Connecting To Power Supply; Preparing The Connection; Input Mode Active/Passive; Connection Procedure - Vega MET 381 EX Mise En Service

5 Connecting to power supply

5 Connecting to power
supply
5.1

Preparing the connection

Note safety instructions
Always keep in mind the following safety inst-
ructions:
•
Connect only in the complete absence of
line voltage
•
If overvoltage surges are expected, overvol-
tage arresters should be installed
Take note of safety instructions for Ex
applications
In hazardous areas you must take note
of the respective regulations, conformity
and type approval certificates of the
sensors and power supply units.
Select power supply
The power supply can be 20 ... 253 V AC,
50/60 Hz or 20 ... 253 V DC.
Select connection cable
The voltage supply of VEGAMET 381 Ex is
connected with standard cable according to the
national installation standards.
The instrument is connected with standard
two-wire cable without screen. If electromag-
netic interference is expected which is above
the test values of EN 61326 for industrial areas,
screened cable should be used.
Cable screening and grounding
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 outside on the
sensor housing must be connected to the
potential equalisation.
If potential equalisation currents are expected,
the screen connection on the side of VEGAMET
381 Ex 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
interference signals remains.
Select connection cable for Ex applications
Take note of the corresponding instal-
lation regulations for Ex applications. In
24
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

Input mode active/passive

On the rear of the instrument you can find a
cover which can be opened with a screwdriver.
Subjacent there is a slide switch by means of
which you can switch over between active and
passive mode of the measuring data input.
•
In active mode, VEGAMET 381 Ex provides
the power for the connected sensors. Power
supply and measurement data are transmit-
ted 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 powe-
red, only the measured value is transmitted.
This input is for connection of transmitters
with their own separate voltage supply (sen-
sors in four-wire version). The VEGAMET
381 Ex can be also looped into the existing
circuit like a normal ammeter.
The position of the slide switch also
influences the preconditions for Ex
implementation. Take note of the type
approval certificate or the conformity
certificate ofVEGAMET 381 Ex.
5.3

Connection procedure

Proceed as follows:
1. Mount VEGAMET 381 Ex
2. Connect sensor cable to terminal 1 and 2,
and where applicable, connect the screen
3. Connect power supply (switched off) to
terminal 5 and 6
4. If necessary, connect fail safe and operating
relay as well as current output
The electrical connection is finished.
After connection, it is absolutely ne-
cessary to plug the blue Ex separating
chamber to terminals 1 and 2 (sensor
input). This ensures the required dis-
tance of at least 50 mm (1.97 in) to other
VEGAMET 381 Ex • 4 ... 20 mA signal conditioning instrument