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DQAP (Quality-Controlled Average)
Inputs
Input
Outputs
Average – Computes the quality-controlled average (mean value) of the samples taken during the
Duration
.
STD – Computes the quality-controlled standard deviation of the samples taken during the
Duration.
Count – Outputs the number of samples that were collected. (The number of samples used in the
output average is the Count minus the Outliers)
Outliers – Outputs the number of samples that were greater than three standard deviations from
the initial sample mean.
Description
The DQAP block is a special modification of the Average block. The Average block is a
Measure block that can output the maximum, minimum, average, standard deviation, and sample
count from a series of data points sampled from a sensor. The DQAP block also computes the
average, and outputs it along with the standard deviation and sample count. The difference is in
the way the average and standard deviation are computed.
The DQAP block makes use of statistical quality control theory to improve the accuracy of the
reported mean and standard deviation. The improvement is obtained by computing the mean and
standard deviation it two passes. In the first pass, the mean and standard deviation are
determined by the usual process of simply using the collect samples “as is”. After the standard
deviation is computed a second pass is made. In the second pass, before a sample is added to a
sum, or squared and added to a sum of squares, it is compared to the mean plus or minus three
standard deviations. Quality Control (QC) theory indicates that such samples are likely to be in
error. An updated mean and standard deviation are computed using only the samples that pass
the QC check.
The DQAP block is used to periodically take a number of samples from a sensor and then output
the quality-controlled mean, standard deviation, sample count, and number of samples failing the
QC check. For example, every half an hour, with a five minute offset, a sensor could be sampled
every two seconds for thirty seconds and then the maximum value sampled outputted (see
example below).
Summary of Contents for Xpert2
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Page 105: ...CHAPTER 5 EXAMPLE SETUPS...
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Page 141: ...Chapter 8 Maintenance and Troubleshooting...
Page 145: ...Appendix A Setup Blocks...
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Page 267: ...Appendix B Updating the Firmware...
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Page 291: ...Appendix E Software Development Kit SDK...
Page 293: ...Appendix F Creating Custom Voice Files...
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