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INZ-TN2ZRE-E
7.5 Adjustment in heat treatment furnace
• What is the adjustment in heat treatment furnaces?
If, in plant gases to be measured actually, 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, including the measuring components, 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 at-
tached to products to be supplied.
Since measurement in a heat treatment furnace has much gas of such composition, it is considering
as the adjustment for heat treatment furnaces.
In order to perform exact measurement, perform the following span calibration.
Composition of the standard gas for span calibration used for each method and its method are ex-
plained using an example. For the standard gas for zero calibration, use N
2
or Air 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 44.3%
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
, 25%CO,
30%H
2
, remaining N
2
*
Perform span calibration
directly.
2 Check gas
0.9% to 1% CO
Remaining N
2
Perform span calibration
indirectly.
* A small amount of gas like 0.2% CH
4
with little effect on span calibration may be excluded from the standard
gas.
(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.
