Moisture sensor with digital signal processing filtering
First Claim
1. A moisture sensor for detecting moisture on the surface of a transparent material and controlling the actuation of a moisture removal system accordingly, said moisture sensor comprising:
- an emitter for generating a pulsatile emitter signal which is influenced by the presence of moisture on the surface of the transparent material;
a detector for receiving said pulsatile emitter signal and contributing to the production of a pulsatile detector output signal;
a pre-demodulation circuit operatively connected to said detector and including an input for receiving said pulsatile detector output signal and an output for providing a pulsatile pre-demodulation signal, said pre-demodulation circuit further including a filter and an amplifier;
a demodulation circuit for converting said pulsatile pre-demodulation signal to a dc signal having fluctuating noise components;
a digital signal processing filter stage for filtering said fluctuating noise components from said dc signal and producing a filtered dc output.
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Abstract
A moisture sensor for detecting moisture on the surface of a transparent material. The moisture sensor includes one or more emitters for producing emitter signals which are influenced by moisture on the transparent material, and one or more detectors for receiving the emitter signals. The detector produces a detector output signal which is filtered and amplified in a pre-demodulation gain and filtering circuit to remove some of the unwanted signal components including noise from ambient light and EMI. Digital Signal Processing filtering is used after the moisture signal is demodulated to a dc signal to discern small signal changes due to moisture events in the presence of large amounts of the noise created by the pre-demodulation gain circuit. The DSP filtering includes a low pass filter stage and a band pass filter stage implemented by a microcomputer using First In First Out shift registers, summing elements and division elements.
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Citations
26 Claims
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1. A moisture sensor for detecting moisture on the surface of a transparent material and controlling the actuation of a moisture removal system accordingly, said moisture sensor comprising:
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an emitter for generating a pulsatile emitter signal which is influenced by the presence of moisture on the surface of the transparent material; a detector for receiving said pulsatile emitter signal and contributing to the production of a pulsatile detector output signal; a pre-demodulation circuit operatively connected to said detector and including an input for receiving said pulsatile detector output signal and an output for providing a pulsatile pre-demodulation signal, said pre-demodulation circuit further including a filter and an amplifier; a demodulation circuit for converting said pulsatile pre-demodulation signal to a dc signal having fluctuating noise components; a digital signal processing filter stage for filtering said fluctuating noise components from said dc signal and producing a filtered dc output. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A method for detecting moisture on the surface of a transparent material with a moisture sensor having an emitter and a detector including the steps of:
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emitting a pulsatile signal from the emitter which is reflected from the surface of the transparent material wherein the pulsatile signal is affected by the presence of moisture on the transparent material; detecting the reflected pulsatile signal to produce a pulsatile detection output signal; amplifying the pulsatile detection output signal; filtering the pulsatile detection output signal; demodulating the pulsatile detection output signal to produce a dc signal having a fluctuating noise component; filtering the dc signal to remove the fluctuating noise component, wherein the filtering includes storing a predetermined number of the dc signal values and summing the predetermined number of dc signal values; and detecting the presence of moisture on the transparent material with the filtered dc signal. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26)
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Specification