5.5 Establishment of the calibration curve
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5.5 Establishment of the calibration curve

Parent topic: 5 Calibration procedure

5.5.1 General guidelines

  5.5.1.1 The analyser calibration curve shall be established by at least five calibration points (excluding zero) spaced as uniformly as possible. The highest nominal concentration shall be greater than or equal to 90% of full scale.

  5.5.1.2 The calibration curve is calculated by the method of least squares. If the resulting polynomial degree is greater than 3, the number of calibration points (zero included) shall be at least equal to this polynomial degree plus 2.

  5.5.1.3 The calibration curve shall not differ by more than ±2% from the nominal value of each calibration point and by more than ±1% of full scale at zero.

  5.5.1.4 From the calibration curve and the calibration points, it is possible to verify that the calibration has been carried out correctly. The different characteristic parameters of the analyser shall be indicated, particularly:

  • .1 the measuring range,

  • .2 the sensitivity, and

  • .3 the date of carrying out the calibration.

5.5.2 Calibration below 15% of full scale

  5.5.2.1 The analyser calibration curve shall be established by at least 10 calibration points (excluding zero) spaced so that 50% of the calibration points are below 10% of full scale.

  5.5.2.2 The calibration curve shall be calculated by the method of least squares.

  5.5.2.3 The calibration curve shall not differ by more than ±4% from the nominal value of each calibration point and by more than ±1% of full scale at zero.

5.5.3 Alternative methods

 If it can be shown that alternative technology (e.g., computer, electronically controlled range switch, etc.) provides equivalent accuracy, then these alternatives may be used.

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