A level switch designed for detecting a high level operates by triggering a signal when the substance (usually a liquid) reaches a predetermined upper point. The exact mechanism depends on the type of switch used, but common principles involve sensing the presence or absence of the substance at the sensor's location.
Here's how some common types, like those referenced, work when placed at a high level:
Understanding the Working Principles
Level switches typically employ different technologies to detect the interface between a liquid and the air or another medium. When installed at a high point within a tank or vessel, the switch activates when the liquid level rises to meet the sensor.
1. Conductive Level Switch (for Conductive Liquids)
This type is effective for liquids that can conduct electricity.
- Mechanism: It uses two or more electrodes. When the conductive liquid rises and touches between the electrodes, a current flows through the electrodes.
- Detection: The switch detects this current flow as the presence of the liquid.
- Output: It then outputs a detection signal, indicating that the high level has been reached.
- Application: Often used for high-level alarms or pump control in water-based systems.
2. Float Level Switch (Magnetic Reed Switch Type)
This is a versatile type suitable for many liquids, including non-conductive ones.
- Mechanism: This switch uses a float that moves up and down according to the principle of buoyancy. Inside the float is a magnet. The switch body contains a sealed reed switch.
- Detection: As the liquid level rises, the float moves up along a stem. When the magnet inside the float gets close to the reed switch at the designated high level point, the magnetic field causes the reed switch contacts to close or open, depending on the design.
- Output: This activation of the reed switch outputs a detection signal.
- Application: Widely used across industries for various liquids, including fuels, oils, and chemicals, for high-level alarms or pump shut-off.
High Level Operation
Regardless of the underlying detection technology (conductive, float, ultrasonic, capacitive, etc.), a "high" level switch simply means the sensor or activation point of the switch is positioned at the specific upper limit you want to monitor. When the liquid reaches that position, the switch changes state, signaling the high-level condition.
| Level Switch Type | Principle | Suitable Liquids | Common Use Case at High Level |
|---|---|---|---|
| Conductive | Current flow between electrodes | Conductive liquids (e.g., water) | High-level alarm |
| Float (Reed Switch) | Magnet in float activates a reed switch | Various liquids (conductive/non-con) | High-level shut-off |
Practical Considerations
- Placement: Accurate placement of the switch is crucial for it to signal the correct high level.
- Liquid Properties: The type of liquid (conductivity, viscosity, density) dictates which switch technology is suitable.
- Environment: Temperature, pressure, and presence of foam or turbulence can affect switch performance.
By understanding these basic principles, you can see how different level switch types function when installed to monitor the high level in a container.
