KROHNE ALTOFLUX 2W IFM 4042K EEx-ATEX EN - Manual (Page 10)

10 ALTOFLUX 2W IFM 4042 K - EEx
2.6.2 Example of IFM 4042 K in 2×2-wire mode (4-wire)
The diagram shows an example of the connection of the IFM 4042 K-EEx in 2x2-wire mode. As in
the previous example (see Sect. 2.6.1), the terminal compartment is again version A.
The additional power supply (terminals 1L=, 0L=) of the IFM 4042 K-EEx is supplied by an
external power supply unit through an "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 notes!
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!
It is strictly interdicted to use the IMoCOM adapter with the IFC040-EEx unit!
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
caused by the end-to-end resistance of the barrier and (if not neglectable) the serie cable
resistance. 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:
U
0
= 28 V
I
0
= 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.
IFM 4042 K-EEx
I
I ⊥
HTT
4-20 mA 4-20 mA
Transmitter Power
Supply (EEx i)
Vs
Hazardous Area
Process/
Display Unit
Safe Area
22 mA
1L=
0L=
+
_
Zener Barrier
External
Power Supply