Process Analyzers generally fulfill two roles in the operation of a plant.
These roles are:
Process Control. In these instances the Process Analyzer is part of an open or closed loop control system with the objective of optimizing the operation of the operating unit. This optimization is achieved by maintaining the process at a target “set point”. When selecting a Process Analyzer one of the key selection criteria is typically Analyzer “Precision”, which is defined as the ability of an analyzer to provide repeatable analytical data for a given sample. “Precision” is almost exclusively a function of the analyzer’s design.
The role of the Process Analyzer Standard in Process Control is to provide Analyzer “Accuracy”. The analyzer accuracy can be no better than the accuracy of the standard upon which its calibration is derived. Recognition that different analyzers & processes can require the same nominal standard (i.e.: 8% Oxygen in Nitrogen) but with different degrees of accuracy is why TWSCO offers multiple classes of standards.
Primary Standard. 2% Analytical Accuracy; 5% Blend Tolerance
A 8% Oxygen in Nitrogen Primary Standard would meet the following specifications; A range of 7.6 % - 8.4% Oxygen in Nitrogen. The Blend Tolerance is the actual value of the Oxygen compared to the target. Thus an 8% target concentration would be “in spec” as long as the absolute value is +/- 0.4% of the 8% target.
Assuming the “named” value of the Oxygen in this cylinder was 8.2% in Nitrogen, the
Analytical Accuracy would be 2% of the named value, thus 8.2% +/- 0.164%. Thus, a Primary Standard labeled 8.2% would be in a range of 8.036% to 8.3164%.
Working Standard. 5% Analytical Accuracy; 10% Blend Tolerance
A 8% Oxygen in Nitrogen Working Standard would meet the following specifications; A range of 7.2 % - 8.8% Oxygen in Nitrogen.
Assuming the “named” value of the Oxygen in this cylinder was 8.2% in Nitrogen, the Analytical Accuracy would be 5% of the named value, thus 8.2% +/- 0.41%. Thus, a Primary Standard labeled 8.2% would be in a range of 7.79% to 8.61%.
Custom Standard. Customer specified Accuracy & Blend Tolerance.
For more complicated blends (many components, wide concentration ranges) or unique applications TWSCO’s Specialty Gas experts can work with you to custom design the standard(s) you need to optimize your process.
Process Reporting/Monitoring. The other common usage of Process Analyzers is to monitor a process point for the purpose of recording or “Monitoring” the composition/content of the material at that location. The most common example being CEMS analyzers (Continuous Emissions Monitoring System) which monitor plant emissions and are the basis for a company’s required reporting to the US EPA (Environmental Protection Agency). These types of analyzer standards can and are governed by very specific manufacturing and analysis procedures. Use of the wrong standards can result in significant penalties to the company. However, use of standards that are improperly characterized can result in the over reporting of emissions and resultant over purchasing of emission credits/taxes.
TWSCO’s Specialty Gas experts are dedicated to keeping your company in compliance by helping you select the most effective standards available. From EPA Protocol gases to moisture standards to HRVOC standards, we’re here to help you meet your regulatory obligations.
