BARCON 21

γ-radiation  is one of different types of nuclear radiation, the physical properties of which can only be distinguished from X-rays by the fact that it has a discrete energy, while X-rays have many energies (i.e. wavelengths) as they arise.

As  with X-rays, γ-radiation can also be used to "illuminate" matter, since both are able to penetrate it, where the denser the material to be penetrated (e.g. bone), the less radiation will pass through.

If  the radiation intensity is so dimensioned that radiation can still be measured even after irradiating two container walls, the additional absorption by the container filling can provide the signal about the filling state, ie full or empty.

For  this purpose, a detector for radioactive radiation is used which theoretically has an unlimited lifespan and which is very sensitive to radiation in order to keep the intensity as low as possible.

The  so-called scintillation counter consists of a crystal with high density, which can absorb a lot of it when incident gamma radiation and generates small flashes of light that are "seen" and amplified by a photomultiplier.

Other  detectors, e.g. The frequently used Geiger-Müller counting tubes are gas-filled tubes which, however, absorb little radiation, since gas is not only of very low density and most of the radiation simply passes through, but it is used up, which means that it has a limited service life and therefore has another disadvantage:
nobody knows whether the counter tube becomes “deaf” or whether it “fires”, ie generates impulses by itself and thus simulates radiation, both of which can lead to major problems with level monitoring.

The  measured intensity of the radiation is processed in an evaluation computer and, depending on the intensity, leads to the actuation of a relay which indicates an empty or full container.

The  radiation produces a pulse rate in the detector, but not a constant frequency, i.e. radiation is only released sporadically from the individual atomic nuclei and the probability of a certain frequency in the detector consequently increases only by a higher intensity, which can, however, be replaced by a longer measuring time, which then also leads to more accurate results.

When an atom has emitted its radiation, it becomes inactive because it can no longer emit any more radiation, so the radiation source loses its activity and intensity over time.

The  higher the number of active atoms, the more precisely it can be said after which time half of the atoms become inactive, which is why this period is called half-life, it is approx. 30 years for the common radiation sources Cs-137, for Co-60 5.2 years.

The drop in intensity would eventually lead to a malfunction, so a microcontroller not only takes on the task of calculating how great the loss of intensity per unit of time is, but at the same time corrects the drop in intensity mathematically via a time function so that the drop in activity does not result in an error .

Switching reliability
The  above-described random frequency of the detector signal can also result in incorrect switching with a certain probability without the state in the container having changed.

Looking  at the pulse rate (imp./s), it fluctuates with a probability of approx. 68% around the measured value ± the square root of it (at 100 it fluctuates around ± 10), which, when doubled, already has a probability of approx. 95% has the effect, which unfortunately also means that 50 out of 1000 measurements are likely to be within the 80-120 pulse / s range. This leads to false triggering for sensitive measurements.

In  the automatic switching point calculation, the BARCON 21 is programmed in such a way that theoretically there is less than one faulty switching per year. However, one cannot completely rule out the likelihood of this.