Datasheet

5. SENSITIVITY CHARACTERISTICS
Concentration (ppm)
FIG. 5. RATIO OF RESISTANCE (R/Ro) vs.
CONCENTRATION FOR $813.
l Remarks: Ra: Sensor resistance in air conlaming
1000ppm of Me!hane.
Fl: Sensor resistance at different
concentrations of gases.
Fig.5 Shows the changing resistance values of the type 8813.sensor in relation
to various types and concentrations of gases.
This graph is fixed at 1000 ppm
of methane.
so once the Ro value is found out by the user it is a simple
process to determine the resistance for other concentrations of gas.
Remember that R/Ro represents the ratio of resistance to the Rs at 1000 ppm
methane and not an actual resistance value.
Therefore,
the R/Ro value for
1000 ppm methane,
according to Fig.5, is 1.
The actual resistance value for a particular gas concentration tan be
calculated as follows:
For instance, if the resistance of the Sensor at 1000 ppm methane is found
out to be 7kQ in your measurement and you want to find the Rs for 4000 ppm of
hydrogen of which R/Ro is 0.3 in Fig.5,
simply
multiply 7KR by 0.3 to result
in 2.1KR
The important thing to remember is that the resistance of the Sensor at 1000 ppm
of methane must be determined by the user before this graph will be of any use
for the
determination of actual resistance values.
Likewise,
this Chart tan be used to determine the various alarm Points for
different types and concentrations of gases.
Again,
if the alarm Point for
methane is set at a concentration of 1000 ppm,
the related alarm Point for
propane will be at 700 ppm,
isobutane at 600ppm and ethanol at 1500 PPm*
However,
it should be noted that the relative sensitivity to various gases
based on methane differs to some extent from one Sensor to another.
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