Description
Non-adjustable on/off level control uses a conductivity probe connected to an electronic controller. The probe typically has three or four tips, each of which is cut to length during installation to achieve the required switching or alarm level (see Figure).
When the tip of the probe is immersed in liquid it uses the relatively high conductivity of the water to complete an electrical circuit via the tank metalwork and the controller.
When the water level drops below the tip, the circuit resistance increases considerably, indicating to the controller that the tip is not immersed in the liquid.
In the case of a simple 'pumping in' system with on/off level control:
- The valve is opened when the tank water level falls below the end of a tip.
- The valve is closed when the water level rises to contact another tip.
- Other tips may be used to activate low or high alarms.
Advantage
A simple but accurate and relatively inexpensive method of level control.
Applications:
The system can be used for liquids with conductivities of 1 µS/cm or more, and is suitable for condensate tanks, feedwater tanks and process vats or vessels. Where the conductivity falls below this level it is recommended that capacitance based level controls are used.
Point to note:
If the tank is constructed from a non-conductive material, the electrical circuit may be achieved via another probe tip.
General arrangement of a non-adjustable on/off level control system for a tank
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