Accessors are the communication links between all field devices and the Central Processing Unit. This communication is made in response to one of several commands, but is entirely automatic. Each Accessor can be uniquely addressed, eliminating the possibility of information mix-ups. In addition to analog values or binary status information, the Accessor also transmits information identifying itself to the Central Processing Unit to facilitate information processing and to protect against errors introduced on the Accessor trunk due to high electromagnetic interference.

The Accessors are used in conjunction with auxiliary transducers to monitor the condition of a dynamic process. The process variables are converted into current values by the selected process sensors. The Analog Input Accessors have been specifically designed to accept the current values within the ranges specified. The Accessor will digitize any current value through these ranges. By providing the analog-to-digital conversion on the Accessor, it is possible to eliminate errors in transmission due to induced EMF signals, thus assuring the absolute minimum of error in transmitting the measured values.

A Current Input Accessor may be placed anywhere along the Accessor trunk and occupied one address and one position in any applicable Accessor housing. It is possible to locate the Current transducer up to 500 feet (150 meters) from the Accessor without any appreciable loss in accuracy.