CONTINUOUS CONTACTLESS WEIGHING

A continuous weighing system is expected to determine the mass per unit of time running over a conveyor. This value must be integrated to get bigger time intervalls or the mass limited to a certain value. The normal way to get this signal is a gravimetric one by measuring the weight carried by the rollers of the conveyor. To achieve a correct signal a part of the belt must be movable to the direction of the gravity.
With a radiometric weigher the mass is not determined by its weight but by its absorption of electro magnetic waves. This results in a contactless measurement which is not depending on a movement and therefore it has not to be clean.

How does a radiometric belt weigher work?
The way why an X-ray photograph can show a bone in a leg is because of the higher density of bones compared with muscles. If the picture show a gray scale it is possible to determine the exact density distribution of the leg. The bones and also bigger legs have a higher absorption then thinner ones. The same way an X-ray photograph of a conveyor belt shows the bigger loading and the density distrubution of the loading. With this measured not by a picture but by a sensitive radiation detector the mass can be determined in kg/m.
The measure of the absorption is the bulk density and the length of the path in the material i.e. the hight of loading. This signal multiplied with the speed gives the tonnage per hour.

When the intensity of the radiation after it has passed the material on the belt is measured by only one detector the measuring result is responsble for all the mass between source and detector. Unfortunatelly this signal is also depending on other influencing facts like distance of a single lumb to the detector or source . If a certain loading is distributed in different ways i.e. the profil changes, the signal will change in spite of the same loading.

For conventional radiometric weighers the accuracy is depending on changes of profil.

The multi-detector principle enables to customize the measuring path as necessary. Whether it is a bucket conveyor or a conveyor screw - the frame and the detectors can be adjusted as to optimze the measurement and many ways without effort and additional costs.

The RGI-belt weigher measures the material on the belt and the profil with normally 5 detectors. When a change of the profil causes a different signal in one detector it must definitelly cause also a change in another one when the loading stayes the same.

The 5 signals comming from all the detectors together show the correct result of the loading.

The RGI multi-detector principle determines the mass independetly on the profil changes.
If it is impossible to fit a straight traverse between the upper and the lower strand the detectors will be assembled according to the shape of the belt.

For a screw conveyor the detectors are fitted nearly on a circle so that the whole material fits in the beam.

TECHNICAL DATA

Evaluation Computer MACON

• 4-line alpha-numerical display
• IP 65 foil keyboard
• calibration via RS 232 and lap top
• current outputs 0/4-20 mA for
• RS 232 output for host computer
• 2 potential free relais contacts
• power supply for detector
• power connection 230/115 V AC, 24 V DC or AC

Multi detector system MS 5/40

• 5 NaJ/Tl crystal detectors
• electronically stabelized 0,1% for 0-45 °C
• crystall size 40 x 40 mm
• power supply MACON
• mounted in one dust tight housing
• weight approx. 18 kg

Measuring frame

• steel frame plastic coated
• with lead shielding and intergrated shutter
• fitted to the conveyor
• weight approx. 75 kg