KROHNE H250 M8-M9-M10 EN - Manual (Page 22)

4
ELECTRICAL CONNECTIONS
22
H250
www.krohne.com 04/2011 - 4000269302 MA H250-R02 en
Power supply M8 with electrical isolation
The circuitry for connection to other devices such as digital evaluator units or process control
equipment 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.
Power supply
The required supply voltage can be calculated using the formula below:
U
ext.
= R
L
. 22 mA + 14.8 V
where
U
ext.
= the minimum supply voltage and
R
L
= the total measuring loop resistance is.
Figure 4-3: Electrical connection M8EG with electrical isolation
1 Terminal connection
2 Converter supply isolator with electrical isolation
3 Power supply (see supply isolator information)
4 Measuring signal 4...20 mA
5 External load, HART
® communication
INFORMATION!
The supply voltage has to be between 14.8 VDC and 30 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 device).
INFORMATION!
The power supply has to be able to supply a minimum of 22 mA.
MA_H250_R02_en_269302_PRT.book Page 22 Tuesday, April 12, 2011 10:17 AM