Root mean square (RMS) metering devices and methods for generating RMS current level to both high or low frequency within signal
AssigneeMaxim Intergrated Products, Inc.
InventorsSung Ung Kwak, Levi Victor, Kenneth Tang
Life of this patent
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Abstract
Embodiments of the present invention provide systems, devices and methods for efficiently calculating a true RMS values (either voltage or current) of an AC signal. The RMS value is generated from both high and low frequency components of the AC signal without a high speed ADC being integrated within the system. The high frequency component is processed by calculating an average current waveform of the high frequency component and approximating a corresponding RMS value using a waveform factor. The waveform factor is effectively a scalar that relates the average current waveform of the high frequency component to an appropriate RMS value.
Claims20
A Root Mean Square (“RMS”) meter comprising:
- a current interface on which a current signal is received;
- at least one analog-to-digital converter that outputs a digitized low frequency current signal corresponding to a low frequency component of the current signal and a digitized averaged absolute value wave form corresponding to a high frequency component of the current signal;
- a first current squarer, coupled to receive the digitized low frequency current signal, the first current squarer generating a digitized low frequency squared current signal;
- a first multiplier, coupled to receive the digitized averaged absolute value waveform and a waveform factor, the first multiplier generating an approximated RMS value corresponding to an RMS value of the high frequency component of the current signal;
- a second current squarer, coupled to receive the approximated RMS value, the second current squarer generating a squared RMS value;
- a summer, coupled to receive the digitized low frequency signal and the squared RMS value, the summer generating a summed squared current output corresponding to both high and low frequency components of the current signal;
- a first low pass filter, coupled to receive the summed squared current output, the low pass filter generating an averaged summed squared current output;
- and
- a square-root module, coupled to receive the averaged summed squared current output, the square-root module generating an RMS current level corresponding to both the high frequency and low frequency components within the current signal.
An RMS metering system comprising:
- a voltage path that receives a digitized voltage signal and generates an RMS voltage corresponding to the digital voltage signal;
- a current path that receives a digitized low frequency component of a current signal and a digitized averaged absolute value waveform corresponding to the high frequency component of the current signal, the current path generates an RMS current by processing the digitized low frequency component, the digitized averaged absolute value waveform and a waveform factor;
- and
- a power path that receives the digitized voltage signal and the digitized low frequency component of the current signal, the power path generates a power value corresponding to the digitized voltage signal and the digitized low frequency component of the current signal.
A method for calculating an RMS current value, the method comprising:
- receiving an analog current signal;
- squaring a digitized low frequency current signal corresponding to a low frequency component of the analog current signal;
- generating an approximate RMS value of a high frequency component of the analog current signal, the approximate RMS value being generated by multiplying a digitized averaged absolute value waveform with a waveform factor;
- squaring the approximate RMS value;
- summing the approximate RMS value with the digitized low frequency squared current signal;
- averaging the summed approximate RMS value and digitized low frequency squared current signal;
- and
- generating an RMS current value by square-rooting the averaged summed approximate RMS value and digitized low frequency squared current signal.
Dependencies are inferred from the claim text.