Tankvision Calculations
Endress+Hauser 53
While the Level gauge is affected by two influences, one related to the thermal effects on the
"wet" part of the tank shell, and one for the "dry" part of the tank shell, the tank capacity is
only affected by the "wet" part of the tank shell.
Hence we also only have to establish the temperature of the "wet" part, i.e. the part in direct
contact with the liquid product.
Wet tank shell temperature
It is unpractical to measure the tank shell temperature for each and individual tank. Hence
one common "estimate" method is used for all tanks. This method is based on the ambien
temperature (Tamb) and the actual liquid product temperature. For most tanks the following
expression is specified in the standards:
L00-NXA82xxx-16-00-00-xx-002
Unfortunately there are also tanks which behave differently. This can be tanks with a real
thermal insulation, but they can also be buried. Hence we had re-write the above equation
so we could use a "insulation factor" I
f
.
L00-NXA82xxx-16-00-00-xx-003
Where:
•T
shell
= Temperature of "wet" tank shell
•T
product
= Temperature of liquid product in tank
•T
ambient
= Ambient temperature
•I
f
= Insulation Factor
Now we can use the I
f
and use one common equation. Selecting the Insulation factor is
simple:
•I
f
= 1.0 for all tanks where the tank is somehow insulated, and
•I
f
= 7/8 for all other tanks
Of course you can modify this setting in the configuration of Tankvision.
Observe the following information!
• In Appendix B you can find a table with some examples as illustration.
• How to obtain the ambient temperature is discussed further on.
Thermal expansion
With the Shell temperature we can now calculated the expansion of the tank capacity. This
factor is indicated with the name CTSh. Late we will see how it applied to the calculated
volume.
The CTSh equation depends on the tank type.
Vertical cylindrical tanks
The equation for vertical cylindrical tanks for the volumetric CTSh is relative easy:
L00-NXA82xxx-16-00-00-xx-004
Where:
• α = Linear thermal expansion coefficient of tank shell material
• δT = Tank Shell Temperature - Tank Calibration temperature
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