PROCESS CONTROL SYSTEM HAVING EQUIPMENT MONITORING FUNCTION
HART-I/O units for sending and receiving input/output signals of HART communications-compatible devices that have HART communications functions, and for sending and receiving, on mutually differing lines, 4-20 mA DC signals, which include the input/output signals, and digital signals that are superimposed on the DC signals. A controller for receiving a DC current that is outputted from the HART-I/O units and for controlling processes based on the DC signals; and a device monitoring portion for receiving digital signals sent and received by the HART-I/O units, and for monitoring the status of the HART communications-compatible devices based on the digital signals.
1 . A process control system comprising:
an input/output device sending and receiving input/output signals of a field device having a HART communications function, and sending and receiving, on respectively differing lines, first signals that are included in the input/output signals and second signals that are superimposed on the first signals;
a controlling portion receiving a first signal, outputted from the input/output device, and controlling a process based on the first signal; and
a monitoring portion receiving a second signal that is sent and received by the input/output device, and monitoring the state of a field device based on the second signal.
2 . The process control system as set forth in claim 1 , comprising:
the first signal is a 4-20 mA DC signal, and the second signal is a frequency signal wherein a digital signal has been converted.
3 . The process control system as set forth in claim 1 , comprising:
the second signal includes a value corresponding to the first signal.