In addition to the larger test racks at the outdoor test sites, a compact, modular system was developed by HCL (known as PERs) to study atmospheric corrosion.

PERs provide a durable and consistent exposure configuration for specimens with a versatile mounting system that allows it to be installed on flat surfaces or utility poles. No external power source or maintenance is required throughout the exposure period.

Each PER consists of a faceplace that can be configured to hold specimens of various sizes and shapes, and also allow specimens to be individually removed at various intervals. Other components include sensors, splash shields and chloride candle shelters that can be easily disassembled and packed in a suitcase or for shipping.

Since 2005, PERs have been used to characterize outdoor environments, shelters used for equipment storage, and accelerated corrosion tests such as GM9540P. More than 160 PERs have been deployed in over 100 locations throughout the world.