Manual

14 Pressure transmitters D76 and D77
Electrical connection
4 Electrical connection
4.1 Connection instructions
The electronics in the pressure transmitter
requires a supply voltage of 12 … 36 V DC. It
is provided by two-wire technology, i.e. sup-
ply voltage and measuring signal are trans-
mitted via the same two-wire connection
cable.
The supply voltage is provided via a power
supply unit, e.g.:
- power supply unit VEGASTAB 690
- processing unit with integrated DC current
source (e.g. active PLC input)
- VEGAMET, VEGALOG or VEGADIS 371
Make sure that the supply voltage is reliably
separated from the mains circuits acc. to DIN
VDE 0106, part 101. VEGA instruments meet
this requirement and protection class III is
therefore ensured.
The terminal voltage on the transmitter de-
pends on the following factors:
- output voltage U
H
of the power supply
under nominal load.
- electrical resistance of the connected in-
struments in the circuit.
Note the following instructions for electrical
connection:
- Connection must be made according to the
specific installation standards (e.g. in Ger-
many acc. to the VDE regulations).
- Terminal voltage must not exceed 36 V, to
avoid damage to the electronics.
- Electrical connection must have a pre-
ventative measure against inadvertent
polarity reversal.
- The pressure transmitter can be connected
with standard two-wire cable.
- Screened cable is recommended, if strong
electromagnetic interference is to be ex-
pected. The screening must be grounded
at both ends. Please note the installation
regulations for mounting in Ex areas.
- If overvoltages are expected, we recom-
mend pressure transmitters with integrated
overvoltage arrester or the installation of
VEGA overvoltage arresters.
- In the cable connection, a seal must be
used which fits the cable.
Safety information for Ex applications
As a rule, do all work in the complete ab-
sence of line voltage. Always switch off the
power supply before you carry out connect-
ing work on the sensors. Protect yourself and
the instruments.
Qualified personnel
Instruments which are operated in Ex areas,
must be connected only by qualified person-
nel. The qualified personnel must observe
and understand the installation regulations
and the attached type approval and con-
formity certificates.
In hazardous areas, the required regulations
and conformity and type approval certificates
of the sensors and separators or safety
barriers must be observed (e.g. DIN VDE
0165). Sensors used in Ex areas must be
operated only on intrinsically safe circuits.
The permissible electrical values are stated in
the type approval or conformity certificate.
Intrinsically safe circuits with more than one
active instrument (delivering electrical en-