INFORMATION ABOUT TUNING AND CALIBRATION
MDS-4 methane sensor module has two analogue signal outputs:
- UT–temperature signal output
- USD –measuring signal output
Processing these 2 signals enables obtaining information about gas concentration.
The sensor module is precalibrated for methane measurement at LMSNT facilities.
Precalibration procedure includes:
obtaining dependence between USD and UTin order to compensate temperature
influence on the measuring signal and determine the level of optical signal
attenuation defined by the gas concentration (but not by the temperature);
obtaining dependence of methane concentration on the optical signal
attenuation level.
The process of manufacturer’s precalibration is described below.
1. The sensor is placed in a heat chamber, where it undergoes the temperature
change from 0°C to 40°C range with 0.2°C/min. During this procedure signal values from
UT(temperature signal) and USD (measuring signal) are measured with 0.04°C resolution.
Basing on this data array, the coefficients (a, band c) for interpolating function of
USD=f(UT)dependence are calculated:
2. Then the sensor is blown-through at a constant temperature (20°C) with a
control gas mixture N2+CH4with methane concentration CCH4 varied in the range from 0
to 5% vol. During this procedure signal values from USD (measuring signal) are measured
and UT(temperature signal) is controlled for stability. Using the USD data array and USD
calc
value at T=20°C, the row of ΔSatt (level of optical signal attenuation) values is calculated:
3. Basing on ΔSatt (level of optical signal attenuation) and known in advance
methane concentration values CCH4, the coefficients (d, eand f) for interpolating
function of CCH4=f(ΔSatt)dependence are calculated:
This formula is the main formula for methane concentration measurement.
