METHOD OF CONTROLLING A PROCESS AND APPARATUS FOR THE PERFORMANCE OF THE METHOD

• US 3,740,533 A
• Filed: 01/19/1971
• Issued: 06/19/1973
• Est. Priority Date: 01/23/1970
• Status: Expired due to Term

• Current Assignee: Gerrit Hendrik Van Zeggelaar
• Original Assignee: Gerrit Hendrik Van Zeggelaar
• Inventors: van Zeggelaar, Gerrit Hendrik
• Primary Examiner(s): Morrison, Malcolm A.
• Assistant Examiner(s): Dildine, Jr., R. Stephen
• Application Number:
  US05/107,716
• Time in Patent Office: 882 Days
• Field of Search: 235/151.3 73/4R
• US Class Current: 700/71
• CPC Class Codes: E02F 7/04 Loading devices mounted on a dredger or an excavator loading devices in general B65G hopper dredgers, also equipment for unloading the hopper
• CPC Class Codes: G01L 27/005 Apparatus for calibrating pressure sensors
• CPC Class Codes: G05B 11/017 using photo-electric means
• CPC Class Codes: G05D 16/2073 with a plurality of pressure sources
• CPC Class Codes: G06G 7/66 for control systems for optimisation G06G7/122

Abstract

A method and apparatus for controlling a process, which requires a control signal which varies linearly with a process variable, by means of an instrumentality which measures the variable but does not produce the required linear output. The deviation of the instrumentality from the desired linear signal is compensated for by calibrating the instrumentality for a number of values of the variable between which successive pairs thereof the output of the instrumentality is reasonably linear. Thus, between each pair Pn and Pn 1 of the variable the ideal control signal is uniquely defined as Y mx+ b where x is the variable P, the slope m equals (Yn-Yn 1)/(Pn-Pn 1) and b equals Yn 1, with Yn and Yn 1 being the ideal values corresponding to the values Pn and Pn 1 of the variable; whereas the output of the instrumentality is at least closely defined as S m1x+ b1 where x is again the variable P, the slope m1 equals (Wn-Wn 1)/(Pn-Pn 1) and b1 equals Wn 1 with Wn and Wn 1 being the calibrated outputs of the instrumentality corresponding to the values Pn and Pn 1 of the variable. With these conditions prevailing for that range of the variable between each pair, the instrumentality output is corrected to equal (S-Wn 1)((Yn-Yn 1)/(Wn-Wn 1))+Yn 1 and is used to control the process with high degree of accuracy.

Claims

1. A method of controlling a process, in which at least one pick-up, with an electric output signal is used, after amplification by means of an amplifier, for the control of the process, comprising performing a measuring cycle comprising at least one measurement preceded by at least two calibrations, during which calibrations the pick-up is subjected to different calibration states to produce initial calibration signals, and during which measurement the pick-up is subjected to a measuring state to produce a measuring signal, and obtaining the reference signal (S'"'"''"'"''"'"''"'"''"'"''"'"'III) relating to the measurement by producing the signal difference (SIII-W2) between the measuring signal (SIII) and the one calibration signal (W2) of the one of the two calibrations, multiplying the signal difference (SIII-W2) by the reference signal difference (Y3-Y2) associated with the state difference (P3-P2), dividing the reference signal difference by the calibration siGnal difference (W3-W2) of the two calibrations, and algebraically adding the result to the one reference calibration signal (Y2) associated with the one calibration state (P2).

2. An apparatus for controlling a process, said apparatus having measuring means comprising at least one pick-up, one electric output of which is connected to an amplifier having its output connected to a device for controlling the process and comprising calibration means for loading the pick-up in the calibration state, comprising:

calibration means which can load the pick-up in at least two different calibration states;

recording means for recording and reproducing during measurement the amplified initial calibration signals of the pick-up;

a subtractor for producing the signal difference (SIII-W2) between the one calibration signal (W2) of the two calibrations and the measuring signal (SIII);

calculating means for calculating the value (SIII-W2) (Y3-Y2)/(W3 - W2) being the product of the signal difference (SIII-W2) and the reference signal difference (Y3-Y2) associated with the state difference (P3-P2), said product being divided by the calibration signal difference (W3-W2) of the two calibrations; and

an adder for algebraically adding the output signal of said calculating means to the one reference calibration signal (Y2) associated with the one calibration state (P2), the adder output being connected to the input of said device.

3. A method of controlling with a signal-producing instrumentality a process which is required to be controlled with respect to a variable over a range of values of the variable between the end values Pn 1 and Pn and which process is controlled correctly over said range by control signals which vary linearly over said range and have the known values Yn 1 and Yn for the respective end values Pn 1 and Pn of the variable and a known slope between such known values, said signal-producing instrumentality having an output over said range in response to variations in said variable which is essentially linear but is of a slope different from said known slope, which comprises the steps of:

a. measuring said variable with said instrumentality and storing the output of the instrumentality at said value Pn 1 of the variable to yield a calibration signal Wn 1;

b. measuring said variable with said instrumentality and storing the output of said instrumentality at said value Pn of the variable to yield a calibration signal Wn; and

thereafter c. measuring said variable within said range thereof with said instrumentality to produce an output Sn; and

d. correcting said output Sn to yield a control signal equal to (Sn-Wn

     1) ((Yn-Yn

     1)/(Wn-Wn

     1))+Yn 1.

4. A method of controlling a process as defined in claim 3 including the steps of:

a. measuring said variable with said instrumentality and storing the output of said instrumentality at a further value Pn 2 of the variable to yield a calibration signal Wn 2;

b. measuring said variable with said instrumentality and storing the output of said instrumentality at a still further value Pn 3 of the variable to yield a calibration signal Wn 3 , said values Pn 2 and Pn 3 being end values of a further range in which the process is controlled correctly by control signals which vary linearly over such further range and have known values Yn 2 and Yn 3 for the respective end values Pn 2 and Pn 3; and

thereafter c. measuring said variable within said further range thereof with said instrumentality to produce an output S1n; and

d. correcting said output S1n to yield a control signal equal to (S1n-Wn

     2)((Yn 3-Yn

     2)/(Wn 3-Wn

     2))+Yn 2.

5. A method of controlling a process as defined in claim 3 including the steps of:

a. measuring said variable with said instrumentality and storing the output of said instrumentality at a further value Pn 2 of the variable to yield a calibration signal Wn 2, said values Pn 1 and Pn 2 being end values of a further range in which the process is controlled correctly by control signals which vary linearly over such further range and have the known values Yn 1 and Yn 2 for the respective end values Pn 1 and Pn 2; and

thereafter b. measuring said variable with said instrumentality and storing the output S1n; and

c. correcting said output S1n to yield a control signal equal to (S1n-Wn

     1)((Yn 2-Yn

     1)/(Wn 2-Wn

     1))+Yn 1.

6. A method of controlling a process which is required to be controlled linearly with respect to a variable P over a range of values of the variable by means of an instrumentality which produces an output S in response to said variable which is non-linear over at least a portion of said range and which yields outputs for discrete values of said variable which differ from those corresponding values of an ideal control signal Y which are required for correct control of the process, which comprises the steps of:

a. measuring said variable with said instrumentality for different values Po, P1 - - - Pn of said variable and storing the corresponding output values Wo, W1 - - - Wn of said instrumentality, said values Po, P1 - - - Pn being selected sufficiently close such that the outputs of said instrumentality within the small ranges between pairs of successive values Wo, W1 - - - Wn are essentially linear; and

thereafter b. measuring said variable with said instrumentality to produce a process control output S; and

c. correcting the process control output of step (b) to yield a control signal equal to (S-Wi 1 ) ((Yi-Yi

     1)/(Wi-Wi

     1))+Yi 1 where Wi and Wi 1 represent that pair of values Wo, W1 - - - Wn between which the process control output S of the instrumentality falls and Yi and Yi 1 are corresponding values of the ideal control signal.