KROHNE H250 M40 FOUNDATION FIELDBUS - Manual (Page 7)

ELECTRICAL CONNECTIONS
3
7
H250 M40
www.krohne.com 02/2014 - 4001208201 - AD H250 M40 FF R02 en
Electrical connections
3.1 Installation in hazardous area and bus cable
We recommend that a Foundation Fieldbus network in the hazardous area should be projected in
accordance with PTB's FISCO model. The FISCO model is based on the following conditions:
• All electrical components which should be connected to the bus must be approved according
to the FISCO model (even the termination).
• The maximum cable length should not exceed 1000 m / 3280.8 ft.
• The approved input values of the field devices (U
0
, I
0
, P
0
) comply to the output values of the
power supply (e.g. segment coupler) according to: U
0
≤ U
i
; I
0
≤ I
i
; P
0
≤ P
i
.
• The values of the cable must be within the following ranges:
R' = 15…150 Ω/km; L' = 0.4…1 mH/km; C' = 45…200 nF/km
equivalent to
R' = 24…240 Ω/mile; L' = 0.65…1.6 mH/mile; C' = 72…320 nF/mile
Other limitations for the cable than the FISCO limitations are not existent. Nevertheless, a
twisted pair and shielded cable is strongly recommended.
Example: a good quality cable could have the following data: 44 Ω/km = 70.4 Ω/mile; <90 nF/km
= <144 nF/mile; attenuation at 39 kHz: <3 dB/km = <4.9 dB/mile; impedance 100 Ω at 31.25 kHz.
3.2 Grounding of measuring section
• The measuring sensor must be properly connected to ground.
• The grounding cable should not transmit any interference voltages.
• Do not use the grounding cable to connect more than one device to ground.
• In hazardous areas, grounding is used at the same time for equipotential bonding.
• The sensors are connected to ground by means of a functional grounding conductor FE.
DANGER!
Special grounding instructions are contained in the "Ex supplement", which are only supplied
together with hazardous-duty equipment.
INFORMATION!
Special grounding instructions for the various measuring sensors are contained in the separate
installation instructions for the measuring sensors. These instructions also contain detailed
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.
AD_H250_M40_FF_R02_en_4001208201_PRT.book Page 7 Friday, February 21, 2014 11:25 AM