The simplest organic compounds are known with the name of Hydrocarbons (composed of Carbon and Hydrogen) and represent the major constituents of  the petrol gas.
Composed of an atom of Carbon and four atoms of Hydrogen, the Methane represents the simplest form of Hydrocarbons: it is the first element of Alkanes.
The first ten alkanes are:
CH4     Methane (gas)     C6H14   Hexane (liquid)
C2H6   Ethane (gas)        C7H16   Heptane(liquid)
C3H8   Propane (gas)      C8H18   Octane (liquid)
C4H10 Butane (gas)        C9H20   Nonane(liquid)
C5H12 Pentane (liquid)    C10H22 Decane(liquid)

Explosive limits
The Lower Explosive Limit (LEL) defines the lowest concentration of a combustible in air that allows the explosion. There could be a high explosion risk even with very small gas concentrations: in fact a great part of flammable gases and vapors have the LEL figure below 5% of volume.The Upper Explosive Limit (UEL) defines the maximum concentration of fuel in air that may causes explosion. Concentrations of the combustible above the UEL cannot generate explosion because of the insufficient concentration of the comburent (typically Oxygen).

SIGMAGUARD

The detection of hazardous gases has always been a complex subject, making the selection of the appropriate sensor, instrument, or equipment a difficult task. Sigma offers infrared (NDIR) sensors for hydrocarbon gases, infrared (NDIR) sensors for CO2, electrochemical sensors for Oxygen or Toxic Gases, and ‘Pellistor’ technology for flammable gases.

Sigmaguard’s  local and remote alarm capability, as well as, that the unit can function as stand alone or as part of a central control system, makes it ideal for these applications as it is easy to use and requires very little maintenance.

Our product range includes

Sigma 95H series

Sigma 95H series wall mounted type of gas detector with alarm light, is monitoring gas concentration in different applications 24h continuously. Using high quality sensors, and advanced micro-process technology, with data display, high/low alarm, offers fast response, high precision and good stability.
Powered by 24V DC, with 4-20mA, RS485, relay signal output and Explosion proof, is suitable for different kinds of applications.

Features
Monitor the specific gas concentration in the environment and activates the alarm when it is over the set point.
With self-calibration and zero calibration function, it makes the detection more accurate and reliable.
With temperature compensation, it is able to function under conditions of different temperatures.
A two-stage alarm (High/Low) with sound and light, is user adjustable.
An Infrared controller can adjust remotely the alarm point settings, zero calibration, and address modification.
Can output one or two on-off signals, can drive ventilator or
solenoid valve and other external devices.
Working Voltage：12-36V DC
Housing：die-cast aluminum + stainless steel (alarm light)

Product advantages
Using high quality sensors.
Standard equipped with three-wire system 4-20mA analog output; relay output; RS485 output (optional)
Unique infrared non contact control
Compatible with all kinds of control alarms, PLC, DCS and
other control systems, can be remote monitored.
Explosion-proof design, fast, reliable and stable.
Explosion-proof grade: II 2G Ex db IIC T6 Gb IP65
With self-calibration function and three standard keys will be used for on-site maintenance.

Technical Specifications
Gas Detected: As ordered from a variety of different gases
Detection Principle: Infrared for CO2, Electrochemical for others
Measuring Range: depending on the application
Installation Method: Wall-mounted, piping type, flow-type(according to the detection application)
Output signal 4-20mA, RS485,  relays (optional)
Precision ≤±3%F.S. (higher precision is optional)
Zero shift ≤±1%（F.S./year）
Display 4 digits Nixie tube display.
Connection mode G1/2 external thread explosion-proof flexible pipe
Thread Size M45*2mm
Temperature –20℃～50℃
Humidity 0-95%RH (non-condensing)
Explosion-Proof Ex dⅡCT6
Degree of protection IP65
Alarm mode Sound, light
Material Case: Die-cast aluminum
Sensor housing: aluminum alloy or 316 stainless steel
Power 12-36V DC
Dimensions 180×150×90mm
Weight ≤1.6kg

Applications
Petrochemical & Chemical Industry
Marine
Food & Pharmaceutical Industry
Electronics
Municipal Engineering & Utilities
Agricultural & Environmental Protection
Other Industries

GD10A Series of Explosion Protected Gas Detectors

Versions available for the detection of:-
Hydrocarbon Gases - using temperature-compensated infrared (NDIR) sensors.
Carbon Dioxide - using temperature-compensated infrared sensors.
Oxygen or Toxic Gases – using electrochemical sensors.
Flammable gases - using ‘Pellistor’ technology

Features
Competitively priced
Non-intrusive calibration and configuration via a magnetic pen
Compact and lightweight
Optional weather guard
Plug-in replaceable gas sensors
Relay outputs for 2 alarm levels and fault
Wide power supply range of 8 to 24 volts dc
4 to 20 mA and RS232 outputs
Non-display version available – GD10B (see separate data sheet)

Description
The GD10A is an explosion protected ATEX and IECEx certified fixed gas detector for use in potentially explosive atmospheres.
It comprises an instrument housing with two cable gland entries and contains the connection terminals, electronics and a gas sensor, which is screwed into the bottom of the unit, and display window. The unit may be optionally fitted with a protective weather guard as shown in the photograph opposite.
Magnetically operated switches allow the unit to be calibrated through the display window using the magnetic pen without the need to remove the cover from the unit.
Three control relays are fitted to provide Alarm Level 1, Alarm Level 2 and Fault outputs via individual changeover contacts. In addition to the 4 to 20 mA analogue, an RS 232 communications output is also provided.
Specify your range requirement when ordering.

Specifications
Materials : Instrument Body – Aluminium Pressure Die Casting
Sensor Insert – Stainless Steel Grade 316
Magnetic Pen – Stainless Steel Grade 316
Optional Weatherguard – Stainless Steel Grade 304 & Nylon 66
Cable entries : 2 x 20mm or ½” NPT or ¾” NPT
Weights : GD10A (excluding weatherguard) – 1.75Kg
Magnetic Pen – 60 grams
Weatherguard – 225 grams
Gas types : Flammable, Oxygen or Toxic
Input voltage : 8 to 24 volts dc
Input power : 5 Watts maximum
Internal fuse : 1 Amp antisurge 'Nanofuse'
Relay contact rating : 3 Amps, 300 Volts ac
Analogue output : 4 to 20mA (10 bit resolution)
RS232 output : Communications with PC at 19200 baud
Sensor types : NDIR Infrared, Electrochemical or Pellistor
Measurement range : Dependant upon sensor type
Response time : Flammable Gases - typically T90 < 15 sec (CH4)
Toxic and Oxygen sensor response times vary according to the sensor type.
Measurement resolution: Flammable gases - 1% LEL or 1% volume.
Toxic gases - 0.1ppm for FSD < 50ppm, 1ppm for FSD> 50ppm.
Oxygen - 0.1% volume.
IP rating : Enclosure IP68, Sensor IP65
Display : 4 Digit, 7 segment liquid crystal
Keypad : 4-Button magnetically operated
Software : Software configuration provided via LCD display and multifunction keypad
Operating temperature : - 20 to +60 O C
Humidity range : 0 to 95% RH non-condensing
Operating pressure : Atmospheric + or - 10%
Performance standards : EN 61779-1:2000, EN 61779-4:2000, EN 61779-5:2000
Hazardous Area Certification
Certificate numbers : IECEx SIR 08.0009X, Code Ex d IIC
SIRA 08ATEX1031X, Code Ex d IIC
Standards : IEC 60079-0 : 2004 (Edition 4) IEC 60079-1 : 2007-04 (Edition 6), EN 60079-0 : 2006 EN60079-1 : 2007
Temperature Codes : T4 (Ta -20 to +60 deg C)
T5 (Ta -20 to +50 deg C)
T6 (Ta -20 to +35 deg C)
Zones : 1 & 2

GD10B Series of Explosion Protected Gas Detectors

Description
The GD10B is an explosion protected ATEX and IECEx certified fixed gas detector for use in potentially explosive atmospheres.
It comprises an instrument housing with two cable gland entries. The housing contains the connection terminals, electronics and gas sensor which is screwed into the bottom of the housing. The unit may be optionally fitted with a protective weather guard as shown in the photograph opposite.

Versions available for the detection of:-
Hydrocarbon Gases - using temperature-compensated infrared sensors.
Carbon Dioxide - using temperature-compensated infrared sensors.
Oxygen or Toxic Gases – using electrochemical sensors.
Flammable gases - using ‘Pellistor’ technology.

Calibration of the GD10B can be carried out simply by using ZERO and SPAN buttons inside the instrument provided that the concentration of the calibration gas is the same as that used for factory calibration of the detector (refer to the instrument calibration certificate for details).
Alternatively, the purpose designed plug-in hand held configuration unit shown above may be used together with any appropriate test gas concentration.
Calibration of the unit requires the removal of the front cover of the flameproof enclosure and therefore must only be carried out under either of the following conditions:-
1. In a safe area where there is no risk of the presence of an explosive gas.
2. Within the hazardous area by authorised personnel under controlled conditions after it has been established that no flammable gases are present in the area. Note that a management or health and safety department permit may be required for this to be carried out.
Specify your range requirements when ordering.

Specifications
Materials : Instrument Body – Aluminium Pressure Die Casting or Stainless Steel 316
Sensor Insert – Stainless Steel Grade 316
Optional Weatherguard – Stainless Steel Grade 304 & Nylon 66
Cable entries : 2 x 20mm or ½” NPT or ¾” NPT
Weights : GD10B (excluding weatherguard) – 1 Kg
Weatherguard – 225 grams
Gas types : Flammable, Oxygen or Toxic,
Input voltage : 8 to 24 volts dc
Input power : 5 Watts maximum
Internal fuse : 1 Amp antisurge 'Nanofuse'
Analogue output : 4 to 20mA (10 bit resolution)
Sensor types : NDIR Infrared, Electrochemical or Pellistor
Measurement range : Dependant upon sensor type
Response time :
Flammable Gases - typically T90 < 15 sec (CH4)
Toxic and Oxygen sensor response times vary according to the sensor type.
Measurement resolution:
Flammable gases - 1% LEL or 1% volume.
Toxic gases - 0.1ppm for FSD < 50ppm, 1ppm for FSD> 50ppm.
Oxygen - 0.1% volume.
IP rating : Enclosure IP68, Sensor IP65
Operating temperature : - 20 to +60 O C
Humidity range : 0 to 95% RH non-condensing
Operating pressure : Atmospheric + or - 10%
Performance standards : EN 61779-1:2000, EN 61779-4:2000, EN 61779-5:2000
Hazardous Area Certification
Certificate numbers : IECEx SIR 08.0009X, Code Ex d IIC
SIRA 08ATEX1031X, Code Ex d IIC
Standards : IEC 60079-0 : 2004 (Edition 4) IEC 60079-1 : 2007-04 (Edition 6)
EN 60079-0 : 2006 EN60079-1 : 2007
Temperature Codes :
T4 (Ta -20 to +60 deg C)
T5 (Ta -20 to +50 deg C)
T6 (Ta -20 to +35 deg C)
Zones : 1 & 2