SMN
Seite 4 SMN K02/0416
5.Operating Principle
The KOBOLD model SMN flow switch is used when extremely low flow switch
points are required in combination with minimum pressure loss at high flow rates.
The flow switch operates on the well-known float principle.
An orifice float with an integrated circular magnet moves within a cylindrical flow
tube in the direction of the flow and against a spring.
The magnetic field of the float activates a reed contact which is mounted on the
outside of the instrument in a sliding protective casing. Due to the special
construction of the float and flow tube only a low flow is required to raise the float
and hence to activate the reed contact. If the flow rate increases further and the
float reaches the top of its travel an additional flow path opens allowing high flow
rates without a significant increase in the pressure loss.
6.Use in Hazardous Areas
6.1. General
The All Metal Flow Switch does not have a potential igniting source of his own as
a mechanical operating resource; it does not get any identification according
to the guideline 94/9/EC ("ATEX 100a”).
The add-on control contacts can under application of EN 60079-14 be used as a
“simple operator” (simple electrical equipment) without other marking in
intrinsically safe equipment. The following limit values for the switching contact
should not be exceeded: U = 30 VDC, I = 100 mA, P = 1,2 W. It does not get any
identification according to the ATEX-guideline.
The units can be used as follows:
a) In the Zone 2 (Gas-Ex, Cat. 3G) into explosion group of IIA, IIB and IIC
b) In the Zone 22 (Dust-Ex, Category 3D) at non-conductive dusts with a
minimum igniting energy of > 3 mJ
c) In the Zone 1 (Gas-Ex, Cat. 2G) into explosion group of IIA, IIB and IIC
d) In the Zone 21 (Dust-Ex, Category 2D) at non-conductive dusts with a
minimum igniting energy of > 3 mJ
The Flow Switch is filled completely with medium in the normal operation. Zone 2
or zone 1 conditions may be obtained for a short time.
