YOKOGAWA MG8G, User Manual, Page: 44 / 63

<9. CALIBRATION>
9-1
IM 11P03A03-01E 6th Edition : Jan. 26, 2022-00
9. CALIBRATION
9.1 Overview
The instrument should be calibrated at two points using zero gas (nitrogen gas with an oxygen
concentration of 0%) and span gas with a known oxygen concentration. Figure 9.1 shows the
relationship between the sensor emf and the oxygen concentration.
Oxygen Concentration (%O
2
)
Sensor emf
(mV)
c
F12.1E.ai
p2
p1
0
c : oxygen concentration of span gas
cz : zero calibration coefficient
p1 : sensor emf at the initial zero calibration
p2 : sensor emf at the initial span calibration
p1’ : sensor emf at zero calibration
p2’ : sensor emf at span calibration
p1’
p2’
cz
Figure 9.1 Sensor emf vs. Oxygen Concentration
The ratio of the oxygen concentration to the sensor emf is calculated from the sensor emf values
( p1 and p2 ) obtained in calibration.
k =
c
p2 – p1
Assuming that the sensor emf when sample gas is applied is ps , the concentration of the sample
gas, cs , is obtained from the following equation.
cs = k × (ps – p1)
Calibration is for obtaining k .
When only a zero calibration is performed, the instrument is calibrated to the zero gas’s value
and the ratio of the oxygen concentration to the sensor emf, k , that was obtained from the
previous calibration, is used.
9.2 Calibration Coefficient
The calibration coefficient is a deviation from the initial calibration value.
9.2.1 Zero Calibration Coefficient
T he zero calibration coefficient is the deviation between the sensor emf obtained when a zero
calibration is performed and the initial calibration value, and is expressed as the one corrected
for oxygen concentration. It is cz (% O
2
) in Figure 9.1. When the zero calibration coefficient, cz , is
outside of ±1.25% O
2
, a zero calibration coefficient error will occur.
9.2.2 Span Calibration Coefficient
The span calibration coefficient is the deviation between the ratio of the oxygen concentration
to the sensor emf,
k’
, obtained when zero and span calibrations are performed and the initial
calibration value, and is expressed as the ratio to the ratio obtained at the initial calibration,
k
.