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Liquid Level Controller with control relay for use in process tanks and vessels


Level Controller

Liquid Level Controllers are designed to offer process control based on the level or height of liquid, most commonly contained within a tank or process vessel.

Liquid level controllers work by providing a low voltage electrical circuit to a an immersion type or dip type level electrode which is submerged into the vessel. The level controller detects the electrical resistance between the electrodes at desired levels and provides a relay contact to a piece of process control equipment or a contact closure to another electrical device (such as an alarm circuit or telemetry device).

Level controllers are commonly used for filling tanks, emptying tanks and our range of level controllers are designed to operate as fail safe to fill or fail safe to empty with a user selectable switch depending on the operation type.

Level Controller Principle of Operation

The Level controller works by providing a low voltage electrical current to the level electrodes - when the rising or falling liquid level makes or breaks the contact between the level electrode - the signal is amplified by the level controller to energise or de-energise the relay.

Using a 2 level electrode principal is the easiest way to operate the level controller - using this principle when a single electrode is covered by the liquid a circuit is not made - when the liquid level rises to cover both electrodes - the circuit is made triggering a change of state in the relay (either energise or de-energise) which can be used trigger an alarm.

As some process solutions are foaming solutions - this can cause problems with conductivity level electrodes and level controllers.

To prevent foaming from causing problems with our level controller - we have an adjustable sensitivity on the level controller, to allow the commissioning engineer to ensure that the sensitivity is reduced so that a circuit contact is made only when the process liquid touches the electrode and not the foam. This ensures that the switching only takes place when the more conductive liquid makes or breaks the level control circuit. 

Level Controller Latching Circuit

One very important principle of operation of a level controller is latching between two points.

We supply our range of level electrode holders with 3 x level electrodes or 5 x level electrodes to ensure that there is always a reference electrode and a minimum of two points for the level controller to work between.

This means that the level controller can be configured so that it operates between two levels.

So - when a tank is being filled - the level controller will wait until the start level electrode is reached and then fill until the second higher level electrode has been reached.

Using the latching nature of the level controller - its possible to use additional relays to ensure that effects such as turbulence on the liquid level caused by industrial mixers can be circumvented. If this effect isn't ignored  - then the relays respond to a rapidly changing level in the tank by "chattering" - this chattering effect results on electrical devices being switched on and off again rapidly.

Liquid Level Controller Operational Life

Our range of liquid level controllers are designed to offer both high level and low level switching in the same enclosure. This means that you only need to purchase a single model of liquid level controller even if you're looking for high level operation, or low level operation.

We've been manufactured our liquid level controller range for a long time, and they are of simple design and construction, to offer many years of reliable service.

Liquid Level Controller Range



The ALC1101 is a compact and powerful liquid level controller.

Fully configurable the ALC1101 offers user selectable high or low level operation as well as user configurable sensitivity selection. 

With a relay state LED indicator the ALC1101 is simple to configure whether as part of a larger control panel or as a single stand alone system.

The ALC1101 is manufactured in a compact housing and is designed to slot into a standard 11-pin relay base. The ALC1101 is available in a surface mounting enclosure for stand alone operation or individually for system integration.

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