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en:calibration [2018/01/29 10:12] (current)
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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)