Rosemount 3491, Справочное руководство, Страница: 51 / 152

Reference Manual
00809-0100-4841, Rev. AA
May 2007
4-19
Rosemount 3490 Series
Setting up Input Channel 1 for a HART input
This section is applicable if a HART transmitter is connected.
NOTE:
The "Duty" Wizard is recommended for configuring an application.
Menu: SETUP / [CONTROL UNIT /] DUTY(Mode) / Duty Wizard
The HART transmitter digitally communicates pre-calculated values of the
four variables (PV, SV, TV and FV) to the 3490 Series Control Unit. The
values are received continuously by the 3490 Series Control Unit and stored
in parameters D900 to D903. Parameter P111 nominates one of these four
variables to be the source for the PV value of Input Channel 1.
Figure 4-17 on page 4-21 is an overview of the data flow through the channel.
P112 is a +ve or -ve % input offset for optimal adjustment of the normalised
percentage i.e. D802 = D842 + P112. As an example, this feature may be
used to accommodate a standing value of level in a tank. The output is
readable on D802 and is the Tertiary Value (TV) of the 3490 Series Control
Unit.
Where pre-calculated content or flow values are coming from the transmitter,
P113 need only be set to "scaled". In such a case, parameter P114 is used
only to adjust the value into units that match the display units you may have
changed (P200).
Where pre-calculated level values are coming in from the HART transmitter,
P113 can be set to "scaled" if wanting just level measurement; use P114 as
above. Otherwise, P113 can be set to a profile for generating content or flow
values. For the programming details involving various supported profiles, refer
to Section “Profile Calculations for Contents and Flow Applications“ on
page 4-24.
P117 is a low cut-off parameter that allows the user to force the channel 1
output (D851) to be zero when the calculated value falls below a user defined
value:
Table 4-5. 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 Channel 1 is readable on D800 and is the PV of the 3490
Series Control Unit, which is shown on the display.
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.