Logix™ 3800zb Digital Positioner FCD AIIOM001030_EN 02/23
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6.2.2 Cable Requirements
The Logix 3800zb digital positioner utilizes the HART
Communication protocol. It is superimposed on the 4-20 mA
current signal. The two frequencies used by the HART
protocol are 1200 Hz and 2200 Hz. Calculate cable length
restrictions to prevent distortion of the HART communication
signal and cable capacitance. The cable length must be limited
if the capacitance is too high. Selecting a cable with lower
capacitance/foot rating will allow longer cable runs. In addition
to the cable capacitance, the network resistance also affects
the allowable cable length.
For installation practices and allowable cable lengths refer to
the latest version of the HART Field Communications Protocol
Application Guide, HART HCF LIT.
NOTE: 24–16 AWG gauge wire sizes should be used for
connection to the spring terminals. Wire sizes outside of this
gauge range may not form a good connection or may cause
damage to the terminals.
The input loop current signal to the Logix 3800zb digital
positioner should be in shielded cable. By tying shields to
ground at only one end of the cable removes environmental
and electrical noise. Connect the shield wire to the source, not
at the positioner.
6.2.3 Conduit
This product has three electrical conduit connections in
thread size 1/2" NPT. Located near the conduit connection is
the thread size for the conduit of the positioner. Conduit
fittings must match equipment housing threads before
installation. If threads do not match, obtain suitable adapters
or contact a FLOWSERVE representative.
6.2.4 Grounding
The grounding terminals, located by the electrical conduit
ports should be used to provide the unit with an adequate and
reliable earth ground reference. Tie the outer grounding
terminal to the same ground as the electrical conduit. Tie the
inner grounding terminal to the cable shield.
NOTE: For maximum conducted immunity tie both sides of
the shield to a common earth reference.
Figure 6 shows the conduit and grounding connections on
the positioner.
Figure 15: Conduit and Grounding (HART)
6.2.5 Electromagnetic Compatibility
The Logix 3800ZB digital positioner has been designed, per
standards EN61000-4-3 Radiated Immunity and EN55011
Radiated Emissions, to operate correctly in electromagnetic
(EM) fields found in typical industrial environments. The
following precautions should be taken to adhere to these
standards:
• Do not use the positioner in environments with
excessively high EM field strengths (i.e. greater than 10
V/m)
• Do not use portable EM devices such as hand-held two-
way radios within 30 cm of the device.
Ensure proper wiring and shielding techniques of the control
lines, and route control lines away from electromagnetic
sources that may cause unwanted electrical noise. To help
eliminate noise use an electromagnetic line filter; contact a
FLOWSERVE representative for line filter recommendations.
In the event of a severe electrostatic discharge near the
positioner, the device should be inspected to ensure correct
operability. It may be necessary to recalibrate the Logix 3820
positioner to restore operation.
6.3 Auxiliary I/O Circuits
The Logix 3820 contains the following auxiliary circuits: an
Analog Output (AO), an Analog Input (AI), two Discrete
Outputs (DO1 & DO2) used specifically for controlling the 4-
Way valve block solenoids, a Discrete Input (DI), and the
Remote Mount. Labels for each connection to each circuit are
on the cover adjacent to the terminals.
6.3.1 Analog Output
The Analog Output function produces a 4-20 mA signal that
corresponds to the position of the valve. Output follows actual
position of the valve, including all failure modes of positioner
except the loss of power. An output of < 1.0 mA is transmitted
when the positioner loses power.
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