Process controller
AssigneePhillips Petroleum Company
InventorsEarl E. Shriver, James E. Layton
Life of this patent
Estimating the term…
Abstract
An analog signal representative of the condition of a process variable and an analog set point signal representative of the desired value of the process variable are compared to provide an analog error signal. In response to the analog error signal the controller generates a sign signal and a pulse rate signal which can be utilized to increase or decrease the digital value stored in a counter from which a process control signal is generated. In a preferred embodiment the process controller of the invention is utilized as a backup controller for a direct digital control system and utilizes the same digital output, digital to analog conversion, and analog output components as the associated direct digital controller.
Claims19
Apparatus comprising:
- analog controller means for receiving a process variable input signal and a set point signal, comparing said process variable input signal and said set point signal to produce an error signal, and delivering in response to said error signal an analog controller output signal having a relationship to said error signal which is one of proportional, derivative, or a combination of proportional and derivative;
- sign detector means for receiving said analog controller output signal and generating in response thereto a sign output signal, said sign output signal comprising a first digital logic state when said analog controller output signal is positive and a second digital logic state when said analog controller output signal is negative;
- absolute value determination means for receiving said analog controller output signal and generating in response thereto an absolute value signal having a magnitude proportional to the magnitude of said analog controller output signal and a fixed polarity which is unchanged by a change in the polarity of said analog controller output signal;
- and
- pulse generating means for generating digital logic pulses at a rate determined by said absolute value signal.
A method comprising:
- generating an analog process variable signal representative of a condition within a process to be controlled;
- comparing said proces variable signal to a set point signal and generating an analog error signal in response to the comparison;
- generating, from said error signal, an analog controller output signal having a relationship to said error signal which is one of proportional, derivative, or a combination of proportional and derivative;
- establishing a direction signal indicative of the arithmetic sign of said analog controller output signal;
- and
- generating a pulse output signal comprising digital logic pulses appearing at a rate determined by the magnitude of said analog controller output signal.
Dependencies are inferred from the claim text.