When limiting electromagnetic interference (EMI) in your system, it is very important to shield cables properly since they are often a large contributor of EMI as well as easily affected by neighboring sources. The technology used to shield cables has been around for decades, but the practical application is commonly misunderstood.
Conductive heat shrinkable tubing (CST) - An alternative to the common braid
The braid is the most common solution for electromagnetic shielding on a cable assembly. It’s an inexpensive solution that provides adequate shielding for most applications. However, installation of the braid is labor intensive and adds bulk and weight, especially in applications with significant EMI where the cables are wrapped in copper or aluminum foil before the braid is applied for excess shielding.
Applications such as satellites, planes, helicopters, vehicles and hand-held equipment need a more light-weight solution than what the common braid provides. For these applications, conductive heat shrinkable tubing (CST) is the appropriate solution. CST is a polyolefin tube with a thin layer of flexible conductive ink applied to the inside. The tube slides over the cable and is shrunk down tightly onto the cable by applying heat. CST provides 100% coverage, is easy to install, is smaller in size and can be easily replaced, as well as providing an environmental shield against outside elements the braid cannot provide. The most notable benefit that CST has over the common braid is its weight savings.
Types of conductive heat shrinkable tubing (CST)
The amount of shielding provided by CST is determined by the type of conductive ink that lines the polyolefin tube. There is a strong correlation between the conductivity of the ink and the amount it shields. For high-end applications such as military and aerospace, one should consider a very conductive CST made from pure silver-based ink. In applications where the potential EMI is moderate to low, a less conductive, commercial grade ink may be more appropriate.
Choosing the correct diameter of tubing
Conductive heat shrinkable tubing is available in a variety of diameters. Most conductive heat shrinkable tubing will shrink at a ratio of 2:1, or approximately half of its original diameter. It is important to keep this shrink ratio in mind when choosing the correct CST. It is a common misconception to purchase CST diameter that is only slightly larger than the tube diameter. Doing this would not allow the tube to fully shrink and thus would not provide maximum shielding.
More information on conductive heat shrinkable tubing (CST)
Conductive heat shrinkable tubing was featured in the January 2013 issue of Wire and Cable Technology International as one of the Top 10 Products of 2012.
For a more detailed look at conductive heat shrinkable tubing (CST), read the original article published in the November/December 2012 issue of Wire and Cable Technology International. To inquire more about CST and other forms of EMI shielding offered by Parker Hannifin, contact the Chomerics Division.
Original article written by: Jesse Hagar, Product Development Engineer, Chomerics Division.