Abstract:
A gas detector system comprises a controller and one or more remote gas sensors. The controller may be a standard personal computer running software for detecting the operational status of the gas sensors and signaling an alarm if the gas sensors indicate an alarm condition. The gas sensors may be connected to the controller by way of a universal serial bus. This architecture provides a gas detection system which can be very flexible and full-featured and yet inexpensive. The gas detectors may include detachable portable units which may be removed from their permanent locations to pinpoint the source of a gas leak or to provide routine monitoring of gas levels. The remote units may include data logging functions so that measurements of gas levels at various locations and times can be stored in the portable units for later transmission back to the controller.

Description:
FIELD OF THE INVENTION 
     This invention relates to gas detection systems. The invention has particular application to systems having multiple gas sensors for detecting hazardous gases at various locations within a facility. 
     BACKGROUND OF THE INVENTION 
     There are many situations in which hazardous gases may accumulate in dangerous concentrations. In such cases health and safety regulations and prudence both require a system capable of detecting accumulations of hazardous gases before a hazardous situation exists. For example, many industrial processes use highly flammable or poisonous gases. An industrial plant which uses such processes typically requires a gas detection system having gas sensors distributed throughout the plant and a central station which receives signals from the gas sensors. If one of the gas sensors detects an excessive amount of a hazardous gas then an alarm condition is triggered at the central station. 
     Such industrial gas detection systems are typically very expensive. The central stations typically include proprietary hardware which has limited upgradability. 
     Self-contained gas detection systems are also available. A self-contained gas detection system comprises a gas sensor, a battery a simple control circuit and an audible and/or visible alarm contained in a small housing. An example of such self-contained gas detectors are the carbon monoxide detectors and smoke detectors which are widely marketed for use in households and small businesses. 
     Industrial plants must typically have both built-in gas detection systems and portable self contained gas detectors. If the built-in system detects a troubling amount of a hazardous gas in the vicinity of a particular gas sensor then personnel may be dispatched to the area of the gas sensor in question with portable gas sensors. The portable gas sensors may be used to confirm the amount of hazardous gas detected and to locate the source of the hazardous gas. The management of such industrial plants typically have rigid policies in place which require measurements made by plant personnel to be carefully documented. 
     Gas sensors are available for detecting a wide range of hazardous gases. Sensors are available for detecting flammable gases, asphyxiating gases of various kinds, radioactive gases, gases containing certain toxins, and so on. 
     There is a need for a gas detection system which is less expensive to supply and configure than are typical built-in gas detection systems which are now available. There is also a need for gas detection systems which assist in the documentation of gas levels measured with portable gas detectors. 
     SUMMARY OF THE INVENTION 
     This invention provides gas detection systems for detecting hazardous gases. The systems use universal serial buses to interconnect gas detectors to a monitoring station. 
     One aspect of this invention provides a gas detection system for detecting hazardous gases within a facility by way of a number of gas detectors situated at various locations in the facility. The system comprises a monitoring station comprising a programmed computer. The programmed computer comprises a universal serial bus port and a universal serial bus port or hub to which universal serial bus devices can be connected. One or more remote gas detectors are electronically communicating with the monitoring station on a data connection. The data connection has a length exceeding five meters and comprises a universal serial bus and a universal serial bus device. The universal serial bus comprises a universal serial bus cable connected to the universal serial bus port or hub of the computer. 
     Another aspect of the invention provides a gas detection system comprising: a monitoring station comprising a programmed computer and one or more remote gas detectors electronically communicating with the monitoring station on a data connection. The data connection comprises: a universal serial bus connected to the computer; a protocol converter connected to the universal serial bus; and an electrical cable connecting the protocol converter to the gas detector. Systems according to this aspect of the invention comprise a step-up switching power supply having an input connected to receive electrical power from the universal serial bus and an output connected to provide electrical power to the gas detector by way of electrical conductors in the cable. 
     A further aspect of the invention provides a gas detection system comprising: a monitoring station comprising a programmed computer, and one or more remote gas detectors electronically communicating with the monitoring station on a data connection, the data connection comprising a universal serial bus connected to the computer. Each of the gas detectors comprises: a portable sensing head and a base. The portable sensing head comprises a hot wire type gas sensor, a gas sensor power supply, a data output, a processor and an audible alarm connected to the processor. The processor is configured to sound the audible alarm when a gas sensor output signal exceeds a threshold value. The base is adapted to detachably hold the portable sensing head and is electronically connected to the monitoring station. The base provides a data connection between the data output and the monitoring station. 
     A still further aspect of the invention provides a gas detection system for detecting hazardous gases within a facility by way of a number of gas detectors situated at various locations in the facility. The system comprises: a monitoring station comprising a universal serial bus interface, a microcontroller, mini-computer or microprocessor and a universal serial bus port or hub. One or more remote gas detectors electronically communicate with the monitoring station by way of a universal serial bus capable of operating on either a synchronous or asynchronous polling basis. The universal serial bus comprises a universal serial bus cable connected to the universal serial bus port or hub. Each of the remote gas detectors comprises: a portable sensing head comprising a gas sensor, a power supply and a data output; and a base adapted to detachably hold the portable sensing head, the base electronically connected to the monitoring station and providing a data connection between tle data output and the monitoring station. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In drawings which illustrate specific embodiments of the invention, but which should not be construed as restricting the spirit or scope of the invention in any way: 
     FIG. 1 is a schematic view of a gas detection system according to the invention; 
     FIG. 2 is a block diagram showing major components of a protocol converter for use in the invention; 
     FIG. 3 is a block diagram of a two-part gas detector according to the invention; 
     FIG. 4 is a functional block diagram of a gas detector according to the invention; and, 
     FIG. 5 is a functional block diagram of a gas detector according to an alternative embodiment of the invention. 
    
    
     
       
         
               
             
               
               
               
               
             
           
               
                   
               
               
                 REFERENCE NUMERALS 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 gas detection system 
                 12 
                 gas detector 
               
               
                 14 
                 monitoring computer 
                 16 
                 data link 
               
               
                 18 
                 USB hub 
                 20 
                 protocol converter 
               
               
                 22 
                 USB connection 
                 24 
                 data connection 
               
               
                 26 
                 data connection 
                 30 
                 USB connector 
               
               
                 32 
                 micro controller 
                 34 
                 data transceiver 
               
               
                 36 
                 cable connector 
                 38 
                 gas detector cable 
               
               
                 40 
                 power supply 
                 42 
                 data buffer 
               
               
                 44 
                 power indicator 
                 46 
                 USB active indicator 
               
               
                 48 
                 gas detector fault indicator 
                 50 
                 base 
               
               
                 50A 
                 alternative base 
                 52 
                 portable module 
               
               
                 52A 
                 tethered module 
                 53 
                 step-down voltage regulator 
               
               
                 54 
                 coupler 
                 56 
                 gas sensor 
               
               
                 58 
                 sensor support circuitry 
                 60 
                 portable power supply 
               
               
                 60A 
                 battery 
                 60B 
                 voltage regulator 
               
               
                 60C 
                 charging circuit 
                 62 
                 processing circuit 
               
               
                 64 
                 communications circuit 
                 66 
                 display 
               
               
                 68 
                 user input 
                 70 
                 audio transducer 
               
               
                 72 
                 tag reader 
                 74 
                 memory 
               
               
                 76 
                 cable 
                 77 
                 signal lights 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     FIG. 1 shows a gas detection system  10  according to a preferred embodiment of the invention. Gas detection system  10  has a plurality of gas detectors  12 . Gas detectors  12  are connected to a common monitoring station  14  by a data connection  16 . Monitoring station  14  preferably comprises a general purpose personal computer running software which receives data from gas detectors  12  by way of data connection  16 . Computer  14  may be connected to one or more remote locations such as an emergency response center, a police department, a fire department, an alarm monitoring center or the like by way of a modem connection or internet connection  26 . 
     Data connection  16  preferably comprises a universal serial bus (“USB”) interface in computer  14  connected to a USB hub  18 . The USB communication protocol is not reliable over cable runs of longer than about 5 meters. If gas detectors  12  are located more than about 5 meters from computer  14  then data connection  16  comprises a plurality of protocol converters  20 . Each protocol converter  20  is a USB device which connects to USB hub  18  with suitable USB wiring. Each protocol converter  20  connects to a gas detector  12  over a communications link  24 . Communications link  24  may comprise a wireless communications link such as an infrared link or a radiofrequency link. Preferably communications link  24  comprises a cable on which data can be exchanged between a protocol converter  20  and its corresponding gas detector  12 . Most preferably communications link  24  operates according to a protocol which will operate reliably over distances of at least 100 meters. Communications link  24  may, for example, operate according to a protocol such as RS-422 or RS-485. 
     It can be appreciated that using a standard general purpose computer  14  for a monitoring station avoids much of the cost associated with the development of a monitoring station having a proprietary design. A person generating software for use in monitoring gas detectors  12  can take advantage of the programming tools available for the operating system used by computer  14 . 
     The use of USB to connect data link  16  to computer  14  is advantageous because USB cables and hubs are readily available. Furthermore, the current version of the USB standard allows up to  127  devices to be attached to a single USB port. USB devices can be added to or disconnected from the USB port while computer  14  is running. Thus computer  14  does not need to be restarted to add additional gas detectors  12  to system  10 . While one would not normally consider USB for use in interfacing to gas detectors in a gas detection system because of the short (5 meter) cable lengths permitted by the USB protocol this disadvantage can be avoided with the use of a protocol converter according to the invention. 
     FIG. 2 shows a protocol converter  20  according to a preferred embodiment of the invention. Protocol converter  20  has a USB connector  30  for receiving a USB cable  22  connected to a port in computer  14  or a USB hub  18 . A micro controller  32  comprising a microprocessor, USB interface engine, timer, program memory is connected to connector  30 . A data transceiver  34  is connected to micro controller  32 . Data transceiver  34  drives data connection  24 . For example, where data connection  24  uses an RS-485 communication protocol then data transceiver  34  may be a RS-485 driver/receiver chip. Data transceiver  34  is connected to a connector  36  which receives a cable  38  connected to a gas detector  12  (unless data connection  24  is a wireless connection). 
     Micro controller  32  is programmed to receive data from USB connector  30  and forward the data to data transceiver  34  for delivery to gas detector  12 . It cannot always be assured that computer  14  will be able to poll gas detector  12  for data and status information as frequently and regularly as would be desired. Therefore, micro controller  32  is preferably programmed to periodically poll gas detector  12  for data and status information by sending a suitable signal to gas detector  12  via data transceiver  34 . Most preferably, micro controller  32  polls gas detector  12  on a fully synchronous basis. Micro controller  32  receives data transmitted by gas detector  12  and stores the data in a data buffer  42  until the data is requested by computer  14 . Computer  14  can then poll protocol converter  20  on an asynchronous basis with no risk of data loss. Data buffer  42  may be integrated with micro controller  32 . By frequently polling gas detector  12 , micro controller  32  not only receives up to the second data from gas detector  12  but also continuously verifies that gas detector  12  and communication link  24  are functioning properly. A further advantage of having protocol converter  20  poll gas detector  12  is that bandwidth is conserved on USB  22 . 
     Protocol converter  20  preferably comprises a status indicator. The status indicator of FIG. 2 simply comprises  3  LEDs. LED  44  is illuminated when protocol converter  20  is powered, LED  46  is illuminated when micro controller  32  detects that protocol converter has been properly enumerated by computer  14  as a USB device, and LED  48  is illuminated when proper communications have been established between protocol converter  20  and a gas detector  12 . LED  48  may be a bi-color LED which changes color when the gas detector  12  connected to protocol converter signals an alarm condition. 
     Preferably protocol converters  20  provide electrical power to gas detectors  12  through cables  38 . Electrical power may not be conveniently available at the locations of gas detectors  12 . Cables  38  may be 4-conductor cables with two conductors being used for simplex data communications between gas detectors  12  and protocol converters  20  and two conductors being used for the power supply. 
     Since some types of gas detector that may be used in system  10  can draw substantial amounts of electrical current and cables  38  may be very long, there can be a substantial voltage drop on the power carrying conductors of cables  38 . This may be dealt with by providing a power supply  40  in protocol converter  20  which supplies power at a higher voltage than the voltage used by gas detectors  12 . A voltage regulator in each gas detector  12  can then step down the supply voltage to a voltage suitable for gas detector  12 . For example, power supply  40  may be a 12 volt direct current power supply and gas detectors  12  may operate on 5 volts. 
     Power supply  40  may draw electrical power from USB  22 . A USB provides 5 volt electrical power. Where power supply  40  draws power from USB  22  then power supply  40  preferably is a switching power supply which increases the voltage received from USB  22  to a higher voltage as described above. Power supply  40  could, in the alternative be supplied with electrical power from the power mains, from a battery or from some other suitable source of electrical power. Where gas detectors  12  may be operated in explosive environments then power supply  40  is preferably an energy-limited power supply. 
     Gas detectors  12  may be fixed gas detectors. Gas detectors  12  preferably are capable of operating in both fixed and portable modes. Where gas detectors  12  operate in potentially explosive or flammable environments then they should be constructed in a manner that eliminates the possibility of a spark which could trigger an explosion or fire. Suitable construction techniques are known to those skilled in the field. 
     As shown in FIG. 3, each gas detector  12  preferably comprises a base  50  and a portable gas sensor module or “sensing head”  52  which is detachably receivable in base  50 . Base  50  is mounted in a fixed location and is connected to a protocol converter  20  by cable  38 . Base  50  receives data and power from protocol converter  20  over cable  38  and couples data and power to portable module  52 . Where power provided by cable  38  is at a higher voltage than the voltage required by portable module  52  then base  50  preferably comprises a voltage regulator  53  mounted on a suitable heat sink. 
     Gas detectors  12  will typically be at different distances from monitoring computer  14  and cables  38  will consequently be of different lengths. The voltage provided by cables  38  at base  50  will therefore vary depending upon the voltage drop caused by cable  38 . Voltage regulator  53  steps down the voltage provided by cable  38  to a value which will be the same for all gas detectors  12  regardless of how far they are from monitoring computer  14 . For example, 12 VDC may be provided at the ends of cables  38  away from gas detectors  12  and voltage regulator  53  may have an output of 7.5 VDC. 
     Base  50  includes an electrical coupler  54  which provides power and data connections to portable module  52 . Electrical coupler  54  may comprise an electrical plug, as shown in the drawings, or may, in the alternative, comprise other suitable reliable couplings. 
     FIG. 4 shows an embodiment of the invention in which the portable unit has several gas sensors. As shown best in FIG. 4, Portable module  52  comprises at least one gas sensor  56 . Each gas sensor  56  is supported by a suitable electronic circuit  58 . For example, if a gas sensor  56  is a hot wire type of gas sensor then circuit  58  will provide the electrical circuitry necessary to generate an electrical current through the hot wire and to measure the voltage drop across the hot wire. Different types of gas sensor require different types of support circuitry as is known in the art. A portable module  52  may have several different types of gas sensor  56 . Gas sensors  56  may include sensors for combustible gases, sensors for toxic gases, sensors for smoke, sensors for bio-hazards or the like. 
     Portable module  52  is self powered by a power supply  60  such as a rechargeable battery, long life disposable batteries or the like. The output voltage of a rechargeable battery can vary significantly as the battery discharges. Since the electronic circuitry of module  52  operates most consistently when powered by a precisely regulated constant voltage, power supply  60  of module  52  preferably comprises a long life rechargeable battery  60 A, a second voltage regulator  60 B and a battery charger  60 C. Voltage regulator  60 B steps down the voltage of battery  60 A to a steady level, for example 5 VDC, which powers portable module  52 . Since the output of voltage regulator  53  is greater than the voltage of battery  60 A, battery  60 A can be charged by charger  60 C when portable unit  52  is plugged into base  50 . Voltage regulator  60 B provides a constant voltage supply for the electronic circuitry of portable module  52  whether or not module  52  is plugged into base  50 . 
     A digital processing circuit  62  which preferably comprises a microprocessor, program memory, data memory, and a timer monitors the outputs from sensors  56 . When portable module  52  is plugged into base  50  then portable module  52  is frequently polled by protocol converter  20 . In response, digital processing circuit  62  transmits readings from sensors  56  and information regarding the operational status of portable module  52 . A digital communications circuit  64  receives data sent over cable  38  by protocol converter  20  and sends data generated by digital processing circuit  62  to protocol converter  20 . 
     Processing circuit  62  preferably compares the readings from sensors  56  with pre-set alarm limits. If the readings indicate gas concentrations in excess of the alarm limits then processing circuit  62  preferably triggers a local alarm. The alarm may comprise, for example, flashing a strobe light  77  on gas detector  12  and/or sounding an audible alarm. 
     If power supply  60  comprises a rechargeable battery then the battery is charged when portable unit  52  is plugged into base  50 . When portable module  52  is removed from base  50  then portable unit  52  operates in stand-alone mode under power supplied by power supply  60 . As shown in FIG. 3, portable unit  52  preferably comprises a display  66 , a user input  68  connected to processor  62 , an audio transducer  70 , and a tag reader  72 . While in stand alone mode an operator can move portable module  52  from place to place in an attempt to localize the source of detected gases. Visual and audible signals may be generated by processor  62  via display  66  and audible signal  70  to provide the operator with feedback regarding the amount of gas being detected by sensors  56 . 
     A relay  71  controlled by processor  62  is located in base  50 . When portable module  52  is connected to base  50 , processor  62  may activate relay  71  when an alarm condition is detected. Relay  71  may switch local loads such as gas shut-off valves, area sirens, strobe lights, ventilation fans, etc. 
     Portable unit  52  preferably comprises a data logger. The data logger may be implemented in digital processing circuit  62  by providing a memory  74  into which digital processing circuit  62  can store data regarding readings made by gas sensor(s)  56  together with information identifying the times and places at which such readings were made. Memory  74  is preferably a non-volatile memory so that data will not be lost if power supply  60  fails. Memory  74  and digital processing circuit  62  may conveniently be integrated on one chip. 
     In one embodiment of the invention machine readable tags are located at points where it may be desired to take readings of gas concentrations. The tags may be, for example, bar coded tags, magnetically coded tags, or other machine readable tags. A user can read the tags with tag reader  72 . Processing circuit  62  records tag identification information from tag reader  72 , time information from a clock in processing circuit  62  and gas concentration information, as measured by sensors  56  in memory  74 . After one or more measurements have been made then portable unit  52  can be placed back into base  50  and the data accumulated in memory  74  can be carried to central station  14  on data connection  16 . 
     In an alternative embodiment of the invention, as shown in FIG. 5, portable unit  52 A remains connected to base  50 A by a cable  76  at all times. Portable unit  52 A is normally held in place on base  50 A but can be removed from base  50 A and moved to various adjacent locations. Cable  76  is long enough to allow portable unit  52 A to extend to such locations. Cable  76  might, for example be  10  meters or less in length. 
     Display  66  may be capable of displaying alphanumeric information generated by processing circuit  62  or central station  14 . For example, central station  14  may convey text messages to a user via data connection  16 . The text messages might instruct the user to proceed to a certain test point and take a gas concentration reading there. Processing circuit  62  receives the text messages and causes them to be displayed on display  66 . 
     The system of the invention makes possible a method for monitoring for and responding to alarm conditions, such as excessive concentrations of hazardous gases. A facility to be protected by a system according to the invention is provided with one or more gas detectors  12  at selected locations. The gas detectors  12  are in data communication with a central station  14 . Software running on central station  14  remotely monitors the gas levels detected by gas detectors  12 . In each gas detector, an electrical signal output from each gas sensor is measured and compared to a preset reference value. Each gas detector transmits its information to central station  14 . If the detected signal value at a gas detector  12  equals or exceeds the reference value (i.e. if an alarm condition exists), then processor  62  in the gas detector  12  activates the detector&#39;s local signal lamps  77 , audio transducer, and relay  71 , and displays details of the alarm event on its display  66 . A message containing the event information is also transmitted to central station  14  where it can be displayed and acted upon by response. personnel. Central station  14  may also broadcast details of the alarm condition to a remote site by way of an internet connection or some other communications link. 
     When the alarm condition has been detected then a human investigator may be sent to the alarm zone. The investigator may wish to isolate the source of the problem. The investigator may remove portable module  52  from its base  50  and perform a series of measurements using the portable module  52  as a portable monitoring instrument. The investigator may have a procedure that entails acquiring readings at predetermined locations to discover the source or cause of the alarm event. In that mode of operation, the alarm lamps, audio transducer and display read-out of the detector respond in real-time to the sensory input and can be used to narrow in on the precise location of the cause of the alarm condition. 
     As each reading is performed, the investigator pushes a button  68  on portable module  52  and records in memory  74  the location, time and physical parameters of the reading. The location may be noted, for example, by entering a location code on a keypad or other data entry button on portable module  52 , or scanning a bar code, or other machine-readable tag identifying the location with a tag reader  72  on portable module  52 . In the alternative, a predefined list of locations could be stored in memory in portable module  52 . The operator may locate the current location by, for example, scrolling through the list of predefined locations. Where a predefined list of locations is stored in module  52 , module  52  may also be programmed to assume that the locations will be visited in a set order. When a first measurement is taken, module  52  will associate that first measurement with a first location in the list, when a second measurement is taken, module  52  will associate the result of the second measurement with a second location in the list, and so on. If the user makes a sequence error or wishes to repeat a sample then module  52  may permit the user to scroll through the list of locations as described above. 
     Upon completion of the investigation procedure, the operator returns the portable module  52  to its base  50  whereupon the portable module  52  uploads the captured data to the central station  14  where it can be analysed, archived and formatted for reports. 
     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example, while the invention is described as using microprocessors to coordinate the operation of protocol converters  20  and portable modules  52 , application-specific integrated circuits could be used instead. While the invention has been described as including sensors for hazardous gases, the term gases should be interpreted expansively to include any potentially hazardous airborne material for which a sensor can be provided. For example, the invention could be used to detect smoke or certain bio-hazardous materials in addition to things more conventionally described as gases. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.