EI 1540, or Engineering and Design, Instrument and Control Systems for Use in Petroleum and Natural Gas Production, Processing, Transportation, and Storage Facilities, is a standard published by the Energy Institute (formerly known as the Institution of Engineering and Technology, or IET).
You're looking for information on the EI 1540 standard, specifically a free PDF download. EI 1540 is a standard related to the engineering and design of instrument and control systems for use in petroleum and natural gas production, processing, transportation, and storage facilities. ei 1540 pdf free download