When a computer system is being considered for purchase or lease, the user should investigate how sensitive that system is to disturbances of the input power. Actual case histories can be studied and user-experience requested, as well as guarantees about tolerance levels to be written into the specifications. The user should realize that the principal function of the power utility is to supply electrical energy and that the presence of large apparatus is going to be noticed at times on the power system. The utility uses protective devices which are adequately fast for the needs of power apparatus but which might be too slow to go unnoticed by electronic instruments. The growing use of SCR devices which provide very important and useful opportunities for improving the degree of control of large amounts of power can often operate to the detriment of computers and other delicate devices. In such cases, there are several options for easing the problems. Some of these can be built into the computer devices themselves so that they are rendered insensitive to many of these normal disturbances on the power systems. The utility works diligently to hold these disturbances within narrow limits so that the amount of the apparatus needed to protect the relatively small computer system is minimized.
The utility, however, is interested in having the user operate the computer with satisfaction as much as possible. When a problem is recognized, (ideally, anticipated during the planning stage), the utility engineering staff should be consulted. Frequently, they can suggest ways of grounding the computer system so that most of the problems will be avoided; improper grounding is the most common type of problem in an installation.
The user of computer devices can provide a high degree of insurance against problems caused by power system disturbances if some of the auxiliary devices described in the subsequent paragraphs are used. These include:
