• Where other electrical methods are not suitable, in that case radiation level detector is used.
• Also, it is most commonly used because it does not need to come in contact with the liquid being measured.
Principle of Radiation Level Indicator
The amount of radiation received by the detector is inversely proportional to the amount of liquid between the radiation source and the detector. The difference in the amount of radiation received by the detector, corresponds to the liquid level.
Radiation Type Level Indicator
Construction and Working of Radiation Level Indicator
Fig. shows a radiation level detector.
• It consists of gamma rays source holder on one side of the tank and a gamma detector on the other side of the tank.
• The gamma rays from the source are directed towards the detector in a thin band of radiation.
• When the gamma rays penetrate the thick wall of the tank, its energy level greatly reduces.
• The radiation received at the gamma detector is inversely proportional to the thickness of the tank wall and the medium between the radiation source and the detector.
• That is, thicker is the medium between source and detector, the less radiation received by the detector and vice-versa.
• When the tank is empty, the gamma rays passes only through the two tank walls and the air or vapour in the empty tank.
• When the liquid enters the tank and its level increases, the rays passes through a path in the liquid as well as the tank walls.
• The liquid in the tank reduces the radiation received by the detector.
• Thus, the amount of radiation received is inversely proportional to the amount of liquid between the radiation source and the detector.
• The difference in the amount of radiation received by the detector, corresponds to the liquid level in the tank.
• Thus, when liquid level increases, the amount of radiation received is reduced and vice-versa.
• The radiation loss received by tank walls is constant either the tank empty or full.
Advantages of Radiation Level Indicator
Advantages of radiation level indicator are:
1. There is no physical contact with the liquid.
2. Suitable for molten metals as well as all types of liquids such as corrosive, abrasive, highly viscous, adherent.
3. Useful at very high temperature and pressures.
4. They have no moving parts.
Disadvantages of Radiation Level Indicator
Disadvantages of radiation level indicator are:
1. The reading is affected by change in density of liquid.
2. Heavy radiation source holder.
3. High Cost.