Vega VEGAPULS 68 Operating Instructions Manual - page 15
5 Connecting to power supply
5.1 Preparing the connection
Always keep in mind the following safety instructions:
l
Connect only in the complete absence of line voltage
l
If overvoltage surges are expected, overvoltage arresters should
be installed
Tip:
We recommend using VEGA overvoltage arresters B63-48 and
ÜSB 62-36G.X.
In hazardous areas you should take note of the appropriate
regulations, conformity and type approval certificates of the sensors
and power supply units.
Power supply and current signal are carried on the same two-wire
cable. The voltage supply range 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 VDE 0106 part 101. The VEGA power supply
units VEGATRENN 149A Ex, VEGASTAB 690 as well as all
VEGAMETs meet this requirement.
Keep in mind the following additional influences on the operating
voltage:
l
Output voltage of the power supply unit can be lower under
nominal load (with a sensor current of 20.5 mA or 22 mA in case of
fault message)
l
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 for industrial areas, screened cable should be
used.
Use cable with round cross-section. A cable outer diameter of 5 … 9 mm
(0.2 … 0.35 in) ensures the seal effect of the cable gland. If you are
using cable with a different diameter or cross-section, exchange the
seal or use a suitable cable gland.
We generally recommend the use of screened cable for HART
multidrop mode.
On the instrument with cable entry ½ NPT and plastic housing there is
a metallic ½" threaded insert moulded into the plastic housing.
Note safety instructions
Take note of
safety instruc-
tions for Ex ap-
plications
Select power supply
Selecting connection
cable
Cable gland ½ NPT
VEGAPULS 68 • 4 … 20 mA/HART two-wire
27
5 Connecting to power supply
29261
-EN
-090305
Caution:
No grease should be used when screwing the NPT cable gland or
steel tube into the threaded insert. Standard grease can contain
additives that corrode the connection between threaded insert and
housing. This would influence the stability of the connection and the
tightness of the housing.
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 equalisation
(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
suppressed, but the protective effect against high frequency interfer-
ence signals remains.
Take note of the corresponding installation regulations for Ex
applications. In particular, make sure that no potential equalisation
currents flow over the cable screen. In case of grounding on both sides
this can be achieved by the use of a capacitor or a separate potential
equalisation.
5.2 Connection procedure
Proceed as follows:
1 Unscrew the housing cover
2 If an indicating and adjustment module is installed, remove it by
turning it slightly to the left.
3 Loosen compression nut of the cable entry
4 Remove approx. 10 cm (4 in) of the cable mantle, strip approx.
1 cm (0.4 in) insulation from the ends of the individual wires
5 Insert the cable through the cable gland into the sensor
6 Lift the opening levers of the terminals with a screwdriver (see
following illustration)
Cable screening and
grounding
Select connec-
tion cable for Ex
applications
28
VEGAPULS 68 • 4 … 20 mA/HART two-wire
5 Connecting to power supply
29261
-EN
-090305