Toughness vs. Durability in Mass Flow Meters

How tough is an Alicat mass flow meter when you drop it? How durable? Are these terms the same? These are the questions we asked ourselves when we filmed what was intended to be a 12-foot drop-test video last week.

Here’s what actually happened:

This video shows a portable Alicat mass flow meter being dropped from increasing heights onto unforgiving concrete. After each drop, we checked the meter’s reading against a mass flow controller that was holding a constant flow rate of 1 slpm. We chose a portable because this type of instrument is the most likely to be dropped in the field. Our first drop height was 3 feet, which is your typically carrying height. Each subsequent drop saw an increase in height of 3 feet, until we reached the top of the graduated 12-foot pole. With the meter still working, we then dropped it from our highest reach of 16.5 feet. Even after this high of a drop, the meter’s reading of 0.994 slpm remained within 0.6% of the reading of the flow controller.

The question remains: Does this demonstrate durability or toughness? These terms are certainly connected, but they have some nuances. In materials research, the opposite of toughness is not softness, but brittleness. “Tough” describes a material that, while absorbing the energy of an impact, can momentarily deform without cracking or breaking. Dropping our meter on concrete leaves the meter’s components to absorb most of the impact energy from the drop. That the meter emerged from the test of 5 drops still within calibrated specifications testifies to the toughness of its construction.

Does this test also demonstrate durability? The word “durable” stems from the verb “to endure”, and so it is the ability of an object to endure over time. You may have seen Alicat’s Impact Tester video, which demonstrates the stability and repeatability of our laminar differential pressure-based method of flow measurement. Even as the mass flow meter drops repeatedly onto the steel plate, the flow reading never deviates more than 0.5% from the reading. This is a durability test, because is demonstrates continued in-spec performance as the meter suffers shock over time.

Toughness and durability may go hand in hand, as they do in an Alicat mass flow meter, but this is not always the case. A tough instrument that can handle great impacts may nevertheless break down internally over long-term use. Conversely, a durable instrument that can stand up under repeated use throughout the years may immediately fail when dropped from a significant height. Many industrial applications necessitate the presence of both qualities in a mass flow device.

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