VEGA VEGAPULS 56V - Manual (Page 12)

12 VEGAPULS 56V
2.2 Configuration of measuring
systems
A measuring system consists of a sensor
and a processing unit. The processing unit
(the signal conditioning instrument VEGAMET
or the processing system VEGALOG) proc-
esses the level proportional digital measuring
signal in a number of processing routines
and provides then the levels as individual
current, voltage or switching signals.
On the signal conditioning instrument VEGA-
MET 515V two sensors can be connected via
one two-wire line. On the processing system
VEGALOG 571 up to 255 sensors can be
connected; 15 sensors (loop powered) on
one two-wire line.
Beside the output of the levels in percent,
cubic metres or other physical units, as cur-
rent, voltage or switching signal (relay or
transistor) the levels can also be processed
via combined processing algorithms. Scal-
ing, linearisation, calculation of linearisation
curves, differential generation, addition or
tendency processing are fixed implemented
in the processing systems VEGALOG and
VEGAMET as processing routines and easily
available via menu choice.
On the following pages you will see different
instrument configurations, called measuring
systems:
• 2 sensors on one two-wire line; (page 13)
• 2 sensors in Ex-area on one two-wire line;
(page 14)
• 15 sensors on one two-wire line; (page 15)
• 5 sensors in Ex-area on one two-wire line;
(page 16)
Ex-area
The sensors with classification EEx␣ ia require
for operation in Ex-areas the Ex-separator
VEGATRENN 548V␣ Ex, providing intrinsically
safe Ex-circuits to the sensors. The sensors
with classification EEx␣ d␣ ia are provided with
a pressure tight encapsulated connection
box. This converts a non-intrinsically safe
supply circuit into an intrinsically safe circuit.
Up to 15 sensors in groups with five sensors
each per two-wire line can be connected to
Ex-separator VEGATRENN 548V␣ Ex
(page
17).
Note!
In Ex-systems earthing on both sides is not
allowed due to the potential difference.
Note:
Sensor lines should be looped in screened
cables. It is suitable (except Ex-systems) to
earth the cable screens on both ends. There-
fore it must be noted that no earth compen-
sation currents flow via the screens. In case
of earthing on both sides earth compensation
currents are avoided by connecting the cable
screen on one earth side (e.g. in the switch-
ing cabinet) via a capacitor (e.g. 0,1␣
µ
F;
250␣ V) to the earth potential.
Sensor lines leading to the same input card
or separator card can be looped together in
a screened multiple wire cable. Sensor lines
leading to other separator cards must be
looped in separated screened cables.
Types and versions