Patent Application
20120176103
This disclosure relates to a voltage-converter configured to respond to a 400 volt and above input signal at its carrier frequency band, by generating an output signal whose voltage amplitude is less, often much less, than ten percent of the input voltage amplitude at the carrier frequency band and operates with a second non-zero gain for a second distinct frequency band.
Before discussing the specifics of the disclosed apparatus, its uses and operations, several terms will be defined. The voltage between two points is the electrical force that drives an electric current between the points, so that a measure of the voltage is in terms of energy per electrical charge.
Electric current will refer to the rate of flow of the electrical charge, which will typically be carried by moving electrons in a power line, which may be a wire or cable. One standard unit for measuring the rate of flow of electric charge is the ampere, which is charge flowing through some surface at the rate of one coulomb per second. The coulomb is a unit of electrical charge and is approximately equal to the charge of 6.24151×1018 protons or −6.24151×1018 electrons.
Electrical current flow will be discussed as either Direct Current (DC) or Alternating Current (AC). In DC, the current flow has a fixed direction, whereas in AC the current flow changes direction in an alternating manner.
As used herein, a signal will refer to an electrical signal including a Direct Current (DC) component with a voltage amplitude at a frequency of 0 Hertz and an Alternating Current (AC) component with voltage amplitudes at all non-zero Hertz frequencies. While most of this disclosure will refer to the conditions of the signal in a finite window in time, this detail will not be repeated except where it is specifically useful.
Medium and high voltage AC signals pose several test and measurement problems. As used herein, a medium voltage AC signal has a voltage amplitude of greater than or equal to 400 volts, or equivalently, not less than 400 volts. The voltage amplitude of a high voltage AC signal is not less than 1000 volts.
Electrical signals, particularly AC signals, lend themselves to a frequency based representation. This representation assigns a voltage amplitude at a given frequency, which is then often summed with other voltage amplitudes at other frequencies to approximate the electrical signal. Frequencies are often measured in terms of Hertz (Hz), which is the number of oscillations in the electron charge direction per second.
Here are a couple of examples: A purely DC signal will have a DC voltage amplitude at the frequency of 0 Hz. However, in practice, DC signals may vary over time, indicating that they also have higher frequency voltage oscillations. The DC voltage amplitude will tend to be much larger than the voltage amplitude of these higher frequency components.
An AC signal averaged over time or window of time can be viewed as essentially the voltage amplitude at 0 Hz, or its DC voltage component. An AC signal has a DC voltage amplitude that is lower than the sum of its higher frequency components.
Several circuits will be disclosed that have a transfer function which describe the transformation of the AC input signal to the output AC signal over a range of frequencies. The gain at a given frequency is the ratio of the frequency component of the output signal divided by the frequency component of the input signal.
The transfer function often operates much the same for an input signal within a frequency band. A frequency band refers to a range of frequencies between a low frequency and a high frequency, for example, a frequency band between 55 Hz and 65 Hz. In such situations the transfer function will be considered to have a single gain across the frequency band between 55 and 65 Hz.
One common class of electrical circuits is called a low pass filter. A low pass filter receives one input signal and generates one output signal. The transfer function of the low pass filter has a non-zero gain from 0 Hz to a cutoff frequency (say 65 Hz). This gain progressively declines to close to 0 for higher frequencies. These circuits are called low pass filters because they pass the low frequencies of the input signal to the output signal, while filtering out the higher frequencies.
A voltmeter is often used to measure a voltage drop across an electrical device. In practice, the voltage drop across a device can be measured directly and safely using a voltmeter that is isolated from ground, provided that the maximum voltage capability of the voltmeter is not exceeded.
However, medium and above voltage AC signals are beyond the voltage range of most inexpensive prior art voltmeters. To interface to relatively inexpensive voltmeters requires a voltage divider circuit that can convert the medium and above voltage AC signals into the operating range of the voltmeters. Step-down transformers are often used as voltage dividers that also act as low pass filters.
The signal for a power line has a carrier frequency that carries essentially all of the energy of the power line. Today, a prior art voltmeter is often used to measure the voltage amplitude of the carrier frequency. However, these prior art voltmeters have problems. The step-down transformers of the prior art voltmeters are often very large and expensive. Measurements that require two or more concurrent measurements need multiple step-down transformers. Therefore, it is often impractical to make these measurements.
One example of this problem is in the measurement of the power in an AC signal. This requires knowing both its voltage amplitude, its current amplitude and the phase difference between the voltage and current signals, requiring concurrent measurements of the voltage and the current. One prior art way to measure the current of a power line places a Rogowsky coil near the power line so that it inductively couples to the carrier signal. The output AC signal of the Rugowsky coil is a voltage varying signal that can be measured by the same or a different voltmeter to determine the current. The output AC signal of the Rugowsky coil is also low pass filtered, this time by at least the inductive coupling. Often, the voltage of the AC signal is found by integrating the output signal of the Rogowsky coil. Assume that the measurements of the voltage and current signals are digitized. There are some problems with this approach:
Many types of electrical machinery generate small, high frequency signals as components malfunction and/or due to manufacturing defects. Prior art voltage dividers present two main issues when dealing with these fault-related signals:
Prior art voltage dividers not only scale down the input voltage by a fixed ratio, but also the voltage dividers interfere with the voltage measurement by adding a baseline level of noise intrinsic to the voltage divider. A digitizer connected at the output of the voltage divider also adds noise to signal before it gets digitized. Both of these sources of noise may have a white spectrum that gets added to the voltage divided signal after voltage dividing. So that the noise added by the sensor and the digitizer, gets multiplied by the inverse of the gain of the voltage divider.
As used herein, Root Mean Square (RMS) refers to the square root of the mean square of one signal to another signal, usually within a window of time. Consider the RMS of the difference between to digitized signals ai and bi for a window from 1≦i≦N may be calculated as √{square root over ((Σi=1N(ai−bi)2)/N)}. The RMS between two continuous signals f and g for a time interval T1≦t≦T2 may be calculated as √{square root over (∫T
For example, consider a sensor with an input range of +−10 kV, an output range of +−10V, a gain of 1/1000, and an RMS output noise of 4 mV, is connected to a digitizer with an RMS intrinsic noise at its input stage of 3 mV. The total noise that gets digitized is √{square root over (42+32)}=5 mV, which would appear as 5V=5 mV/gain of noise at the input of the voltage divider.
A voltage-converter is disclosed that includes an input coupling to receive an input signal, an output coupling to provide a low voltage signal, and a converter body configured to respond to the input signal based upon a transfer function to generate the low voltage signal. The input signal at a carrier frequency has a voltage amplitude that is not less than 400 volts. The low voltage signal at the carrier frequency may have a voltage amplitude of not more than ten percent of the input voltage amplitude. The transfer function may have distinct gains in at least two separate frequency bands, with the gain at the carrier frequency of not more than ten percent.
The voltage-converter may be configured to measure power lines and/or electrical equipment. The voltage-converter generates the low voltage amplitude at the carrier frequency of not more than ten percent of the input voltage amplitude, and may also provide amplified, rather than suppressed, small signals at higher and/or other frequencies. These amplified, small signals may be used to indicate component malfunctions and/or flaws of the power lines and/or of the electrical equipment.
The voltage-converter may include multiple interchangeable components. These components may be coupled together to create the appropriate transfer function of the voltage-converter. Each of these components may at least partly create the gain in one or more distinct frequency bands. For example, a first component may create a first gain in a first frequency band and a second component may create a second gain in a second, distinct frequency band, for a voltage-converter including them both.
Two separate voltage-converters used to monitor two different equipments, may have different frequency band profiles. In particular, the two implementations may have different higher frequency bands devoted to the detection of different sets of potential failures, while sharing the same gain in the same carrier frequency band.
Even if a higher frequency is shared, the small signals may need a different gain when they are amplified. For example, a first electrical device may have a first small signal in the volt range, whereas a second electrical device may have a second small signal in the millivolt range. The second small signal needs to be amplified by a gain of 1000 to be about the same voltage as the first small signal.
The voltage-converters made from these components provide an advantage by creating specific transfer functions for measuring specific equipment. A component collection of these interchangeable components is also disclosed that provides a valuable resource for technical staff members. They can rapidly reconfigure the voltage-converter using the component collection to inspect and/or troubleshooting equipment with different measurement requirements.
The voltage-converter may have a length that is at most a scale length (Lvd) multiplied by the voltage amplitude of a carrier frequency divided by 10000 volts. Lvd may be no more than 40 centimeters (cm), or 20 cm, or 10 cm, or 6 cm. An outer wall of the voltage-converter may be the length of the voltage-converter. A cylinder-like shape may form some, or all, of the outer wall of the voltage-converter. Coupling a selected combination of the interchangeable components may form at least part of the cylinder-like body for targeting specific equipment.
A signal processing circuit is disclosed and claimed for use with the voltage-converter and may include the following: An analog to digital converter may be configured to receive the low voltage signal as an analog input from the output coupling to create a digital sample. A digital signal processor may be configured to use the digital sample to create a digital reconstruction of the input signal that stimulated the voltage-converter to generate the low voltage signal received by the analog to digital converter. An output device may be configured to respond to the digital reconstruction.
Several examples of the signal processing circuit are disclosed and claimed:
Various process steps are disclosed and claimed for making, operating and/or using one or more of the components, voltage-converters, signal processing circuits and/or voltmeters:
The voltage-converter, the voltmeter, the power meter and/or the three-phase meter may be products of the various disclosed process steps.
The voltmeter may be used to make low noise measurements of an input signal. Apparatus are disclosed including at least one power line, at least one plant, a controller and a feedback path coupling to the power line and the controller. The power line may be configured to transmit a power signal with a carrier voltage of not less than 400 Volts in a carrier frequency band. The plant may be configured to respond to at least one control state to generate at least one output signal. The control state and/or the output signal may include the power line.
The feedback path includes at least one sensor coupled to the power line and configured to respond to the power signal to generate a feedback signal presented to the controller. The sensor may include at least one of the voltage-converter, the voltmeter, the power meter and the three-phase meter. The controller is further configured to respond to the feedback signal to at least partly generate the control signal for the plant.
The plant may be configured to perform one or more of the following: Generate the power signal to drive the power line. Transmit the power signal on the power line. Store power from the power signal on the power line. And/or use the power signal to drive at least one machine.
The feedback signal may be based upon at least one of the low-voltage signal, the digital sample, the digital reconstruction, the voltage estimate, the current estimate, the phase estimate, the power estimate and/or one or more of the parameters. Other parameters that may be of value include range and threshold detections or indications and counts of these detections or indications, possibly sampled at specific time intervals.
This disclosure relates to a voltage-converter configured to respond to a 400 volt and above input signal at its carrier frequency band, by generating a low voltage signal whose voltage amplitude is less, often much less, is a small fraction of the input signal at the carrier frequency band and operates at a second gain for a second distinct frequency band.
As used herein, a signal is an electrical signal including a Direct Current (DC) component with a voltage amplitude at a frequency of 0 Hertz and an Alternating Current component with voltage amplitudes at all non-zero Hertz frequencies.
The voltage-converter has a transfer function describing the transformation of the input signal to the output signal over a range of frequencies.
The gain at a given frequency is the ratio of the frequency component of the output signal divided by the frequency component of the input signal.
The transfer function of the voltage-converter has distinct gains in at least two distinct frequency bands, one of which will be referred to as the carrier frequency band.
Additional circuitry is also disclosed that uses the output signal to diagnose electrical conditions. This circuitry supports inexpensive and/or very accurate sensors for power lines, power generators, power transmission equipment and electrical machinery.
The voltage-converter 100 may be configured to measure power lines and/or electrical equipment. The voltage-converter 100 provides the low voltage amplitude 136 at the carrier frequency 131 within an acceptable input voltage range for measurement with the first gain G1 that is much smaller than 1, and may also provide amplified, rather than suppressed, small signals such as the small telltale output spike 138. This may be done using the second gain G2 greater than G1. The gain G2 may further be greater than one in some situations. These amplified, small signals 138 may be used to indicate component malfunctions and/or flaws of the power lines and/or of the electrical equipment.
Voltage converters 100 may have a different frequency band profiles, for example, if they have been configured to monitor different equipment with differing telltale spikes 134 that may be in different frequency bands FB.
Even if a frequency band such as FB2 is shared, the small signals may need a different gain G2 and G2′ when they are amplified. For example, a first electrical device may have a first small telltale spikes 134 in the volt range, whereas a second electrical device may have a second small telltale spikes 134′ in the millivolt range. The second small telltale spikes 134 needs to be amplified by a gain of 1000 to be about the same voltage as the first small signal.
The voltage-converters 100 and the converter bodies 130 made from these interchangeable components 132, 134 and 134′ provide an advantage by creating specific transfer functions 150 and 150′ for measuring specific equipment.
In some embodiments of the voltage-converter 100, multiple identical RC networks may be found in series at branch receiving the input signal 112 to achieve a high voltage rating.
This method of operating a voltmeter may be applied to other sensors, for instance, current sensors, magnetic field sensors, possibly including attenuated MEMS magnetometers, and/or electric field sensors or any other system in which there is a strong signal and a comparatively weak signal that may be separated in terms of their frequency as found in Fourier signal processing and/or some other frame related separation as found in wavelet signal processing.
Multi-Layer Chip Capacitors (MLCC) using C0G/NP0 dielectric may be used in the voltage-converters 100 where capacitances have to be precisely controlled, and special attention is required to meet signal integrity and accuracy goals. C0G/NP0 MLCCs are found in critical applications like RF tuning networks, high fidelity sound quality, detectors for scientific applications, avionics, radar systems, telemetry, communication systems, medical applications, etc. but to date not in voltage measuring applications involving medium and/or high voltage lines.
The voltage-converter 100 may at least one MLCC including a form of C0G/NP0 dielectric. While these capacitors have some excellent performance properties, they have had been restricted to low voltage applications, and in particular, kept away from power line monitoring. The reason for this is that the processes involved in making C0G/NP0 MLCCs are far too expensive to be scaled to make these capacitors match the medium and/or high voltage and high capacitance values that are typically used on power line monitoring systems. In other words, oil-base capacitors used for power line monitoring can achieve relatively medium and/or high voltage and capacitance targets at a much lower cost than a C0G/NP0 MLCC with similar voltage and capacitance values.
However, the inventors have used some new properties of the C0G/NP0 MLCCs to enable the disclosed voltage-converters 100. Recent developments in C0G/NP0 dielectrics had increased the capacitance per unit of volume for C0G/NP0 MLCCs. Using low-noise circuitry decreases the output current requirements throughout the voltage-converter 100. And the use of multiple gains G1 and G2 in separate frequency bands FB1 and FB2 supports digital reconstructions 204 of unparallel accuracy and with new capabilities to resolve small telltale signal spikes 138, which have not been visible in field measurement devices.
In certain embodiments of the voltmeter 300, the signal processing circuit 200 may have a length Lspc that is essentially fixed for a wide range of voltage amplitudes Vin at a carrier frequency for which the voltage converter 130 may be configured. For instance, the Lspc may be less than or equal to 20 cm. In certain embodiments, Lspc may less than or equal to 10 cm. Lspc may further be less than or equal to 8.5 cm.
The voltmeter package 310 have an outer wall 312 that form essentially a cylinder as shown in
A tubular voltmeter package 310 may be advantageous because materials with strong dielectric properties can be easily found as tubes and rods. This simplifies the manufacturing process and makes it very easy to change the voltage rating just by extending the circuit and cutting the outer tube of the package longer. Other solutions often are cast and require a complete redesign of the package for every voltage rating. Using a G10/FR4 material in the package offers tremendous rigidity and robustness to the voltmeter as these materials are incredibly difficult to break, fire retardant and widely available at very low cost.
These voltage-converters 100 require less current because of their use of low noise circuitry with low noise components, low noise architecture, and low noise layout. The inventors recognized that if one cuts by half the noise level of a circuit, there is a decrease in the amount of current required from the input network by half to get the same signal to noise ratio. So, by using very low noise circuitry much lower capacitance values are required in the voltage-converter 100.
In certain embodiments of the voltage-converter 100, when the input voltage amplitude 131 at the carrier frequency 131 may be from 10 KV and upwards, the voltage converter 100 may include only capacitors with little or no temperature dependence , little or no Estimated Series Resistance and/or little or no leakage current. Such a voltage-converter 100 may be fundamentally smaller than prior art voltage dividers using oil filled capacitors and/or transformers. The voltage converter may be about 30 cm long for every 30 kVolts.
The analog to digital converter 210 may respond to the low voltage signal 122 of the voltage-converter 130 as a comparison to further create the digital sample 202 as an in-range indication.
The DSP 220 may include at least one instance of a computer and/or a finite state machine. As used herein, the computer may include at least one instruction processor and at least one data processor, with each of the data processors instructed by at least one of the instruction processors. As used herein, a finite state machine receives at least one input, may have and alter at least one state and generate at least one output based upon the value of at least one of the inputs and/or the value of at least one of the states.
For example, the ADC 210 may include two analog comparators 211 and 213, whose outputs will, to simplify this discussion, be assumed to be compatible with a logic gate 215 performing the Nand function. The first comparator 211 receives an upper voltage limit, Vupper 214 on its positive terminal and the analog input 212 on its negative terminal. The second comparator 213 receives a lower voltage limit, Vlower 216 on its negative terminal and the analog input 212 on its positive terminal. Assume that the low voltage signal 122 is below the Vlower 216 voltage, then the first range output 217 of the first comparator 211 is true and the second range output 219 of the second comparator is false, making the digital sample 202 true. In a similar fashion, the following table summarizes the operation of the ADC 210:
The DSP 220 may respond to the digital sample 202 by counting the changes of the in-range indication to generate a count 206 as part or all of the digital reconstruction 204. Further, the count 206 may represent an accumulation of how much of the time the low voltage signal 112 is outside the voltage range between Vupper 214 and Vlower 216. This can be an important service metric for some installations and may also be used to show the overall reliability of a generation and/or transmission system or component.
The output device 230 may display the count 206 on a screen 232 for a human to read.
The signal processing circuit 200 may use the digital reconstruction 204 as a representation of one of the frequency bands, such as FB1 or FB2 of
The transmitter 234 may be a radio frequency device, a light frequency device, such as a fiber optic cable driver. The transmitter 234 may support wireline protocols such as Ethernet, ICAN and/or SCADA. As shown in the Figure, the DSP 220 may communicate with the output device 230, or more specifically, the transmitter 234, possibly by directing the transmitter 234 to access the digital reconstruction 204 to transmit 236 one or more messages 250 that may communicate a form of the digital reconstruction 204.
The removable device interface 238 may support a Universal Serial Bus (USB) socket and/or a socket compatible with a version of the Institute for Electrical and Electronic Engineers (IEEE) 1394 communications protocol, sometimes referred to as Firewire. The removable device interface 238 may be communicatively coupled to a removable device 252. The digital reconstruction 204 may be loaded and/or updated based upon the state of the digital reconstruction 204 stored and/or maintained in the signal processing circuit 200.
The signal processing circuit 200 may respond to the received message 262 by using the digital reconstruction 204 as the count 206 of the in-range indications of the digital samples 202 as in
By way of further example,
The signal processing circuit 200 may be further configured to generate a first digital sample 202-1 of the first low voltage signal 122-1, a second digital sample 202-2 of the second low voltage signal 122-2 and a third digital sample 202-3 of the third low voltage signal 122-3. The first, second and third digital samples 202-1, 202-2 and 202-3 may be synchronously generated, possibly by the use of Sample and Hold amplifiers.
Consider using the Sample and Hold amplifiers SH 2 and SH 3 for synchronous generation of the digital samples 202-1, 202-2 and 202-3:
One skilled in the art will recognize that all the low voltage signals 122-1, 122-2 and 122-3 may be represented to Sample and Hold amplifiers in certain embodiments.
In the Examples shown in previous Figures, the ADC instances referenced as 210, 210-1, 210-2 and/or 210-3 may have additional circuit components involved with the sampling of the analog inputs 212, 212-1, 212-2 and/or 212-3.
AC power measurements are of great value in a number of industrial and technical settings, such as determining power line loss and the real-time drain of equipment on AC power supplies and/or power lines.
Coupling the field-to-voltage-converter 520 to one of the analog inputs 212 of the ADC 210 of the signal processing circuit 200 can be used to create a current estimate or reconstruction 204-I of the power line 480 inductively coupled by the electromagnetic field 538 to the field-to-voltage-converter 520. This, when combined with the voltmeter 300 may create the power meter 500 by configuring the signal processing circuit 200 to further generate a phase estimate 204-phase of the power line 480, and from the voltage estimate 204-V, the current estimate 204-I and the phase estimate 204-phase, calculate a power estimate 204-power of the power line 480.
The transducer 510 includes a voltage-converter 100 coupled through the input coupling 110 to the voltage coupling 502, a field-to-voltage-converter 520 and possibly a power supply 510.
The voltage coupling 502 may connect the disclosed voltage-converter 100 through the input coupling 110 to generate the input signal 112 as shown in
The field-to-voltage-converter 520 uses a second transfer function 150-2 to generate a second low voltage signal 122-2 in response to the electromagnetic field 538 that is essentially determined by the current 534 of the power line 480.
The power supply 510 may use the power coupling 506 to generate at least one internal power signal 512 that may be used within the power meter 500. For example, the internal power signal 512 presented to the signal processing circuit 200 to supply its operational requirements. The power supply 510 may include another instance of the disclosed voltage-converter 100 rather than a less efficient step down transformer.
Multiple instances of the voltmeters 300 may collaborate: Communicating from one voltmeter a parameter of a first input signal to a second voltmeter creating the phase estimate of the input signals. The parameter may be an estimate of one or more of the following: voltage, current, power, power phase and phasor. More than one parameter may be communicated in some embodiments.
The voltmeter 300 may be used to make low noise measurements of an input signal. This will be discussed in terms of an ideal prior art voltage divider and an implementation of the disclosed voltage-converter 100:
Consider the ideal prior art voltage divider to have a uniform gain over its whole bandwidth, whereas actual voltage dividers are more likely to act as low pass filters. To recover the voltage at the input of the divider, the output voltage has to be multiplied by the inverse-gain of the voltage divider. For example, if the output of a voltage divider with a gain of 1/1000 is 5V, this means that the voltage at the input of the voltage divider is 5V*1000=5000V. This also means that the noise added at the output of the divider will show as part of the signal, and will also get multiplied by this same inverse-gain. For example, 1 mV of noise at the output of the voltage divider with a gain of 1/1000, will appear as 1V of noise in the input signal.
The disclosed voltage-converter 100 can greatly reduce this effect. Consider an example voltage-converter 100 with a gain of 1/1000 for a carrier frequency band from 0 to 200 Hz, and a gain of 1/10 for the second frequency band from 200 Hz to 20 MHz. Assume the noise is 1 mV RMS white noise spread evenly from 0 Hz to 20 MHz. In this case, the noise level referenced at the input signal of the voltage-converter is (1*1000*200+1*10*19999800)/20000000 which is about 10 mV.
Although the noise level of the measurement setup is the same in both cases, once the noise is referenced to the input signal, the level of noise in the second example is 100 times smaller.
The feedback path 1280 includes at least one sensor 1200 coupled to the power line 480 and configured to respond to the power signal 1002 to generate a feedback signal 1210 presented to the controller 1400. The sensor 1200 may include the voltage-converter 100, the voltmeter 300, the power meter 500 and/or the three-phase meter 320. The controller 1400 may be further configured to respond to the feedback signal 1210 to at least partly generate the control signal 1110 for the plant.
The feedback signal 1210 may be based upon at least one of the low-voltage signal 122, the digital sample 202, the digital reconstruction 204, the voltage estimate 204-V, the current estimate 204-I, the phase estimate 204-phase, the power estimate 204-power and/or one or more of the parameters.
Examples of the means for generating 1110 include but are not limited to steam or water powered turbines driving electrical generators and/or dynamos, wind power electrical generators, solar cell arrays, solar furnaces driving stirling engines, photo-voltaic arrays, fission nuclear reactors, and/or fusion nuclear reactors. Some may question the last entry, fusion reactors, but plasma bottles have been maintained for measurable time durations, and those time durations are progressively getting longer. Some experiments have generated as much power as they have used providing a first reduction to practice.
Examples of the means for transmitting 1120 may include but are not limited to the power lines 480 that may include but are not limited to transmission lines operating above 50 K Volts, distribution lines operating at lower voltages, the coils of inductive devices such as transformers and isolation circuitry as well as possibly switches to control the power lines, coils, transformers and isolation circuitry.
Examples of the means for storing 1130 power may include but are not limited to battery packs, fly wheels, and potential energy batteries storing power by displacing water to a height.
Examples of the means for converting 1140 may include but are not limited to transformers and inverters that may either receive the power signal 1002 and/or contribute to generating the power signal 1002.
Machines 1150 may include but are not limited to all devices on this planet or in space powered by or controlled by the power signals 1002 having a voltage amplitude 114 of at least 400 Volts at a carrier frequency 131.
The preceding embodiments provide examples of the invention and are not meant to constrain the scope of the following claims.
This patent application claims priority to provisional patent application No. 61/239,777, entitled “Method and Apparatus for Voltage Dividing, Measurement, and/or Use of Voltage Measurements” filed Sep. 3, 2009, which is incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2010/047838 | 9/3/2010 | WO | 00 | 3/4/2012 |
| Number | Date | Country | |
|---|---|---|---|
| 61239777 | Sep 2009 | US |
