|
|
The measuring system LB 440 is used for the contactless, continuous measurement of the level of liquids and bulk materials in reactors, vessels and bunkers. The measurement is not affected by the chemical and physical properties of the product being measured and is adapted to the specific geometry of the vessel. Features include intrinsically-safe two wire connection to detectors, ASK signal modulation for interference suppression, noncontact design and fieldbus compatibility.
Features
|
 |
Principles of Measurement The Level Gauge LB 440 operates according to radiometric principle, utilizing the physical law that gamma radiation is attenuated as it passes through matter. According to this physical law, the attenuation is dependent only on the type of source, the length of the absorption path and the density of the medium. Since the source type and the absorption path are constant, the measurement is affected only by the presence of the medium. All other physical properties such as pressure, temperature, viscosity and colour have no influence. Since the absorption law follows an exponential curve, the measuring effect with normal container dimensions becomes practically independent of any density changes in the product. Therefore, physical as well as all chemical properties have no influence on the measuring effect. As a consequence, the radiometric measuring method features a very high level of operational safety and requires practically no maintenance, even under difficult operating and ambient conditions.
The use of scintillation counters as radiation detectors and careful project engineering ensure that the lowest possible source activities and the best shieldings will be used. The radiation exposure of the operating staff will clearly stay below the extremely low values permitted by law, which are about as low as the natural environmental background radiation.
Measuring Arrangement A typical measuring arrangements comprises a source mounted on the outside of the container, a detector, and the connection cable from the detector to the evaluation unit LB 440. Source and detector form a radiation field corresponding to the size of the measuring range. This can be achieved by using a rod-shaped source and a point detector (Fig. 1) or a point-shaped source and a rod detector (Fig. 2). For special applications a rod source and rod detector (Fig. 3) can be used together. Which of these options is selected is dependent upon the measuring geometry, the measuring task, ambient factors or even considerations of space and money. For larger measurement ranges several rod detectors can be used together. Signals from individual detectors are transmitted via slave units to a master evaluation unit for indication of product level.
 |
 |
 |
| Figure 1 | Figure 2 | Figure 3 |
Evaluation unit The LB 440 evaluation unit incorporates state of the art technology with a 32-bit processor for high speed and precision in even the most demanding applications.
 |
Radiation sources and shielding All radioactive sources used for industrial applications are encapsulated in welded stainless steel so that radioactive substance is kept separate and isolated from the material being measured. Depending on the measuring task one can work with either 60Co or 137Cs sources. The radioactive material of the 60Co rod source is a metal wire wound around a mandrel of the required length. By varying the winding pitch any linearization can be achieved, even for complicated measuring geometries. The shielding container is adapted to the source for low radiation levels, and a lockable exit channel for the radiation beam is used. The shielding is installed vertically on a bracket for simple and non-critical installation. |
 |
Detector A scintillation counter with an NaI crystal is used as a detector. Photoflashes are produced in the crystal when radiation is absorbed. The number of flashes is proportional to the intensity of the radiation field. The crystal is optically linked to a photoelectric multiplier which, together with the electronics, converts the photoflashes into electrical impulses. Compared to other detectors, eg. ionisation chambers, the advantages are obvious: high sensitivity to gamma radiation, low source activities, temperature stability and practically unlimited service life. The compact shape of the crystal allows it to be easily shielded against fluctuations in ambient radiation which could otherwise influence the measurement. The signals are transmitted to the evaluation unit using a two wire technique with ASK modulation to ensure the suppression of interference. |
Application Notes
Engineering data To prepare our
quotation we require the following application data:
|
for more information, email
SE Asia and Australasia: industrial@berthold.com.au
North America: usinfo@berthold.com.au
Europe: euroinfo@berthold.com.au
Home Industrial Level Contact Site Images 