Calibration and Bump Test Gas

Bump Test on a Gas Detector

Calibration and Bump test gas can often be the same thing. They are gas that is used to verify that the sensors in your gas detector are responding to gas in the correct way. For instance you may have a single gas unit for hydrogen sulphide that has a cell that operates from 0 to 50ppm. So your gas test cylinder could have 25ppm hydrogen sulphide with a balance of either nitrogen or air. When passed over the gas detector at the correct flow it will prove if the sensor is responding correctly. So you would expect to see a reading of 25ppm. If doing a bump test the unit would pass the bump test if the amount verified was within the parameter that the unit has defined for a bump test, usually 5 to 10%. If a calibration is made, the same test gas can be used but once the reading is verified the gas detector internal software will adjust the sensor range so that it reads exactly 25ppm.

Cocktail Gases

This describes a cylinder of test gases rather than a single gas. This can be used to Bump Test or Calibrate a gas detector that may have a number of detection cells fitted, for instance; oxygen, flammable, hydrogen sulphide and carbon monoxide. When this gas is passed over the gas detector it will ensure that all of the cells are verified as working for a bump test or be able to be used to calibrate the unit. Care must be taken when specifying test gas as not all gases can be mixed together and some gas detector cells are cross sensitive. For specialist exotic cells and gases please seek advice.

Test Gas Use By Dates

This can vary from gas to gas with reactive gases posing the most problems. Reactive gases leach through the actual cylinder it is contained in and these will be given much shorter use by date. For instance hydrogen sulphide is a reactive gas and this will have a maximum expiry time of 24 months but certain cylinders may only be 12 months. Methane is not a reactive gas and may have 5 or more years of usable life. If you have a cylinder containing a cocktail of gases the most reactive gas life will be the one used to set the use by date.

Calibration Gas Identification

Each cylinder of calibration / bump test gas will have a batch or serial number. This will relate to a certificate of conformity ensuring that the values stated have been verified. This number should always be quoted on the calibration certificate along with the gas values used. The label will also list all of the gas contained in it along with their concentrations. Some gas detectors may require specific concentrations to perform the bump test or calibration.

Flow Valve for Calibration / Bump Test

This is the valve for connection to the cylinder. There are two different types of valve, a vacuum operated valve which is used with the manufacturers test rig or a manual direct flow valve. The manual valve usually has a simple thumb screw control for on / off with a preset flow rate. The standard flow required by the majority of manufacturers is 1 litre per minute although certain gases may require higher or lower flow rates. These valves usually last for many years and can be used on each new cylinder purchased.

Calibration Cylinder Sizes

These are available in a range of sizes from a small 5 litre aerosol can through to 30 or 40 litre water content sizes. The cylinder size of 100 to 120 litres is a normal size for calibration and bump testing a number of gas detectors up to 50 or 60. With a flow valve of 1 litre per minute on a 120 litre cylinder you could expect to be able to do around 240 calibrations or 360 to 480 bump tests dependent upon the gas detector response time.