en: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**_{1}=ax_{1}+b

**y**_{2}=ax_{2}+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 _{1}-y_{2})/(x_{1}-x_{2})**

y

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

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

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

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