SGOES Infrared Combustible Gas Detector
820-0006
Operating Manual
Page 27
Appendix 1
– Calculating Values
SGOES Nominal Static Conversion Formula
Nominal conversion of the SGOES employs the following formula:
Ii =16Сi /CMAX +4
Ii is the output current value, in mA;
Ci is the concentration value for the gas analyzed, % LEL
C
MAX
is the maximum value of converted concentration, % LEL.).
To determine the concentration of the detected gas in %LEL , calculate by the formula:
Ci = 6.25(Ii-4)
Under calibration with standard gas mixture, the measuring concentration of the detected component (in %LEL) is calculated by the
formula:
Ci = 100 Cpasp/Cp
Cpasp is the value of the converted range of the detecting component concentration labeled on the cylinder of a specific control gas
mixture.
Cp is the upper value of the converted gas range of the detecting component equaling 100% LEL.
Calculation of absolute error
The absolute error is calculated using the formula:
Са= Сi
-
Сt
Сi
–
indicated concentration
—
value reported by SGOES in %vol or %LEL.
Сt
–
known trueconcentration of gas used for calibration in %vol or % LEL
Example
Using a calibration gas mixture labeled 61.7 LEL.
The measured value %LEL resulted 60% LEL.
Calculate the measurement error of absolute error:
Са=60 LEL
-61.7%LEL = -1.7%
LEL
Thus the absolute error of this gas mixture is equal to -1.7% LEL.
Relative error estimate of gas analyzer is calculated by formula:
б= (Сi
-
Сt/ Сt)х100
using the above to determine absolute error.
б=(60
-
61.7/61.7)х100 =
-2.8%
The calibration results are considered accurate if the basic error of gas analyzer calculated by the formulas given above in all
calibrating points does not exceed limits of Table 1-A
