In a subscriber interface control method, a plurality of subscriber interface sections set with different unique accommodation location numbers corresponding to accommodation locations thereof and a subscriber interface control section connected to the subscriber interface sections via a control/monitor signal line to control the subscriber interface sections and monitor operation states thereof. Management number sections in which different management numbers are set are arranged in the subscriber interface sections. The subscriber interface control section controls the subscriber interface sections and monitors the operation states thereof by sending the management numbers to the control/monitor signal line.

A field apparatus for controlling a controlled element includes a diagnosis unit for diagnosing abnormality of the field apparatus and/or the controlled element and a bidirectional digital communication device to send a digital signal which shows a diagnosis result to outside and to receive a digital signal from outside in order to execute a control of the controlled element. Other predetermined functions are effected based on a command signal in the form of an analog signal received from outside by a analog communications device of the apparatus. Electric power for operation is supplied through a switching means that can switch either a electric power that is supplied by the analog communications device or a electric power that is supplied by the bidirectional digital communication device.

A method and apparatus for notifying a receiving device of fault conditions in a sensing element or an instrument. The instrument generates an analog signal that has an amplitude which is representative of a variable. The analog signal amplitude has a range defined by a lower limit and an upper limit. The instrument transmits the analog signal to the receiving device. When the instrument detects a fault condition in itself or in the sensing element, the transmitter periodically changes the analog signal amplitude by a predetermined amplitude for as long as the fault condition exists. The predetermined amplitude and its polarity are such that the amplitude of the periodically changed analog signal lies within the range. The receiving device generates an alarm when it detects the pulses.

An industrial control system incorporating a plurality of human/machine interfaces provides for the identification of an operator using the human/machine interface so as to forward output from an ongoing application tool program to the operator as the operator moves about the factory without interruption of the tool program. Location of the human/machine interface may be used to alter the tool program to refer to data relevant to the particular part of the process near the HMI providing for intuitive and efficient use of software type tools by roving operators.

A circuit for compensating variables in a measurement transmitter. Within the transmitter, a sensor senses a primary process variable such as differential pressure and a converter digitizes the sensed process variable. The sensor senses pressures within a span of pressures values. A memory inside the transmitter stores at least two membership functions, each membership function having a non-zero value over a predetermined region of the process variable span and a substantially zero value over the remainder of the span. The memory also stores a set of compensation formulas, each formula corresponding to a membership function. A selection circuit in the transmitter selects those membership functions which have a non-zero value at the digitized process variable and a correction circuit provides at least one correction value, each correction value calculated from a compensation formula corresponding to a selected membership function. A weighting circuit multiplies each correction value by its corresponding selected membership function, and combines the multiplicands to provide a compensated process variable. The compensated process variable is coupled to a control circuit connecting the transmitter to a control system.