Power Supply - Emerson Rosemount 148 Reference Manual

Installation
June 2019
2.6

Power supply

The power supplied to the transmitter should not drop below the transmitter lift-off
voltage of 12 Vdc.
2.6.1 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 lightening strikes, welding, heavy electrical
equipment, or switching gears, can damage both the transmitter and the sensor.
2.6.2 Ground the transmitter
The transmitter will operate with the current signal loop either floating or grounded.
However, the extra noise in floating systems affects 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 at 500 Vac rms (707 Vdc) at 50/60 Hz, 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, 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 the
grounded housing option (the most common).
Ground the transmitter: Option 1
Use this method for grounded housing.
Procedure
1. Connect sensor wiring shield to the transmitter housing.
2. Ensure the sensor shield is electrically isolated from surrounding fixtures that may
3. Ground signal wiring shield at the power supply end.
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be grounded.
Reference Manual
00809-0100-4148
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