All Environics systems, with the exception of the Series 7000 Zero Air Generator, are calibrated using a NIST (National Institute of Standards and Technology) recognized and traceable primary flow measurement standard, the Sierra Cal-Bench, Serial Numbers #1010, 1069 or 1089 prior to delivery.
We highly recommend a yearly recalibration and will send a reminder 90 days prior to the recalibration time. You can request a recalibration here or by calling our Service Department at (860) 872-1111.
During calibration, the commanded output flow of the system is connected to the Sierra Cal-Bench which contains a sonar detection device sensitive to movements no greater than 0.005” (5.0 X 10-4 inches). The Cal-Bench accurately measures the actual flow of the system by sonar detection of the flow-induced movement of a mercury-sealed piston within a glass tube, the diameter of which has been determined using NIST-traceable measuring tools.
During the flow measurement, ambient barometric pressure, ambient humidity, ambient temperature and gas temperature are also measured and considered. In this calculation, the mass flow controller performance is referenced to standard pressure and temperature conditions (760 TORR. 0oC). After testing each of the flow controllers at eleven (11) points over its range plus zero, by comparing command flow with actual flow, the resulting data is stored in the instrument computer in the form of a reference table. The system performs a linear interpolation, between points in the table, and uses all data (tested points plus interpolated values) to select proper voltages in response to flow commands during operation.
The Cal-Bench is re-certified at intervals recommended by its manufacturer using suitable methods and standards including NIST-traceable ring gauges to measure the inner diameters of all tubes. A copy of the most recent certification is available upon request.
All instruments requiring calibration are calibrated as described above. Therefore, these instruments are part of an unbroken chain of NIST traceability and when a system is used with traceable source gases, the combination (traceable instrument, traceable source gas) produces a traceable gas standard that meets or exceeds US Federal Government criteria for accuracy.
To read more about the accuracy of the Environics systems, click here.