EATON TN02 520-1001 Rev 3 MTL Zirconia Oxygen Analyser User Guide
- June 12, 2024
- EATON
Table of Contents
EATON TN02 520-1001 Rev 3 MTL Zirconia Oxygen Analyser
Product Information
The MTL Zirconia Oxygen Analyser is designed to measure the dewpoint of furnace atmospheres. It operates under specific conditions, which include the presence of a known amount of hydrogen in the gas being measured and the balance of the gas being either nitrogen or inert. The analyser can be used in pure hydrogen, cracked ammonia, and hydrogen/argon or hydrogen/helium mixtures. However, it is not suitable for carburising gases that contain CO/CO2. The analyser provides measurements that are useful for determining the oxygen concentration in furnace atmospheres.
Technical Specifications
Dewpoint (°C)| Water Concentration (ppm H2O)| MTL Zirconia Oxygen Sensor
Output (mV)
---|---|---
0| 6025| 1192 (100% H2)
32| 2566| 1180 (75% H2)
-10| 1021| 1076 (5% H2)
14| 376| 1227 (5% H2)
-20| 127| 1215 (5% H2)
-4| 39| 1110 (5% H2)
-30| 10.6| 1256 (5% H2)
-22| 2.55| 1244 (5% H2)
-40| 0.53| 1140 (5% H2)
-58| | 1302 (5% H2)
-60| | 1291 (5% H2)
-76| | 1186 (5% H2)
-70| | 1346 (5% H2)
-94| | 1334 (5% H2)
-80| | 1228 (5% H2)
-112| | 1392 (5% H2)
-90| | 1380 (5% H2)
-94| | 1274 (5% H2)
-112| | 1442 (5% H2)
-130| | 1432 (5% H2)
-122| | 1326 (5% H2)
-148| | 1498 (5% H2)
-140| | 1487 (5% H2)
-132| | 1382 (5% H2)
-160| | 1560 (5% H2)
-152| | 1549 (5% H2)
-144| | 1443 (5% H2)
Product Usage Instructions
- Ensure that the gas to be measured contains a known amount of hydrogen and the balance of the gas is either nitrogen or inert.
- Connect the MTL Zirconia Oxygen Analyser to the gas source following the manufacturer’s instructions.
- Power on the analyser and allow it to warm up for the specified time, as mentioned in the user manual.
- Adjust any necessary settings on the analyser, such as temperature and pressure, according to the furnace atmosphere conditions.
- Initiate the measurement process by selecting the appropriate mode on the analyser.
- Observe the dewpoint measurement displayed on the analyser’s screen or interface.
- Refer to the provided table or graph to interpret the relationship between dewpoint, water concentration, and MTL Zirconia Oxygen Sensor output.
- Use the measured data to determine the oxygen concentration in the furnace atmosphere and make necessary adjustments if required.
Note: For further technical information and related applications, refer to the provided Technical Notes: TN01 – Oxygen sensors – theory and application and TN03 – The Use of Zirconia Oxygen Analysers in Heat Treatment. If you need any further assistance or have any questions, please contact Eaton Electric Limited at the provided contact details.
Measure the Dewpoint
Using MTL Zirconia Oxygen Analysers to Measure the Dewpoint of Furnace Atmospheres:
A MTL Zirconia Oxygen Analyser will measure dewpoint only under certain conditions:
- that the gas to be measured contains a known amount of hydrogen;
- that the balance of the gas is either nitrogen or inert. As a result it works in pure hydrogen, cracked ammonia, and hydrogen/argon or hydrogen/helium mixtures, but not in carburising gases, which also contain CO/CO2, although very useful measurements can be made in these atmospheres too – see Technical Note TN03.
In order to appreciate the advantages of using MTL zirconia oxygen analysers to monitor furnace atmospheres, it is helpful to understand why in such atmospheres the dewpoint is measured. The measurement of the dewpoint of a gas is, in reality, just a way of measuring its water content. The reason this is important is because too much water in the furnace atmosphere will spoil the work going through it; not because of the water itself but because, at the high temperatures within a furnace, it dissociates into hydrogen and oxygen. This is illustrated by the following chemical equation:
is a constant. (p is the concentration or activity of the reactant in the bracket). Similar equations can be written to describe a metal in equilibrium with oxygen. The values of the constants are well defined by standard data. In fact, what is happening inside the furnace is a kind of competition between the contents, say iron and hydrogen, for the oxygen. At any particular temperature, a metal will have a precise oxygen concentration, or activity, at which it will oxidise. If the oxygen activity is kept below that point, no oxidation will take place, and vice versa. What the formula illustrates is that by adding more hydrogen to an atmosphere, the oxygen activity is reduced. This is because the only way the ratio of activities can be maintained constant, as determined by the laws of chemistry, is by the oxygen decreasing and/or the water increasing. Adding more hydrogen is a standard cure for overcoming problems when the water content (dewpoint) becomes too high.
This is why furnace operators always wanted the dewpoint to be measured;
because, in less enlightened times, it was the only way to determine how much
oxygen was in the furnace. To avoid the complication of translating this
figure into oxygen concentration, the atmosphere quality used to be expressed
in terms of dewpoint and hydrogen concentration.
The key factor however is oxygen, and its activity, and MTL zirconia oxygen
analysers measure this directly. The zirconia sensor is uniquely capable of
measuring the extremely low concentrations of oxygen to be found in these
atmospheres. For convenience, some analysers can be fitted with a meter scaled
in dewpoint. However there is no real reason to have the analyser scaled in
dewpoint; we offer it only because some users are used to it. It could be
scaled in parts per million of water vapour, sensor millivolts or, more
pedantically, in oxygen potential; the figure that the user really needs to
know. Oxygen potential is no more than the oxygen activity expressed in
chemical units. As such it relates easily to the oxygen values that a chemist
would use when determining the point at which a metal would oxidise at a
particular temperature. All of our microprocessor based analysers of this type
display in oxygen potential (kilo-calories or kilo-joules). See Technical
Notes TN01 & TN03 for a fuller explanation of zirconia oxygen cell theory,
etc.
The table shows the relationship between dewpoint and the water concentration
and also gives the related output in millivolts of the MTL zirconia oxygen
sensor in various concentrations of hydrogen.
The graph below illustrates the relationship of dewpoint to cell output and
oxygen potential at various concentrations of hydrogen.
Note: The MTL Z210 and MTL Z1110 analysers are used for this type of application.
Additional related Technical Notes:
- TN01 – “Oxygen sensors – theory and application”
- TN03 – “The Use of Zirconia Oxygen Analysers in Heat Treatment”
Eaton Electric Limited,
Great Marlings, Butterfield, Luton
Beds, LU2 8DL, UK.
Tel: + 44 (0)1582 723633
Fax: + 44 (0)1582 422283
E-mail: mtlgas@eaton.com
www.mtl-inst.com
© 2016 Eaton
All Rights Reserved
Publication No. TN02 520-1001 Rev 3
October 2016
EUROPE (EMEA):
+44 (0)1582 723633
mtlenquiry@eaton.com
THE AMERICAS:
+1 800 835 7075
mtl-us-info@eaton.com
ASIA-PACIFIC:
+65 6 645 9888
sales.mtlsing@eaton.com
The given data is only intended as a product description and should not be regarded as a legal warranty of properties or guarantee. In the interest of further technical developments, we reserve the right to make design changes.
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