Flowserve Logix 3800zb User Manual

Logix™ 3800zb Digital Positioner FCD AIIOM001030_EN 02/23
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7 OPERATION - HOW IT WORKS
7.1 Basic Operation (HART)
The Logix 3800ZB digital positioner is a two-wire 4-20 mA
input digital valve positioner which uses the HART protocol to
allow two-way remote communications. The positioner is
completely powered by the 4-20 mA input signal. Start-up
current must be at least 3.8 mA. The positioner is configurable
through the local user interface, hand-held or DTM. The Logix
3800zb positioner can control both double and single-acting
pneumatic actuators with linear or rotary mountings.
The Logix 3800zb digital positioner is an electronic and
pneumatic closed-loop feedback instrument. Figure 21 shows
a schematic of the Logix 3800zb.
7.2 Position Definition
Inn Analog HART mode, the position at 0% is always defined
as the valve in a closed position and 100% is always defined
as the valve in an open position.
In HART Analog Source, the 4-20 mA signal is converted to a
position (in percent). During loop calibration, the signals
corresponding to 0% and 100% are defined.
7.3 Command Input and Final Command
The Command Input signal (in percent) passes through a
characterization/limits modifier block. This function is done in
software, which allows for in-the-field customer adjustment.
The characterization block can apply no adjustment (Linear),
one of several pre-defined characterization curve adjustments
(including several Equal Percent), or a 21-point custom
characterization curve adjustment. In Linear mode, the input
signal is passed straight through to the control algorithm in a
1:1 transfer. With the pre-defined Equal Percent (=%)
characterization curve, the input signal is mapped to a
standard rangeability equal percent curve. If custom
characterization is enabled, the input signal is mapped to a
custom, user-defined 21-point output curve. The custom user-
defined 21-point output curve is defined using a handheld or
ValveSight software. Also, two user-defined features, soft
limits and tight shutoff may affect the position. The actual
command being used to position the stem after the evaluation
of characterization curves and user limits is called the final
command.
Figure 21: Principles of Operation of Logix 3800zb
Air Supply
4-Way
Valve
Digital
Output
Control
Position
Feedback
Control
Valve
Actuator
Final
Command
Command
Input
Signal
Characterization,
Soft Limits,
Tight Shutoff
Digital
Command
Input
Analog
Command
Input
(4-20 mA)
P
+
_
Σ
HART

Flowserve Logix 3800zb Specifications

General

Brand	Flowserve
Model	Logix 3800zb
Category	Industrial Equipment
Language	English