ABB 266 DDS, Manual

Page: 43 / 60

Damping (DAMPING)
Pressure transmitter output signals that are noisy as a result of
the process can be smoothed (damped) electrically.
The additional time constant can be set between 0 s and 60 s
in increments of 0.0001 s. Damping does not affect the value
shown on the digital display as a physical unit. It only affects
the parameters derived from this, such as the analog output
current, free process variable, input signal for the controller,
and so on.
The damping adjustment can be performed in different ways:
• Via the the local HMI:
Enter the menu: > Device Setup > Output Scaling > Damping.
Set the damping to the desired value.
• Via the DD/FDI Software:
See DD/FDI Software Operating Instructions.
• Via the Hand Held Terminal:
See relevant operating instruction.
Transfer function
The 266 Pressure Transmitter provides a selection of output
functions, as follows:
• Linear for differential, gauge and absolute pressure or
level measurements.
• Sq. Root (x) for flow measurements using restriction type
primary element, like orifice plate, integral orifice, Venturi
or Dall tube and similar.
• Sq. Root (x3) for open channel flow measurements using
rectangular or trapezoidal weir.
• Sq. Root (x5) for open channel flow measurements using
V-notch (triangular) weir.
• Bidirectional Flow.
• Custom linearization table.
• Cylindrical lying tank.
• Spherical tank.
These output functions can be activated using a Configuration
Tool (Digital LCD Integral Display, Hand Held Communicator or
PC based software as
ABB Field Information Manager
). The
transfer function can be applied to the analog signal 4 to 20 mA
only or also to the indication (in engineering units).vant
operating instruction.
Linear
Using this function, the relationship between the input
(measured value), expressed in % of the calibrated span and
the output is linear (i.e.: at 0% input, corresponds 0% output -
4mA, at 100% input corresponds 100% output - 20mA).
No further settings are possible here.
Square root
Using this function, the relation between the indicator scele /
output value and the input value is square root.
Figure 50: Linear output
To avoid the extremely high gain errors with the input value
approaching 4 mA, the indicator scale / output value is equal to
Zero Point up to a programmable CUTOFF value. Cutoff value
can be customized between 0% and 20%, referred to the
indicator scale / output range; default value is 6%.
The indicator scale / output value can then be linear with
proper slope and intercept zero up to a programmable LIN
POINT value. The linearization point value could either be 0% or
in between 5% and 20% referred to the indicator scale / output
range; default value is 5%. Square root transfer funtion is finally
applied.
Figure 51: Square-Root transfer functions
LINEAR
POINT
CUTOFF
Y= 0
Y= mX
Y
X
Y= √ X
Cylindric lying tank
This function is used to measure the volumetric level into a
cylindrical horizontal tank with flat ends.
The transmitter calculates the volume from the measured filling
level.
Spherical Tank
This function is used to measure the volumetric level into a
spherical tank.
The transmitter calculates the volume from the measured filling
level.
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