Emerson 3051S Dokumentacja Strona 26

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24
Reference Manual
00809-0100-4803, Rev DA
Section 2: Installation
April 2013
Installation
Note
Grounding the transmitter case using the threaded conduit connection may not provide a
sufficient ground. The transient protection terminal block (Option Code T1) will not provide
transient protection unless the transmitter case is properly grounded. See “Grounding” on
page 2-25 to ground the transmitter case. Do not run transient protection ground wire with
signal wiring; the ground wire may carry excessive current if a lightning strike occurs.
Signal wire grounding
Do not run signal wiring in conduit or open trays with power wiring, or near heavy electrical
equipment. Ground the shield of the signal wiring at any one point on the signal loop. See 2-12.
The negative terminal of the power supply is a recommended grounding point.
Figure 2-12. Signal wire grounding
Power Supply 4–20 mA transmitters
The dc power supply should provide power with less than two percent ripple. Total resistance
load is the sum of resistance from signal leads and the load resistance of the controller,
indicator, and related pieces. Note that the resistance of intrinsic safety barriers, if used, must
be included.
See “Load limitationson page 2-17 for transmitter resistance load limits.
Note
A minimum loop resistance of 250 ohms is required to communicate with a 375 Field
Communicator. If a single power supply is used to power more than one 3051S MultiVariable
transmitter, the power supply used and circuitry common to the transmitters should not have
more than 20 ohms of impedance at 1200 Hz.
DP
Trim shield and
insulate
Insulate Shield
Connect Shield
Back to the Power
Supply Negative
Terminal
Minimize Distance
Positive
Negative
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