KROHNE OPTITEMP Compact sensors - Manual (Page 20)

3
INSTALLATION
20
OPTITEMP TRA-CXX
www.krohne.com 02/2014 - 4003290501 - MA OPTITEMP TRA-Cxx R01 en
3.5 Load limits
The load limits of compact sensors depend on several factors:
• Dimensions and design of the measuring tip (especially the insertion length and diameter)
• Tip material
• Mechanical conditions the tip is subject to due to the measured medium (pressure,
temperature, flow velocity, viscosity, density)
• Sealable pressure of the process connection
• Vibration load
The sheer number of factors at play illustrates the difficulty in making universally valid
statements about the load limits. For further information, please contact the manufacturer.
3.5.1 Vibration load
All industrial temperature assemblies that feature an insert and neck tube and are attached to
the process connection have two components that can vibrate: the insert and the neck tube with
the neck tube. That is why the terms "insert resonance" and "neck tube resonance" are
commonly heard.
An insert 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.
3.5.2 Temperature load
The temperature of the measured medium and the thermal dissipation via thermowell and neck
tube also cause the connection to heat up. After some time, the interior of the neck tube and any
existing transmitter heat up to the temperature of the neck tube.
This occurs in thermometers with and without neck tubes. A neck tube, however, causes thermal
decoupling and can prevent the connection or temperature transmitter from overheating at high
process temperatures.
INFORMATION!
The "sealable pressure" is the maximum pressure the process connection can seal against.
CAUTION!
Permanently operating the sensor tip in its natural resonance can quickly damage or destroy the
temperature assembly! So, prior to installation, ensure that this does not happen and select a
sensor tip with a different length, a different diameter or another material if necessary.
CAUTION!
When the temperature is too high, the connection and the components found in the neck tube
(e. g. temperature transmitter) can be damaged or destroyed! It is your responsibility as the
operator to ensure that the connection and transmitter does not get too hot. If this does happen,
select another installation site or a longer neck tube.
.book Page 20 Friday, February 7, 2014 9:17 AM