Process measurements are instantaneous, but analyzer responses never are. From the tap to the analyzer, there is always a delay. That delay in sample systems is the most common cause of inappropriate results from process analyzers.
To calibrate an analyzer, a calibration fluid of known contents and quantities is passed through the analyzer. If the resulting measurements don't match the known quantities in the calibration fluid, the analyzer must be adjusted accordingly.
If you want your analytical instrumentation system to give a reliable picture of the fluid in the process line, you need a good sample. If the sample gets altered anywhere in the process, the data from the analyzer won't be useful.
There is always a delay between the moment you grab a sample and the time you get a reading from your process analyzer. You might assume your time delay is one minute, which is the industry benchmark. But if your assumption is way off, your readings may no longer be relevant.
We've written about the many causes of time delay in sample systems, and how that can hurt the results that come out of an analyzer. The industry standard to aim for is one minute from the process line to the analyzer, but many potential delays lurk along the way. View some tips.
If your sample is liquid and the analyzer in your analytical system requires gas, the only option is to convert the liquid to gas. With vaporization, also known as flash vaporization, you aim to turn all the liquid into vapor instantly—without changing the composition.
In the past 50 years, process analyzers of all kinds have gotten better and better, but sampling systems haven't. Many don't even fulfill their intended purpose, which is to deliver an uncontaminated, representative sample to the analyzer without excessive time delay.
Some mistakes are easy to spot, such as a fast loop flowing backward. Others are a matter of making the right adjustments in pressure and temperature. Still others have to do with failing to make sure that the materials in your components are properly matched to your sample fluid.
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