# US 2013/0154657 A1 · Method and Apparatus for Detecting Smoke in an ION Chamber

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- Number: US 2013/0154657 A1
- Document ID: US20130154657A1
- Status: Published application
- Kind: A1
- Application number: 13/667,196
- Filed: 2012-11-02
- Published: 2013-06-20
- Earliest claimed: 2011-12-14
- Assignees: Microchip Technology Incorporated
- Inventors: Benjamin T. Cooke; Joseph Julicher; Keith Edwin Curtis
- Web page: https://patentgrep.com/patent/US20130154657A1

## CPC

- G01N 27/221: {by investigating the dielectric properties (using microwaves G01N22/00; measuring loss factors or dielectric constants per se G01R27/26)}
- G01N 27/66: and measuring current or voltage
- G01R 27/2605: {Measuring capacitance (capacitive sensors G01D5/24)}
- G08B 17/11: using an ionisation chamber for detecting smoke or gas
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G08B: SIGNALLING SYSTEMS, e.g. PERSONAL CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS

## 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.

## Claims

### Claim 1

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; and
detecting the presence of smoke by detecting a predetermined change in the capacitance.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the step of determining the change in the capacitance of the ionization chamber further comprises the steps of:
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.

### Claim 3 (depends on 1)

The method according to claim 1, where the predetermined change in the capacitance is a change in the capacitance within a certain time.

### Claim 4 (depends on 1)

The method according to claim 1, where the step of determining the change in the capacitance of the ionization chamber comprises the steps of:
charging the capacitance of a first capacitor to a first voltage;
charging the capacitance of the ionization chamber to a second voltage;
coupling the first capacitor to the capacitance of the ionization chamber, wherein a third voltage on the first capacitor and the capacitance of the ionization chamber results;
converting the third voltage to a digital representation thereof;
comparing the digital representation of the converted third voltage with a previously stored digital representation thereof;
detecting the presence of smoke when the digital representation of the converted third voltage has changed from the previously stored digital representation by at least the predetermined change; and
storing the digital representation of the third voltage.

### Claim 5 (depends on 1)

The method according to claim 1, where the step of determining the change in the capacitance of the ionization chamber comprises the steps of:
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;

### Claim 6 (depends on 1)

The method according to claim 1, where:
in a first measurement, a housing of the ionization chamber is coupled to the CVD circuit; and
in a second measurement, a collector plate of the ionization chamber is coupled to the CVD circuit.

### Claim 7 (depends on 6)

The method according to claim 6, further comprising the steps of subtracting a measurement value of the first measurement from a measurement value of the second measurement then dividing by the second measurement value;
and comparing the count numbers of subsequent time periods to determine whether the count number of any one or more of the subsequent time periods has changed by a certain number of counts.

### Claim 8 (depends on 1)

The method according to claim 1, further comprising the step of compensating for temperature change with temperature information from a temperature sensor.

### Claim 9 (depends on 1)

The method according to claim 1, further comprising the step of compensating for relative humidity change with relative humidity information from a relative humidity sensor.

### Claim 10 (depends on 1)

The method according to claim 1, further comprising the step of compensating for voltage change with voltage information from a voltage sensor.

### Claim 11 (depends on 4)

The method according to claim 4, wherein the first voltage is approximately a power supply voltage and the second voltage is approximately a power supply common.

### Claim 12 (depends on 4)

The method according to claim 4, wherein the first voltage is approximately a power supply common and the second voltage is approximately a power supply voltage.

### Claim 13 (depends on 5)

The method according to claim 5, wherein the fourth voltage is approximately a power supply voltage and the fifth voltage is approximately a power supply common.

### Claim 14 (depends on 5)

The method according to claim 5, wherein the fourth voltage is approximately a power supply common and the fifth voltage is approximately a power supply voltage.

### Claim 15

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.

### Claim 16 (depends on 15)

The apparatus for detecting smoke according to claim 15, further comprising 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.

### Claim 17 (depends on 15)

The apparatus for detecting smoke according to claim 15, wherein the CVD circuit is a peripheral device in a microcontroller.

### Claim 18 (depends on 15)

The apparatus for detecting smoke according to claim 15, further comprising a digital processor and memory coupled to the CVD circuit and an alarm circuit.

### Claim 19 (depends on 18)

The apparatus for detecting smoke according to claim 18, further comprising a temperature sensor coupled to the digital processor and a temperature compensation look-up table stored in the memory coupled to the digital processor and used to compensate temperature induced changes of the capacitance of the ionization chamber.

### Claim 20 (depends on 18)

The apparatus for detecting smoke according to claim 18, further comprising a humidity sensor coupled to the digital processor and a humidity compensation look-up table stored in the memory coupled to the digital processor and used to compensate humidity induced changes of the capacitance of the ionization chamber.

### Claim 21 (depends on 18)

The apparatus for detecting smoke according to claim 18, further comprising a voltage sensor coupled to the digital processor and a voltage compensation look-up table stored in the memory coupled to the digital processor and used to compensate voltage induced changes of the capacitance of the ionization chamber.

### Claim 22 (depends on 15)

The apparatus for detecting smoke according to claim 15, further comprising an audible alert actuated by the presence of smoke in the ionization chamber.

### Claim 23 (depends on 15)

The apparatus for detecting smoke according to claim 15, further comprising a visual alert actuated by the presence of smoke in the ionization chamber.

### Claim 24

An apparatus for detecting smoke, comprising:
a first ionization chamber coupled to a capacitive voltage divider (CVD) circuit for determining a capacitance of the first ionization chamber, wherein the first ionization chamber is open to smoke entrance;
a second ionization chamber coupled to the CVD circuit for determining a capacitance of the second ionization chamber, wherein the second ionization chamber is closed to smoke entrance;
wherein a predetermined difference in the capacitances of the first and second ionization chambers indicates the presence of smoke in the first ionization chamber.

### Claim 25 (depends on 24)

The apparatus for detecting smoke according to claim 24, further comprising a smoke detection timer used in determining whether the predetermined difference occurs within a certain time period.