JPS6247257B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an electronic watt-hour meter, and particularly to an electronic watt-hour meter having a failure detection function.

Generally, in a single-phase electronic watt-hour meter, if a disconnection failure occurs in the voltage conversion part, for example, the voltage transformer, the multiplication function is stopped and pulses proportional to the electric power are no longer output, so it can be easily determined from the outside that there is an abnormality. However, in the case of a three-phase electronic watt-hour meter, even if a failure occurs in one of the phases, as long as the other phase is operating normally, an integrated value can be obtained and the failure cannot be confirmed from the outside.

Therefore, conventionally, a failure detection circuit having a configuration as shown in FIG. 1 has been adopted to avoid the above-mentioned inconvenience. In the figure, reference numeral 1 denotes an instrument transformer that extracts a signal proportional to the load voltage.A resistor 2 for detecting current is connected to the primary side of this transformer, and the voltage obtained by this resistor 2 is transferred to an amplifier 3. After being appropriately amplified, the output value is rectified by a rectifier circuit 4, and this rectified output value is compared with a predetermined reference value by a comparator circuit 5. If there is an abnormality, it is displayed on a display section 6.

However, the above-described failure detection means places a heavy burden on the potential transformer 1, worsening its characteristics, and as a result, it becomes necessary to compensate for the characteristics of a multiplier section (not shown) connected to the secondary side of the transformer 1. However, there are also disadvantages in terms of power measurement accuracy.

The present invention has been made in view of the above circumstances, and provides an electronic watt-hour meter having a failure detection function that allows failure of the voltage conversion unit to be detected without placing a burden on the voltage conversion unit. It is something to do.

Below, in explaining one embodiment of the present invention,
First, a general electronic watt-hour meter to which a failure detection function is added, which is the gist of the present invention, will be explained with reference to FIG. In the figure, reference numeral 11 denotes a voltage converter (instrument transformer) that detects a signal proportional to the load voltage of the power supply line. A pulse width modulation circuit 12 that performs width modulation and outputs a pulse width duty cycle signal is connected. Also, separate from the voltage converter 11, a current converter 13 detects and outputs a signal proportional to the current consumption of the power supply line.
(current transformer), a resistor 14 is connected to both ends of the secondary winding of this transformer to convert it into a voltage signal and supply it to a time division multiplier circuit 15. This time division multiplication circuit 1
5 is composed of a plurality of analog switches, and while selectively controlling the analog switches with the pulse width duty cycle signal of the pulse width modulation circuit 12, a voltage signal proportional to the current consumption is taken in to perform time division multiplication. is being carried out. The multiplication result is transferred to the subsequent integrating circuit 16a, 1 consisting of a resistor and a capacitor.
After integrating at 6b and obtaining a voltage signal proportional to the power,
This is converted into a pulse with a frequency proportional to the electric power by a voltage-pulse frequency conversion circuit 17, and further divided by a frequency dividing circuit 18, and the integrated value is displayed on a display section 19.

Next, FIG. 3 shows a specific configuration of the pulse width modulation circuit shown in FIG. 2. In other words, this circuit configures an integrating circuit by providing a resistor R ₁ at the inverting input section of operational amplifier A1 and a capacitor C ₁ between the inverting input section and the output section, and connects the output section of the integrating circuit to a comparator. Connected to the non-inverting input of A2. This comparator A2 has a voltage e _h =〓1/2e _r (this 〓1/2e _r is obtained by inverting the reference voltage ±e _r with an inverter circuit IN and resisting the voltage e h =〓1/2e r where the integral output e _k having hysteresis characteristics is supplied to the inverting input section). Each time the voltage reaches R ₃ = the value divided by R ₄ ), it is inverted and output from the logic circuit. In other words, the output of the comparator A2 is configured to have an amplitude of + _er when the logic signal is "1" and _-er when the logic signal is "0". R ₂ is the resistance.

Now, assuming that e _v =0 and the output of comparator A2 is set to a logic signal "1", the inverting input voltage e _h of comparator A2 is R ₃ = R ₄ as shown in Figure 4a. _-er /2 is applied by. Furthermore, a reference voltage +e _r is introduced into the operational amplifier A1 by means of a resistor R ₂ . As a result,
The output of the integrating circuit A1 slopes downward in the negative direction as shown in FIG. 4b, and when e _k =-e _r /2 is reached, e _k ≦e _h
Therefore, the output of comparator A2 is "0", that is, -e
Set to _r .

Then, a voltage of + _er /2 is now applied to the inverting input of the comparator A2, while _-er is introduced into the operational amplifier A1 by the resistor _R2 . As a result, the output e _k of the integrating circuit increases with an integral slope in the positive direction, reaches + _er /2, and when e _k ≧e _h , the comparator A2 normally rotates to the logic signal "1".

Now, the output of comparator A2 is a logic signal “1”
When the time interval of is t _a and the time interval of logic signal "0" is t _b , the output e _k of the integrating circuit is e _k (t _a )=-(1/R ₁ C ₁ ∫ ^ta ₀ e _v dt+1 /R
₂ C ₁ ∫ ^ta ₀ e _r dt) = _-er ...(1). Here, if R ₁ = R ₂ , then t _a = e _r R ₁ C ₁ / e _r + e _v ...(2) e _k (t _b ) = -(1/R ₁ C ₁ ∫ ^tb ₀ e _v dt-1/R
₂ C ₁ ∫ ^tb ₀ e _r dt) = + e _r ... (3) t _b = e _r R ₁ C ₁ / e _r - e _v ... (4). Therefore, the pulse width duty cycle signal output from the pulse width modulation circuit 12 is D=t _a /t _a +t _b = _er − e _v / _2er (5) =t _b /t _a +t _b = e _r + e _v /2 e _r (6).

Next, an example of detecting a failure in the voltage conversion section based on the operating principle of the pulse width modulation circuit 12 as described above will be described with reference to FIGS. 5 to 7.
Note that FIGS. 5 and 6 are premise explanations for better understanding, and FIG. 7 is a configuration as an example.

Now, if a disconnection or other failure occurs on the voltage circuit side, the output on the secondary side of the voltage converter 11 becomes 0,
As is clear from equations (5) and (6), the duty cycle signal of the pulse width modulation circuit 12 becomes 50% as shown in FIG.
If one cycle is integrated at 6b, it becomes 0. Therefore, when a failure occurs, even if the integral is integrated for a certain period of time, the result is 0, as is clear from FIG. 5b. Voltage converter 1
1 is normal, the pulse width is constantly modulated, so the duty cycle signal is as shown in Figure 6a.
It's changing like this. Therefore, if the integration circuits 16a and 16b perform integration for a certain period, an integrated value as shown in FIG. 6b will always come out. Therefore, if the output of the pulse width modulation circuit 12 is integrated over a certain period and is 0, then
If an abnormality occurs in the voltage converter 11 and an integral output is output, it is known that the voltage converter 11 is normal.

Next, FIG. 7 is a circuit configuration diagram that is connected to the output section of the pulse width modulation circuit 12 to detect a failure on the voltage circuit side. The output part of the pulse width modulation circuit 12 is connected to the non-inverting input parts of a plurality of comparators A3 and A4 via a switch circuit _S1 , a resistor _R5 , and an integrating circuit including a capacitor _C2 . One comparator A3
A voltage obtained by dividing the voltage V _DD by resistors R ₆ and R ₇ is applied to the inverting input portion of the comparator A4, and a voltage obtained by dividing the voltage −V _SS by resistors R ₈ and R ₉ is applied to the inverting input portion of the comparator A4. is being applied. These comparator circuits A3 and A4 are connected to resistors via an exclusive logic circuit OR.
R ₁₀ is connected to, for example, a light emitting diode LED, which emits light in the event of a failure, via the drive transistor Tr. R ₁₁ is the resistance.

Next, the operation of the circuit shown in FIG. 7 will be explained. After taking in the output of the pulse width modulation circuit 12 via the switch circuit _S1 , it is input for a certain period of time (e _v
1/2 cycle) and supplies this integrated output to the inverting input of comparator A3. When the integrated output of the comparator A3 becomes equal to or higher than the voltage _VDD , the comparator A3 attains an "H" level and is supplied to one input of the exclusive OR circuit OR. Further, when the integrated output of the comparator A4 becomes equal to or higher than the voltage divided by the voltage -V _SS , the comparator A4 attains an "H" level and is supplied to the other input section of the exclusive OR circuit OR. Same circuit OR
calculates the exclusive OR of these two comparators A3 and A4 and outputs the result.

Now, when the output of the integrating circuit consisting of R ₅ and C ₂ is 0, the output of comparator A3 becomes "L", the output of comparator A4 becomes "H", and the transistor
The light emitting diode LED emits light due to the operation of the Tr. Otherwise, the output of the exclusive OR circuit OR is "L", so the light emitting diode LED does not emit light. In this way, a failure on the voltage circuit side can be easily detected by lighting the display section using the output of the pulse width modulation circuit 12.

It goes without saying that the present invention can be modified in various ways without departing from the spirit thereof.

As detailed above, according to the present invention, the pulse width duty cycle signal of the pulse width modulation circuit is used to compare it with a certain voltage, and a failure on the voltage circuit side is determined based on the comparison result. It is possible to provide an electronic watt-hour meter that can detect a failure without placing any burden on the circuit, and that can measure electric power with high precision because it does not affect the circuits subsequent to the pulse width modulation circuit.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional failure detection circuit, Figure 2 is a general configuration diagram of an electronic watt-hour meter, and Figure 3 is a configuration diagram of a conventional failure detection circuit.
Figures 4a to 4c are diagrams explaining the operation of Figure 3. Figures 5 and 6 are prerequisites for detecting failures on the voltage circuit side. FIG. 7 is a configuration diagram of a failure detection circuit showing the main part of the present invention. 11... Voltage converter, 12... Pulse width modulation circuit,
13...Current converter, 15...Time division multiplication circuit, 16
a, 16b... Integrating circuit, 17... Voltage-pulse frequency conversion circuit, 18... Frequency dividing circuit, 19... Display unit,
_R5 , _C2 ...Integrator circuit, A3, A4...Comparator, OR...Exclusive OR circuit, Tr...Drive transistor, LED...Light emitting diode.

Claims (1)

[Claims] 1 Convert the signal e _v proportional to the load voltage of the power supply line into a pulse width duty cycle signal using a pulse width modulation circuit, use this signal to select multiple switches, and generate a signal proportional to the current consumption of the power supply line. In an electronic watt-hour meter that imports data and performs time-sharing multiplication,
A fault in which the output section of the pulse width modulation circuit includes an integrating circuit that integrates the pulse width duty cycle signal over 1/2 cycle of the signal e _v , and a circuit that determines the presence or absence of an output of the integrating circuit. An electronic watt-hour meter characterized by being equipped with a detection circuit.