en:calibration

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+ | ===== Calibration ===== | ||

+ | ==== Two point calibration ==== | ||

+ | For this way of calibration there must be a linear response of measuring tool on change of meassured variable and two samples with known value of measured variable (eg. ion concentration). | ||

+ | |||

+ | Thats all we need. Because linear characteristic is a line in two dimensional space (plane). And the line in 2-D space can be described definitely by two points (calibration samples). And position of point in 2-D is defined by two coordinates. The first coordinate is a response of measuring tool and the second one is value of measured variable. | ||

+ | |||

+ | Measuring tool need to know the equation of this line for correct meassuring. It is: | ||

+ | |||

+ | **y=ax+b** | ||

+ | |||

+ | In this case **y** is the value of measured variable and **x** is meassuring tool response **a** and **b** are constants which we need to assign. | ||

+ | We have got this two equations for two unknown:\\ | ||

+ | - **y<sub>1</sub>=ax<sub>1</sub>+b**\\ | ||

+ | - **y<sub>2</sub>=ax<sub>2</sub>+b**\\ | ||

+ | Now it's up to our decision, how do we solve the equation. | ||

+ | |||

+ | Example:\\ | ||

+ | We want to calibrate our EC metr. | ||

+ | At first we need two samples with known conductivity (eg. EC(1)=2, EC(2)=6)\\ | ||

+ | From equations 1 and 2 we express **a** by subtracting them\\ | ||

+ | **a=(y<sub>1</sub>-y<sub>2</sub>)/(x<sub>1</sub>-x<sub>2</sub>)**\\ | ||

+ | y<sub>1</sub>,y<sub>2</sub> are concentrations of our samples(2,6)\\ | ||

+ | Now we need to know the response of meassurig tool to our samples. We get 65 for EC=2 and 256 for EC=6\\ | ||

+ | We substitute into our equations:\\ | ||

+ | a=(6-2)/(256-65)≅0,0209\\ | ||

+ | and we get **a**, which is slope of the line. Sustituting **a** into one of equations we get exact position of the line. \\ | ||

+ | b=y-a*x=6-256*0,0209=0,6496\\ | ||

+ | So the equation for our meassuring tool is:\\ | ||

+ | EC=0,0209*meassuring tool response+0,6496\\ | ||

+ | {{wiki:kalibrace.png}} | ||

+ | |||

en/calibration.txt · Last modified: 2018/01/29 10:12 (external edit)

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