JP2023064362A - Method for controlling switch of watt-hour meter and watt-hour meter - Google Patents

Abstract

To provide a method for controlling the switch of a watt-hour meter that suppresses damage to contacts and improves the reliability and life of contacts, and provide the watt-hour meter.SOLUTION: Provided is a watt-hour meter equipped with a switch 4 in which a fixed contact 7a and a movable contact 7b are provided between a power system and a load, and which supplies or cuts off the power of the power system to the load with the movable contact exerting opening or closing operation on the fixed contact by supplying or cutting off a current to an excitation coil 5. The watt-hour meter comprises: a current sensor 8 for detecting the peak value of a contact current flowing between the movable contact and the fixed contact; a control unit 22 for controlling a contact opening time when the movable contact makes opening operation from the time at which the peak value of contact current is detected, and after delaying by the contact opening time from the detected time, outputting a drive signal to the switch for the movable contact to make opening operation; and a switch control circuit 6 for outputting a drive signal to the excitation coil and reducing the contact current to zero or close to zero when the movable contact goes to an open state a prescribed time after the time at which the drive signal is outputted.SELECTED DRAWING: Figure 1

Description

The present invention relates to a switch control method for a power meter and a power meter.

In the switch installed between the power system (Source) and the load (Load) of the watt-hour meter, when the movable contact provided in the switch is closed against the fixed contact, current flows through

Next, when the movable contact of the switch is opened with respect to the fixed contact, the current flowing between the movable contact and the fixed contact is interrupted.

Japanese Patent No. 2892717 Japanese Patent No. 3716691

However, if the current is not zero, an arc (spark) will occur between the moving and stationary contacts, damaging the moving and stationary contacts. Damage to both contacts is determined by the magnitude of the arcing current and the duration of the arcing.

For this reason, opening the movable contact with respect to the fixed contact at a timing when the current is zero or near zero can suppress damage to both contacts and protect both contacts.

SUMMARY OF THE INVENTION An object of the present invention is to provide a switch control method for a watt hour meter and a watt hour meter that can suppress damage to contacts and improve the reliability and life of the contacts.

In order to solve the above problems, claim 1 of the switch control method for a watt-hour meter according to the present invention provides a fixed contact and a movable contact between the electric power system and the load, and supplies current to the exciting coil. A control method for a switch of a watt-hour meter that cuts off supply of electric power of the power system to the load by opening and closing the movable contact with respect to the fixed contact by supply or cutoff, the method comprising: detecting the peak value of the contact current flowing between the movable contact and the fixed contact; controlling the contact opening time for opening the movable contact from the time when the peak value of the contact current is detected; After delaying by the contact opening time, a drive signal for opening the movable contact is output to the exciting coil, and the movable contact is in an open state after a predetermined time has passed from the time when the driving signal is output to the exciting coil. The contact current is set to zero or near zero when

According to a second aspect of the present invention, there is provided a switch control method for a watt-hour meter according to the first aspect, wherein the first control unit detects the time of the peak value of the contact current, and the contact opening time is reached from the detected time. After the delay, the drive signal is output to a second control unit in the switch, and the time at which the second control unit outputs the drive signal to the excitation coil and outputs the drive signal to the excitation coil The contact current is set to zero or near zero when the movable contact is opened after a lapse of a predetermined time.

Claim 3 is the switch control method for a watt-hour meter according to claim 1 or 2, wherein the predetermined time is a constant value predetermined for each switch, and the contact opening time is: It is characterized in that it is set based on the time when the peak value is detected, the predetermined time, and the cycle of the contact current.

According to a fourth aspect of the present invention, there is provided a switch control method for a watt-hour meter according to the second aspect, wherein the predetermined time associated with variations in the characteristics of the excitation coil is stored in a memory, and the first control unit comprises: The predetermined time is read from the memory, and the contact opening time is set based on the read predetermined time, the time when the peak value of the current is detected, and the cycle of the contact current.

According to a fifth aspect of the present invention, a fixed contact and a movable contact are provided between a power system and a load, and the movable contact opens and closes the fixed contact by supplying or interrupting current to an exciting coil. A watt-hour meter comprising a switch that cuts off the supply of power from the power system to the load, the current sensor detecting a peak value of a contact current flowing between the movable contact and the fixed contact; A contact opening time for opening the movable contact is controlled from the time detected by the current sensor, and after delaying the contact opening time from the detected time, a driving signal for opening the movable contact is supplied to the exciting coil and a control unit that outputs the contact current to zero or near zero when the movable contact is opened after a predetermined time has elapsed from the time when the drive signal was output to the exciting coil. .

According to a sixth aspect of the present invention, there is provided a watt-hour meter according to the fifth aspect, wherein the control section detects the time of the peak value of the contact current, and delays the contact opening time from the detected time by the contact opening time. a first control unit provided in the switch for outputting a drive signal to the switch, and outputting the drive signal to the excitation coil after a predetermined time has elapsed from the time when the drive signal was output to the excitation coil and a second control section for setting the contact current to zero or near zero when the movable contact is in an open state.

Claim 7 is the watt-hour meter according to Claim 5 or 6, wherein the predetermined time is a constant value predetermined for each switch, and the contact opening time is the peak value detected. It is characterized in that it is set based on the time, the predetermined time, and the cycle of the contact current.

According to an eighth aspect of the present invention, there is provided a watt-hour meter according to the sixth aspect, further comprising a memory for storing the predetermined time associated with variations in the characteristics of the excitation coil, wherein the first control unit stores the predetermined time The contact opening time is set based on the predetermined time read out from the memory, the time when the peak value of the current is detected, and the cycle of the contact current.

According to claims 1 and 5, the contact opening time for opening the movable contact is controlled from the time when the peak value of the contact current is detected, and after delaying the contact opening time from the detection time, the movable contact is opened. A drive signal is output to the exciting coil. Since the moving contact opens after a predetermined time has passed since the drive signal was output to the excitation coil, by controlling the contact opening time, the contact current can be reduced to zero or near zero when the moving contact opens. do. Therefore, damage to the contacts can be suppressed, and the reliability and life of the contacts can be improved.

According to claims 2 and 6, the drive signal is output to the second control section in the switch after the contact opening time is delayed from the time when the first control section detects the peak value of the contact current. The contact current can be reduced to zero or near zero when the movable contact is opened after a predetermined time has passed from the time when the second control unit outputs the drive signal to the exciting coil.

According to claims 3 and 7, the contact opening time is set based on the time when the peak value is detected, the predetermined time, and the cycle of the contact current. or can be near zero.

According to claims 4 and 8, the contact opening time is set based on the predetermined time corresponding to the variation in the characteristics of the exciting coil, the time when the peak value of the current is detected, and the cycle of the contact current. Even if there is variation, the contact current can be zero or near zero when the movable contact is opened.

1 is a diagram showing a watt-hour meter according to a first embodiment of the present invention; FIG. FIG. 4 is a diagram showing a contact state and a contact current waveform when the switch of the watt-hour meter according to the first embodiment of the present invention is closed. FIG. 5 is a diagram showing a contact state and an arc discharge current waveform generated between the contacts when the movable contact of the switch of the watt-hour meter according to the first embodiment of the present invention is opened. FIG. 5 is a diagram showing that the arc is least generated when the movable contact is opened at the instant when the contact current is zero in the switch of the watt-hour meter according to the first embodiment of the present invention. 1 is a diagram showing that the arc time is the longest when the movable contact is opened immediately after the contact current passes zero in the switch of the watt-hour meter according to the first embodiment of FIG. FIG. 4 is a diagram showing control of the opening operation of the movable contact that suppresses arcing at the contact of the switch of the watt-hour meter according to the first embodiment of the present invention; FIG. 10 is a diagram showing control of the opening operation of the movable contact that suppresses arcing at the contact of the switch of the watt-hour meter according to the second embodiment of the present invention; FIG. 10 is a diagram showing control of opening operation of a movable contact that suppresses arcing at the contact of the switch of the watt-hour meter according to the third embodiment of the present invention;

Hereinafter, a contact control method for a switch of a watt hour meter and a watt hour meter according to an embodiment of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows a configuration diagram of a power meter according to the first embodiment. The watt-hour meter 1 detects the system voltage and current of the power systems 1S and 2S (Source side), and calculates the electric energy based on the detected voltage and current. The power system 1S supplies AC voltage and AC current of commercial frequency (50 Hz or 60 Hz) to loads.

The watt-hour meter 1 includes a CPU 2 (central processing unit), a voltage signal conversion circuit 3, a switch 4, a switch control circuit 6, a current sensor 8, a current signal conversion circuit 10, and a power supply circuit 11, as shown in FIG. ing.

The voltage signal conversion circuit 3 converts the system voltage of analog signals of the electric power systems 1S and 2S (Source side) into voltage signals of digital signals. The CPU 2 includes an arithmetic unit 21 , a control unit 22 and a memory 23 .

The calculation unit 21 receives the voltage signal from the voltage signal conversion circuit 3 and the current signal from the current sensor 8, and multiplies the voltage of the voltage signal by the current of the current signal to calculate the power consumption. The memory 23 stores a contact opening time Δt1, which will be described later.

The control unit 22 corresponds to the first control unit, reads out the contact opening time Δt1 from the memory 23, and calculates the peak value and the peak value of the contact current based on the contact current input from the current sensor 8 via the current signal conversion circuit 10. is detected, and after delaying the contact opening time Δt1 from the detected time, a drive signal for driving the exciting coil 5 is output to the switch control circuit 6 .

The current sensor 8 is provided on the electric wire 9 between the electric power system 1S and the load 1L, and detects contact current flowing from the electric power system 1S to the load 1L when the movable contact 7b is closed with respect to the fixed contact 7a. . Current sensor 8 includes a magnetic sensor, a current transformer (CT), a shunt resistor, and the like.

The current signal conversion circuit 10 converts the analog current signal detected by the current sensor 8 into a digital current signal and outputs the digital current signal to the CPU 2 . The power supply circuit 11 supplies power to the CPU 2 and the switch control circuit 6 .

The switch control circuit 6 drives the exciting coil 5 in the switch 4 with a drive signal based on the drive signal from the CPU 2 .

The switch 4 consists of a latching relay, and is provided with a fixed contact 7a and a movable contact 7b between the excitation coil 5, the power system 1S and the load 1L, and the movable contact 7b opens and closes with respect to the fixed contact 7a. cuts off the supply of power from the power system to the load 1L.

When an exciting current is passed through the exciting coil 5 in one direction, an electromagnetic force is generated, and the electromagnetic force causes the movable contact 7b to close with respect to the fixed contact 7a. On the other hand, when an exciting current is passed through the exciting coil 5 in the direction opposite to the one direction, the movable contact 7b opens with respect to the fixed contact 7a.

FIG. 2 is a diagram showing the contact state and the contact current waveform during the closing operation of the switch of the watt-hour meter according to the first embodiment of the present invention. As shown in FIG. 2(a), when the movable contact 7b is closing to the fixed contact 7a, power is consumed on the load side. current is flowing.

FIG. 3 is a diagram showing the contact state and the arc discharge current waveform when the movable contact 7b is opened during the opening operation of the switch of the watt hour meter according to the first embodiment of the present invention. As shown in FIG. 3(a), when the movable contact 7b is caused to open to the fixed contact 7a, as shown in FIG. 3(b), if the current is not zero, a An arc (spark) is generated.

When an arc occurs, as shown in FIG. 3B, the arc continues from time t10 when the movable contact 7b is opened to time t11 (zero cross) when the current becomes zero. Therefore, as shown in FIG. 4, the arc is least generated when the movable contact 7b is opened at time t12 when the contact current becomes zero.

Contrary to the above, as shown in FIG. 5, when the movable contact 7b is opened at time t13 immediately after the contact current passes zero, an arc is generated from time t13 to time t14 when the contact current crosses zero. and the arc time is the longest.

When the timing of the opening operation of the movable contact 7b of the switch 4 is not controlled in this manner, the timing of the opening operation of the movable contact 7b is either timing shown in FIG. 4 or FIG.

Arcs produce large amounts of light and heat, and the longer the arcing time, the more heat is produced. Even if the arc time in one opening operation of the movable contact 7b is 1/4 wave of the current, the movable contact 7b and the fixed contact 7a are deformed by the generated heat.

By repeating the opening operation of the movable contact 7b many times, the damage to the movable contact 7b and the fixed contact 7a accumulates, eventually leading to failure of the contacts.

If the arc time is constant, the only way to improve the life of the number of switching operations until the contact fails is to strengthen the material and structure of the contact. If the movable contact 7b can be always controlled to open in a short time without arcing or even if an arc occurs, the damage to the contact can be reduced and the service life (opening/closing times) until failure can be extended.

Therefore, in the watt-hour meter according to the first embodiment, the control unit 22 detects the peak value of the contact current from the current sensor 8 (the current waveform shown in FIG. 6B) and the time t1 of the peak value. , at time t2 delayed by the contact opening time (t2-t1=Δt1) from the time of detection, the drive signal for driving the exciting coil 5 (control signal from the CPU 2 shown in FIG. 6A) is sent to the switch. Output to the control circuit 6 . The contact opening time Δt1 is an adjustment time for opening the movable contact 7b when the current shown in FIG. 6(b) crosses zero.

The switch control circuit 6 drives the exciting coil 5 according to the drive signal from the control section 22 . A predetermined time Δt2 from time t2 to time t3 at which the current crosses zero is the time until the current flows through the exciting coil 5 and the movable contact 7b opens (separates). The predetermined time Δt2 is approximately a constant value for each switch 4 .

If the opening operation of the movable contact 7b is controlled without considering the contact opening time .DELTA.t1, arc times as shown in FIGS. 4 and 5 are obtained as described above.

On the other hand, when the contact opening time Δt1 is controlled to aim at the zero crossing of the current, arc generation can be suppressed as shown in FIG. 4, thereby suppressing damage to the contacts.

The peak value of the current waveform, as shown in FIG. 6B, is used as the reference for the start time of the contact opening time Δt1. Since current waveforms take various forms, control based on the current peak value is preferable.

The contact opening time Δt1 is set based on the time when the peak value of the current is detected, the predetermined time Δt2, and the cycle of the contact current. Assuming that the commercial frequency of the AC power source of the electric power system is 50 Hz, the period of the current waveform shown in FIG. 6(b) is 20 ms. Since the period is 20 ms, the time from time t1 to time t3 is 35 ms.

Since the predetermined time Δt2 is known as a substantially constant value for each switch 4, if the predetermined time Δt2 is, for example, 23 ms, the contact opening time Δt1 is 12 ms.

Therefore, when the driving signal is output to the excitation coil 5 at time t2, which is 12 ms after the time t1 when the peak value is detected, the movable contact 7b opens at time t3 after the lapse of the predetermined time Δt2, and the current crosses zero at that time. .

Therefore, arc generation can be greatly suppressed, and damage to the contacts can be suppressed. This can improve the reliability and life of the contacts.

(Second embodiment)
Next, a watt-hour meter according to a second embodiment will be described. When the switches 4 of the same type are mass-produced, the characteristics of the exciting coils 5 in the switches 4 vary. In this case, the predetermined time .DELTA.t2 is not a constant value, but varies and changes for each exciting coil 5. FIG.

However, if the contact opening time Δt1 is set using a constant time Δt2 as in the watt-hour meter according to the first embodiment, the current does not cross zero when the movable contact 7b is opened, and an arc is generated. Uncontrollable.

That is, the time Δt2 from when the current flows through the exciting coil 5 to when the contact operates has variations. For this reason, in the watt-hour meter according to the second embodiment, the time Δt2 is set to a fixed value by using a statistical method, taking into account the average time and variations of the predetermined time Δt2.

It is assumed that when measuring a large amount of predetermined time (coil excitation time) from receiving a control signal to opening a contact in a switch manufactured by a certain manufacturer, the measurement results follow a normal distribution. Assume mean time=Δt2av, standard deviation=σ.

Due to variations in the characteristics of the exciting coils 5-1 to 5-n of the plurality of n switches 4-1 to 4-n, the predetermined times Δt2-1 to Δt2-n also vary. Find the average time Δt2av of 1 to Δt2-n. The average time Δt2av is obtained by Equation (1).
Δt2av=(Δt2−1+Δt2−2+Δt2−3 …Δt2−n)/n (1)
Ideally, even if the switch has the longest time (here, treated as Δt2av+3σ), it is desirable that the switch should be in the “open” state just before the current crosses zero. That is, it becomes as shown in FIG.

In this case, Δt2=Δt2av+3σ is set as a fixed value, and the predetermined time Δt2=Δt2av+3σ is stored in the memory 23 . Whether the control upper limit value is set to +3σ or another value may be determined according to the actual state of the switch to be adopted.

The control unit 22 sets the averaged contact opening time Δt1av based on the predetermined time Δt2=Δt2av+3σ read from the memory 23, the time when the peak value of the current is detected, and the period of the contact current.

Therefore, when the drive signal is output to the exciting coil 5 at a time delayed by the contact opening time Δt1av from the time when the peak value is detected, the movable contact 7b opens when the time Δt2=Δt2av+3σ elapses, and the current becomes zero cross or near zero cross. Therefore, arc generation can be greatly suppressed, and damage to the contacts can be suppressed. This can improve the reliability and life of the contacts.

In addition, there is no need to set the time Δt2 according to each individual switch to be used, and the memory 23 built into the watt-hour meter handles the predetermined time Δt2=Δt2av+3σ as a fixed value, so the manufacturability of the watt-hour meter is good.

(Third embodiment)
Next, a power meter according to the third embodiment will be described. As described for the watt-hour meter according to the second embodiment, the predetermined time Δt2 varies for each exciting coil 5 . If the predetermined time Δt2 has a large variation and the predetermined time Δt2 is treated as a fixed value, as shown in FIG. Reliability will be lost.

Therefore, the predetermined time Δt2 in the switch is individually measured, the result is stored in the memory 23 built into each watt-hour meter, and the predetermined time Δt2 is read out from the memory 23 and used during control.

That is, in the watt-hour meter according to the third embodiment, the control unit 22 performs control to change the contact opening time Δt1 according to variations in the predetermined time Δt2.

In this control method, a current is passed through each exciting coil 5 of each switch, each predetermined time Δt2 is measured, and each measured predetermined time Δt2 is stored in the memory 23 in the CPU 2 . Specifically, in the plurality of switches 4-1 to 4-n, the memory 23 stores predetermined times Δt2-1 to Δt2-n associated with variations in the characteristics of the exciting coils 5-1 to 5-n. do.

Next, in the switch 4-1, the controller 22 reads from the memory 23 the predetermined time Δt2-1 associated with the variation in the characteristics of the exciting coil 5-1. The control unit 22 sets the contact opening time Δt1-1 based on the predetermined time Δt2-1, the time when the peak value of the current is detected, and the cycle of the contact current.

In the switch 4-n, the controller 22 reads out from the memory 23 the predetermined time Δt2-n associated with the variation in the characteristics of the excitation coil 5-n. The control unit 22 sets the contact opening time Δt1-n based on the predetermined time Δt2-n, the time when the peak value of the current is detected, and the cycle of the contact current.

As described above, according to the watt-hour meter according to the third embodiment, the control unit 22 controls the predetermined time corresponding to the variation in the characteristics of the exciting coil 5, the time when the peak value of the current is detected, and the cycle of the contact current. Set the contact opening time based on

Therefore, even if the characteristics of the exciting coil 5 vary, the contact current can be zero or near zero when the movable contact 7b is opened. As a result, arcing can be greatly suppressed, damage to the contacts can be suppressed, and the reliability and life of the contacts can be improved. In addition, since there is no need to worry about variations in the switches, contact opening control can be performed with high accuracy.

1 watt hour meter 2, 2a CPU
3 Voltage signal conversion circuit 4 Switch 5 Exciting coil 6 Switch control circuit 7a Fixed contact 7b Movable contact 8 Current sensor 9 Electric wire 10 Current signal conversion circuit 11 Power supply circuit 21 Operation unit 22 Control unit 23 Memory

In order to solve the above problems, claim 1 of the switch control method for a watt-hour meter according to the present invention provides a fixed contact and a movable contact between the electric power system and the load, and supplies current to the exciting coil. A control method for a switch of a watt-hour meter that cuts off supply of electric power of the power system to the load by opening and closing the movable contact with respect to the fixed contact by supply or cutoff, the method comprising: A peak value of a contact current flowing between the movable contact and the fixed contact is detected, a control unit detects the time of the peak value of the contact current, and the movable contact is detected from the time when the peak value of the contact current is detected. A drive signal for opening the movable contact is output to the switch control circuit at the time delayed by the contact opening time for the opening operation, and from the time when the switch control circuit outputs the drive signal to the excitation coil The contact current is set to zero or near zero when the movable contact is opened after a predetermined time has elapsed .

According to a second aspect of the present invention, there is provided the switch control method for a watt-hour meter according to the first aspect, wherein the predetermined time is a constant value predetermined for each switch, and the contact opening time is equal to the peak time. It is characterized in that it is set based on the time when the value is detected, the predetermined time, and the cycle of the contact current.

According to a third aspect of the present invention, there is provided a switch control method for a watt-hour meter according to the first aspect , wherein the predetermined time associated with variations in the characteristics of the excitation coil is stored in a memory, and the control unit comprises: The predetermined time is read from the memory, and the contact opening time is set based on the read predetermined time, the time when the peak value of the current is detected, and the cycle of the contact current.

According to a fourth aspect of the present invention, a fixed contact and a movable contact are provided between the electric power system and the load, and the movable contact opens and closes the fixed contact by supplying or interrupting current to an exciting coil. A watt-hour meter comprising a switch that cuts off the supply of power from the power system to the load, the current sensor detecting a peak value of a contact current flowing between the movable contact and the fixed contact; The time of the peak value of the contact current is detected, and a driving signal for opening the movable contact is generated at a time delayed by the contact opening time for opening the movable contact from the time of detection of the peak value of the contact current . a control unit for outputting to a switch control circuit , when the movable contact is opened at a time after a predetermined time has elapsed from the time when the switch control circuit outputs the drive signal to the excitation coil. The contact current is set to zero or near zero.

A fifth aspect of the present invention is the watt-hour meter according to the fourth aspect, wherein the predetermined time is a constant value predetermined for each switch, and the contact opening time is the time when the peak value is detected. It is characterized in that it is set based on the predetermined time and the cycle of the contact current.

According to a sixth aspect of the present invention, there is provided a watt-hour meter according to the fourth aspect, further comprising a memory for storing the predetermined time associated with variations in the characteristics of the excitation coil, wherein the control section stores the predetermined time The contact opening time is set based on the predetermined time read out from the memory, the time when the peak value of the current is detected, and the cycle of the contact current.

According to claims 1 and 4 , the drive signal for opening the movable contact is output to the switch control circuit at the time delayed by the contact opening time for opening the movable contact from the time when the peak value of the contact current is detected. do. Since the movable contact is opened at a predetermined time after the switch control circuit outputs the drive signal to the excitation coil, by controlling the contact opening time, the contact is opened when the movable contact is opened. Make the current zero or near zero. Therefore, damage to the contacts can be suppressed, and the reliability and life of the contacts can be improved.

According to claims 2 and 5 , the contact opening time is set based on the time when the peak value is detected, the predetermined time, and the cycle of the contact current. or can be near zero.

According to claims 3 and 6 , the contact opening time is set based on the predetermined time corresponding to the variation in the characteristics of the exciting coil, the time when the peak value of the current is detected, and the cycle of the contact current. Even if there is variation, the contact current can be zero or near zero when the movable contact is opened.

Claims (8)

A fixed contact and a movable contact are provided between an electric power system and a load, and the electric power of the electric power system is generated by opening and closing the movable contact with respect to the fixed contact by supplying or interrupting current to an exciting coil. A control method for a switch of a watt-hour meter that cuts off the supply to the load of
detecting a peak value of a contact current flowing between the movable contact and the fixed contact;
A drive signal for controlling a contact opening time for opening the movable contact from the time when the peak value of the contact current is detected, delaying the contact opening time from the detection time by the contact opening time, and then opening the movable contact. to the excitation coil,
Control of a switch for a watt-hour meter, characterized in that the contact current is set to zero or near zero when the movable contact is opened after a predetermined time has passed from the time when the drive signal is output to the excitation coil. Method. After the first control unit detects the time of the peak value of the contact current and delays the contact opening time from the detected time, the drive signal is output to the second control unit in the switch,
When the second control unit outputs the drive signal to the excitation coil and outputs the drive signal to the excitation coil after a lapse of a predetermined time, the contact current is reduced to zero or when the movable contact is opened. 2. The method of controlling a switch of a watt hour meter according to claim 1, wherein the switch is set to near zero. The predetermined time is a constant value predetermined for each switch, and the contact opening time is set based on the time when the peak value is detected, the predetermined time, and the cycle of the contact current. 3. The method for controlling a switch of a watt hour meter according to claim 1 or 2. storing in a memory the predetermined time associated with variations in the characteristics of the exciting coil;
The first control unit reads the predetermined time from the memory, and sets the contact opening time based on the read predetermined time, the time when the peak value of the current is detected, and the cycle of the contact current. 3. The method for controlling a switch of a watt hour meter according to claim 2. A fixed contact and a movable contact are provided between an electric power system and a load, and the electric power of the electric power system is generated by opening and closing the movable contact with respect to the fixed contact by supplying or interrupting current to an exciting coil. A watt-hour meter comprising a switch that cuts off the supply to the load of
a current sensor that detects a peak value of contact current flowing between the movable contact and the fixed contact;
A contact opening time for opening the movable contact is controlled from the time detected by the current sensor, and after delaying the contact opening time from the detected time, a driving signal for opening the movable contact is supplied to the exciting coil a control unit that outputs the contact current to zero or near zero when the movable contact is in an open state after a predetermined time has elapsed from the time when the drive signal was output to the exciting coil;
A watt hour meter comprising: The control unit
a first control unit that detects the time of the peak value of the contact current, delays the contact opening time from the detected time, and then outputs the drive signal to the switch;
provided in the switch and outputting the drive signal to the excitation coil, and outputting the contact current when the movable contact is opened after a predetermined time has passed since the time when the drive signal was output to the excitation coil. A second control unit to be zero or near zero;
The electricity meter according to claim 5, comprising: The predetermined time is a constant value predetermined for each switch, and the contact opening time is set based on the time when the peak value is detected, the predetermined time, and the cycle of the contact current. The electricity meter according to claim 5 or 6. A memory that stores the predetermined time associated with the variation in the characteristics of the excitation coil,
The first control unit reads the predetermined time from the memory, and sets the contact opening time based on the read predetermined time, the time when the peak value of the current is detected, and the cycle of the contact current. The electricity meter according to claim 6.

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