ELECTRICAL CONNECTIONS
4
47
IFC 300
www.krohne.com
06/2009 - 4000069802 - MA IFC 300 R03 en
4.6 Grounding the measuring sensor
4.6.1 Classical method
•
The measuring sensor must be properly grounded.
•
The grounding cable should not transmit any interference voltages.
•
Do not use the grounding cable to connect more than one device to ground at the same time.
•
In hazardous areas, grounding is used at the same time for equipotential bonding. Additional
grounding instructions are provided in the separate Ex documentation, which are only
supplied together with hazardous-duty equipment.
•
The measuring sensors are connected to ground by means of a functional grounding
conductor FE.
•
Special grounding instructions for the various measuring sensors are provided in the
separate documentation for the measuring sensors.
•
The documentation for the measuring sensors also contain descriptions on how to use
grounding rings and how to install the measuring sensors in metal or plastic pipes or in pipes
which are coated on the inside.
4.6.2 Virtual reference
For pipelines which are electrically insulated on the inside (e.g. have an inner liner or are made
completely out of plastic), it is also possible to measure without additional grounding rings or
electrodes.
The signal converter's input amplifier records the potentials of both measuring electrodes and a
patented method is used to create a voltage which corresponds to the potential of the
ungrounded medium. This voltage is then the reference potential for signal processing. That
means there are no interfering potential differences between the reference potential and the
measuring electrodes during signal processing.
Ungrounded use is also possible for systems with voltages and currents in the pipelines, e. g.
electrolysis and galvanic systems.
Thresholds for measuring operation with the virtual reference
DANGER!
There should be no difference in potential between the measuring sensor and the housing or
protective earth of the signal converter!
Size
≥
DN10 /
≥
3/8"
Electrical conductivity
≥
200
µ
S/cm
Signal cable
use only A (type DS 300)
Signal cable length
≤
50 m /
≤
150 ft
Ex operation
is possible, consult with us first
.book Page 47 Wednesday, June 10, 2009 4:20 PM
