An insulated electrode is placed in the boiler and the length should be
sufficient to reach the water at all acceptable levels. The insulated electrode
and the boiler work as a capacitor with the water and the steam as a variable
dielectric medium. The capacitance of the ”capacitor” is converted
into a current signal. 0% of water in the level glass corresponds to 4 mA and
100% corresponds to 20 mA.
The measuring result is rather sensitive to
foam in the boiler and deposits on the electrode influences
negatively on the measuring results.
This capacitance electrode measuring method is relatively new as level control
in steam boilers although it has been used for a long time for dry substances
such as grains in warehouses.
|
