Surges/Transients; Ground The Transmitter - Emerson Rosemount 248 Reference Manual

Reference Manual
00809-0100-4825, Rev CB
2.7.1

Surges/transients

The transmitter will withstand electrical transients of the energy level encountered in static
discharges or induced switching transients. However, high-energy transients, such as those
induced in wiring from nearby lightning strikes, welding, heavy electrical equipment, or
switching gears, can damage both the transmitter and the sensor. To protect against
high-energy transients, install the transmitter in a suitable connection head with the
Rosemount 470 Transient Protector. Refer to the Rosemount 470 Transient Protector Product
Data Sheet (Document No. 00813-0100-4191) for more information.
2.7.2

Ground the transmitter

The transmitter operates with the current signal loop either floating or grounded. However,
extra noise in floating systems may affect many types of readout devices. If the signal appears
noisy or erratic, grounding the current signal loop at a single point may solve the problem. The
best place to ground the loop is at the negative terminal of the power supply. Do not ground the
current signal loop at more than one point.
The transmitter is electrically isolated to 500 Vac rms (707 Vdc), so the input circuit may also be
grounded at any single point. When using a grounded thermocouple, the grounded junction
serves as this point.
Note
Do not ground the signal wire at both ends.
Ungrounded thermocouple, mV, and RTD/ohm inputs
Each process installation has different requirements for grounding. Use the grounding options
recommended by the facility for the specific sensor type, or begin with grounding Option 1 (the
most common).
Option 1:
1.
2.
3.
Installation
Connect sensor wiring shield to the transmitter housing (only if the housing is
grounded).
Make sure that the sensor shield is electrically isolated from surrounding fixtures that
may be grounded.
Ground signal wiring shield at the power supply end.
A
B
D
A. Transmitter
B. Sensor wires
C
D
C. 4-20 mA loop
D. Shield ground point
Section 2: Installation
March 2014
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