Field-mounted control unit

A smart field-mounted control unit for coupling to a DC current two-wire process control loop, comprising:

• a housing;
• communications circuitry in the housing coupled to the two-wire process control loop to receive power over the two-wire process control loop, the communications circuitry comprising:
• a receiver for receiving process signals over the two-wire process control loop, and for sending information over the two-wire process control loop;
• and
• a storage element which stores the process signals received from the two-wire loop, at least one of the process signals representative of a process variable;
• and
• control circuitry in the housing coupled to the communications circuitry, which provides a command output for controlling a process, the process variable in a carrier modulated format and superimposed thereon, the control circuitry storing previous values of the command output, where the command output is a function of a stored process signal and a stored previous value of the command output.

An apparatus for improving a smart transmitter which is powered by a DC current two-wire process control loop and which is coupled to a process, the transmitter having a sensor which senses a process variable, output circuitry coupled to the sensor which compensates and couples the process variable to the two-wire process control loop, the apparatus comprising:

• a housing;
• communications circuitry in the housing coupled to the two-wire process control loop which receives process signals and power over the two-wire process control loop and which sends information related to the transmitter over the loop;
• and
• control circuitry in the housing coupled to the communications circuitry which provides a command output to the process, where the command output is a function of a process signal, the process variable and a previously stored value of the command output.

An apparatus for improving a smart transmitter which is powered by a DC current two-wire process control loop and which is coupled to a process, the transmitter having a sensor which senses a process variable, output circuitry coupled to the sensor which compensates and couples the process variable to the two-wire loop, the apparatus comprising:

• a housing;
• communications circuitry in the housing coupled to the two-wire process control loop which receives process signals and power over the two-wire process control loop, at least one of the process signals representative of a process variable;
• and
• control circuitry in the housing coupled to the communications circuitry which provides a command output to the process, the command output having the process variable superimposed thereon in a carrier modulated format, where the command output is a function of a process signal, the process variable and a previously stored value of the command output.

A smart field-mounted control unit for controlling a process, the unit communicating over a DC current two-wire process control loop which powers the unit, comprising:

• a housing;
• input circuitry in the housing coupled to the two-wire process control loop which receives power and process signals over the two-wire process control loop, and sends information over the two-wire process control loop;
• a process signal storage element in the housing coupled to the input circuitry which stores process signals received from the two-wire loop;
• a command output storage element which stores a command output;
• control circuitry in the housing coupled to the input circuitry, the process signal storage element and the command output storage element, the control circuitry providing the command output for controlling the process and storing previous values of the command output in the command output storage element, where the command output is a function of a stored process signal and a stored previous value of the command output;
• a source of energy capable of being regulated for controlling the process;
• and
• an energy conversion unit in the housing coupled to the control circuitry which regulates
• energy from the source and applies the energy to the process as a function of the command output.

A smart field-mounted two-wire transmitter, comprising:

• a housing;
• a sensing device in the housing which senses a process variable;
• communications circuitry in the housing coupled to a DC current two-wire process control loop which receives power and process signals over the two-wire process control loop;
• a storage element in the housing coupled to the communications circuitry which stores at least some process signals received from the two-wire process control loop at least one of the process signals representative of a process variable;
• a command output storage element in the housing which stores a command output;
• and
• control circuitry in the housing coupled to the sensing device, communications circuitry and the storage elements, which provides a command output to a remote device which controls a process, the process variable in a carrier modulated format and superimposed on the command output where the command output is a function of a stored process signal, the process variable and a previously stored value of the command output.

A smart field-mounted control unit for coupling to a DC current two-wire process control loop, comprising:

• a housing;
• communications means disposed in the housing coupled to the two-wire loop for receiving power over the loop, the input means comprising:
• receiving means for receiving process signals over the loop, and for sending information related to the transmitter over the loop;
• means for storing at least some of the process signals;
• and
• controlling means carried in the enclosure coupled to the communications means for providing a command output for controlling a process and for storing previous values of the command output, where the command output is a function of a stored process signal and a stored previous value of the command output.

A smart field-mounted control unit for coupling to a DC current two-wire process control loop, comprising:

• a housing;
• communications means disposed in the housing coupled to the two-wire loop for receiving power over the loop, the communications means comprising:
• receiving means for receiving process signals over the loop, at least one of the process signals representative of a process variable;
• means for storing at least some of the process signals;
• and
• controlling means carried in the housing coupled to the communications means, the controlling means providing a command output for controlling a process, the process variable in a carrier modulated format and superimposed on the command output, the controlling means storing previous values of the command output, where the command output is a function of a stored process signal and a stored previous value of the command output.

A smart field-mounted control unit for coupling to a DC current two-wire process control loop, comprising:

• a housing;
• communications circuitry in the housing coupled to the two-wire process control loop to receive power over the two-wire process control loop, the communications circuitry comprising:
• a receiver for receiving process signals over the two-wire process control loop, and output circuitry for sending information over the two-wire process control loop;
• and
• a storage element which stores the process signals received from the two-wire loop;
• and control circuitry in the housing coupled to the communications circuitry, which provides a command output for controlling a process and which stores previous values of the command output, where the command output is a function of a stored process signal and a stored previous value of the command output, and is adjusted to a predetermined value in response to a predetermined event.