TN5A1191-E
29
What is the adjustment for heat treatment furnaces?
If, in plant gases to be measured, a large amount of other lower-molecular-weigh gases than nitrogen (N
2
) such as
hydrogen (H
2
), or a large amount of other higher-molecular-weight gases than nitrogen (N
2
) such as argon (Ar) are
contained, it is known that the calibration curve (output performance to gas concentration) of gas analyzers will be
affected (pressure broadening).
In such a case, analyzer is adjusted with gases similar to plant gas compositions in manufacturing (adjustment by scale
gas). After this adjustment, the analyzer is checked the calibration curve with N
2
balance gas (calibration curve by check
gas). Graphs with these calibration curves drawn are attached to products to be supplied.
Since measurement in a heat treatment furnace has much gas of such composition, it is the adjustment for heat treatment
furnaces.
In order to perform exact measurement, there are two methods in span calibration:
Composition of the standard gas for span calibration used for each method and its method are explained using an
example:
For the standard gas for zero calibration, use dry N
2
in any case so that zero point will not be affected.
<Example>
Assume that a 0 – 1% CO
2
meter of the infrared ray gas analyzer measures CO
2
contained in plant gases.
When plant gases are composed of 0.5% CO
2
, 23% CO, 30% H
2
, 0.2% CH
4
and 46.3% N
2
, either of the following is
used as the span calibration standard gas.
Standard gas type
Composition of standard gas
Method for span adjustment
1 Standard gas with the same
composition as plant gases
(scale gas)
0.9% to 1% CO
2
23% CO, 30% H
2
, N
2
*
Directly
2 Check gas
0.9% to 1% CO
balance is N
2
Indirectly
* A small amount of gas like 0.2% CH
4
with little effect on span calibration may be excluded from the standard
gas.
6.1 Method for span calibration by standard gas with the same
composition as plant gas
When using the standard gas with the same composition as plant gases given in 1, calibration can be performed
without correction, as an error in calibration curve does not occur.
1)
Set CO
2
concentration to span calibration concentration set value.
2)
Perform span calibration by using the operation key.
6. ADJUSTMENT FOR HEAT TREATMENT FURNACES
Summary of Contents for ZPA
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