Duty: To measure the concentration of H2S in a process gas stream.

The principle of operation is as follows. A reel of paper tape impregnated with lead acetate is exposed to the gaseous process sample in the sample chamber. Hydrogen sulphide (H2S) in the process sample reacts with the lead acetate, after acidification, to form lead sulphide (PbS), a brown compound that stains the tape. The higher the concentration of H2S the darker the stain. A focused LED and single photo detector system continuously measures the darkening stain and the analyser reports this as a 4-20mA output of the concentration of H2S.

Incremental measurements are made on the same spot until saturation occurs, when the tape is advanced to a fresh portion of tape. This reduces tape usage and avoids the need for frequent zero or span calibrations.

With its wide-ranging ability to measure H2S from % levels down to ppb levels, the HG400 range of H2S process analysers can be utilised in many process industries, including:

• Natural Gas pipelines 
• Reformer recycle gas
• Offshore gas production
• Fuel gas monitoring
• Sour gas treatment plants
• Gas processing
• Biogas