Emerson Rosemount 3308, Справочное руководство

Страница: 58 / 128

Reference Manual
00809-XXXX-4811, Rev AA
February 2012
Rosemount 3308
5-4
PRELIMINARY
Tank Height
The Tank Height is the distance from the Upper Reference Point to the bottom
of the tank. The transmitter measures the distance to the product surface and
subtracts this value from the Tank Height to determine the level.
Probe Length
The probe length is the distance between the Upper Reference Point and the
end of the probe. If a weight is used at the end of the probe it shall not be
included.
This parameter is pre-configured at factory. It must be changed if the probe is
shortened.
Probe Type
The transmitter is designed to optimize measurement performance for each
probe type.
This parameter is pre-configured at factory. This value needs to be changed if
the probe type is changed.
Dielectric Constant of Upper Product
For interface measurements the dielectric constant of the upper product is
essential in order to obtain good accuracy. See section “Interface” on
page 2-7 for further information on dielectric constants.
If the dielectric constant of the lower product is significantly smaller than the
dielectric constant of water, you may need to make special adjustments. See
section “Interface Measurements for Semi-Transparent Bottom Products” on
page 7-5 for further information.
For level measurements the Upper Product Dielectric parameter corresponds
to the actual dielectric constant of the product in the tank. Normally this
parameter does not need to be changed even if the actual dielectric constant
of the product deviates from the Upper Product Dielectric parameter value.
However, for some products measurement performance can be optimized by
setting the proper product dielectric constant.
Dielectric Constant of Vapor
In some applications there is heavy vapor above the product surface having a
significant influence on the level measurement. In such cases the vapor
dielectric can be entered to compensate for this effect.
The default value is equal to 1 which corresponds to the dielectricity of
vacuum. Normally this value does not need to be changed since the effect on
measurement performance is very small for most vapors.