Emerson Rosemount 3490 Series Reference Manual page 64

Getting started
January 2021
Figure 4-11: Transmitter Input Channel 1 for 4–20 mA Input
P111 = "mA in"
A
A. mA Input
B. Conditioning and damping
C. 4-20mA Limit Alarm Check
D. Normalize mA to %
E. Input Source Select
F. Apply Input Offset
G. Apply Input Scaling
H. Channel Profile Select
I. Low Cut-off Check
J. PV Damping
K. Non-Linear Profile
L. Post Scale NLP
Optional damping of mA readings ten times a second: mA = [mA_before + ((mAnow -
mA_before)/(1+10 × P321))]
Optional damping of control unit PV ten times a second: D800 = [D800before +
((D800now - D800before)/(1+10 × P210))]
Signal conditioning and damping stages
Analog measurements (level, pressure, and temperature, etc.) are input to the control unit
as a 4–20 mA signal, and pass through a conditioning stage (to remove spikes) and a
damping stage (to smooth out large jumps in signals).
The damping can be adjusted by changing the time setting (in seconds) in parameter
P321. Navigate to the menu SETUP → [CONTROLLER] → INPUT CHANNEL → Cur I/P
Damping.
Signal limits check
The signal is then checked to ensure it is within the range of 3.7 to 20.75 mA. Signals
outside this range cause an alarm condition, which may be externally signaled using a
control unit relay (see
Conversion of signal into a percentage value
By default, the mA signal (readable via D840) is converted (normalized) into a percentage
in the range 0 to 100% (readable via D842), where 4 mA is 0% and 20 mA is 100%.
64
P321 <3.7mA
mA mA
B C D840
>20.75mA
Scaled
H
P115
P113
K
Alarm indication
P111
mA
% %
D D842 E
P116
P117
L
selection).
Reference Manual
00809-0100-4841
P112 P114
(TV)
% % %
F D802 G
(PV)
(CH1 O/P)
I J
D851 D800
P210
Emerson.com/Rosemount
(SV)
D801