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What Technology is Best for Precision Vacuum Measurement?

Posted by Tom Bassi on Aug 20, 2014 10:00:00 AM

INTRODUCTION:

Any time you try to do a job with inaccurate data, it will take longer and cost more. You know this deep down, but if your gauge is sub-par, maybe you're just a bit attached to that ol' hunk-o-metal you've been using. There are many industry discussion groups out there with posts from seasoned professionals in the vacuum industry which urge that technicians should not opt for cheap equipment, which often sacrifices accuracy in vacuum measurement. If the inaccuracies are great enough, 
a job will never get done properly. For this reason, it is important for professionals and technicians who 
work with vacuum to:
  • Understand which technologies are best for ultimate digital vacuum gauge accuracy,
  • ensure that the gauge they are using has no fatal flaws in the underlying technology upon which the gauge was built, and
  • pick a gauge manufacturer that has a practice of properly calibrating each and every gauge to the NIST standard before it leaves the factory.

WHAT IS THE ULTIMATE TEST OF ACCURACY?

The ultimate test of accuracy is how well a gauge tracks with a calibrated standard before and after it has been in the field. There are a lot of specsmanship games that can be played with accuracy of a gauge. It can be broken down into components, some of which are able to be adjusted for with a simple zero and span calibration. Others, like repeatability and non-linearity, are somewhat irreducible. 

OTHER DIMENSIONS IMPACTING ACCURACY

With limited exceptions, Pirani and Thermistor suffer from temperature compensation issues. In addition, range can impact accuracy: many gauges do not have a wide enough range (i.e, from a fraction of a micron to above Atmoshere). Without a wide range, gross problems cannot be identified (e.g., like a leaky hose or a seal, where, less accurate other offerings will just read off scale).
THERMOCOUPLE: TIME-TESTED, INDUSTRY-VALIDATED ACCURACY

For measuring medium vacuum, the extreme accuracy of thermocouple technology has been concretely proven in the lab. Additionally, thermocouple exhibits few of the variances found in other electronic gauges.
WITHOUT CALIBRATION, YOU'LL STILL HAVE AN ACCURACY ISSUE
Note ideally that every thermocouple sensor should be calibrated in the factory against the NIST standard for its superior benefits to be realized.  We're pretty much the only supremely cool manufacturer that hand-calibrates under real vacuum against a NIST standard, has a wide temperature operating range, and has among the best repeatable accuracy in the indusry.

 

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Related Blogs: Understanding Vacuum Measurement: Key Terms 

Topics: HVAC, Calibration, Accuracy