Different calibration technologies exist because there is no perfect calibrator for every situation. Mesa Labs currently offers two separate technologies to provide quick and accurate calibrations: the venturi and the dry piston calibrators. Choosing which calibrator is best for you will depend on your specific application. This entry provides a review of the two technologies available and guidance on how to choose which one fits your needs.
The BGI calibrators measure air flow by drawing air through a venturi, or a tube with a constriction in the middle. As air passes through the venturi tube, the speed increases at the constriction point. Higher air flow produces a lower pressure. In fact, when air flow velocity doubles through the venturi, the pressure must drop by a factor of four. Using this relationship, air flow can be measured using pressure transducers before and at the point of the constriction. The calibrator uses these pressure measurements, ambient temperature, and ambient pressure to provide an instantaneous reading of standardized air flow.
This patented technology is a rare primary standard that uses two SI base units to give accurate and fast gas flow. When air is diverted into the measurement cell, the piston rises until it reaches the top of the cell, at which point the valve temporarily closes to allow the piston to fall. The DryCal measures the time it takes the piston to travel across a known distance, which encompasses a known volume. Thus, the DryCal measures the time it takes for a known volume of air to pass through the measurement cell.
To determine which of these calibrators is best for you, you should consider the following questions:
- What flow rate and accuracy do you need?
The most important specification that your calibrator must meet is your accuracy and flow range needs.
Calibrator Comparison and Ideal Applications
|BGI Calibrators||0.75% standardized||0.1 – 1500 LPM|
|Defender||1% volumetric, 1.2% standardized||5 – 30,000 ccm|
|Definer||0.75% volumetric, 1% standardized||5 – 30,000 ccm|
|1Total flow range of calibration series. Actual flow range depends on model.|
- What environment will your calibrator be used in?
Our BGI series was designed for use with ambient air samplers and are rugged, field-ready devices. The venturi is relatively insensitive to harsh field conditions and transport. Our DryCal series was designed with industrial hygiene and laboratory applications in mind. The precise fitting of the piston within the glass cell allows for the unique primary measurement of flow rate, with the caveat that it can be vulnerable to particulates and dust in the air. If dust enters the cell, it can coat the interior of the cell and eventually cause the piston to stick. When you send your DryCal back to our calibration lab for its annual calibration, we will fully clean and refurbish your unit to prevent the build-up of excess dust. However, you should keep this in mind if trying to perform calibrations in particulate-heavy environments.
- How do you want to connect your calibrator to your instrument?
The Defender series is designed to connect directly to your sampler using tubing. The Definer features Swagelok compression fittings common in many environment air instruments. The BGI calibrators feature tubing fittings in one model and direct instrument installation in the remaining two models for ambient particulate samplers and analyzers.
Both of Mesa’s calibration lines are manufactured in our ISO 17025 and ISO 9001 certified facility and follow fully NIST-traceable standards. If you have any questions about which calibrator would best meet your needs, please contact us and we will help find the right technology for your application.
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