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Safety instructions
Voltage supply
Connection cable
Cable gland ½ NPT
Cable screening and
grounding
LEVEL TRANSMITTER 8136 • 4 ... 20 mA/HART - two-wire
5
Connecting to power supply
5.1
Preparing the connection
Always keep in mind the following safety instructions:
Warning:
Connect only in the complete absence of line voltage.
•
The electrical connection must only be carried out by trained
personnel authorised by the plant operator.
•
If overvoltage surges are expected, overvoltage arresters should
be installed.
Power supply and current signal are carried on the same two-wire
cable. The operating voltage can differ depending on the instrument
version.
The data for power supply are specified in chapter "Technical data".
Provide a reliable separation between the supply circuit and the
mains circuits according to DIN EN 61140 VDE 0140-1.
Keep in mind the following additional influences on the operating
voltage:
•
Lower output voltage of the power supply unit under nominal load
(e.g. with a sensor current of 20.5 mA or 22 mA in case of fault)
•
Influence of additional instruments in the circuit (see load values in
chapter "Technical data")
The instrument is connected with standard two-wire cable without
screen. If electromagnetic interference is expected which is above the
test values of EN 61326-1 for industrial areas, screened cable should
be used.
Use cable with round cross section for instruments with housing and
cable gland. To ensure the seal effect of the cable gland (IP protection
rating), find out which cable outer diameter the cable gland is suitable
for.
Use a cable gland fitting the cable diameter.
We generally recommend the use of screened cable for HART multi-
drop mode.
With plastic housing, the NPT cable gland or the Conduit steel tube
must be screwed without grease into the threaded insert.
Max. torque for all housings see chapter "Technical data".
If screened cable is required, we recommend connecting the cable
screen on both ends to ground potential. In the sensor, the screen
must be connected directly to the internal ground terminal. The
ground terminal on the outside of the housing must be connected to
the ground potential (low impedance).
In Ex systems, the grounding is carried out according to the installa-
tion regulations.
5 Connecting to power supply
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