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Unformatted text preview: 061 061 Error Error is the difference between an ideal (or correct) value and an actual value. Several different types of error can be measured. An error type can be expressed in several ways. 061 EE 4770 Lecture Transparency. Formatted 8:29, 25 January 1999 from lsli06. 061 062 062 Expression of Error Notation I denotes an ideal value . A denotes an actual value. Absolute error defined I  A . Percent error defined 100 I  A I for I 6 = 0. Consider a transducer designed to measure process variables in the range I [ x min , x max ]. Percentfullscale error defined 100 I  A x max for x max 6 = 0. 062 EE 4770 Lecture Transparency. Formatted 8:29, 25 January 1999 from lsli06. 062 063 063 Types of Error Model Error. Error in transducer model, H t . Repeatability Error. Transducer change from occasion to occasion. Stability Error. Transducer change during use. Calibration Error. Difference between two transducers of same kind. 063 EE 4770 Lecture Transparency. Formatted 8:29, 25 January 1999 from lsli06. 063 064 064 Model Error Let y = H t ( x ) denote a transducer output, response, and process variable. The accuracy of H t ( x ) depends upon how well the transducer is understood and how complex a transfer function can be tolerated. For example, the following are all for the same transducer: Okay: H t1 ( x ) = R o (1 + ax ). Good: H t2 ( x ) = R o (1 + ax + bx 2 ). Better: H t3 ( x ) = R o (1 + ax + bx 2 + cx 3 )....
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 Fall '99
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