One of the many considerations you may have when selecting a strain gauge for your application is the type of sealing it has. Gauges must be sealed to protect against damage from moisture, chemicals and other foreign particles entering the gauge. There are several different ways a gauge can be sealed and certain applications may dictate that one type of seal be used over another. The types of seals are: environmentally sealed, hermetically sealed and welded sealed.
What does “environmentally sealed” mean? “Environmentally sealed” means that the gauge will be protected from foreign material like dust and debris. It will also be protected from small amounts of humidity or drops of water (but not submersion). Potting, rubber boots and glued-on covers are different ways of achieving environmental sealing on the gauge itself, while o-rings and washers give the seal for the point where the cable enters the body of the unit. IP (Ingress Protection) ratings are given to define the level of protection an enclosure provides against the entrance of objects and liquids. IP ratings are usually written as “IP” followed by a two digit number. The first digit defines the level of protection from objects or particles and the second digit defines the level of protection from water. Most load cells have a rating of IP5X or better, meaning that they are dust-protected.
What does “hermetically sealed” mean? Wikipedia defines a “hermetic seal” as having “the quality of being airtight. In common usage, the term often implies being impervious to air or gas.” A hermetically sealed strain gauge will be sealed against air and other gas, moisture, humidity and other contaminants. This is generally accomplished by using not only a welded cover or sleeve around the gauge pocket, but also a welded header at the point of cable entry to prevent humidity and moisture from following the cable into the load cell. Commonly, hermetically sealed load cells are constructed of stainless steel. Hermetically sealed load cells are usually more expensive, but far more durable in hostile, corrosive or washdown environments.
What does “welded sealed” mean? A load cell that has been “welded sealed” has been sealed using a welded cover or seal around the gauge pocket just like with a hermetically sealed unit. The difference is that with a welded sealed unit, there is no additional protection given to the cable entry point. The cable attachment will be the same as you would find on an environmentally sealed unit. A unit with this type of seal would be appropriate for applications where the strain gauge may be exposed to moisture periodically, but where there is not a total washdown environment.
Choosing the right kind of seal for your application will affect the initial cost of purchasing your load cell and also the cost of maintaining it. A welded sealed or hermetically sealed unit will cost more initially, but in high-humidity and washdown environments, this cost will be offset by lower repair and replacement costs in the future. In most other environments, there is no need for this higher degree of sealing and the lower-cost environmental seal will be sufficient to protect your load cell.
As always, our dedicated sales professionals at Cooper Instruments are ready to help you select the right equipment for your application. Contact us today at (800) 344-3921 or email@example.com.