Field-mounted control unit

• US 5,485,400 A
• Filed: 04/10/1995
• Issued: 01/16/1996
• Est. Priority Date: 10/02/1989
• Status: Expired due to Term

• Current Assignee: Fieldbus Foundation (FieldComm Group, Inc.)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Warrior, Jogesh, Orth, Kelly M., Jacobson, Vincent C., Tielens, Craig R.
• Primary Examiner(s): Cosimano, Edward R.
• Application Number:
  US08/420,434
• Time in Patent Office: 281 Days
• Field of Search: 340/310.01, 364/138, 364/139, 364/550
• US Class Current: 700/67
• CPC Class Codes: G05B 15/02 electric
• CPC Class Codes: G05B 19/418 Total factory control, i.e. centrally controlling a plurality of machines, e.g. direct or distributed numerical control [DNC], flexible manufacturing systems [FMS], integrated manufacturing systems [IMS] or computer integrated manufacturing [CIM]
• CPC Class Codes: G05B 19/4185 characterised by the network communication
• CPC Class Codes: G05B 2219/31119 Fielddevice comprises also controller and pneumatic actuator and sensor
• CPC Class Codes: G05B 2219/31154 Actuator sensor bus, asi, intelligent actuator, motor, sensor
• CPC Class Codes: Y02P 90/02 Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS]

Abstract

A smart field-mounted control unit, for controlling a process, receives signals and sends a command output over a two-wire circuit which powers the control unit. An input section receives the signals, which can be instructions representative of commands or instruction sets, process variables sensed by external control units or setpoints representative of a desired process state. The instructions are representative of a control requirement of the process and adjust a controlling section in the control unit to generate the command output in conformance with the control requirement. The command output can be a function of the difference between the process setpoint and a process variable, or a function of a linear combination of a process variable and its calculated time integral and time derivative functions. A sensing section in the control unit can sense and scale a process variable for generating the command output as well. The control unit can include a regulator section, controlled by the command output, which regulates application of a mechanical, hydraulic, pneumatic or electromagnetic force applied to the process.

Claims

1. 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 related to the control unit 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 provided 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.

3. The control unit of claim 1 or 2 where the process signals include information for determining the function for providing the command output.

4. The control unit of claim 1 or 2 where the process signals include instructions for operation of the control circuitry.

5. The control unit of claim 1 or 2 where the process signals include commands directing operation of the control circuitry.

6. The control unit of claim 1 or 2 where the process signals are digitally represented on the two-wire process control loop.

7. The control unit of claim 1 or 2 where the command output is coupled in an analog manner to a remote device over the two-wire process control loop.

8. The control unit of claim 1 or 2 further comprising a process variable sensor providing a process variable output related to a process, where the command output is determined as a function of at least a stored process signal, a stored previous value of the command output and the process variable output.

9. The control unit of claim 1 including means for receiving a process variable.

12. The control unit of claim 1 or 11 wherein the information comprises status information.

13. The control unit of claim 12 wherein status information is selected from the group consisting of:

process control statistics, current modes of operation, process variable values and unit serial numbers.

2. 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.

10. The control unit of claim 2 or 9 where the process signals include a setpoint and where the control circuitry adjusts the command output as a function of the setpoint and the process variable.

11. 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.

15. The apparatus of claim 11 or 14 where the process signals include information for determining the function for providing the command output.

16. The apparatus of claim 11 or 14 where the process signals include instructions for operation of the control circuitry.

17. The apparatus of claim 11 or 14 where the process signals include a setpoint and where the control circuitry adjusts the command output as a function of the setpoint and the process variable.

18. The apparatus of claim 11 or 14 where the control circuitry adjusts the command output proportionally to a substantially linear combination of the process variable, a time integral of the process variable and a time-rate-of-change of process variable.

19. The apparatus of claim 11 or 14 where the control circuitry adjusts the command output, q_k, according to the equation, ##EQU2## where q_k is the command output at a kth time, r_i and y_i are a setpoint and process variable values at an ith time respectively, i varies from 0 to k and a_i and b_i are application specific constants which may be time varying.

20. The apparatus of claim 11 or 14 where the process signals are digitally represented on the two-wire process control loop.

21. The apparatus of claim 11 or 14 where the command output is analogly coupled to a remote device over a pair of wires.

22. The apparatus of claim 11 or 14 where the sensor comprises a sensor selected from the group of sensors sensing pressure, temperature, flow, mass, conductivity, moisture, pH, oxygen concentration, chlorine concentration, density, force and turbidity.

23. The apparatus of claim 11 or 14 where the process signals are representative of redundant process variables.

14. 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.

24. 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.

25. The control unit of claim 24 where the process signals include information for determining the function for providing the command output.

26. The control unit of claim 24 where the process signals include instructions for operation of the control circuitry.

27. The control unit of claim 24 where the process signals include commands for directing operation of the control circuitry.

28. The control unit of claim 24 where the process signals are digitally represented on the two-wire process control loop.

29. The control unit of claim 24 where the command output is coupled in an analog manner to a remote device over the two-wire circuit.

30. The control unit of claim 24 where the information sent over the two wire process control loop is information representative of the status of the control unit.

31. The control unit of claim 24 further comprising a process variable sensor providing a process variable output related to a process, and where the process signals include at least one setpoint, and where the control circuitry adjusts the command output as a function of the setpoint and the process variable.

32. The control unit of claim 31 where the function is a difference between the setpoint and the process variable.

33. 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.

34. The transmitter of claim 33 where the process signals include information for determining the function of providing the command output.

35. The transmitter of claim 33 where the process signals include instructions for operation of the control circuitry.

36. The transmitter of claim 33 where the process signals include setpoints and where the control circuitry adjusts the command output as a function of the difference between the setpoint and the scaled process variable.

37. The transmitter of claim 33 where the process signals are digitally represented on the two-wire process control loop.

38. The transmitter of claim 33 where the command output is coupled in a analog manner to the remote device over a pair of wires.

39. The transmitter of claim 33 where the format for analogly coupling the command output to the pair of wires is selected from the group of formats comprising 4-20 mA, 10-50 mA and 1-5 V.

40. The transmitter of claim 33 where the sensing device comprises sensors selected from the group of sensors sensing pressure, temperature, flow, mass, conductivity, moisture, pH, oxygen concentration, chlorine concentration, density, force and turbidity.

41. The transmitter of claim 33 where the control circuitry adjusts the command output proportionally to a substantially linear combination of the process variable, the time integral of the process variable and the time-rate-of-change of process variable.

42. The transmitter of claim 41 where the control circuitry adjusts the command output, q_k, according to the equation, ##EQU3## where q_k is the command output at the kth time, r_i and Y_i are the setpoint and process variable values at the ith time respectively, i varies from 0 to k and a_i and b_i are application specific constants which may be time varying.

43. 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.

44. 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.

45. A smart field-mounted control unit coupled to a remote device for controlling a process, the control unit comprising:

communications means for receiving process signals over a DC current two wire loop which provides power to the control unit and to a remote device, the control unit and the remote device in series;

storing means for storing the process signals, at least one of the process signals representative of a process variable;

controlling means coupled to the communications means and the storing means for providing a command output to the remote device over the loop, the process variable digitally superimposed in a carrier modulated format on the command output, the controlling means including a storage element for storing a previous value of the command output, the controlling means providing the command output as a function of a stored previous value of the command output and a process signal.

46. 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.

47. The control unit of claim 46 including a process variable sensor providing a process variable output related to a process, wherein the predetermined event occurs when the process variable output indicates a predetermined condition.

48. The control unit of claim 46 wherein the predetermined event occurs upon receipt of a process signal.

49. The control unit of claim 48 where the process signal is a shutdown command.