Topic: Process Analyzers

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New Technology for Analyzing HF Alkylation Processes
The ACA.HF Analyzer: The New Standard in Safety, Simplicity and Accuracy for Analyzing HF Catalyst

Keep the Process Analyzers On-Stream
Despite Computer Operation Simplicity, Personal Skills Are Still Needed to Achieve the Full Benefits of Process Monitoring

Gas Chromatographs Rule
What Comes First--the Analyzer or the Analyzer Application?

Process Analyzers. Analyze This!
Fewer Analyzer Specialists Are Left Working at the Plant Floor, Could It Be Because Newer Anaylyzer Systems Come Available as Complete Packages?

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White Papers: In Depth Research

Ensuring an Accurate Result in an Analytical Instrumentation System Part 2: Calibrating the Analyzer
Author: Doug Nordstrom and Tony Waters, Swagelok Company
Posted: 11/18/2010
In many analytical instrumentation systems, the analyzer does not provide an absolute measurement. Rather, it provides a relative response based on settings established during calibration, which is a critical process subject to significant error. To calibrate an analyzer, a calibration fluid of known contents and quantities is passed through the analyzer, producing measurements of component concentration. If these measurements are not consistent with the known quantities in the calibration fluid, the analyzer is adjusted accordingly. Later, when process samples are analyzed, the accuracy of the analyzer's reading will depend on the accuracy of the calibration process. It is therefore, imperative, that we understand how error or contamination can be introduced through calibration; when calibration can - and cannot - address a perceived performance issue with the analyzer; how atmospheric pressure or temperature fluctuations can undo the work of calibration; and when and when not to calibrate.

Ensuring an Accurate Result in an Analytical Instrumentation System Part 3: Maintaining a Representative Sample
Author: Doug Nordstrom and Tony Waters, Swagelok Company
Posted: 11/18/2010
The objective of an analytical instrumentation (AI) system is to provide a timely analytical result that is representative of the fluid in the process line at the time the sample was taken. If the AI system alters the sample so the analytical result is changed from what it would have been, then the sample is no longer representative and the outcome is no longer meaningful or useful. Assuming the sample is properly taken at the tap, it may still become unrepresentative under any of the following conditions:
- If deadlegs or dead spaces are introduced at inappropriate locations in the AI system, resulting in a "static leak," a bleeding or leaking of the old sample into the new sample;If the sample is altered through contamination, permeation, or adsorption;
- If the balance of chemicals is upset due to a partial change in phase; or
- If the sample undergoes a chemical reaction.

This article will review the major issues leading to an unrepresentative sample and provide recommendations on how to avoid a compromised sample. It will discuss deadlegs and dead spaces; component design and placement; adsorption and permeation; internal and external leaks; cross contamination in stream selection; and phase preservation.

Ensuring an Accurate Result in an Analytical Instrumentation System Part 1: Understanding and Measuring Time Delay
Author: Doug Nordstrom and Tony Waters, Swagelok
Posted: 11/18/2010
Process measurements are instantaneous, but analyzer responses never are. From the tap to the analyzer, there is always a delay. Unfortunately, this time delay is often underestimated or not accounted for or understood. Time delay in sample systems is the most common cause of inappropriate results from process analyzers.

In many cases, it is invisible to operators and technicians, who are focused on the necessity of making the sample suitable for the analyzer. It is not unusual for operators to assume that the analytical measurement is instantaneous. In fact, sample systems often fail to achieve the industry standard of a one minute response.

As a general rule, it's always best to minimize time delay, even for long cycle times, but delays extending beyond the industry standard are not necessarily a problem. The process engineer determines acceptable delay times based on process dynamics.

Delays become an issue when they exceed a system designer's expectations. A poor estimate or wrong assumption about time delay will necessarily result in inferior process control.

This article is intended to enhance understanding of the causes of time delay and to provide the tools required to calculate or approximate a delay within a reasonable margin of error. We will also provide some recommendations for reducing time delay. The potential for delay exists in the follow sections of an analytical instrumentation (AI) system: process line, tap and probe, field station, transport line, sample conditioning system, stream switching system, and analyzer.

Evaluation of an Alternate Soft Charge Circuit for Diode Front End Variable Frequency Drives
Author: Mahesh Swamy, Tsuneo J. Kume and Noriyuki Takada, Yaskawa Electric America
Posted: 05/17/2010
Variable Frequency Drives (VFDs) with diode rectifier front end are typically equipped with a resistorcontactor arrangement to limit the inrush current into the dc bus capacitors, thereby providing a means for soft charging the dc bus capacitors. Because of the mechanical nature of the magnetic contactor typically used in VFDs, there exists a concern for fatigue. In addition, during a brown out condition, typically the contactor remains closed and when the voltage recovers, the ensuing transient is often large enough to possibly cause unfavorable influence to surrounding components in the VFD. Many researchers and application engineers have thought about this issue and many are actively seeking non-mechanical solutions in a cost effective manner.

In this paper, a new topology to soft charge the dc bus capacitor is proposed. Other techniques that have been evaluated are also introduced. The relative advantages and disadvantages are discussed. Experimental tests to show the feasibility of the proposed idea is also provided.

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