Method and apparatus for determining weighted average of process variable

• US 4,926,364 A
• Filed: 07/25/1988
• Issued: 05/15/1990
• Est. Priority Date: 07/25/1988
• Status: Expired due to Fees

• Current Assignee: Westinghouse Electric Sweden AB (Brookfield Asset Management Incorporated)
• Original Assignee: Westinghouse Electric Company LLC (Brookfield Asset Management Incorporated)
• Inventors: Brotherton, Walter W.
• Primary Examiner(s): Lall, Parshotam S.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US07/223,306
• Time in Patent Office: 659 Days
• Field of Search: 364/575, 364/581, 364/571.02.557, 307/357, 307/441, 328/137, 340/501, 340/508, 376/246, 376/247, 376/249
• US Class Current: 702/179
• CPC Class Codes: G08B 29/16 Security signalling or alarm systems, e.g. redundant systems

Abstract

A method and apparatus for determining a weighted average of three input values under the control of a processor includes a step of determining which of the three input values is the median value, with the remaining input values being first and second values. Then, first and second weighting factors are calculated based on a predetermined median weighting factor and the three input values. Finally, a weighted average is calculated based on the first and second weighting factors, the predetermined median weighting factor, the first and second input values and the median input value. The three input values may be sensed values provided by a temperature sensor in a nuclear power plant.

Claims

1. A method for converting sensor signals into a combined sensor signal which is a weighted average of three input sensor values corresponding to a single process variable under control of a processor, comprising the steps of:

(a) determining which of the three input sensor values is a median input value, the input sensor values other than the median input value being first and second input values;

(b) calculating first and second weighting factors based on a predetermined median weighting factor and the three input sensor values; and

(c) producing the combined sensor signal by calculating a weighted average based on the first and second weighting factors, the predetermined median weighting factor, the first and second input values and the median input value.

2. A method according to claim 1, wherein said step (b) comprises the substeps of:

(b1) calculating first and second absolute values which are equal to absolute values of differences between the median input value and the first and second input values, respectively;

(b2) calculating the first weighting factor based on the predetermined median weighting factor and the first and second absolute values; and

(b3) calculating the second weighting factor based on the first weighting factor and the predetermined median weighting factor.

3. A method according to claim 2, wherein said step (c) comprises calculating the weighted average by adding together results of multiplying the predetermined median weighting factor times the median input value, multiplying the first weighting factor times the first input value, and multiplying the second weighting factor times the second input value.

4. A method according to claim 3, wherein:

said substep (b2) comprises performing the calculation f/(1+(A₁ /A₂)²) to obtain the first weighting factor, where f is equal to the predetermined median weighting factor, and A₁ and A₂ are the calculated first and second absolute values; and

said substep (b3) comprises calculating the second weighting factor based on the first weighting factor and the predetermined median weighting factor.

5. A method according to claim 4, wherein a sum of the first weighting factor, the second weighting factor and the predetermined median weighting factor is 1.

6. A method according to claim 2, wherein a sum of the first weighting factor, the second weighting factor and the predetermined median weighting factor is 1.

7. A method according to claim 1, wherein said step (b) comprises the substeps of:

(b1) calculating first and second absolute values which are equal to absolute values of differences between the median input value and the first and second input values, respectively;

(b2) calculating the first weighting factor based on the predetermined median weighting factor and the first and second absolute values; and

(b3) calculating the second weighting factor based on the predetermined median weighting factor and the first and second absolute values.

8. A method according to claim 7, wherein said step (c) comprises calculating the weighted average by adding together results of multiplying the predetermined median weighting factor times the median input value, multiplying the first weighting factor times the first input value, and multiplying the second weighting factor times the second input value.

9. A method according to claim 8, wherein:

said substep (b2) comprises performing the calculation f/(1+(A₁ /A₂)²)) to obtain the first weighting factor, where f is equal to the predetermined median weighting factor, and A₁ and A₂ are the calculated first and second absolute values; and

said substep (b3) comprises performing the calculation f/(1+(A₂ /A₁)²)) to obtain the second weighting factor.

10. A method according to claim 1, wherein the three input sensor values correspond to a sensed process variable, and wherein said step (b) comprises the substeps of:

(b1) calculating first and second absolute values which are equal to absolute values of differences between the median input value and the first and second input values, respectively;

(b2) calculating the first weighting factor based on the predetermined median weighting factor and the first and second absolute values; and

(b3) calculating the second weighting factor based on the first weighting factor and the predetermined median weighting factor.

11. A method according to claim 10, wherein said step (c) comprises calculating the weighted average by adding together results of multiplying the predetermined median weighting factor times the median input value, multiplying the first weighting factor times the first input value, and multiplying the second weighting factor times the second input value.

12. A method according to claim 11, wherein:

said substep (b2) comprises performing the calculation f/(1+(A₁ /A₂)²) to obtain the first weighting factor, where f is equal to the predetermined median weighting factor, and A₁ and A₂ are the calculated first and second absolute values; and

said substep (b3) comprises calculating the second weighting factor based on the first weighting factor and the predetermined median weighting factor.

13. A method according to claim 12, wherein the sum of the first weighting factor, the second weighting factor and the predetermined median weighting factor is 1.

14. Apparatus for converting sensor signals into a combined sensor signal which is a weighted average of three input sensor values corresponding to a single process variable, comprising:

means for providing the three input sensor values; and

a processor for receiving the three input sensor values, for determining which of the three input sensor values is a median input value, the input sensor values other than the median input value being first and second input values, said processor for calculating first and second weighting factors based on a predetermined median weighting factor and the three input sensor values, and for producing the combined sensor signal by calculating a weighted average based on the first and second weighting factors, the predetermined median weighting factor, the first and second input values, and the median input value.

15. Apparatus according to claim 14, wherein said means for providing the three input sensor values comprises first, second and third sensors for sensing a process variable and for providing the three input sensor values.

16. Apparatus for converting sensor signals into a combined sensor signal which is a weighted average of a process variable for a nuclear power plant, comprising:

first, second and third sensors for measuring a process variable corresponding to operation of a portion of the nuclear power plant, and for generating respective sensed values; and

a processor for receiving the sensed values, for determining which of the sensed values is a median value, the sensed values other than the median value being first and second sensed values, said processor for calculating first and second weighting factors based on a predetermined median weighting factor and the second values, and for producing the combined sensor signal by calculating a weighted average based on the first and second weighting factors, the predetermined median weighting factor, the first and second sensed values and the median value.