WIKA FLM - Handbuch (Seite 16)

GB
A copper cable having a length of 100 m (100 m forward and 100 m
return line) has a resistance of 3.4 Ω in a cable cross-section of 1 mm².
(R = 0.034 Ω x L(m)/F(mm²). If a supplier generates, for example, 13 V
at 21.5 mA, the resistivity R is allowed to be 3 V/0.0215 A = 139 Ω. If the
cable is of a cross-section of 0.5 mm² , the feeder line is allowed to have
a length L = R(Ω) x F(mm²)/0.034 m = 2044 m.
Connecting pattern in an area exposed to danger of explosion
16 WIKA operating instructions level sensor model FFG
13445627.01 12/2010 GB/D/F
Fig. 5: Connecting diagram of the Ex-design
Model FFG (Ex-design Separating amplifier
5. Electrical connection
Minimum voltage: U
min
= 10 V + 0.0215 A x ∑R
∑R = Sum of all cable resistancess including feeder line and burden
Adjusting measures
Measuring range span
Two keys and one illuminated diode (LED) in the connecting area of the
probe head serve for adjusting the 4 mA- and 20 mA-points. The level
sensor system is adjusted, ex factory, to the maximum range from 4 mA
on the probe base to 20 mA at the probe head. The range of measure-
ment for adaptation to the given container can be individually adjusted;
however, the distance must be no less than 5 mm. Otherwise the indica-
tion direction of the sensor is automatically reversed.
For further details of adjusting the range of measurement reference
(see Fig. 6):
■ Unscrew lid (1) of probe head with open-end wrench
■ Keep 4 mA-key (2) pressed for no less than 3 seconds
Power supply