What is an AGREE Chamber?
Have you ever been cornered by a know-it-all asking you if you are using “AGREE chambers” to do your environmental testing? Did you feel silly not knowing the answer? Let me help you next time this happens. AGREE chambers are named after the US military consortium that first issued specifications requiring their use. They were especially popular during the 1980s when the US military build-up was in full swing. Many used models still circulate today. In most simplistic terms, AGREE chambers combine temperature and humidity testing with vibration.
Our industry started building chambers with open space underneath and a special floor, thus accommodating a vibration shaker below the chamber. Because vibration systems vary by brand and size, AGREE chambers often had to be built to work with a specific shaker. This helped keep the design of these chambers flexible, so that they are easy to customize, even if they aren’t going to be using a shaker. They aren’t the prettiest thing to look at, though.
How does a chamber floor accommodate a shaker?
The floor is removable, so that it can be integrated with the shaker and then moved into place when ready. Also, this allows flexibility to use different shakers or shaker heads.This removable floor is called a “diaphragm floor plug”. Before I go too far… the type of shakers I am referring to are vertical (up and down) electrodynamic units. The shaker head is what is used to interface the shaker to the product to hold it securely.
In addition the shaker head sometimes has a special fixture to hold the product. The diaphragm floor plug has two layers. The top layer is a silicone sheet that stretches to seal around the inserts in the shaker head underneath it, allowing an air-tight seal. Below the silicone sheet is dense-cell foam, which is cut to fit snugly around the shaker, as the primary insulation for the floor. Because of the imperfect nature of these floor plugs, ESPEC adds additional features:
• Wire heaters in the frame to fight frosting during extremely cold tests.
• Drains on the silicone sheet so that accumulated moisture from humidity tests can drain away
So now you know what an AGREE chamber is. And next time some smart-aleck comes asking about your test chambers, ask them if they know what AGREE stands for:
AGREE: Advisory Group on Reliability of Electronic Equipment
To learn more about vibration testing, please check with these training companies: