Application Examples
Sand
Glass aggregate
Gravel
Moulding sand
Lime
Ore, crushed
Plaster
Aluminium shavings
Cement
Grain
Pumice
Flour
Dolomite
Sugar beet chips
Kaolin
Fodder
and similar bulk solids
The Nivocompact is an electronic switch.
The entire measuring system consists of:
•
Nivocompact FTC
…
•
power supply and
•
connected control systems, switches,
signal transmitters
(e.g. process control systems, PLC,
relays, microcontactors, lamps, sirens
etc.)
The probe (rod or rope) and the silo wall
form the two electrodes of a capacitor,
with a high frequency voltage between
them.
The limit value is based on the principle
of a discharge circuit:
As long as the probe is in air with a
dielectric constant of
ε
r
= 1, then the
discharge time constant is
τ
= R x C
A
where R is the resistance of the circuit
and C
A
the capacitance of the capacitor
formed by the probe and silo wall.
If bulk material with a high dielectric
constant moves into the electrical field
between the probe and silo wall, then
the capacitance C
A
increases and with
it the time constant
τ
.
The change in the time constant is
evaluated and the Nivocompact is
activated according to its switching
mode.
Note:
Bulk solids should have dielectric
constants
ε
r
≥
2.5.
The Nivocompact is extremely
insensitive to low build-up on the probe
and silo wall as long as the material
does not form a bridge between the
probe and wall (e.g. on the threaded
boss).
The Complete
Measuring System
TI133Y01
FTC 231/331
Power
supply
FTC 131
Power
supply
The capacitance
level limit switches
Nivocompact
FTC 131...FTC 331
in practice
Operation
TI133Y12
ε
r
> 1
ε
r
= 1
The capacitor
consisting of the silo
wall and probe
2
