LOW POWER CURRENT METER FIELD OF THE INVENTION

The invention generally relates to electrical parameter meters. In particular, the invention relates to current meter configured to operate in ultra low ampere range with energy harvesting scheme.

BACKGROUND OF THE INVENTION

Current meters are used in an electrical network to measure current flowing through a wire or cable. Typically, the current meters sense the current in the wire by inductive or non-inductive coupling. Conventionally, the current meters include a front-end building block of a current transformer (CT) for sensing current magnetically, a current measurement or control unit for measuring current by down converting and digitizing the sensed current, and a power storage system for supplying power to the current meter. Conventionally, the current meters include a main power supply and an auxiliary power supply. The main power is drawn from an electrical line through an adaptor, and the auxiliary power supply is generally an energy storage device such as a battery or a capacitor. If a fixed life battery is used for auxiliary power supply, it needs to be replaced after it is discharged. However in case of a rechargeable battery, it needs to be recharged periodically. Hence, a power supply switching device is required to switch to battery charge operation when the current meter is not measuring the current.

As discussed above, the conventional current meter requires a separate dedicated power supply for energizing it. However, it does not utilize the measurable quantity e.g. current to supply power to the system.

Therefore, an improved current meter may be provided which uses the sensed current for supplying power to the current meter by employing energy harvesting scheme.

SUMMARY OF THE INVENTION

The main object of the present invention is to utilize the sensed current of a current meter to energize the current meter by employing energy harvesting scheme.

Another object of the present invention is to utilize the sensed current of a current meter to energize the current meter, which reduces energy consumption by incorporating less number of components such as power supply switching unit.

Yet another object of the present invention is to utilize the sensed current of a current meter to energize the current meter, which reduces the product cost and increases life of the product.

In order to achieve the above mentioned objects the present invention discloses an apparatus for measuring electricity flowing through a wire in ultra low range. The apparatus includes a current transformer for magnetically sensing the electricity flowing through the wire, a control unit coupled to the current transformer for measuring the sensed electricity and producing an output signal indicative of the measured electricity, an energy storage unit coupled to the control unit for supplying power thereto. The energy storage unit is coupled to the current transformer and electricity sensed thereby is used to charge the energy storage unit simultaneously with measuring the sensed electricity.

In an embodiment of the present invention, the control unit further includes a transceiver unit for transmitting the output signal to a remote control system, an analog-to-digital converter (ADC) for converting the sensed electricity to digital data, an ultra low power controller which operates in two modes alternatively, in first mode the output signal is generated based on the digital data received from the analog-to-digital converter, and in the second mode the output signal is transmitted to the remote control system by the transceiver unit, the energy storage unit being charged in both the said modes.

In another embodiment, the control unit further includes a system power monitor unit for monitoring health status of the energy storage unit. Upon pressing a low power switch with integrated LED, the LED lits once to indicate the health status of the energy storage unit and turns off automatically.

In another embodiment, the apparatus includes a programmable current sense switch for detecting electricity from the current transformer. A zero stand by switch powers off the control unit if electricity detected by the programmable current sense switch goes below a threshold value.

In yet another embodiment, the apparatus includes a burden resistor which enables adjusting the sensed electricity before feeding to the analog-to-digital converter.

It is to be understood that both the foregoing general description and the following detailed description of the present embodiments of the invention are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and together with the description serve to explain the principles and operation of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features and other advantages of the invention will be better understood and will become more apparent by referring to the exemplary embodiments of the invention, as illustrated in the accompanying drawings, wherein FIG. 1 schematically illustrates a circuit of a current meter configured to operate in ultra low ampere range employing energy harvesting scheme according to one embodiment of the present invention; and

FIG. 2 schematically illustrates a circuit of a current meter configured to operate in ultra low ampere range employing energy harvesting scheme according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to the exemplary embodiments of the invention, as illustrated in the accompanying drawings. Where ever possible same numerals will be used to refer to the same or like parts.

Disclosed herein is a current meter which employs energy harvesting scheme to energize the current meter by the sensed current. FIG. 1 schematically illustrates the circuit of such a current meter 100. The current meter 100 includes a current transformer (CT) 102, an energy storage unit 104, a control unit 106, a zero standby switch 108, and a low power switch with integrated LED 110. The current meter 100 magnetically senses the current, and down-converted current value is used for measurement. The down-converted current value is not only used for measurement, but also for charging the energy storage unit 104. Furthermore, the current meter 100 may be employed to measure single phase and three phase current. In the present embodiment, the current meter is employed to measure current in the ultra low range such as micro and nano ampere range.

The current meter 100 includes a front-end building block of the current transformer (CT) 102 for sensing the current magnetically. The current transformer 102 may be magnetic, conductive insulated device. Further, it may have different forms for measuring current, for example, ring core type with PCB mount or on-board enclosed in a case, wired core type, split core clamp-on type and so forth. In the present embodiment, the current transformer 102 is a split core clamp-on type CT. The sensed current value may be down-converted with the help of secondary windings of the current transformer 102. For accuracy in measurement with optimum power the output from the current transformer 102 may be increased or decreased linearly over quite a wide range by adjusting a burden resistor 118.

The down-converted current value is applied to the control unit 106. The control unit 106 includes an analog-to-digital converter (ADC) 114, an ultra low power controller 112, a system power monitor unit and a transceiver unit. The ADC 114 converts the analog value of sensed current to the digital values. The digitized data is supplied to the ultra low power controller 112 for measurement and control. The ultra low power controller 112 monitors the functionalities and controls over all operations of the current meter 100. The system power monitor unit checks system power at the regular interval. If the system power is found low or battery/ health status is found lower than a threshold value, the low power switch with integrated LED 110 indicates such system failure to the user. The transceiver unit transmits the measured value of the sensed current to a remote control system for further processing. The transceiver unit may be connected to the remote control system by wired or wireless means.

The ultra low power controller 112 operates in two modes alternatively. In the first mode the sensed current is measured, and in the second mode the measured value is transmitted to the remote control system by the transceiver unit. However, the energy storage unit 104 is charged by the sensed current in both the above mentioned modes.

The energy storage unit 104 supplies power to the different components of the current meter 100. The energy storage unit 104 is charged by the down-converted current from the secondary windings of the current transformer 102. For example, the energy storage unit 104 may be a rechargeable battery, a capacitor and the like. The power supply scheme is employed in such a way that it eliminates the need for building a dedicated auxiliary power supply unit and an associated switching power supply block. This in turn reduces the number of components within the current meter 100 thereby reducing the energy consumption.

The control unit 106, apart from measuring the sensed current, monitors the health status of the energy storage unit 104 by the system power monitor unit. If the battery charge falls below a predefined threshold value, the critical condition is indicated to the user by the low power switch with integrated LED 110. In order to save consumption of energy, continuous indication is avoided in the present embodiment. When the low power switch with integrated LED 110 is pressed, a bicolor LED integrated within the switch 110 lits green or red and turns off, depending on the health status of the energy storage unit 104.

A programmable current sense switch 116 senses current based on the input current sensed by the current transformer 102. If the sensed current, falls below a predefined threshold value, the current meter 100 may switch to shut down mode by the zero standby switch 108. In the shut down mode, the internal components are powered off. However the current meter 100 continues to charge the energy storage unit 104 with the low current. This leads to zero power consumption and hence the operating life of the current meter 100 is extended. Further, when the sensed current increases and exceeds the predefined threshold value, the programmable current sense switch 116 automatically turns on and power on all the components of the current meter 100.

However, in another embodiment the current meter 100 includes a DC low voltage jack/terminal 202 as shown in FIG. 2. In case the battery charge is low, the energy storage unit 104 may be independently charged from a wall powered AC-DC adapter primarily to measure very low current, for example hundreds of micro-amperes.

As the current meter 100 of the present invention is designed to operate at very low current range (such as micro and nano ampere), and it is solely powered by the sensed current, a number of schemes have been adopted to ensure low power consumption of the device.

1. The ultra low power controller 112 operates in one of the two modes sense and measurement and transmission at a time. Further, the duty cycle of operating in the two modes is adjusted in such a way that the overall system power consumption is reduced. Further the operating time is doubled for increasing charging time for both the modes.

2. The current meter 100 does not include any internal data storage medium, as the data storage mediums and data storage operations are power hungry and will add to the number of components. This also enables to reduce the overall system cost.

3. The transceiver unit is configured to perform faster and efficient data transmission.

4. The programmable current sense switch 116 controls optimized system shut down and restart based on the predefined threshold current value. This scheme eliminates the microcontroller leakage.

5. The current meter does not include any display device as the displays consume more power. Further, continuous indication of the low power switch with integrated LED 110 is avoided in order to reduce power consumption. Instead, the one pulse LED is employed in the programmable current sense switch 116, which lits for one or more pulses and turns off automatically when the programmable current sense switch 116 is pressed to know the health status of the energy storage unit 104.

6. In one embodiment, the current transformer 102 may be configured to operate periodically instead of continuously.

In the present embodiment, as the input current is magnetically sensed and the sense and measurement units are completely isolated, this interface scheme eliminates the creepage and clearance requirements associated with high voltage AC/DC circuits. Further the component count is reduced significantly and mechanical construction such as size of the printed circuit boards (PCBs) is reduced. This scheme brings the overall system cost lower and makes the present system more reliable.

In this way the present current meter is capable of capturing, converting, storing, and delivering energy in a form that can be used to provide the power needed by the system that operates the ultra low power controller 112.

It is to be understood by a person of ordinary skill in the art that various modifications and variations may be made without departing from the scope and spirit of the present invention. Therefore, it is intended that the present invention covers such modifications and variations provided they come within the ambit of the appended claims and their equivalents.

We claim:

1. An apparatus for measuring electricity flowing through a wire in ultra low range
comprising:

a current transformer for magnetically sensing the electricity flowing through the wire;

a control unit coupled to the current transformer for measuring the sensed electricity and producing an output signal indicative of the measured electricity; and

an energy storage unit coupled to the control unit for supplying power thereto,

wherein the energy storage unit is coupled to the current transformer and electricity sensed thereby is used to charge the energy storage unit simultaneously with measuring the sensed electricity.

2. The apparatus for measuring electricity according to claim 1, wherein the control unit further comprises a transceiver unit for transmitting the output signal to a remote control system.

3. The apparatus for measuring electricity according to claim 2, wherein the control unit further comprises an analog-to-digital converter (ADC) for converting the sensed electricity to digital data.

4. The apparatus for measuring electricity according to claim 3, wherein the control unit further comprises an ultra low power controller which operates in two modes alternatively, in first mode the output signal is generated based on the digital data received from the analog-to-digital converter, and in the second mode the output signal is transmitted to the remote control system by the transceiver unit, the energy storage unit being charged in both the said modes.

5. The apparatus for measuring electricity according to claim 1, wherein the control unit further comprises a system power monitor unit for monitoring health status of the energy storage unit.

6. The apparatus for measuring electricity according to claim 5, further comprises a low power switch with integrated LED, wherein upon pressing the low power switch the LED lits one or more times to indicate the health status of the energy storage unit and turns off automatically.

7. The apparatus for measuring electricity according to claim 1, further comprises a programmable current sense switch for detecting electricity from the current transformer.

8. The apparatus for measuring electricity according to claim 7, further comprises a zero stand by switch which powers off the control unit if electricity detected by the programmable current sense switch goes below a threshold value.

9. The apparatus for measuring electricity according to claim 3, further comprises a burden resistor which enables adjusting the sensed electricity before feeding to the
analog-to-digital converter.