Damping; Overview Of The Linearization/Strapping Tables - ABB LMT100 Operation Instructions Manual

L M T S E R I E S | M A G N E TO S T R I C T I V E L E V E L T R A N S M I T T E R | O I/ L M T 1 0 0/ 2 0 0 - E N R E V. B

Damping

Level transmitter outputs signals which are noisy as a result of
the process can be smoothed (damped) electrically Damping is
a setting designed to delay the mA output response to a
change in measured level If the process is agitated or splashing
of the liquid is possible, a higher damping value may be
required If the process changes rapidly, a lower damping value
may be needed to increase the response time to a level change
Damping can be described as the time responsiveness of the
device to the change in measured level The relationship
between damping to changes in input can be described in the
following formula where A equals change in measurement
signal, τ equals time and equals the damping value
A(τ) = A*(1-2.71828-t/τ)
From this equation a table and graph can be derived to
illustrate the delay in reaction time due to changes in the
damping value
1.2
1
0.8
0.6
0.4
0.2
0
0 2 4
Response time in multiples of damping input value
Time Multiplier 1τ
% of Input Value 0.63
Figure 30 Damping
The additional time constant can be set between 0 1 seconds
and 60 seconds in increments of 0 1 seconds Damping does
not affect the value shown on the digital display as a physical
unit Damping only affects the parameters derived from it, such
as analog output current, free-process variable, input signal for
the controller and so forth The damping adjustment can be
performed through the HMI display or DTM or handheld
terminal
6 8 10
2τ 3τ 4τ
0.86 0.95 0.98
Damping adjustment through HMI display
Level transmitter outputs signals which are noisy as a result of
the process can be smoothed (damped) electrically
1 Enter the menu: Device Setup
2 Press
to select PV Setup
3 Press to confirm the selection
4 Press to select PV Damping time
5 Press to confirm the selection
6 Press to edit the PV Damping Time

Overview of the linearization/strapping tables

Linearization is an approximation to a function at a given point
The LMT has 21 linearization points available for implementing
up to 20 segments of linear calibration
Linearization allows significant improvements of the accuracy
of the measurement in tanks and vessels with irregular shapes
where otherwise the resulting PV calculation would not meet
the expected accuracy due to the non-linear function between
the level in the tank and the resulting PV
For effective use of the multipoint calibration using
linearization tables is important to understand the advantages
that it provides and the limitation of its use
Typically, there is need for linearization/strapping tables when
the user intends to use Volume or Flow as the PV and the
application is in tanks and vessels with irregular shapes where
the function between the level in the tank and the resulting PV
is non-linear
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