Level Measurement Technologies: Electrical, Ultrasonic, Radar, Laser, Radiation

Level Instruments Based on Electrical Characteristics

Conductive or Resistive Meter

This instrument consists of a probe with two electrodes. When the tip of the electrodes contacts a conductive liquid, it closes an electrical circuit. An amplifier unit then switches a meter contact.

Applications: These serve as level switches for conductive liquids in containers, provided the liquids are not excessively viscous or corrosive.

Ultrasonic Level Meter

This meter uses tunable, high-frequency sound waves that propagate through the gas phase until they collide with the liquid or solid surface.

Usage:

• As an alarm level indicator: The frequency is damped when the liquid wets the sensors.
• As a continuous level indicator: The emitted signal reflects off the liquid/solid, and the echo is perceived by the receiver.

How it works:

1. A high-frequency sound pulse is transmitted from the sensor towards the surface.
2. The sound pulse hits the product surface and reflects back to the sensor as an echo.
3. The time between transmission and reception of the echo determines the level. The received echo marks a period for synchronization.

Applications: Used for level measurement in both liquids and solids (like pulp).

Microwave Radar Level Meter

This type uses the propagation of an electromagnetic wave. Its measurement is generally not influenced by temperature or density changes. Foam is often transparent to the radar signal, making it less problematic.

How it works:

1. A solid-state oscillator generates a frequency sweep (e.g., 10 to 11 GHz).
2. The signal is focused on the liquid/solid surface through an antenna.
3. The signal reflects off the surface and returns to the antenna.
4. The frequency difference between the transmitted and returned signals (or the time-of-flight) is proportional to the distance, indicating the level.

Advantages: Maintains excellent performance in turbulent fluid applications.

Laser Level Meter

This system typically involves a laser beam sent (envía) through a guiding tube and directed by a mirror to reflect off the surface, such as molten metal.

How it works: The instrument measures the time lag between the emitted laser impulse and the reflected impulse received by a high-resolution photodetector. This time lag is proportional to the distance to the surface, indicating the fluid height.

Radiation Level Meter (Radiometric)

This meter consists of a radioactive source located in a shielded holder (portafuentes) installed on one side of the receptacle, and a radiation detector placed on the opposite side. Radiation passes from the source, through the desired path within the vessel, to the detector.

How it works: The material inside the vessel absorbs some of the radiation. As the level of the liquid or solid rises, more radiation is absorbed, and less reaches the detector. The detector provides a signal based on the received radiation intensity.

Measurement Types:

• Point Level (Switch): The detector signals if the level is above or below a specific point (all or nothing signal).
• Continuous Level: The linear transmission of the rays is inversely proportional to the level of the material, allowing for continuous measurement as the material absorbs varying amounts of radiation based on its height.