Apparatus and method for filtering a digital signal
AssigneeJohnson Controls Technology Company
InventorsKirk H. Drees, Nebil Ben-Aissa, John E. Seem
Life of this patent
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Abstract
A closed loop feedback control system operates to maintain a process variable at or near a process variable setpoint. A digital filter is implemented with the controller to filter the process variable signal input to the controller. The filter includes both an amplitude filter to clip signal spikes and glitches and low pass filter to remove higher order, noise related frequencies from the signal, that could adversely affect computational speed of the controller.
Claims16
A method of filtering a digital signal, comprising the steps of:
- conditioning a process variable signal for filtering, wherein the process variable signal is digital and varies in amplitude with variation in magnitude of a process variable and thus contains amplitude information;
- filtering the process variable signal through an amplitude filter to remove a first noise component, while retaining the amplitude information;
- filtering the process variable signal through a frequency filter to remove a second noise component from the process variable signal;
- and
- adjusting outputs of the amplitude and frequency filters in response to changes in the process variable signal.
A digital filter, comprising:
- an input that receives an input signal including a low pass process variable and noise components;
- an adaptive amplitude filter that clips the input signal and outputs a clipped signal, the adaptive amplitude filter having an amplitude window that permits small changes in the input signal, but clips changes exceeding a predetermined amplitude wherein the amplitude window is expandable in an exponential manner to conform to variations in the input signal;
- and
- a frequency filter that filters the clipped signal to eliminate associated high frequency noise from the clipped signal and produces a filter output signal.
A method of filtering a digital signal, comprising the steps of:
- conditioning a digital process variable signal for filtering;
- filtering the digital process variable signal through an amplitude filter to remove a first noise component by clamping an output of the amplitude filter if a present input to the amplitude filter is greater than a previous output from the amplitude filter, or if the present input to the amplitude filter is less than the previous output from the amplitude filter;
- filtering the digital process variable signal through a frequency filter to remove a second noise component from the digital process variable signal;
- and
- adjusting outputs of the amplitude and frequency filters in response to changes in the digital process variable signal.
Dependencies are inferred from the claim text.