266CRx, 266JRx, 266CSx, 266JSx | OI/266CXX/266JXX/HART-EN Rev. B 61
Customer-specific linearizaton characteristic curve
The transmission function with a customer-specific
linearization curve is normally used for volume measurement in
tanks with unusual shapes. There is an assignment to a freely-
definable transmission characteristic curve with a maximum of
22 reference points. The first reference point is always the
zero point, the last is the upper range value. These two
reference points cannot be changed. In between a maximum
of 20 points can be freely entered.
These max. 22 points are defined by extrapolating the tank fill
data.
After they are determined, the 22 reference points are loaded
into the device, via a HART handheld terminal or via an
appropriate configuration program such as “Asset Vision
Basic”.
Flow measurement with bidirectional characteristic curve
This method is used if the transmitter is connected to a
bidirectional flow meter (e.g. a wedge meter - wedge-shaped
narrowing). The main characteristics:
The bidirectional transmission function acts an the transmitter
input (x) as a percentage value of the calibrated measuring
span and is calculated with the following formula:
Output = 1/2 + 1/2 sign (x) ∙ x 1/2
In this regard x and the output signal of the transmitter are
scaled in the range from 0 to 1 for the calculation. The output
has the following meaning:
— Output = 0 = analog output signal 4 mA;
— Output = 1 = analog output signal 20 mA;
This function can be used for bidirectional flow rates, for which
the primary device is configured for this application.
Example of a bidirectional flow measurement with the following
data:
— Max. negative flow: -100 t/h
— Max. positive flow: +100 t/h
The differential pressure generated by the primary element of
the flow meter is 2500 mm H2O for the max. positive flow and
2500 mm H2O for the max. negative flow.
Thus the transmitter must be configured as follows:
Set measuring span:
4 mA = LRV = -2500 mm H2O
20 mA = URV = 2500 mm H2O
Transmission function = Bidirectional
Afte
r the transmitter has been configured as described above,
it supplies the following for:
Negative flow of 100 t/h: Output signal = 4 mA
No flow: Output signal = 12 mA
Positive flow of 100 t/h: Output signal = 20 mA
Cylindri
cal horizontal tank
This function is used for the volume measurement in cylindrical
horizontal tanks with straight ends. The transmitter calculates
the volume and / or the mass from the measured fill level.
Spherical tank
This function is used for volume measurement in spherical
tanks. The transmitter calculates the volume and / or the mass
from the measured fill level.
Change from two to one column
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