The basic method of nuclear level measurement is sending radiation through the liquid and the intensity of the transferred radiation is measured using a detector. The intensity of the radiation detected is the function of the level of liquid in the tank.
These “sources” may be locked out for testing and maintenance by moving a lever that hinges a lead shutter over the “window” of the box. This lead shutter acts as an on/off switch for the radioactive source. Geiger Counter or Geiger Tube is an instrument for detecting the presence of and measuring ionizing radiation such as alpha particles, beta particles, and gamma rays.
Nuclear level – continuous measurement:
The continuous nuclear level measurement directs a narrow radiation fan through the vessel to a detector. As the level of the process increases, it protects the detector from radiation. The more radiation “detects” the detector, the lower the process level (discernible at 1% of the interval). The less radiation is detected, the higher the level of the process.
Device for detection of ionizing radiation by measuring the electric current generated when radiation ionizes the gas in the chamber and therefore makes it electrically conductive.
Advantages:
- Sometimes works, when no other method is available
- External mounting often possible
- Easy zero check
- Motor-driven models available for high-accuracy applications
Disadvantages:
- Costly to install
- Requires licensing by a regulatory agency
- Errors caused by density variations in measured materials
- Lack of application data
- Difficult to obtain linear readout over wide ranges
Point level measurement:
Point level detection uses a focused beam of radiation directed at a small detector, that senses the presence or absence of the beam. When the beam is blocked by the process, the detector sees the radiation from the source. Point level detectors can be set as either high or low alarms.
The Geiger Muller counter is used as the detector, the counter count individual particles at rates up to about 10,000 per second and is used widely in medicine and in prospecting for radioactive ores.
Advantages:
- Sometimes work when other methods fail
- Mounted outside the process
Disadvantages:
- Costly to purchase and install
- Requires licensing by a regulatory agency
- Dangerous to handle unless precautions are followed
- Lack of application data
- Problems presented by the buildup of material on vessel walls
