Signal Integrity - Emerson Rosemount 2151N Reference Manual

Reference Manual
00809-0000-4851 Rev AD
December 2023

Signal Integrity

Installation
Signal wiring need not be shielded, but twisted pairs yield the
best results. Shielded cable should be used for best results in
electrically noisy environments. Do not run signal wiring in
conduit or open trays with AC power wiring, or near heavy
electrical equipment.
For installations with EMC performance requirements, consult
the applicable EMC test reports for additional details regarding
recommended practices for electrical wiring per various
national and international codes and regulations.
The capacitance sensing element uses alternating current to
generate a capacitance signal. This alternating current is
developed in an oscillator circuit with a nominal frequency of
110 kHz +/- 11 kHz. This 110 kHz signal is capacitively-
coupled to the transmitter case ground through the sensing
element. Because of this coupling, a voltage may be imposed
across the load, depending on choice of grounding.
This impressed voltage, which is seen as high frequency
noise, has no effect on most instruments. Computers with
short sampling times in a circuit where the negative transmitter
terminal is grounded can detect a significant noise signal.
Filter this signal out by using a large capacitor (1 uf) or a 110
kHz LC filter across the load. Signal loops grounded at any
other point are negligibly affected by this noise and do not
need filtering.
Signal wiring may be ungrounded (floating) or grounded at any
one point in the signal loop.
The transmitter case may be grounded or ungrounded.
Grounding should be completed in accordance with national
and local electrical codes. Transmitter case can be grounded
using either the internal or external ground connection.
Internal Ground Connection: The Internal Ground
•
Connection screw is inside the terminal side of the
electronics housing (see Figure 2-7). The screw is
identified by a ground symbol (
2151N transmitters.
External Ground Assembly: The External Ground
•
location is indicated by the ground symbol (
module (see Figure 2-5). An External Ground
Assembly kit can be ordered as an option on the
2151N transmitter. This kit can also be ordered as a
spare part. Please contact Rosemount Nuclear for
ordering information.
Rosemount 2151N
), and is standard on
) on the
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