Published March 2017
Traditional optical methods for detecting blockages, such as proximity through-beam sensors, cannot cope with the hostile environments encountered in these applications, where the extreme dust and high vibration culminate in repeated failures when sensitive optics are damaged or become coated in dust.
As a result, nucleonic devices have historically been considered the only reliable form of instrumentation capable of providing effective blocked chute detection in such demanding conditions. However, although nucleonics provides a technically competent technology, this measurement technique requires a radiation source from a radioactive isotope such as Caesium Cs137 or Cobalt 60 in order to detect the presence of material in the hopper. The radioactive source must be specially shielded so that radiation is only directed through the hopper wall towards the product. Levels of radiation detected on the opposite side of the hopper are then used to determine whether there is a blockage or not.
These devices are very expensive to install and, although considered relatively safe to operate, there is still concern about safety aspects and the long-term environmental impact. As one would expect, controls on the use of these radioactive devices are extremely strict and extensive training is required to operate them. They need initial licensing and also have to be periodically verified, either by the manufacturer or an authorised external authority.
