meters have a rotating disk, so the load status can be checked by checking this disk. In addition, it can be determined by checking whether the disk is rotating or not in an earth leakage check or the like. However, with electronic watt-hour meters that operate as described above, the operation status is often displayed when the load is close to the rated load, so it is easy to check the operating status. Since the step motor rotates frequently for several minutes or more, it is extremely difficult to determine whether there is no load or a small amount of current is flowing.

Therefore, as a result of various studies in order to overcome all the problems of the conventional electronic watt-hour meters mentioned above, the inventor of the present invention detected power from the load voltage and load current, and developed a pulse generator with a frequency proportional to the power. In an electronic watt-hour meter that includes a power-pulse converter that generates a power-to-pulse converter and a counter that counts the pulses from the power-pulse converter and displays them as electric energy, the period of the pulses from the power-pulse converter is is compared with a period of a predetermined length, and when the period of the pulse from the power-pulse converter is longer, the power-pulse converter is configured to generate a slight negative offset current. It was discovered that when the load current is 0, the generation of pulses can be prevented and erroneous measurements due to voltage creep can be reliably prevented.

In addition, when the power-pulse converter configured in this manner is equipped with a charge-balanced AC-DC converter, the saturation point reached when the load current becomes 0 or negative on the output side of the AC-DC converter and the normal By providing a level discrimination circuit that sets a reference level located midway between the operating range, no-load detection and display can be easily achieved.
It has been found that the above problems can be solved.

Therefore, an object of the present invention is to be able to reliably prevent erroneous measurements due to the occurrence of voltage creep in a no-load state, to be able to determine and display the no-load state, and to detect the occurrence of the voltage creep. An object of the present invention is to provide an electronic watt-hour meter that can maintain proper measurement of electric energy even if a means for measuring electric power is out of order.

In order to achieve the above object, the present invention includes a power detection circuit that detects power from load voltage and load current, a frequency conversion circuit that generates pulses with a frequency proportional to this power, and a frequency conversion circuit that counts the pulses. An electronic watt-hour meter equipped with a counter that displays the amount of electric power, which is cleared by the output pulse of the frequency conversion circuit via the differentiating circuit, and counts the output signal of the oscillation circuit by being cleared, The present invention is characterized by comprising a binary counter that outputs a predetermined output when the counting is completed, and a minute signal generation circuit that applies an offset signal to the input side of the frequency conversion circuit based on the output from the binary counter.

Next, embodiments of the electronic watt-hour meter according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block circuit diagram showing an embodiment of an electronic watt-hour meter according to the present invention. That is, in FIG. 1, reference numeral 10 indicates a power-frequency conversion circuit, which inputs a load voltage V and a load current I to detect power, and generates a pulse train f proportional to this power.
is configured to output. The pulse train f outputted from the power-frequency conversion circuit 10 is frequency-divided by a frequency dividing circuit 12 and counted by a counter 14, so that the amount of power can be displayed. However,
In the present invention, the power-frequency conversion circuit 1
A period comparison circuit 16 is connected to the output side of the pulse train f, and when the pulse train f is larger than a predetermined period, the minute signal generation circuit 18 is operated to send a predetermined minute signal to the power-frequency conversion circuit 10. The configuration is such that the voltage is applied in the direction in which the voltage decreases. In addition,
The period set by the period comparison circuit 16 is set to be slightly larger than the period of the pulse train f output by the power-frequency conversion circuit 10 when the load current I is 0 and no minute signal is added. Further, from the minute signal generation circuit 18 to the power-frequency conversion circuit 1
The minus minute signal applied to the frequency converter circuit 10 has the power to generate a pulse train f having the same period as the period set by the period comparator circuit 16.
By applying a minute signal when the pulse train f is being input to 0, the pulse train f is set substantially equal to a value such that it becomes 0. That is, the power-frequency conversion circuit 1
If a large negative signal is applied to 0, the pulse train f
will no longer occur, but if the pulse train f in this case is 0
This refers to the critical state in which a pulse is generated or not.

According to the electronic watt-hour meter of this embodiment having the circuit configuration as described above, when the load current is 0, the power-frequency conversion circuit 10 is given a negative offset current, and the pulse train f is not outputted at all. As a result, the frequency divider circuit 12 and the counter 14 do not function, and erroneous measurements due to voltage creep are reliably prevented.

FIG. 2 is a block circuit diagram showing another embodiment of the electronic watt-hour meter according to the present invention. That is,
In FIG. 2, reference numeral 20 is a power detection circuit;
21 indicates a frequency conversion circuit, respectively. The power detection circuit detects power from the load voltage V and load current I, and generates a current I _p (or voltage) proportional to this power.
is configured to output. Further, the frequency conversion circuit 21 is configured to convert the output I _p of the power detection circuit 20 into a pulse train f proportional to this output. Therefore, the pulse train f outputted from the frequency conversion circuit 21 is frequency-divided by the frequency dividing circuit 22 and counted by a counter (not shown) to display the amount of electric power. However, in this embodiment, the pulse train f output from the frequency conversion circuit 21
is input to the clear input terminal CL of the binary counter 26 via the differentiating circuit 24. On the other hand, a signal from the oscillation circuit 28 is inputted to the clock input terminal CK of the binary counter 26 via the NOR gate 30. In this case, the output of the binary counter 26 is inputted from the output terminal _Qo to the input terminal of the NOR gate 30 and the inverter 32, respectively. Therefore, when the output of the inverter 32 is at a low level L, the line (-Vref) is connected from the output point _P1 of the power detection circuit 20 through the diode _D2 and the resistor _R0 .
Offset current _I0 flows through. At this time, the input signal of the frequency conversion circuit 21 becomes I _p -I ₀ . On the other hand, when the output of the inverter 32 is at a high level H,
Current from inverter 32 flows into line (−Vref) through diode D ₁ and resistor R ₀ ;
Since a reverse voltage is applied to the diode _D2 , the offset current _I0 becomes 0, and the input signal to the frequency conversion circuit 21 is only _Ip .

Therefore, the operation of the embodiment circuit having the configuration shown in FIG. 2 will be explained with reference to the time charts shown in FIGS. 1 to 5.

First, when a predetermined pulse train f (see FIG. 3 1) is output from the frequency conversion circuit 21, this pulse train f is passed through the differentiating circuit 24 to the binary counter 2.
6 [see FIG. 3 2], and at the same time clears the binary counter 26, the NOR gate 30
The output signal f ₂ of the oscillation circuit 28 which is input via the oscillation circuit 28 is counted (see FIGS. 3 and 4). In this way,
A predetermined number of pulses f ₂ in the binary counter 26
When it counts, it generates a high level H output _f4 [see _FIG . 3, see Figure 5]. As a result, the current flowing into the frequency conversion circuit 21 is
I _p -I ₀ , and the period of the output pulse train f becomes longer than that without the offset current I ₀ or is not output at all (in the illustrated example, the pulse train f remains unchanged for convenience).

On the other hand, if the period of the pulse train f is sufficiently short,
The binary counter 26 counts the pulses (see Fig. 3), and before the output _f4 reaches a high level, it is cleared by the next pulse _f1 , so the output _f4 does not reach a high level and is Therefore, even the offset current _I0 does not flow, and normal power measurement can be achieved.

However, it is preferable to set the relationship between the counting pulse period in the binary counter 26 (see t in FIG. 3) and the offset current _I0 according to the following equation.

1/t/f _o =-I ₀ /I _po ...(1) However, f _o : Frequency of pulse train f at rated time I _po : Current flowing into the frequency conversion circuit 21 at rated time At this time, the power detection circuit The relationship between the output current I _p of the frequency conversion circuit 20 and the output pulse train f of the frequency conversion circuit 21 is as shown in FIG. 4, assuming that the current I _p and the pulse train f are proportional. That is, when the current I _p gradually decreases and the pulse train f decreases accordingly, and 1/f = t, the offset current I ₀ flows [4th
See point a in the figure]. As a result, I _p −I ₀ =0,
The output of the frequency conversion circuit 21 is in a critical state of 0 (see point b in FIG. 4). When the current I _p decreases further, the frequency conversion circuit 2 due to the offset current I ₀
The input of 1 becomes negative, and the pulse train f is no longer generated. Conversely, when the current I _p increases from 0, the process is reversed, and when |I _p |>|I ₀ |, the offset current I ₀ does not occur, and normal metering can be achieved.

From the offset current I ₀ calculated by the above formula (1),
If the actual offset current I ₀ ^* is small, the fifth
The result will be as shown in the figure. That is, when the current I _p decreases and the period of the pulse train f becomes longer than t [see point a in FIG. 5], an offset current I ₀ ' flows, but
Since the current flowing into the frequency conversion circuit 21 satisfies I _p -I ₀ '>0, the pulse train f is output although its period is longer. Furthermore, when the current I _p decreases to I _p -I ₀ '=0, the pulse train f becomes 0 [see point b in FIG. 5].
Conversely, even if the current I _p increases, the same process will occur.

Furthermore, the offset current calculated by the above formula (1)
If the actual offset current I ₀ ^* is larger than I ₀ , then
The result is as shown in FIG. That is, when the current I _p decreases and the period of the pulse train f becomes longer than t [see point a in FIG. 6], an offset current I ₀ '' flows, but the current flowing into the frequency conversion circuit 21 is I _p −
Since I ₀ ″<0, the pulse train f immediately stops being output [see point b in Figure 6].Furthermore, the current I _p
increases and becomes I _p -I ₀ ''=0, a pulse is output [see point c in Figure 6], but when one pulse is output, the offset current I ₀ is cut off [see d in Figure 6] ,
Can perform normal weighing. Therefore, it is understood that in this case, hysteresis occurs in the relationship between the current I _p and the pulse train f.

As is clear from the above, in any of the cases shown in FIGS. 4 to 6, when the current I _p = 0, the offset current I ₀ flows and the complete voltage creep prevention function works. , offset current I ₀
It is not necessary to set it strictly. Further, the setting of the offset current _I0 is given by the following equation in the case of the embodiment circuit shown in FIG.

I ₀ = Vref - V _D /R ₀ ... (2) However, V _D : Forward voltage of diode D ₂ In the above equation (2), voltage V _D changes depending on temperature, but in practice it hardly changes. This is at a level that does not pose a problem. However, if high accuracy is required, it is preferable to add compensation to Vref to cancel the change in _VD , as shown in FIG. Furthermore, if the resistor R ₀ is also configured with a variable resistor, the offset current I ₀ can be set with high accuracy.

Furthermore, in the embodiment circuit shown in FIG. 2, the binary counter 26, oscillation circuit 28, and NOR gate 30 can be replaced with a one-shot multivibrator that can be triggered repeatedly.

FIG. 8 shows another embodiment of the electronic watt-hour meter according to the present invention, and particularly shows a circuit diagram configured to determine and display a no-load state. That is, in FIG. 8, reference numeral 40 is a power detection circuit, 42 is an integration circuit consisting of an operational amplifier OPA and a capacitor C, 44 is a first level discrimination circuit, 46 is a constant width pulse generation circuit, 4
8 represents a constant current circuit, and 50 represents a switch. The power detection circuit 40 detects power from a load voltage V and a load current I, and generates a current proportional to this power.
Configured to output I _p (or voltage). Further, the integration circuit 42 and the first level discrimination circuit 44
The constant width pulse generating circuit 46, the constant current circuit 48, and the switch 50 constitute a load balanced AC-DC converter 41. This charge-balanced AC-DC
In the converter 41, the operational amplifier of the integrating circuit 42 _is
The voltage waveform at the output point _P1 of the OPA changes, and as a result, the AC-DC converter 41 is configured to output a pulse train proportional to the electric power to the output point _P2 .

In this way, the AC-DC converter 41
The output pulse train obtained by
4 and the amount of power is displayed. In this case, the pulse train is
6, the cycle comparison circuit 56 compares the periods of the pulse train, and if the period of the pulse train becomes larger than a predetermined pulse period t, the minute current generation circuit 58 is operated to generate a minute offset current _I0. Similarly to the previous embodiment, the AC-DC converter 41 does not output any pulse train at all, thereby preventing erroneous metering due to voltage creep. Note that reference numeral 60 is an oscillation circuit for generating a signal to be supplied to the synchronous comparison circuit 56 and constant width pulse generation circuit 46.

However, in the circuit of this embodiment, the AC
- Operational amplifier OPA that constitutes the DC converter 41
It is characterized in that a no-load display circuit 64 is connected to the output terminal of the circuit via a second level discrimination circuit 62. The circuit operation in this case will be explained with reference to the time charts shown in FIGS. 1 to 4.

First, after the current I _p is input to the AC-DC converter 41 and a predetermined pulse train output is received,
1, 2, and 3], when the load current I becomes 0, that is, the current I _p becomes 0 [see point a in Fig. 9 2], the output of the operational amplifier OPA does not change and maintains its voltage value. 9 See point d in Figure 2]. Next, when a predetermined time t has elapsed since the last pulse of the pulse train was generated (see point b in FIG. 9), the period comparison circuit 5
An offset current I 0 is generated in the minute current generating circuit 58 by the signal from the offset current I ₀ . Since this offset current _I0 is opposite in direction to the current _Ip , the output of the operational amplifier OPA increases due to the offset current _I0 , and finally reaches the saturation voltage of the operational amplifier OPA [point c in Figure 9 2]. reference〕. At this time, a comparison level [level] is set between this saturation voltage and the normal operating region [level], and the second level discrimination circuit 62 compares this comparison level with the output of the operational amplifier OPA. conduct. Therefore, the second level discrimination circuit 62 generates an output signal when the output of the operational amplifier OPA exceeds the comparison level [see FIG. 9, 4], and supplies this signal to the no-load display circuit 64. , it is possible to properly display the no-load state.

In the example circuit shown in FIG. 8, even if the period comparison circuit 56 and the minute signal generation circuit 58 are not provided, the polarity of the current I _p will change when the direction of flow of the load current is reversed. change, 9th
Similar to the characteristics shown in the figure, the output voltage of the operational amplifier OPA increases and becomes saturated, but when the load current is 0, the output of the operational amplifier OPA remains unchanged [a, b in Figure 9 2, See point d]. In this case, the output voltage gradually increases due to the internal offset of the operational amplifier OPA and reaches the comparison level.
However, there is a risk that the voltage will drop due to internal offset and reach the normal operating range (level), causing the AC-DC converter 41 to generate pulses and cause voltage creep. There is. Therefore, in the present invention, it is extremely important to add the period comparison circuit 56 and the minute signal generation circuit 58 to prevent the occurrence of voltage creep.

In addition, in the circuit of this embodiment, if the load current flows after the load current becomes 0 and after the output voltage of the operational amplifier OPA rises and the no-load display circuit 64 is activated, it takes time for the pulse to be generated. , the actual power between them is not output as a pulse. However, the power discarded in this way is so small that it can be ignored.

As is clear from the various embodiments described above, according to the present invention, the output frequency of the power-frequency conversion circuit is compared with a predetermined period, and when the period of the output frequency becomes longer, the power-frequency conversion is performed. By generating a minute negative offset current or voltage in the circuit, it is possible to prevent the generation of pulses that cause voltage creep even when the load current is 0, and to reliably prevent erroneous metering.

Since the period comparison circuit and the minute signal generation circuit are connected in parallel between the power-frequency conversion circuit and the counter, even if either the period comparison circuit or the minute signal generation circuit fails, the voltage Although it will not be possible to prevent the occurrence of creep,
Since the measurement of electric energy can be continued as it is, the worst case scenario of stopping the measurement does not occur.

In addition, charge-balanced AC is used in the power-frequency conversion circuit.
- When a DC converter is used, the voltage creep prevention circuit is provided, and the load current is zero on the output side of the integrating circuit that constitutes the AC-DC converter.
Alternatively, by providing a level discrimination circuit with a reference level set between the saturation voltage that occurs when the direction is reversed and the normal operating area, the output level of the integrating circuit can be discriminated and no-load detected and displayed. can be easily achieved.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various design changes can be made without departing from the spirit of the present invention.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing one embodiment of the electronic watt-hour meter according to the present invention, FIG. 2 is a block circuit diagram showing another embodiment of the electronic watt-hour meter according to the present invention, and FIG. 1 to 5 are operating waveform diagrams of the embodiment circuit shown in FIG. 2, FIGS. 4 to 6 are operating characteristic diagrams of the embodiment circuit shown in FIG. 2, and FIG. 7 is the embodiment shown in FIG. 2. FIG. 8 is a block circuit diagram showing still another embodiment of the electronic watt-hour meter according to the present invention; FIGS. 9 1 to 4 show the embodiment shown in FIG. 8; FIG. 3 is an operation waveform diagram of the circuit. 10... Power-frequency conversion circuit, 12... Frequency dividing circuit, 14... Counter, 16... Period comparison circuit, 18... Minute signal generation circuit, 20... Power detection circuit, 21... Frequency conversion circuit, 22... Frequency divider circuit, 24... Differential circuit, 26... Binary counter, 28... Oscillator circuit, 30... NOR gate,
32... Inverter, 40... Power detection circuit, 4
1...Charge balanced AC-DC converter, 42...
Integrating circuit, 44...First level discrimination circuit, 46...
... constant width pulse generation circuit, 48 ... constant current circuit,
50... Switch, 52... Frequency divider circuit, 54...
Counter, 56... Period comparison circuit, 58... Minute current generation circuit, 60... Oscillation circuit, 62... Second
Level discrimination circuit, 64... No-load display circuit.

Claims (1)

[Claims] 1. A power detection circuit that detects power from load voltage and load current, a frequency conversion circuit that generates pulses with a frequency proportional to this power, and a counter that counts the pulses and displays them as electric energy. In an electronic watt-hour meter, the output signal of the oscillation circuit is counted by being cleared by the output pulse of the frequency conversion circuit via the differentiation circuit, and the output signal of the oscillation circuit is counted by the clearing, and when the counting is completed, An electronic watt-hour meter comprising: a binary counter that outputs a predetermined output; and a minute signal generation circuit that applies an offset signal to the input side of the frequency conversion circuit based on the output from the binary counter.