Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With probe – prod or terminals
Reexamination Certificate
1999-10-05
2001-08-14
Strecker, Gerard R. (Department: 2862)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With probe, prod or terminals
C324S072500, C324S115000, C324S132000
Reexamination Certificate
active
06275022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to voltmeters and in particular, voltmeters for use with high voltage transmission lines.
2. Discussion of Background
Voltmeters for high voltage transmission lines are well known. Electric utility employees must test voltages on transmission lines after storms or in other situations. Obviously, voltmeters testing these lines must have sufficient accuracy to alleviate the inherent safety problems with the high voltage lines. The design simplicity of the voltmeter furthers helps in maintaining safety. Various types of voltmeters have been devised for measuring high voltages, such as U.S. Pat. No. 4,594,546 to Green et al. and U.S. Pat. No. 3,969,671 to Smith.
Due to OSHA regulations, electric utility employees must test the nominal line voltage on a de-energized electric line prior to beginning work on the line. Depending on the type of line to be tested, the voltages can range from 200 volts for a secondary distribution line to 14,000 volts for a primary distribution line while primary transmission lines carry voltages up to 300,000 volts. The wide ranges of voltages encountered by utility employees necessitates the use of several voltmeters capable of handling various voltage ranges. A voltmeter with a high resolution is necessary for measuring secondary and primary distribution lines while the high voltages for primary transmission lines require a voltmeter with relatively low resolution.
Various measuring devices, such as ohmmeters and flow meters, have been devised with logarithmic displays; however, the logarithmic output is a natural consequence for these measurements and not produced by additional thought or equipment. An ohmmeter comprises a fixed internal voltage source with a regulating resistor. When a resistor is connected to the ohmmeter, the deflection of the meter movement is inversely proportional to current flowing through the resistor and regulating resistor due to Ohm's Law; consequently, the high-resistance end of the scale is compressed. Also, the energy required to compress the spring in a flowmeter is expressed by a logarithmic equation thereby causing the meter range to be compressed. Although the scale in ohmmeters and flowmeters are naturally compressed, a voltmeter inherently produces a linear output; however, it is necessary to have a voltmeter with a compressed display for high-voltage lines to allow a single meter to measure the wide range of voltages. Therefore, there is need for voltmeter capable of accurately measuring a wide range of voltages while providing a higher degree of resolution at lower voltages than higher voltages.
SUMMARY OF THE INVENTION
According to its major aspects and broadly stated, the present invention is a passive voltmeter capable of accurately measuring and displaying a wide range of voltages. A d'Arsonval type meter movement is preferably used in conjunction with the voltmeter wherein the scale contains a first portion and a second portion. A circuit controls the pointer in such a way that the deflection is linear for a lower, first portion of the range of voltages while a high range of voltages is deflected in a compressed manner in the second, higher portion of the range. The term “compressed” means that the display is scaled in a non-linear manner, particularly one where the spacing between voltage increments becomes smaller and smaller higher up the range, although not necessarily an exact logarithmic function. The circuit comprises a plurality of parallel branches with a meter movement an da resistor in the first branch; each additional branch contains a resistor and at least one diode connected in series. The additional branches have an increasing number of serially connected diodes so that the turn-on voltage for each branch increases with additional branches, while the resistors contain a decreasing value for each additional branch. Thus, a branch will not carry current until the turn-on voltage for the branch has been exceeded. Consequently, resistor values can be selected so that the meter movement operates in an approximately linear fashion for a portion of branches while having a compressed response when additional branches are turned on.
Although the circuit may be used with any voltmeter, preferably the voltmeter is passive. The voltmeter comprises a housing internally coated with a conductive material, a high resistance probe extending from the housing, an da meter movement connected to the housing. As the probe touches the transmission line, a capacitive charge is formed with the housing as the first plate and the physical surroundings of the meter as the second plate. The meter movement is deflected by the charging current since the current will be proportional to the voltage in the transmission line.
A major feature of the present invention is the use of a scale with linear and a compressed portions. The circuit branches containing an increasing number of serially connected diodes enables this feature by having the different branches' ability to carry current dependent upon the input voltage. For an utility employee where the voltage ranges below 14,000 volts for primary and secondary distribution lines, but up to 300,000 volts for primary transmission lines, the ability to have a higher resolution for lower voltages but yet adequate resolution for higher voltages on one scale in one meter is an important convenience. It eliminates the need for a range select switch and allows one meter to be used to meet all electrical transmission metering requirements.
A major advantage of the present invention is the ability to display a wide range of voltages using a single voltmeter. This advantage avoids use of several meters that each handle a different range of voltages.
Another important advantage of the present invention is the simplicity of design for the passive voltmeter. The voltmeter does not have a power source, amplifier or other complex circuitry that might easily fail. As a result of this design simplicity, safety is increased because the utility and accuracy of the meter does not depend on the goodness of the batteries that have a shelf life.
REFERENCES:
patent: 2091521 (1937-08-01), Pattison
patent: 2988700 (1961-06-01), Rosinek
patent: 3041535 (1962-06-01), Cochran
patent: 3257616 (1966-06-01), Andrushkiw et al.
patent: 3268813 (1966-08-01), Pendleton
patent: 3522533 (1970-08-01), Bergero
patent: 3969671 (1976-07-01), Smith
patent: 4336494 (1982-06-01), Shindo et al.
patent: 4594546 (1986-06-01), Greene
patent: 4634968 (1987-01-01), Aslan
patent: 4714916 (1987-12-01), Schweitzer, Jr.
patent: 4794329 (1988-12-01), Schweitzer, Jr.
patent: 6016105 (2000-01-01), Schweitzer, Jr.
Mann Michael A
Nexsen Pruet Jacobs & Pollard LLC
Strecker Gerard R.
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