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 voltage values by the selected process sensors. The Analog Input Accessors have been specifically designed to accept the voltage values within the ranges specified. The Accessor will digitize any voltage 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.