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Method and apparatus for detecting smoke in an ion chamber

An ion chamber and smoke technology, which is applied to fire alarms, measuring devices, instruments, etc. that rely on smoke/gas interaction, can solve the problem of affecting the overall performance of the ionization chamber smoke detection function, high ion chamber impedance, and increasing device costs And other issues

Inactive Publication Date: 2014-09-24
MICROCHIP TECH INC
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

This condition affects the overall performance of the ionization chamber smoke detection function
Therefore, this increase in leakage current can cause various problems, such as inaccuracy, etc., which can require additional compensation circuits when designing a smoke detector and thus can increase the cost of the device
[0005] In addition, the ion chamber has a very high impedance, and any leakage current (for example, printed circuit board leakage current) will mask the ion chamber current

Method used

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  • Method and apparatus for detecting smoke in an ion chamber
  • Method and apparatus for detecting smoke in an ion chamber
  • Method and apparatus for detecting smoke in an ion chamber

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Embodiment Construction

[0025] A radioactive source in the ion chamber ionizes some of the gas (eg, air) molecules in the chamber. The result is a higher than normal permittivity of the gas due to a higher than normal number of electrically polarized (ionized) gas molecules. Therefore, when setting the voltage across both of the ion chamber electrodes (see figure 1 ), a small current will flow through this ionized gas. When the smoke enters the ion chamber, the smoke reacts with the ionized gas molecules, thereby changing the permittivity ε of the ionized gas molecules and reducing the number of ionized gas molecules. This results in a lower leakage current through the ion chamber. Ion chamber current leakage will vary with temperature, relative humidity, and voltage. But these changes are changing very slowly. However, the smoke causes a sudden change in the ion chamber leakage current (reducing the ion current). Therefore, according to various embodiments, a sigma-delta converter may be used ...

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Abstract

A smoke detection sensor ion chamber has a leakage current that is dependent upon the permittivity of the ionized gas (air) in the chamber. 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 the permittivity thereof that is large enough to detect by measuring a change in the leakage current of the ion chamber.

Description

[0001] Related patent applications [0002] This application asserts the title of the December 14, 2011 application by Benjamin T. Cooke, Joseph Julicer, and Keith Edwin Curtis Priority to commonly-owned U.S. Provisional Patent Application No. 61 / 570,436 for "Method and Apparatus for Detecting Smoke," by Joseph Zhulitzer, Keith Curtis ) and Paul N. Katz (Paul N. Katz) on October 2, 2012, entitled "Differential Current Measurements to Determine Ion Current in the Presence of Leakage Current), both of which are hereby incorporated by reference herein for all purposes. technical field [0003] The present invention relates to smoke detection devices, and more particularly, to smoke detection devices that use sigma-delta analog-to-digital converters for determining when smoke is present in an ion chamber. Background technique [0004] Smoke detectors typically use an ionization chamber containing a radioactive ion source coupled to a high input impedance operational amplifier...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G08B17/11G01N27/66H03M3/00
CPCG08B17/11G01N27/66G08B29/181H03M3/30
Inventor 本杰明·T·库克约瑟夫·朱利谢基思·埃德温·柯蒂斯
Owner MICROCHIP TECH INC