KROHNE ALTOFLUX IFM4042K EEx EN - Manual (Page 9)

8
Figure 3 on the previous page shows an example of the connection of the IFM 4042 K-EEx in
2x2-wire mode. As in the previous example (figure 2), the terminal compartment of the IFM
4042 K-EEx is performed as version A, which means that it is providfed with type of
protection "EEx de [ib]".
The additional power supply (terminals 1L=, 0L=) of the IFM 4042 K-EEx is supplied by an
external power supply unit through a ATEX approved "EEx i" zener barrier with a linear
output load. The connection of the current output (terminals I, I
⊥
) and the additional power
supply (terminals 1L=, 0L=) is insensitive for polarity reversal.
IMPORTANT !
Only one of the two connected circuits of the IFM 4042 K-EEx, namely the "currrent
output" or the "additional power supply" may be earthed to maintain the required
galvanic separation between the two circuits !
The voltage of the external power supply unit must be carefully chosen to keep it within the
allowed limits. The upper limit is determined by the maximum working voltage of the zener
barrier, which in general lies a few volts below the maximum open voltage value Uo of the
used zener barrier. The lower limit is determined by the sum of the minimum working voltage
of the additional power supply of the IFM 4042 K-EEx flowmeter of 14 V and the voltage drop
over the zenerbarrier that is caused by the end-to-end resistance of the barrier. This voltage
drop can be significant. The above described determination of the external power supply
voltage is explained by the following example.
Example with typical parameters:
Zener barrier data: Uo = 28 V
Io = 93 mA
Maximum working voltage = 25.5 V.
End-to-end resistance = 340
Ω
.
The voltage drop across the end-to-end resistance of the zener barrier is:
22 mA x 340
Ω
= 7.5 V
This means that the external power supply must supply an output voltage to the zener barrier
that lies in the range somewhere between 21.5…25.5 V. The voltage over the terminals of
the additional power supply of the IFM 4042 K-EEx is in that case between the required
14.0…18.0 V.
3. OPERATION OF THE SIGNAL CONVERTER
The IFM 4042 K-EEx contains the IFC 040-EEx signal converter electronics unit, which is
equipped with a display unit that contains magnetic Hall sensors. These Hall sensors enable
the settings of the IFC 040-EEx electronics unit to be set respectively reset with the help of
the with the apparatus delivered bar magnet without opening the flameproof signal converter
housing in the hazardous area.
Consult the standard Installation and Operating Instructions for the program functions of the
software of the IFC 040-EEx electronics unit.