Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Plural inputs
Reexamination Certificate
2000-05-26
2002-11-19
Sherry, Michael (Department: 2829)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Plural inputs
C324S107000, C324S074000
Reexamination Certificate
active
06483291
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of Invention
This invention relates to an apparatus for measuring the power consumption of an electricity powered device or machine. More specifically, this invention relates to an apparatus which measures the power consumption by calculating the wattage consumed by the electrical device from the measured voltage and current.
2. Description of the Related Art
The power consumed by any process is an important parameter useful for optimizing a process. For example, in grinding, the power consumed is indicative of the efficiency of a grinding wheel to remove material in a given operation. Thus, between two grinding wheels removing material at a certain rate under identical grinding conditions, the grinding wheel consuming less power is more efficient. Accordingly, it is desirable to measure the power consumed by a given machine.
Efficiency may also be calculated based upon the current draw of the load; however, the current draw is typically nonlinear for an inductive motor load wherein the power is a multiple of the voltage, the current, and a “power factor” which is the cosine of the lag angle between the voltage and the current. The power factor varies depending upon the load. For example, an AC motor at idle may have a typical power factor of approximately 0.1 while the power factor of same motor at full load may be approximately 0.8. Measurement of the power consumed by an electrical load containing resistance, capacitance, and inductance requires the measurement of the actual values of the voltage, the current, and the phase angle representing the lag angle between the voltage and the current.
Other devices have been developed to calculate the power consumption by measuring the voltage and the current. Typical are those devices disclosed in the following United States Patents:
U.S. Pat. No.
Inventor
Issue Date
5,537,029
Hemminger, R. C., et al.
Jul. 16, 1996
5,475,303
Kobayashi, S.
Dec. 12, 1995
5,467,012
Nystrom, R. W.
Nov. 14, 1995
5,438,258
Maruyama, R.
Aug. 1, 1995
5,414,349
Kobayashi, S.
May 9, 1995
5,003,252
Nystrom, R. W.
Mar. 26, 1991
4,764,720
Nystrom, R. W.
Aug. 16, 1988
4,535,287
Milkovic, M.
Aug. 13, 1985
Typically in the inventions disclosed in the aforementioned patents, the power consumption is calculated by the Hall device which senses the magnetic field created in a current carrying line by the Hall Effect and multiples it by the line voltage, e.g., U.S. Pat. No. 5,438,258, issued to Maruyama and U.S. Pat. No. 4,764,720 issued to Nystrom. The prior art sensors based on the Hall device are essentially limited to lower frequency applications. The power calculated using a typical Hall device is limited by the frequency response of such a device and typically loses significant accuracy at frequencies above 1000 Hz. U.S. Pat. No. 5,537,029, issued to Hemminger et al., teaches a sophisticated microprocessor-based system having elaborate software for monitoring power consumption and, more important, testing the operation of the power meter. The present invention is capable of accurate measurements at frequencies above the 1000 Hz mark by using a Hall sensor only to obtain a voltage proportional to the current and independently obtaining and attenuating the input voltage. The input-current voltage and the input voltage are multiplied and summed to calculate the total power consumption using simple, discrete components.
Additionally, the prior art devices typically require a complex setup procedure requiring the operator to select both the maximum input current and the maximum input voltage. The present invention reduces the need for additional settings requiring the operator to simply select the desired output range of the power meter.
Finally, the prior art devices are limited in the customization and information available to the operator. The devices are typically intended for self-contained use. For example, when using a portable power meter which is not associated with a single machine, it is desirable to be able to adjust the scale of the output to read the power consumption with some precision. Further, prior art devices typically provide instantaneous power consumption readings using an analog display which suffers from a slow response time and hides small effects from the operator. Additionally, the prior art meters, particularly those with analog displays, do not provide the operator with important information such as peak power. Prior art devices incorporating digital displays have not been taught having differing measurement units available to the operator. While the analog displays may have multiple scales, the analog devices typically only provide an approximation of the total power consumption subject to the operator's interpretation of the needle position. The present invention provides an unscaled output along with an operator selectable scaled output allowing more precise measurement of power consumption significantly less than the full scale maximum of the power meter in addition to a default range, full scale output. Additionally, the present invention utilizes a bar LED display for rapid response when displaying the instantaneous power usage and a digital display with user selectable measurement units to provide accurate, non-discretionary power consumption readings coupled with a peak power hold feature. Finally, the power meter of the present invention, while self contained, provides for intelligent communication with external devices.
Accordingly, there is a need for a power meter which does not require setting of the maximum input current and the maximum input voltage prior to making a measurement. Additionally, there is a need for a power meter which is capable of measuring the power consumption of a load requiring a high frequency power supply without degradation of the measurement accuracy. There is also a need for a power meter providing a fast responding display of instantaneous power consumption, a display of peak power consumption, and providing operator selectable measurement units. Further, there is a need for a power meter providing both scaled and unscaled outputs for external monitoring of the system and providing both high and low trip points. Finally, there is a need for a power meter capable of communicating with and responding to external devices.
Therefore, it is an object of the present invention to provide a power meter which requires only the maximum power range to be set prior to making a measurement.
It is another object of the present invention to provide a power meter which is capable of measuring the power consumption of a load requiring a high frequency power supply without degradation of the measurement accuracy.
Yet another object of the present invention is to provide a power meter which provides a fast responding display of the instantaneous power consumption of the load.
A further object of the present invention is to provide a power meter which communicates with external devices for remote control of the power meter and remote display of the power meter settings and outputs.
A still further object of the present invention is to provide a power meter which simultaneously provides scaled and unscaled output signals.
An additional object of the present invention is to provide a power meter which can store and display the peak power consumption of the load.
Another object of the present invention is to provide a power meter having both high and low trip points in a single unit.
Yet another object of the present invention is to provide a power meter which is capable of scaling the output to a unit of measure selected by the operator.
BRIEF SUMMARY OF THE INVENTION
An apparatus for measuring electrical power consumption is provided. The power is measured by multiplying the instantaneous voltage of the load by the instantaneous current of the load. The current is measured using a Hall Effect current sensor. The output of the Hall current sens
Bhateja Chander P.
Bhateja Rajiv K.
Hollington Jermele
Pitts & Brittian P.C.
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