VEGA VEGAFLEX 81 4 … 20 mA_HART - four-wire Coax probe - Manual (Page 19)

19
5 Connecting to power supply
VEGAFLEX 81 • 4 … 20 mA/HART - four-wire
42280-EN-130314
5 Connecting to power supply
5.1 Preparing the connection
Always keep in mind the following safety instructions:
•
Connect only in the complete absence of line voltage
•
If overvoltage surges are expected, overvoltage arresters should
be installed
In this case, the instrument is designed in protection class II. To main-
tain this protection class, it is absolutely necessary that the ground
conductor be connected to the internal ground terminal. Take note of
the general installation regulations.
Supply voltage and current signal are carried on separate connection
cables if reliable separation is required. The supply voltage range can
differ depending on the instrument version.
The data for power supply are specified in chapter "Technical data".
In this case, the instrument is designed in protection class II. Gener-
ally connect the instrument to vessel ground (potential equalization)
or with plastic vessels to the next ground potential. For this purpose, a
ground terminal is located laterally on the instrument housing.
An approved, three-wire installation cable with PE conductor is
required for voltage supply with mains voltage.
The 4 … 20 mA current output 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.
For instruments with housing and cable gland, use cable with round
cross-section. To ensure the seal effect of the cable gland (IP protec-
tion rating), you have to check for which cable outer diameter the
cable gland is suitable.
•
5 … 9 mm (0.20 … 0.35 in)
•
6 … 12 mm (0.24 … 0.47 in)
•
10 … 14 mm (0.40 … 0.55 in)
Use a cable gland fitting the cable diameter.
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 necessary, connect 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 potential equalisa-
tion (low impedance).
If potential equalisation currents are expected, the connection on the
processing side must be made via a ceramic capacitor (e. g. 1 nF,
1500 V). The low-frequency potential equalisation currents are thus
Safety instructions
Voltage supply via mains
voltage
Voltage supply via low
voltage
Connection cable
Cable gland ½ NPT
Cable screening and
grounding