Mass flow leak testing/Mass extraction leak testing:
There are many different methods to measure air mass flow. Most use a hot element, like a hot wire, a hot pearl or a hot silicon chip, to measure the air flow.
When the air flows around a hot element, it cools it down and the cooling down creates a change in electrical properties that is measured by electronics.
The heat exchanged based air mass flow is inherently slow since it involves cooling down something with an air flow. Of course, the smaller the heating element is the faster it gets,
and the larger the flow, the faster. The second disadvantage of heat exchange based mass flow measurement is that cooling down gives no direction to the flow.
The modern heat based mass flowmeters are smaller to be faster and use two hot elements to try to find a direction to the flow.
A hot element also means a necessary warm up time before taking any measurement.
In order to compensate for the slow response time of a heat based mass flow element, some manufacturers advertise the time it takes for the measurement to start to change,
instead of the time it takes to get a fully stabilised signal. If the measurement has to be that fast, then the measurement would be done on a non stabilized signal.
Anyone can calibrate an instrument on a non stabilized signal but there is a trade off: non linearity of the measurement, unless the element is relinearized on multiple calibration points, and
significant drift of the measurement with time.
Mass flow means that was is measured by the instrument is the quantity of molecules (mass) of the air that flows . It can also be measured by non heat exchange based elements.
ATEQ offers both heat exchange based mass flow meters and more sophisticated mass flow measurement. The heat exchange based are mostly used on slow applications with large flows,
or when the budget is limited. On all other applications, ATEQ can propose inherently fast, inherently directionnal, linear, non drifting mass flow measurement, without warm up time.
When mass flow is expressed in vacuum, it is sometime called mass extraction. ATEQ can provide both mass flow in pressure and vacuum. The sensitivity of heat exchange based mass flow
diminishes in vacuum, and increases with pressure, so the recommended vacuum mass flow technology is not heat exchange based. Working in high vacuum has advantages,
such as being less sensitive to heat exchange and increased sensitivity of the non heat exchange mass flow sensing element.
There is no mass flow technology that is the best for every test scenario. There is just a technology that matches better than another your application and your budget.
Beware of companies who promote one technology as the latest discovery universal leak test solution, and claim they have patented the wheel. That's just a clever marketing ploy.
The ATEQ applications engineer is there to listen to your needs, and recommend the better matching solution accordingly. Not a one shoe size fits everyone approach.
Mass flow can be experessed in weight units by time like grams per hour, ounces per year, or in form of a volume of air in standard conditions of temperature and pressure per unit of time,
.like standard cubic centimeters per minute (meaning at 1013 mbar of atmospheric pressure and 20 celsius of temperature in most industries).
Most automotive and other industry air leak test specifications are written in volumetric flow in strandard conditions, at a given test pressure.
A test specification like this is independent on the volume of the component tested plus test fixture, unlike a pressure drop specification, so it is a better way to write an air leak test specification..

ATEQ uses 3 configurations for mass flow leak testing .
They all have advantages and disadvantages depending on applications.

advantages:as the air flow comes from a reference part or reference tank, the supply pressure has less fluctuations ,
so it is a good system for a leak test. Also the reference part stabilises like the part under test which makes the test faster,
like a differential pressure decay test is faster than regular pressure decay.
Environmental influences are reduced since both the reference and the test are affecyed in the same way.
Disadvantages: The test is volume dependent. Needs a sometime bulky reference part or reference volume.