74
MAN0530 Issue 09 October 03
Searchline Excel
2104M0506
5.3
CALIBRATION CHECK USING THE GASSING CELL
The gassing cell is designed to allow easy calibration checking using a high concentration test
gas as opposed to the standard plastic test filters. The integrated LEL.m reading of the gas
concentration in the cell can be calculated using the following formula:
Int(lel.m)
xl
= L
cell
*
(Conc
gas
/ LEL
gas
)
where:
Int(lel.m)
xl
=
Integrated LEL.m reading output by Searchline Excel in LEL.m.
L
cell
=
Length of cell in metres.
Conc
gas
=
Gas concentration in %v/v.
LEL
gas
=
Lower Explosion Limit of the gas in %v/v.
The test gas must be the same as the test gas used during the factory calibration of the Searchline Excel
unit and ideally the concentration should be between 2 and 5 LEL.m and never below 1 LEL.m.
Note: Where a different test gas is used, the typical value for cross-sensitivity is not sufficiently precise to
enable valid calibration checks to be performed using the Gassing Cell, however, response tests
can be easily performed with the plastic Test Filters as described in section 5.1.2.
WARNING
Take the necessary precaution to ensure safety when dealing with
these high concentration gases.
The gassing cell supplied by Zellweger Analytics (Part No: 2104B2326) is 0.15m long and the
following table outlines the response expected when using this gassing cell:
Gas type
LEL
Concentration
Calculated
4-20mA output
of the gas
applied
response with
0.15m gas cell.
Methane
5.0 %v/v
100 %v/v
3 LEL.m
13.6mA
Ethane
3.0 %v/v
50 %v/v
2.5 LEL.m
12mA
Propane
2.0 %v/v
50 %v/v
3.75 LEL.m
16mA
Butane
1.5 %v/v
50 %v/v
5 LEL.m
20mA
For the Ethylene version of Excel, the following gas concentrations are suggested
Gas type
LEL
Concentration
Calculated
4-20mA output
applied
Response
Ethylene
2.7%
54%
3 LELm
13.6mA
Propylene
2.0%
50%
3.75 LELm
16mA
Butadiene
2.1%
42%
3 LELm
13.6mA
5. MAINTENANCE
