Radiometric level measurement

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In the radiometric level measurement , there are methods to determine the filling state as tank containers using gamma radiation.

Physical principle

In the area of level measurement technology , different physical processes are available today. They all have in common the detection and signaling of fill levels or limit levels. The radiometric measuring principle is based on the fact that gamma rays are weakened when they penetrate matter. It can be used for various measurement tasks:

Point level detection

A gamma emitter and a corresponding transmitter are attached to opposite sides of the container at the height of the desired fill level limit. The transmitter converts the received radiation intensity into a percentage signal. "0%" means that the beam path is free, so the level is below the limit. "100%" means that the beam path is completely covered, i.e. the fill level is above the limit.

Continuous level measurement

If the density of the medium is known, the fill level can be determined from the absorption when the container is irradiated from bottom to top (or vice versa). Another method is to place a gamma emitter and a rod-shaped gamma detector on opposite sides of the container. The fill level can be calculated from the total radiation intensity that hits the detector.

Interface measurement

A gamma emitter and a transmitter are mounted on opposite sides of the container so that both liquids are irradiated. The gamma emitter can also be placed inside the container. The transmitter calculates the position of the boundary layer from the intensity of the radiation received. Their value is between 0% (lowest possible position) and 100% (highest possible position).

Density or concentration measurement

A gamma emitter and a transmitter are attached to opposite sides of a measuring tube. From the intensity of the radiation received, the transmitter calculates the density or concentration of the material to be measured. If a temperature sensor (5) is also connected, the transmitter takes into account the thermal expansion of the material to be measured. Then it does not output the measured density directly, but uses it to calculate the density that the material to be measured would have at a standard temperature selected by the user. In addition, the density signal of the transmitter can be combined with the signal from a volume flow meter (6) and the mass flow can be calculated from these two signals.

Construction of a radiometric measuring device

A radiometric measuring system typically consists of the following components:

Gamma emitters

A 137 Cs or 60 co-preparation is usually used as the gamma emitter. Gamma emitters of different activity are selected to adapt to the respective application.

Source container

The gamma emitter is built into a radiation protection container, which only allows radiation to escape in one direction and shields it in all other directions. Different source containers differ in size and beam exit angle.

Compact transmitter

The compact transmitter contains a scintillator, a photomultiplier and the evaluation electronics. Gamma radiation that hits it generates flashes of light in the scintillator . These reach the photomultiplier, where they are converted into electrical impulses and amplified. The pulse rate (number of pulses per second) is a measure of the intensity of the radiation. Depending on the calibration , the pulse rate is converted by the evaluation electronics into a level, limit switch, density or concentration signal. The transmitter with an NaJ crystal or plastic scintillators in various lengths is selected to adapt to the respective application.

How a compact radiometric transmitter works

How a radiometric compact transmitter works: (1) Gamma rays generate flashes of light in the scintillator, (2) The photomultiplier converts the flashes into electrical impulses and amplifies them, (3) The evaluation electronics calculate the measured value from the impulse rate.

Typical applications

The area of ​​application of a radiometric measuring device is the continuous, contactless measurement in liquids, solids, suspensions or slurries. This is the case with extreme measuring conditions, e.g. B. high pressure, high temperature, corrosiveness, toxicity and abrasion possible in a wide variety of process vessels such as reactors, autoclaves , separators , acid tanks, mixers, cyclones or cupolas . Further applications are the use for point level detection, density measurement, gammography detection or interface measurement.

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