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 avoids the need for frequent zero or span calibrations.
The benefits of this technology can be summarised as follows:
PRINCIPLE OF OPERATION 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 avoids the need for frequent zero or span calibrations.
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