KROHNE OPTITEMP TRA-TCA EN - Manual (Page 34)

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OPERATION
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OPTITEMP TRA/TCA
www.krohne.com 08/2010 - 4000630501 - MA OPTITEMP TRA/TCA R01 en
Temperature indication too high or too low
When reference measurements result in an incorrect temperature indication, three causes
come into question:
• Severe thermal dissipation caused by too short insertion length of thermowell or measuring
insert: the thermometer indicates a temperature that is too low when it is above the ambient
temperature and one that is too high when it is below the ambient temperature.
• Severe thermal dissipation via the process connection, the pipeline or the tank wall due to a
lack of insulation.
• Incorrect thermowell dimensions (diameter, wall thickness).
To keep thermal dissipation to a minimum, either increase the insertion length of the
thermometer or improve the insulation of the measuring point. You can implement these
measures together or separately.
Slow response to changes in temperature
If the measuring insert is not resting firmly on the bottom of the thermowell, the response to any
changes in temperature may be slowed. So, ensure that the measuring insert touches the
bottom of the thermowell using the spring-loaded mounting. If the thermometer is to react to
changes in temperature as quickly as possible, the manufacturer recommends thermowells
with a tapered or reduced tip.
Damage to the thermowell and penetrating liquid
If the thermowell is not sufficiently resistant to chemically aggressive media, corrosion may
occur and the measured medium may penetrate. In case of doubt, choose a thermowell made of
the same material as the pipe or tank in which the medium is located.
Breaks or tears
It is possible for breaks or tears to occur due to the force of the media flowing against the
thermowell. It is also possible for vibrations in the resonance range to damage or destroy the
thermowell. Superimposition of the two causes or a combination of insufficient mechanical and
chemical resistance is also possible. The following are starting points for troubleshooting:
• Selection of a thermowell with different dimensions
• Change in neck tube length at critical head resonances
• Selection of a different installation site
.book Page 34 Tuesday, August 17, 2010 12:18 PM