As I know 3% percent methane & 97% nitrogen mixture gas indicate 60% LEL. What I know if I apply this gas to Gas Detector it will indicate 60%. But my question is how much flow to be maintain and if I apply large amount of this gas is the Gas Detector will indicate 100%? Could anyone please clarify these questions and tell me the exact procedure for the calibration of Gas Detector?

 

plz can u tell which kind of gas detector u want to calibrate? i want to know the medium/gas on which the detector installed, as there are different ways and methods to calibrate the different kind of detectors.

 

The method of calibration specific to your installation depends on the type/manufacturer of your gas detector, and the process media which is being monitored.

The exact mixture (% methane AND the balance components) you need would be based on the gas detector manufacturer's calibration procedure and your company's procedure, and the media stream in question.

The flammability range of methane is generally 5% to 15% methane in air. This puts your 3% methane concentration at 60% of the lower flammability limit (LFL), a.k.a. lower explosive limit (LEL).

If you need to read exactly 100% LEL in order to set a calibration point (100% span, for example), then you need to have that exact concentration of methane in your calibration gas.

For example, my gas detectors (natural gas, i.e. methane) are used to monitor the atmosphere inside compressor buildings of a natural gas plant. As such, we use a CERTIFIED calibration gas comprised of 2.5% methane and the balance is AIR, not just nitrogen (this equals a 50%LEL mixture). I use this for both my catalytic bead and IR type sensors.

Some instruments cannot detect %LEL in a media stream such as XX % methane and balance of Nitrogen only, since oxygen is needed to support combustion (or a catalytic reaction) within the gas detector thus producing the reading.

Also, for proper setting of zero gas, we use clean, dried instrument air from our plant's instrument air system. That prevents improper calibration due to elevated hydrocarbon levels which might be found in ambient/background atmospheres. If none is available, you can get a bottle of "Zero Air" from a compressed gas supplier. This is compressed air which is hydrocarbon-free.

 

If you ask the service/technical department of the gas detector manufacture, they will tell you and even supply to you for a reasonable cost all the information, tools and equipment and containers of calibration gases you could every want or need in calibrating, serviceing and otherwise maintaining your gas detector.

Not knowing the specifics of the gas detector, I can not tell you how to calibrate, what percentage of gas to use or what flow rate, get out the fine technical manual, call the technical support number contained within and ask all the question you can.

 

Once the gas detector reaches its detection level the flow rate will not affect it. What you DO need to be aware of is that calibrating with methane in an environment in which butane is the actual combust bible gas will give you an incorrect calibration. You need to calibrate with the gas or gas mixture you expect to be present when the flammable gases are released.

Ian Verhappen