Operating instructions

12
5 Connecting to power supply
VEGAMET 625 • Double channel HART
28970-EN-150129
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hazardousareasyoumusttakenoteoftherespectiveregulations,
conformityandtypeapprovalcerticatesofthesensorsandpower
supply units.
Thevoltagesupplycanbe20…253VAC/DC,50/60Hz.
The voltage supply of VEGAMET 625 is connected with standard
cable according to the national installation standards.
Standard two-wire cable can be used for connecting the sensors. The
screening is absolutely necessary to ensure interference-free opera-
tion with HART sensors.
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 sensor housing
must be connected to the potential equalisation (low impedance).
If potential equalisation currents are expected, the screen connection
on the side of VEGAMET 625 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eectagainsthighfrequency
interference signals remains.
Take note of the corresponding installation regulations for Ex applica-
tions. In particular, make sure that no potential equalisation currents
ow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 Input mode active/passive
Through the selection of the terminals, you can choose between ac-
tive and passive operation of the measuring data intput.
•
In active mode, VEGAMET 625 provides the power for the
connected sensors. Power supply and measurement data are
transmitted over the same two-wire cable. This mode is provided
for connection of measuring transducers without separate voltage
supply (sensors in two-wire version).
•
In passive mode the sensors are not powered, only the measured
value is transmitted. This input is for connection of transmitters
with their own separate voltage supply (sensors in four-wire
version). The VEGAMET 625 can be also looped into the existing
circuit like a normal ammeter.
Note safety instructions
Take note of safety
instructions for Ex
applications
Select power supply
Select connection cable
Cable screening and
grounding
Select connection
cable for Ex applica-
tions