Abstract:
A method and apparatus for protecting workers from casualty due to a combustible gas. A portable combustible gas detector is disclosed which is particularly suitable for portable use. The detector generally comprises a circuit, housed in the same chamber as the sensor, for controlling the operation of the gas detector; and operation software for operating the detector through the circuit. The circuit of the detector is encased in armor to protect the circuit from electromagnetic wave disturbance. 
     The detector is particularly suitable for measurement of a combustible gas with a low concentration. Advantageously, the present invention enables a worker to conveniently carry a small and lightweight combustible gas detector into a hazardous worksite to improve the safety of each worker carrying the device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to combustible gas detectors, and more particularly to a miniature combustible gas detector operable within a limited space. 
     2. Description of the Related Art 
     The risk of an explosion due to a combustible gas at an industrial work site has always existed. Conventional gas detectors offer one possible preventive measure in the hopes of curtailing this risk. Conventional gas detectors, however, are impractical for a few reasons; first, they are too large for workers to carry to such sites, and secondly, their production costs are prohibitive for mass production. That is, portability and economy were never considerations in their design. 
     A need therefore exists for a combustible gas detector, which is miniaturized, lightweight and affordable. The miniaturization, however, should not mitigate the performance of the detector. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a miniaturized combustible gas detector is provided in which both the sensor and the processing circuitry are configured in a common housing, the detector comprising: a control circuit for controlling the operation of the gas detector, operational software for operating the detector via the control circuit; an armor case providing electromagnetic protection for the control circuit; a clip installed at one side of the armor case for clipping the detector on a worker&#39;s uniform, a power switch for operating the detector; power supply means for supplying a direct current power for operating the control circuit; and an LED display for displaying the operational status of the detector. 
     The control circuit further includes a sensor for sensing a combustible gas when the power switch is turned on; a sensor driving circuit for driving said sensor, a signal conditioner for amplifying and converting the signals sensed by said sensor; an A/D converter for converting analog signals received from the signal conditioner into digital signals, a CPU for processing the digital signals under control of said operational software; an EEPROM for storing the data processed by said CPU and for storing said operational software; and an alarm for providing an alarm indication depending on the result processed by said CPU. 
     A method for operating the combustible gas detector according to the present invention generally comprises the steps of: driving the combustible gas detector; initializing the combustible gas detector; conducting a self-diagnostic of the combustible gas detector upon completion of the initialization step; activating a measurement mode upon completion of the conducting step; confirming whether a key-in is activated after said measurement mode has been activated; activating a sub-menu in the event said key-in is activated; otherwise activating a power saving mode in the event said key-in is not activated. 
     The detector of the present invention is advantageously designed so that it may be conveniently carried and worn with ease. 
     According to one aspect of the invention, the detector is constructed such that once a user turns on the detector it cannot be turned off for safety reasons. That is, the detector is continuously operable for 24 hours under battery power, preferably of an alkaline variety. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing features of the present invention will become more readily apparent and may be understood by referring to the following detailed description of an illustrative embodiment of the present invention, taken in conjunction with the accompanying drawings, where: 
     FIG. 1 is a perspective view of the combustible gas detector according to the present invention; 
     FIG. 2 is a block diagram of a control circuit in the combustible gas detector according to the present invention; and 
     FIG. 3 is a flowchart of a method for operating the combustible gas detector according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Illustrated in FIGS. 1 and 2 is an embodiment of the combustible gas detection and measurement apparatus of the present invention. 
     FIG. 1 is a perspective view of the combustible gas detection and measurement apparatus of the present invention, generally indicated as reference numeral  10  and hereinafter referred to as detector  10 . Detector  10  meets the Ex ib IIC T4 class, as defined in the IEC79-11 intrinsic safety class, and further is resistant against electromagnetic disturbances. The detector  10  includes the following additional features: an inhibition resistance in consideration of the inhibition which occurs when any particular compound combines with the reaction surface of the catalyst inhibiting the combination of the combustible gas. The detector  10  is preferably constructed with fully certified flameproof components. Further, the detector  10  is constructed such that once a user turns on the detector  10  for safety it cannot be turned off, as it is continuously operable for 24 hours under battery power, preferably of an alkaline variety. 
     FIG. 2 is a block diagram of a circuit  1000  of the detector  10  comprising a sensor driving circuit  1200 , a sensor  1100 , a signal conditioner  1300 , an A/D converter  1400 , a CPU  1500 , an EEPROM  1600  and a buzzer  1700 . Circuit  1000  advantageously eliminates voltage drops, which may otherwise occur in prior art constructions, between the sensor  1100  and sensor detection circuitry. Such voltage drops are eliminated by virtue of the integrated construction of control circuit  1000 . Control circuit  1000  also compensates for fluctuations in the power voltage caused by the CPU  1500 . Sensor  1100 , sensor driving circuit  1200  and signal conditioning circuit  1300  comprise sensor/signal processing section  210 . Sensor/signal processing section  210  converts an output of the sensor  1100  into a data format that can be processed by the CPU. Sensor driving circuit  1200  maintains the operational condition of the sensor  1100  and converts a sensor output signal  1101  into a voltage signal  1102 . The sensor driving circuit  1200  is designed to minimize power consumption. Minimum power consumption is achieved in three ways. First, a source voltage is applied directly to the sensor  1100  thereby eliminating voltage drops. Second, source voltage fluctuations are compensated for by the CPU  1500 . Third, the buzzer  1700  is designed as a low power consumptive module. Further, the adoption of the surface mount device (SMD) enables the sensor/signal processing section  210  to be miniaturized and lightweight. 
     Sensor  1100  is preferably of a catalytic oxidization type. While thermal conductive type sensors, catalytic oxidation type sensors, and non-dispersive infrared ultraviolet rays NDIR type sensors are used in prior art applications to measure combustible gas, a catalytic oxidation type sensor is preferably used in the present invention because it is the most widely used sensor type for industrial safety applications and is also suitable for measurement of the combustible gas up to a low concentration 100% lower explosive limit (LEL). 
     Sensor  1100  has shock resistance to prevent the platinum wire used from being broken by any mechanical impact and further to prevent a permanent drift from being generated due to any change in the hot wire length. 
     The sensor  1100  of the present invention also includes poison resistance. Poison resistance is utilized to prevent the harmful effects which occur when the catalytic oxidation sensor combines with an external catalyst thereby diminishing the activation level of the sensor. Poisonous external catalysts include atmospheric silicon and hydrogen sulfide. 
     Circuit  1000  further comprises operational software section  220  which preferably includes a self-calibration function (not shown) and a self-diagnostic function (not shown). Section  220  comprises a central processor unit (CPU)  1500  for processing analog signals  1103  received from the sensor/signal processing section  210 , an A/D converter  1400  for converting the analog signals received from the sensor/signal processing section  210 , and an EEPROM  1600  for storing data processed by the CPU  1500 . Operational software section  220  includes two safeguards against incorrect keypad operations initiated by an operator. The safeguards include a zero calibration prevention safeguard and a span calibration prevention safeguard. These safeguards prevent the unintended initiation of either zero calibration or span calibration from being performed by requiring that an operator depress a calibration mode entry key for at least 7 seconds (i.e., perform a key-in operation). 
     Section  220  also extends the usable life of the apparatus of the present invention by utilizing a power saving mode. In particular, the CPU  1500  operates in two modes, a normal operation mode in which the CPU  1500  actively measures gas densities and generates alarms when required. In the normal operation mode energy use (i.e., battery power) is maximized. In the normal operation mode, the CPU  1500  can measure gas densities rapidly (e.g., on the order of microseconds). Such rapid measurement rates are achievable because the density of the external atmosphere varies much more slowly in comparison to the CPU  1500  measurement rate. When the CPU  1500  is not operating in the normal operation mode it transitions to a sleep mode where the current consumption is maintained at 20 microamperes. The CPU  1500  operates alternately in the normal and sleep modes in accordance with a pre-determined time rate thereby allowing the gas density to be measured with minimum current consumption. 
     Control circuit  1000  further comprises an alarm section  230  configured to provide the following alarms. A main alarm is sounded in response to the detection of an instantaneous concentration level of any combustible gas and/or vapor, where the concentration level exceeds 25% LEL. Different LEL levels may be established in alternate embodiments. In the present invention a device malfunction alarm is sounded in three cases: (1) a low voltage condition in the detector  10 , (2) where a malfunction is detected in either the sensor  1100  and/or circuit  1300 , and (3) where a malfunction is detected in circuit  1000  for other than a sensor abnormality. Section  230  further comprises a buzzer  1700  and an LED display window  600  which is operable in concert with the buzzer  1700  for displaying detection events. 
     Circuit  1000  further includes an intrinsic safety/electromagnetic wave-proof housing (not shown) which is coated with an aluminum vacuum layered coating over the housing exterior. The coating prevents electromagnetic waves from propagating through the device. 
     The sensing range of the sensor  1100  is 100% LEL CH 4 . Major functions of the detector  10  include a self-diagnostic function, an operation confirmative function (i.e., confidence bleep), a zero calibration function which utilizes clean air, and is initiated by a one touch-type operation, and a span calibration function using a standard gas, preferably 20% LEL (methane), also initiated by a one touch-type operation. 
     1. Startup Operation 
     The startup operation of the detector  10  according to the present invention is described as follows. Referring to FIG. 1, upon turning on the power switch  300 , a green LED lamp is turned on in the LED display window  600  in parallel with a alarm  1700  sounding 5 times, thereby informing a user that the detector  10  was turned on. Then, the detector  10  conducts a self-diagnostic procedure to check for malfunctions. If there are no detected malfunctions, the detector  10  stabilizes and then goes through a warm up stage lasting approximately 1 minute. As the detector  10  is warming up, the green LED lamp is turned on every 3 seconds to inform the operator of the warm up state. When warm up is normally completed, the green LED lamp flickers in the LED display window  600  in parallel with a alarm  1700  sounding two times. Otherwise, if there is any detected malfunction during warmup, a red LED lamp flickers in the LED display window  600  in parallel with the alarm  1700  sounding one time. 
     2. Preferred Method of Operation 
     FIG. 3 is a flowchart of a method for operating the combustible gas detector  10  according to the present invention subsequent to a successful startup operation. 
     At step  100 , when the detector  10  is turned on, it is initialized. Specifically, an external interrupt and timer are initialized, and parametric values are read from the EEPROM  1600  including an alarm-setting value, a zero value and a span calibrating value. 
     At step  200 , upon completing the initialization step, a self-diagnostic step is conducted where a number of data read/writes are performed to determine whether the EEPROM  1600  is operational. Data is read from and written to the EEPROM to perform this check. Also, the voltage of the battery and the detector  10  are checked. More particularly, at step  200 , the battery voltage is checked to determine whether a low voltage condition has occurred and whether there is any malfunction in the sensor  1100  and the circuit  1000 . It is noted that self-diagnostic step  200  is conducted by a one touch key operation (i.e., pressing a test switch for a predetermined time). That is, if the test switch is pressed for more than 1 second and less than 7 seconds self-diagnosis is conducted. During self-diagnosis the respective operational conditions of the sensor  1100 , the battery (not shown) and the internal circuit  1000  are checked. If the detector  10  is operating under NORMAL conditions, a green LED lamp flickers in the LED display window  600  parallel with two separate audible alarms. If on the other hand, any malfunctions are detected, a red LED lamp flickers in the LED display window  600  in parallel with a single audible alarm. In sum, the self-diagnostic step is provided as a precautionary step to assure that the detector  10  is operating normally prior to a person carrying the detector  10  into a dangerous worksite. 
     At step  300 , upon completion of self-diagnostic step  200 , a measurement mode is activated to measure gas density for comparison with a threshold gas density value. In this step, the external stable voltage is activated, AD conversion is performed, the gas value is measured, the alarm is checked and then the time-out is checked. 
     At step  400 , while in the measurement mode, it is determined whether a key-in operation is activated (i.e., whether an operator has pressed the power switch for more than one second and less than seven seconds) while the detector is turned on. In this event, a sub-menu is activated at step  500 . 
     At step  500 , when the sub-menu is activated in response to the key-in operation of step  400 , automatic calibration functions including a zero calibration function and a span calibration function are performed. 
     Span calibration is required if the detector  10  is exposed to a poor air environment for an extended duration. When this occurs the respective zero points of the sensor  1100  and the electronic circuit may be slightly varied. Also, when a worker is exposed to a high concentration of a combustible gas or is exposed to a poor environment for an extended period, the respective span points of the sensor  1100  and the electronic circuit  1000  may be slightly varied. 
     Span calibration uses a standard calibration gas, such as 25+/−0.5% LEL, CH4 (Methane) in air. To perform span calibration, the POWER button should be pressed for at least than 7 seconds in an ON state of the detector  10 . Upon pressing the POWER button for at least 7 seconds, the detector  10  goes into SPAN ready state. In the SPAN ready state a self-diagnosis procedure is performed. If self-diagnosis procedure is completed successfully the LED  600  flashes green in parallel with the alarm  1700  sounding twice. Otherwise, the LED  600  flashes red and the alarm  1700  sounds once. Further, if self-diagnosis is not successful, the span calibration procedure is aborted and the calibration factors are maintained at their former values. 
     In the case where self-diagnosis is performed successfully, while the detector  10  is in span ready status, a standard calibration gas should be supplied. The detector informs the operator that Span calibration is being performed with the LED  600  flashing green every 3 seconds. Upon completion, if the span calibration procedure was successful, the LED  600  flashes green and the alarm  1700  sounds five times. Otherwise, if the span calibration procedure was unsuccessful, the LED  600  flashes red and the alarm  1700  sounds once. 
     Next, a zero calibration procedure is performed. Room air is used to perform the zero calibration. By pressing the test switch for at least 7 seconds under clean air conditions, a zero calibration cognitive alarm green LED lamp flickers and the alarm sounds twice after which a zero calibration procedure is carried out lasting approximately 30 seconds. Here, the green LED lamp flickers approximately every 3 seconds, which indicates that the detector  10  is performing the zero calibration. If the zero calibration is successful, the green LED lamp flickers in parallel with the alarm sounding twice. Otherwise, if there is any malfunction in the detector  10 , or the influent air contains any combustible gas, a red LED lamp flickers along with a single audible alarm. In the event of a malfunction, a problem will be detected in the zero calibration process. Accordingly, the zero calibration procedure is automatically nullified and the previously performed zero calibration is maintained intact. That is, calibration factors are preserved as former values obtained in a most recent calibration. 
     In the case where the zero calibration procedure is performed without incident (e.g., a clean air condition) the accuracy of an alarm state is improved. The zero calibration procedure is preferably performed at least once per week in a gas free and clean atmosphere. 
     If the key-in operation is not performed at step  400 , the power saving mode is activated at step  800 . In this step, a watchdog timer is reset, and the detector  10  transitions from the measurement mode to the sleep mode. The watchdog timer controls the state of the CPU to alternately change between the sleep mode (i.e., current saving mode) and the measurement mode. 
     In sum, the present invention advantageously enables a worker to conveniently carry a small and lightweight combustible gas detector  10  on his/her person to enhance the worker&#39;s safety. Further, the portable gas detector  10  according to the present invention is more affordable to manufacture than the conventional detector  10  so that it can be widely distributed among work sites and consequently contribute toward worker safety. 
     In addition, since the detector  10  according to the present invention includes a self-diagnostic function, the reliability of the detector  10  is enhanced. Further, the detector  10  includes a power saving mode, which allows its usable lifespan to be appreciably extended. A further advantage of the detector  10  of the present invention is that it eliminates electromagnetic wave disturbances. In addition, the detector  10  of the present disclosure is particularly suitable for measurement of a combustible gas having a low concentration. 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and have been described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as set forth in the claims below.