Calibration Check Using The Gassing Cell - Honeywell Searchline Excel Open-Path Technical Handbook

MAN0530 Issue 09 October 03
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:
where:
Int(lel.m) = Integrated LEL.m reading output by Searchline Excel in LEL.m.
xl
L = Length of cell in metres.
cell
Conc = Gas concentration in %v/v.
gas
= Lower Explosion Limit of the gas in %v/v.
LEL
gas
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.
Take the necessary precaution to ensure safety when dealing with
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
Methane
Ethane
Propane
Butane
For the Ethylene version of Excel, the following gas concentrations are suggested
Gas type
Ethylene
Propylene
Butadiene
5. MAINTENANCE
Int(lel.m) = L
xl
WARNING
these high concentration gases.
LEL Concentration
of the gas applied
5.0 %v/v 100 %v/v
3.0 %v/v 50 %v/v
2.0 %v/v 50 %v/v
1.5 %v/v 50 %v/v
LEL Concentration
applied
2.7% 54%
2.0% 50%
2.1% 42%
*
(Conc / LEL
cell gas
Calculated
response with
0.15m gas cell.
3 LEL.m
2.5 LEL.m
3.75 LEL.m
5 LEL.m
Calculated
Response
3 LELm
3.75 LELm
3 LELm
74
Searchline Excel
)
gas
4-20mA output
13.6mA
12mA
16mA
20mA
4-20mA output
13.6mA
16mA
13.6mA