Rosemount 1151GP - Grounding

Reference Manual
00809-0100-4360, Rev BA
August 2008
Rosemount 1151
2-16
Shielded cable should be used for best results in electrically noisy
environments. Refer to “Grounding” on page 2-16 for more details.
NOTE
When conduit lines are used, signal wiring need not be shielded, but twisted
pairs should be used for best results. Wiring must be 24 AWG or larger and
not exceed 5,000 feet (1500 meters).
NOTE
A minimum loop resistance of 250
 is required to communicate with a
hand-held HART-based communicator. With 250
 of loop resistance, the
transmitter requires a minimum of 17 volts to output 20 mA. If a single power
supply is used to power more than one Rosemount 1151 Smart transmitter,
the power supply used, and circuitry common to the transmitters should not
have more than 20  of impedance at 1200 Hz.
Grounding Use the following techniques to properly ground the transmitter signal wiring
and case:
Signal Wiring
Do not run signal wiring in conduit or open trays with power wiring or near
heavy electrical equipment. It is important that the instrument cable shield be:
• Trimmed close and insulated from touching the transmitter housing
• Connected to the next shield if cable is routed through a junction box
• Connected to a good earth ground at the power supply end
Signal wiring may be grounded at any one point on the signal loop or may be
left ungrounded. The negative terminal of the power supply is a
recommended grounding point.
Transmitter Case
The transmitter case must be grounded in accordance with national and local
electrical codes. The most effective transmitter case grounding method is a
direct internal connection to earth ground with minimal impedance. The
transmitter case may also be grounded through the process or conduit
connections.
Internal Ground Connection: Inside the field terminals side of the
electronics housing is the internal ground connection screw. This screw is
identified by a ground symbol: .
NOTE
Grounding the transmitter case via threaded conduit connection may not
provide sufficient ground continuity.
NOTE
The transient protection terminal block (page 2-25) does not provide transient
protection unless the transmitter case is properly grounded. Use the
preceding guidelines to ground the transmitter case.
Do not run the transient protection ground wire with signal wiring as the
ground wire may carry excessive current if a lightning strike occurs.