Emerson Rosemount 644 Reference Manual page 72

Section 4: Operation and Maintenance
April 2015
Shielding recommendations
The following are recommended practices from API Standard 552 (Transmission Standard)
section 20.7, and from field and laboratory testing. If more than one recommendation is given
for a sensor type, start with the first technique shown or the technique that is recommended for
the facility by its installation drawings. If the technique does not eliminate the transmitter
alarms, try another technique. If all of the techniques do not eliminate or prevent the
transmitter alarms because of high EMI, contact an Emerson Process Management representa-
tive.
To ensure proper grounding, it is important that the instrument cable shield be:



Ungrounded thermocouple, mV, Ohm, and RTD 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.
62
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
Connect sensor wiring shield to the transmitter housing.
Ensure the sensor shield is electrically isolated from surrounding fixtures that may be
grounded.
Ground signal wiring shield at the power supply end.
A
A. Sensor wires
B. Transmitter
C. Shield ground point
B
C
Reference Manual
00809-0200-4728, Rev RA
Electrical Installation