Gas alarm

• US 5,764,150 A
• Filed: 04/10/1996
• Issued: 06/09/1998
• Est. Priority Date: 04/10/1996
• Status: Expired due to Fees

• Current Assignee: MarketSpan Corporation (National Grid PLC)
• Original Assignee: MarketSpan Corporation (National Grid PLC)
• Inventors: Fleury, Byron, Stanton, Andrew
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): LIEU, JULIE BICHNGOC
• Application Number:
  US08/631,642
• Time in Patent Office: 790 Days
• Field of Search: 340/632, 340/633, 340/634, 72/23.2, 72/23.31, 72/25.01, 72/31.05, 72/31.06, 364/550, 364/496, 422/94, 422/98
• US Class Current: 340/632
• CPC Class Codes: G01N 33/004 CO or CO2
• CPC Class Codes: G01N 33/0063 using a threshold to release an alarm or displaying means
• CPC Class Codes: G08B 21/12 responsive to undesired emission of substances, e.g. pollution alarms
• CPC Class Codes: G08B 21/14 Toxic gas alarms G08B21/16 takes precedence
• CPC Class Codes: G08B 21/16 Combustible gas alarms
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters

Abstract

A gas detector is disclosed which includes a CO sensor and a processor. The CO sensor senses an environmental CO concentration and provides a variable electrical output in response. The processor receives digitized samples of the sensor'"'"'s electrical output and computes, with each measurement sample, a COHb level of a hypothetical person exposed to the CO concentration sensed. The computation involves determining an equilibrium COHb level for each measurement sample, which is compared with a previously computed COHb level associated with previously measured samples. The previously computed COHb level is updated based on the comparison. When the computed COHb level is above a predetermined danger threshold, the processor preferably causes an audible and visual alarm to be activated to alert any persons present. The gas detector can further include a CH₄ sensor coupled to the processor for independently sensing CH₄ levels such that an alarm is activated when the CH₄ levels are above a predefined threshold. A hydrophobic zeolite filter is disposed on the sensor elements of one or both of the CO and CH₄ sensors to prevent erroneous readings.

Claims

1. A gas detector comprising:

a carbon monoxide (CO) sensor for measuring an environmental CO concentration and providing a variable electrical output responsive thereto; and

a processor responsive to samples of said electrical output for computing a carboxyhemoglobin (COHb) level of an individual as if exposed to the measured CO concentration and providing an output signal based on the COHb level computed, wherein

a computed COHb level is obtained with each measurement sample, said computed COHb level associated with a current measurement sample being based on a relationship between a previously computed COHb level associated with previously measured samples and an equilibrium COHb level corresponding to the environmental CO concentration of the current measurement sample,

said computed COHb level associated with the current measurement sample is an incrementally higher level than the previously computed COHb level when the equilibrium COHb level corresponding to the current sample is higher than the previously computed COHb level; and

said incrementally higher level being based on a rate of COHb level increase associated with the environmental CO concentration of a current measurement sample;

or

said computed COHb level associated with the current measurement sample is an incrementally lower level than the previously computed COHb level when the equilibrium COHb level corresponding to the current sample is lower than the previously computed COHb level; and

said incrementally lower level being based on an exponential decrease in COHb level from the previously computed COHb level towards the equilibrium COHb level corresponding to the current measurement sample;

or

said computed COHb level associated with a current measurement sample equals the previously computed COHb level when the equilibrium COHb level of the current measurement sample equals the previously computed COHb level.

2. The gas detector according to claim 1, wherein said exponential decrease is based on a half life of about six hours.

3. The gas detector according to claim 1, further comprising a memory coupled to said processor for storing the computed COHb level in a log for subsequent retrieval.

4. The gas detector according to claim 1, wherein said processor is further operable to transmit an alarm signal to an alarm center whenever the computed COHb level exceeds a predefined threshold.

5. A method for monitoring carbon monoxide (CO) concentrations, comprising the steps of:

periodically measuring environmental CO concentration in an area;

determining a carboxyhemoglobin (COHb) equilibrium level corresponding to the measured CO concentration and an individual'"'"'s physiology;

computing a COHb level of the individual as if exposed to the environmental CO level based on a relationship between a previously computed COHb level and the COHb equilibrium level; and

providing an output signal based on the COHb level computed,

wherein the step of computing a COHb level includes;

increasing or exponentially decreasing a previously computed COHb level associated with previously measured samples when the equilibrium COHb level corresponding to the current sample is higher than or less than the previously computed COHb level, respectively, said increasing being based on a rate of COHb level increase associated with the environmental CO concentration of a current measurement sample, said exponentially decreasing being based on an exponential decrease in COHb level from the previously computed COHb level towards the equilibrium COHb level corresponding to the current measurement sample; and

maintaining the previously computed COHb level when the equilibrium COHb level of the current sample equals the previously computed COHb level.