InterTech’s Air Flow Testing Technology
Mass Flow Technology
Mass flow leak testing provides a quick and direct measurement of leakage independent of pressure. InterTech’s patented mass flow transducers test volumes from less than 1 cc to over 10 liters with an accuracy of up to 0.01 sccm. The key difference between this and the differential pressure method is that the mass-flow transducer reads the flow of air moving from the reference volume into the leak test item. The result is a direct reading of the leakage rate.
Mass flow sensing is done by measuring heat transfer to a flowing gas from the leakage flow directed across a heated element. Temperature-sensitive resistors measure the temperature of the incoming and outgoing flow, and the transducer creates an output voltage proportional to the mass flow creating the leakage-rate measurement.
There is actually a wide range in the capability of mass flow leak detectors one finds in the marketplace. The sensors used in mass flow leak testers vary in quality. Some manufacturers merely take standardized sensors and fit them into one or more instrument models. However, if the sensors are customized components in instruments, and selected for functioning in the ranges that are most important to the specific leak testing application, they can improve speed and accuracy.
A second consideration is how the instruments are calibrated and how their standardization is validated. If an instrument relies on mechanical devices for calibration they are subject to much greater variation in testing results when compared to calibration and validation using solid-state technology. Solid-state technology also minimizes equipment breakdown or the need for repairs.
Thirdly, mass flow sensors also vary in terms of how they compensate for temperature variations. This is particularly important when testing newly cast prototypes that may still be warm from a casting process. In these instances, either time must be added to allow the parts to cool to room temperature, or the mass flow has to be calculated taking the temperature variation into consideration.
InterTech airflow testing technology automates temperature compensation while many of our competitors do not.
Downstream Testing Method
Failsafe leak testing where one never misclassifies a bad part as a good part is doable. Better yet, good parts are never misclassified as bad parts, and yield are maximized. However, this standard of perfection is achievable only if one understands and manages all the factors that can undermine leak testing integrity.
InterTech has developed and patented the bias leak flow testing method to allow true test part leakage to be measured more precisely in less time and is especially helpful in testing low leak limits. This bias leak testing technique couples downstream (bell jar) leak testing with a known preliminary airflow that confirms a leak-tight bell jar seal or sets a known leak reference.
Downstream mass flow leak testing is used for difficult applications where there is a requirement for testing at pressures in excess of 150 psig, short test times, measurement of small leaks, very accurate and repeatable results, and/or precise temperature compensation.
The downstream method has the advantage of providing faster test times because the volume affecting the leak system response and the related stabilization time required is minimized. The best-in-class mass flow sensors are custom-tuned for maximum stability in relevant ranges, and as a result, can accurately measure very small test part leaks.
When failsafe leak testing is the goal, the promise of greater accuracy usually makes downstream testing the method of choice. Sometimes the high pressures under which products or components function and where they are leak tested also mandate that the downstream testing method is used, despite the added costs for downstream test fixturing.