System for detecting occurrence of an event when the slope of change based upon difference of short and long term averages exceeds a predetermined limit

• US 6,463,347 B1
• Filed: 07/08/1999
• Issued: 10/08/2002
• Est. Priority Date: 09/15/1997
• Status: Expired due to Term

• Current Assignee: International Paper Company
• Original Assignee: International Paper Company
• Inventors: Thomasson, Fred Y., Shuman, Lysette H., Nevruz, Albert A.
• Primary Examiner(s): Lee, Thomas
• Assistant Examiner(s): DU, THUAN N
• Application Number:
  US09/254,822
• Time in Patent Office: 1,188 Days
• Field of Search: 710/15, 710/18, 710/19, 702/1, 702/50, 702/51, 700/108, 700/110, 700/8, 700/9, 700/11, 700/28, 700/67
• US Class Current: 700/108
• CPC Class Codes: F22B 35/18 Applications of computers to steam boiler control
• CPC Class Codes: F22B 37/421 Arrangements for detecting leaks
• CPC Class Codes: F28F 2265/00 Safety or protection arrangements; Arrangements for preventing malfunction

Abstract

A method and system are disclosed for detecting an occurrence of an event in a target system having at least one operational variable that provides an indication of one or mine conditions of the target system which change in response to the event. The method comprises the steps of: (a) periodically calculating short and long term averages of sequentially recorded values of the operational variable, the long term average including values in addition to those included in the short term average; (b) calculating the difference between the short and long term averages; and (c) determining the occurrence of an event based upon the difference by performing a statistical evaluation selected from the group consisting of determining the significance of the difference, monitoring a particular pattern of differences, monitoring change in the differences, and combinations of two or more thereof.

Claims

1. A method for detecting an occurrence of an event in a target system based upon sequentially recorded values of at least one operational variable of said target system, said operation variable providing an indication of one or more conditions of the target system which change in response to the event, said method comprising the steps of:

(a) calculating a pair of a short term average and a long term average of said values wherein said long term average includes values in addition to those included in said short term average;

(b) calculating the difference between said pair;

(c) reiterating steps (a) and (b) at least once wherein each reiterated pair of short and long term averages includes at least one value that is more recent Oman any value included in a previously calculated pair of short and long term averages; and

(d) calculating the change in the differences calculated in step (b) over the change in the number of sequentially recorded values to determine slope and indicating the occurrence of an event if said slope exceeds a predetermined limit.

2. The method of claim 1, wherein in step (d) an event is indicated when said slope of the differences, slope_Δ

, exceeds slope<sub>Δ

max</sub> having the following formula;

${\mathrm{SLOPE}}_{{\mathrm{\Delta <br><br>}}_{\max }}=\frac{\frac{N_2-N_1}{N_2}*{\mathrm{\Delta <br><br>}}_{\max }}{N_1}$

wherein Δ

_max is a predetermined value representing the maximum tolerable difference between said long term and short term averages, N₁ represents the number of said values included in said short term average, and N₂ refers to the number of said valises included in said long term average.

3. The method of claim 2, wherein in step (d) an alarm condition is indicated when a t_test value exceeds a predetermined value, said t_test having the formula:

$t_{\mathrm{test}}=\frac{{\mathrm{Slope}}_{\mathrm{\Delta <br><br>}}-{\mathrm{Slope}}_{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>\max }}{{\mathrm{\sigma <br><br>}}_{{\mathrm{Slope}}_{\mathrm{\Delta <br><br>}}}<br><br>\sqrt{\frac{1}{N_i-N_o}}}$

wherein σ

_Δ

is the standard deviation for the Δ

s used to calculate said slope_Δ

.

4. The method of claim 1, wherein in step (a) more tar one pair of short and long term averages are calculated, each pair varying in the number of values included in at least the long term average.

5. The method of claim 3, wherein an indication of an event depends upon the number of values considered in the pair of short and long term averages used in determining the differential which indicates said event.

6. The method of claim 1, wherein said operational variable is a system balance.

7. The method of claim 6, wherein said target system is a boiler having equatable inputs and outputs such that a drum balance is determinable.

8. A method for detecting an occurrence of an event in a target system having at least one operational variable, said operation variable providing an indication of one or more conditions of the target system which change in response to the event, said method comprising the steps of:

sequentially recording values of said operational variable;

calculating a first short term average and a first long tern average by averaging a certain number, N₁ and N₂ respectively, of sequentially recorded values, said first short and long term averages including a common most recent first value;

calculating at least a second short tern average and a second long term average of N₁ and N₂ sequentially recorded values respectively, said second short and long term averages including a common most recent second value, wherein said second value is more recent than said first value;

calculating a first Δ

between said first short and long term averages and a second Δ

between said second short and long term averages; and

determining the change in Δ

between said first and second Δ

s over the change in the number of sequentially recorded values to determine a first slope and indicating an event if said first slope exceeds a predetermined first limit.

9. The method of claim 8, said process further comprising:

calculating at least a third short term average and at least a third long term average by averaging a certain number, N₁, and N₂, respectively, of sequentially recorded values, wherein said N₁, and N₂. are different from said N₁ and N₂ respectively, said third short and long term averages including a common most recent third value;

calculating at least a fourth short term average and a fourth long tern average of N₁, and N₂, sequentially recorded values respectively, said second short and long term averages including a common most recent fourth value wherein said fourth value is more recent than said third value;

calculating a third Δ

between said third short and long term averages and a fourth Δ

between said fourth short and long term averages; and

determining the change in Δ

between said third and fourth Δ

s over the change in the number of sequentially recorded values to determine a second slope and indicating an event if said second slope exceeds a predetermined second limit.

10. The method of claim 9, wherein a first indication is provided if said first slope exceeds said first limit, and a second indication is provided if said second slope exceeds said second limit.

11. A system for detecting an occurrence of an event in a target system having at least one operational variable that provides an indication of one or more conditions of the target system which change in response to the event, said system comprising:

(a) means for calculating a pair of a short term average and a long term average of said values wherein said long term average includes values in addition to those included in said short term average;

(b) means for calculating the difference between said pair;

(c) means for reiterating steps (a) and (b) at least once wherein each reiterated pair of short and long term averages includes at least one value that is more recent than any value included in a previously calculated pair of short and long term averages; and

(d) means for calculating the change in the differences calculated in step (b) over the change in the number of sequentially recorded values to determine slope and indicating the occurrence of an event if said slope exceeds a predetermined limit.