Method and apparatus for detecting smoke in an ion chamber
AssigneeMicrochip Technology Incorporated
InventorsBenjamin T. Cooke, Joseph Julicher, Keith Edwin Curtis
Life of this patent
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Abstract
A smoke detection sensor ion chamber has a capacitance and a change in the permittivity of that capacitance dielectric (ionized air in the chamber) may be used to detect the presence of smoke therein. Smoke from typical fires is mainly composed of unburned carbon that has diffused in the surrounding air and rises with the heat of the fire. The permittivity of the carbon particles is about 10 to 15 times the permittivity of clean air. The addition of the carbon particles into the air in the ion chamber changes in the permittivity thereof that is large enough to measure by measuring a change in capacitance of the ion chamber.
Claims23
A method for detecting smoke, comprising the steps of:
- coupling an ionization chamber to a capacitive voltage divider (CVD) circuit;
- determining a change in a capacitance of the ionization chamber using the CVD circuit by:
- determining a first change in the capacitance of the ionization chamber when the ionization chamber is at a first polarity;
- determining a second change in the capacitance of the ionization chamber when the ionization chamber is at a second polarity;
- determining a difference between the first change and the second change;
- and
- using the difference in determining the change in the capacitance of the ionization chamber;
- and
- detecting the presence of smoke by detecting a predetermined change in the capacitance.
A method for detecting smoke using an ionization chamber, wherein the ionization chamber comprises a first ionization chamber open to smoke ingress and a second ionization chamber closed to smoke ingress, the method comprising the steps of:
- coupling the ionization chamber to a capacitive voltage divider (CVD) circuit;
- and
- determining a change in a capacitance of the ionization chamber using the CVD circuit by:
- charging the capacitance of a first capacitor to a first voltage;
- charging the capacitance of a first ionization chamber open to smoke entrance to a second voltage;
- coupling the first capacitor to the capacitance of the first ionization chamber, wherein a third voltage on the first capacitor and the capacitance of the first ionization chamber results;
- converting the third voltage to a digital representation thereof;
- storing the digital representation of the third voltage;
- charging the capacitance of the first capacitor to a fourth voltage;
- charging the capacitance of a second ionization chamber closed to smoke entrance to a fifth voltage;
- coupling the first capacitor to the capacitance of the second ionization chamber, wherein a sixth voltage on the first capacitor and the capacitance of the second ionization chamber results;
- converting the sixth voltage to a digital representation thereof;
- storing the digital representation of the sixth voltage;
- subtracting the digital representation of the third voltage from the digital representation of the sixth voltage and dividing by the digital representation of the sixth voltage to produce a resulting representation;
- comparing the resulting representation with a previously stored resulting representation;
- detecting the presence of smoke when the resulting representation has changed from the previously stored resulting representation by at least the predetermined change;
- and
- storing the resulting representation.
An apparatus for detecting smoke, comprising:
- an ionization chamber coupled to a capacitive voltage divider (CVD) circuit for determining a capacitance of the ionization chamber;
- wherein a predetermined change in the capacitance of the ionization chamber indicates the presence of smoke in the ionization chamber;
- and
- circuits for alternately coupling to the ionization chamber at a first polarity for determining a first capacitance of the ionization chamber and coupling to the ionization chamber at a second polarity for determining a second capacitance of the ionization chamber, whereby a difference between the first and second capacitances is used in determining the presence of smoke in the ionization chamber.
Dependencies are inferred from the claim text.