KROHNE BW 25 EN - Manual (Page 22)

4
ELECTRICAL CONNECTIONS
22
BW25
www.krohne.com 09/2010 - 4000432302 MA BW25 R05 en
The circuitry to other devices must be designed with especial care. In some circumstances
internal connections in these devices (e.g. GND with PE, ground loops) may lead to
impermissible voltage potentials, which can compromise the function of the device itself or a
connected device. In such cases a protected extra-low voltage (PELV) is recommended.
HART ® communication
When HART ® communication is carried out with the M10, this will not in any way impair analogue
measured data transmission (4...20 mA).
Exception for multidrop operation. In multidrop operation, a maximum of 15 devices with
HART
® TM function can be operated in parallel, for which the current outputs are switched to
inactive (I approx. 4 mA per device).
Power supply
The required supply voltage can be calculated using the formula below:
U
ext.
= R
L
. 22 mA + 16 V
where
U
ext.
= the minimum supply voltage and
R
L
= the total measuring loop resistance.
1 Terminal connection
2 Converter supply isolator with electrical isolation
3 Power supply (see supply isolator information)
4 Measurement signal 4...20mA
5 External load, HART
® communication
INFORMATION!
The supply voltage has to be between 16 VDC and 32 VDC. This is based on the total resistance of
the measuring loop. To determine this, add up the resistances of each component in the
measuring loop (not including the level meter).
MA_BW25_R05_en_432302_PRT.book Page 22 Tuesday, September 28, 2010 8:17 AM