Rosemount 3491, Reference Manual, Page: 46 / 152

Reference Manual
00809-0100-4841, Rev. AA
May 2007
Rosemount 3490 Series
4-14
Table 4-3. P117 Options
This feature is particularly useful in an Open Channel Flow application (OCF)
where a small standing or remaining liquid level in the channel would cause
continued totalising of flow when no actual flow exists. For example, set P117
to a +ve (positive) value of flow units, usually around 2% of maximum flow, to
overcome this problem.
P210 allows the user to apply damping to the calculated value of D851.
The final output of Input Channel 1 is readable on D800 and is the PV of the
3490 Series Control Unit, which is shown on the factory default display.
Figure 4-15. 4-20mA Txr Input
Blocks and Parameters (Ch. 1)
Notes:
Optional damping of mA readings:
mA = [mA_ ((mAnow - mA_before)/(1+10 * P321))], @ 10Hz.
P111 Channel 1 Input Source
Select "mA In 1" from list of options. (All other options are for HART.)
P112 Channel 1 input Offset
Use for optional adjustment to the D842 value.
P113 Channel 1 profile selection. Keep the "Scaled" option unless requiring a
profile calculation (see “Profile Calculations for Contents and Flow
Applications“ on page 4-24)
P114 Channel 1 Scaling Factor
This is for scaling the D802 value into required units (P200).
If PV value is liquid level, set P114 to the level measurement represented by
the 20mA output from transmitter.
P117 Channel 1 Output Action
+ve value Drop immediately to zero.
None Continue measuring.
0.0 Hold output at zero.
-ve value Rise immediately to zero.
Conditioning
and damping
mA Input
P321
Normalise
mA to %
Input
Source
Select
P111
D842
mA mA
% %
Apply
Input
Offset
P112
Channel
Profile
Select
D802
(TV)
D840
Apply
Input
Scaling
P114
% % %
mA
D801
(SV)
P113
Low
Cut-off
Check
Scaled
Pr
of
ile
s
Non-Linear Profile Post Scale NLP
(PV)
D800
4-20mA Limit
Alarm Check
<3.7mA
>20.75mA
P117
P115 P116
D851
(CH1 O/P)
P111 = “mA in”
PV
Damping
P210