VEGA VEGADIF 55 4 … 20 mA_HART - Manual (Page 27)

5 Connecting to power supply
5 .1 Preparing the connection
A
lways keep in mind the following safety instructions:
l C onnect only in the complete absence of line voltage
l I f overvoltage surges are expected, overvoltage arresters should
be installed.
Tip:
W
e recommend using VEGA overvoltage arresters B63-48 and
ÜSB 62-36G.X.
I
n hazardous areas you should take note of the appropriate
regulations, conformity and type approval certificates of the sensors
and power supply units.
P
ower supply and current signal are carried on the same two-wire
cable. The voltage supply range can differ depending on the
instrument version.
D
ata for power supply is specified in chapter "Technical data".
P rovide a reliable separation between the supply circuit and the mains
circuits according to DIN VDE 0106 part 101. The VEGA power supply
units VEGATRENN 149AEx, VEGASTAB 690, VEGADIS 371 as well
as all VEGAMETs meet this requirement.
B ear in mind the following factors regarding supply voltage:
l O
utput 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)
T he instrument is connected with standard, twisted and screened two-
wire cable with round cross section. An outer cable diameter of 5 ...
9
mm (0.2 ... 0.35 in) ensures the seal effect of the cable gland.
O
ptimum shielding agains intefering influences can be achieved if the
screening is connected to both sides (in the switching cabinet and on
the instrument). If potential equalisation currents are expected, the
screening must be earthed only on one end, preferably on the
transmitter.
N ote the corresponding regulations when used in hazardous areas. All
E x instruments are shipped with a separate Ex documentation with
additional technical data and instructions.
P rovide potential equalisation inside and outside hazardous areas.
C onnect all instruments to the local potential equalisation.
I nstruments with integrated overvoltage protection must be grounded.
Note safety instructions
Take note of
safety instruc-
tions for Ex ap-
plications
Select power supply
Selecting connection
cable
Cable screening and
grounding
Select connec-
tion cable for Ex
applications
VEGADIF 55 • 4 … 20 mA/HART 27
5 C onnecting to power supply
31731
-EN
-081119