Monitoring of steam and water from the steam power generation process has gone through many stages. The design of sampling probes, sample lines, sample coolers, the number of points sampled, methods for pressure reduction, and the analytical tests performed on each sample source have all become more complex. Sampling is considered to be the key to longer boiler and piping life by allowing quick reaction to excursions from optimal water chemistry, according to Duff and Macintosh .
Over the years, sample transfer practices have evolved to a more sophisticated and accurate level. It is now common practice to sample with continuous flow through sample lines and analysers. EPRI Project RP 2712-2 prepared a report defining the state of the art in sampling, analysis, and control as applied to domestic fossil power plants.
A new sampling system called Sample SentryR II has undergone field trails to automatically maintain a constant sample flow rate under all operating conditions in order to meet these very specific guidelines to obtain representative samples:
The sample conditioning system automatically adjusts a motorized pressure-reducing valve as conditions change to achieve a constant and continuous sample flow rate. The system automatically shuts off sample flow if the flow rate cannot be maintained above a shutdown set point or if a sample temperature alarm occurs. Additional features allow the system to conform to unique sampling requirements.