Reference Manual
00809-0100-4841, Rev. AA
May 2007
Rosemount 3490 Series
4-24
The 3490 Series Control Unit has a library of non-linear profiles. After a profile
is selected through parameter P113, the 3490 automatically recalls the profile
from memory and populates P115. The standard non-linear profiles require an
input signal over the range 0 - 1.0. Parameter P114 is therefore used to scale
the input signal over the range 0 - 1.0, as described below:
Standard 4-20mA input (Figure 4-15 on page 4-15):
• P200 (PV units) must have changed from "%" to the required units of
measurement.
• The transmitter's 4-20mA output should be scaled to give a 4-20mA signal
over the full height of the vessel, in which case P114 may be left at the
default value of 1.0.
• If the transmitter's 4-20mA output is not scaled to give a 4-20mA signal
over the full height of the vessel, P114 must be used to re-scale the signal
ready for input to the NLP calculation.
• For example, if the maximum current input is below 20mA for a full vessel,
say 18mA, re-scale using P114, calculating: P114 = (Current span Actual
current span) = 16 (18-4) = 1.143
• Refer now to “Non-linear Profile (NLP) calculation”.
HART digital input (Figure 4-17 on page 4-21):
• P200 (PV units) must be set to the required units of measurement.
• The maximum value of level from the HART transmitter must be equal to
the height of the liquid when the vessel is full.
• The level measurement, after any input offset has been applied, must be
re-scaled to the range 0 - 1.0 ready for input to the NLP calculation.
For example, if the level range is 0 - 4.0, then P114 = (1.0 / 4.0) = 0.25.
• Refer now to Section “Non-linear Profile (NLP) calculation”.
Non-linear Profile (NLP) calculation
With P113 set to the NLP required and P114 correctly calculated, P115 will
have been automatically programmed with the correct NLP. P116 is always
programmed with the maximum contents of the vessel in the units chosen
(P200).
Some examples of popular NLP applications are shown below:
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