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<9. Calibration>
9-3
IM 11M13A01-04E
9.1.3 Compensation
The deviation of a measured value from the theoretical cell electromotive force is checked by the
method in Figure 9.2 or 9.3.
Figure 9.2 shows a two-point calibration using two gases: zero and span. Cell electromotive forces
for a span gas with an oxygen concentration p1 and a zero gas with an oxygen concentration p2 are
measured while determining the calibration curve passing between these two points. The oxygen
concentration of the sample gas is determined from this calibration curve. In addition, the calibration
curve corrected by calibration is compared with the theoretical calibration curve for determining the
zero correction ratio represented by B/A x 100 (%) on the basis of A, B and C shown in Figure 9.2 and
a span correction ratio of C/A x 100 (%). If the zero correction ratio exceeds the range of 100±30% or
the span correction ratio becomes larger than 0±18%, calibration of the sensor becomes impossible.
21.0 p1 p2 0.51
81.92
ez
e2
e1
es
0
C
A B
Zero correction ratio = (B/A) x 100 (%) Correctable range: 100 ± 30%
Span correction ratio = (C/A) x 100 (%) Correctable range: 0 ± 18%
Cell
electromotive
force, mV
Calibration curve
before correction
Corrected calibration
curve (theoretical
calibration curve)
Zero origin
Span gas concentration Zero gas concentration
Span origin
Oxygen concentration (vol%O
2
)
F9-2E.ai
Figure 9.2 Calculation of a Two-point Calibration Curve and Correction Ratios using
Zero and Span Gases
Figure 9.3 shows a one-point calibration using only a span gas. In this case, only the cell
electromotive force for a span gas with oxygen concentration p1 is measured. The cell electromotive
force for the zero gas is carried over from a previous measurement to obtain the calibration curve. The
principle of calibration using only a span gas also applies to the one-point calibration method using a
zero gas only.
21.0 p1 0.51
81.92
ez
e1
es
0
C
A B
Zero correction ratio = (B/A) x 100 (%) Correctable range: 100 ± 30%
Span correction ratio = (C/A) x 100 (%) Correctable range: 0 ± 18%
Cell
electromotive
force, mV
Calibration curve before
correction
Previous
zero gas data
Corrected calibration curve
(theoretical calibration curve)
Zero origin
Span origin
Span gas concentration
Oxygen concentration (vol%O
2
)
F9-3E.ai
Figure 9.3 Calculation of a One-point Calibration Curve and Correction Ratios Using a
Span Gas