Electromagnetic compatibility
Use this information to plan for system installation in an environment that has a high electromagnetic-radiated field.
Information technology equipment installation might occasionally be planned in an area that has a high electromagnetic-radiated field environment. This condition results when the information technology equipment is near a radio frequency source such as a radio-transmitting antenna (AM, FM, TV, or two-core radio), civilian and military radar, and certain industrial machines (rf induction heaters, rf arc welders, and insulation testers). If any of these sources are near the proposed site, a planning review might be appropriate to assess the environment and determine whether any special installation or product considerations are advisable to reduce interference. Consult your seller. Workstations located near devices like transformers or buried electrical conduits can experience jitter on the workstation display in the presence of strong magnetic fields.
Most products can tolerate low-frequency to very-high-frequency rf levels of 3 volts per meter. Field strengths greater than 3 volts per meter might cause operational or serviceability problems. Products have different tolerance levels to electromagnetic-radiated fields in different frequency ranges. Radar (frequency of 1300 MHz, and 2800 MHz) signals with field strengths of a maximum of 5 volts per meter are acceptable. If problems occur, reorientation of the system or selective shielding might be required.
Two-core radio or cellular telephone usage should be properly controlled in the computer room. To reduce the likelihood of a problem, the following recommendations should be considered when operating such equipment:
- Keep hand-held transmitters (for example, walkie-talkies, radio paging, and cellular telephones) a minimum of 1.5 m (5 ft) from information technology equipment.
- Use only an operator-controlled transmitting device (no automatic transmissions). Develop specific rules, such as do not transmit within 1.5 m (5 ft) of a fully covered operating system. If covers are open, do not transmit.
- Choose the minimum output power that will accomplish your communication needs.
Extremely low frequency (ELF) fields
With the exception of some video display cathode ray tubes (CRT), most information technology equipment is tolerant of extremely low frequency (ELF) electromagnetic fields. The video displays that use cathode ray tubes are more sensitive because they use electromagnetic fields to position the electron beam in normal operation. The extremely low frequency range covers frequencies between 0 and 300 Hz. It is also referred to as electrical power frequency because most world electrical power is generated at either 50 or 60 Hz.
Many products tolerate ELF electromagnetic fields in the following ranges:
- Cathode ray tube video display: 15-20 milligauss
- Liquid crystal display (LCD) : 10 Gauss
- Magnetic tape equipment: 20 Gauss
- Disk drive equipment : 20 Gauss
- Processors or systems : 20 Gauss
Typical information technology centers exhibit an ambient electromagnetic field of 3 - 8 milligauss. Some equipment within a center might, under normal operation, produce fields in excess of 100 milligauss. Examples of equipment that produces large magnetic fields include: power distribution units, electric motors, electrical transformers, laser printers and uninterruptible power systems. However, magnetic field density decreases rapidly with distance. If a CRT display is located near equipment that produces large electromagnetic fields, the display might exhibit distortion such as poor focus, change in image shape or slight motion in static display images. Moving the CRT away from the equipment might remedy the problem.