KROHNE OPTITEMP TRA-TCA Plus EN - Manual (Page 32)

3
INSTALLATION
32
OPTITEMP TRA/TCA PLUS
www.krohne.com 01/2012 - 4000630301 - MA OPTITEMP TRA/TCA Plus R01
3.5.2 Vibration load
All thermometers that feature a thermowell and neck tube and are attached to the process
connection have two components that can vibrate: the thermowell and the connection head with
the neck tube. That is why the terms "thermowell resonance" and "head resonance" are
commonly heard.
A thermowell surrounded by the measured medium is a body behind which vortices periodically
are released ("Kármán vortex street"). If the frequency of the vortex detachment is equal to the
resonance frequency of the thermowell, it starts to vibrate. If this happens for a short period of
time, such as when starting up the system and the frequency of the vortex detachment passes
through the resonance range of the thermowell, there is generally no damage is caused. The
opposite is true, however, if the vibrations remain permanently in the resonance range.
3.5.3 Temperature load
For this reason, all of the industrial thermometers for advanced requirements feature a neck
tube. It causes extensive thermal decoupling and can prevent the connection head and the
temperature transmitter from overheating at high process temperatures.
CAUTION!
Permanently operating the thermowell in its natural resonance can quickly damage or destroy
the thermometer! So, prior to installation, ensure that this does not happen and select a
thermowell with a different length, a different diameter or another material if necessary.
CAUTION!
When the temperature is too high, the connection head and the components found in it
(e. g. temperature transmitter or display) can be damaged or destroyed! It is your responsibility
as the operator to ensure that the connection head does not get too hot. If this does happen,
select another installation site or lengthen the neck tube or, with insertion-type thermometers,
increase the distance between the connection head and the process connection.
CAUTION!
Sometimes even a neck tube cannot prevent the maximum permissible temperature in the
connection head from being exceeded! It does cause extensive thermal decoupling of the
connection head but you still have to always take into consideration the installation situation as
well as the ambient and process temperatures!
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