Ronan X96S LEVEL GAGE Manuel d'utilisateur télécharger pdf (Page 8)

Theory

Theory of Radiation Gaging

Radiation gages operate on the principle of radiation absorption and transmission.

A beam of gamma radiation is directed from the source holder, through the vessel and its process material, and onto the surface of

the detector.

Radiation which is not absorbed by the material through which it passes, is transmitted to the surface of the detector.

Process measurement is possible because the amount of radiation absorbed and transmitted is predictable.

The absorbed radiation is directly related to the level of process material in the vessel while the transmitted radiation is inversely

related to the level of process material in the vessel.

Therefore, an increased process level results in a decrease of transmitted radiation.

Since the radiation that's not being absorbed is being transmitted, the process level can be inferred by measuring the amount of

radiation reaching the detector at any point in time. The detector's output signal, in counts, also varies inversely to the process

level.

When the process level is low the detector is exposed to a maximum amount of radiation which produces a HIGH output of

counts. When the process level is high the process material "shields" the detector and prevents radiation from reaching the

detector, producing a LOW output of counts.

The X96S Microprocessor converts the detector signal to user's measurement units of level: m, mm, cm, in, ft.

The X96S displays the output measurement range in the selected user units. The "zero" of the measurement range represents the

lowest level of interest, while the "span" of the measurement range represents the highest level of interest.

Reduction of the signal "noise" due to radiation statistics is handled in the stage of signal processing known as digital filtering.

Digital filtering is a form of statistical averaging used to smooth, or dampen, random radiation as well as process-related noise.

Increasing the digital filter’s “time constant” decreases signal noise.

Dynamic tracking permits the gage response to temporarily by-pass the digital filter. This is helpful in some processes where

sudden or drastic step changes in process must be observed in their true, or unfiltered, state.

Software also compensates for the decay of the radioactive source activity. On-going adjustments are made automatically for the

rate of decay, or source half-life.

Principles of Operation

The detector's raw output signal is processed through several stages of software in the X96S.

Some of the more significant stages of signal processing are:

• Units Conversion – conversion of counts into user-selected level units

• Measurement Range – 4-20 mA output defined by the user-selected range in user-selected units.

• Digital Filtering – signal smoothing to reduce statistical radiation noise

• Dynamic Tracking – quick gage response to quick process changes.

• Source Decay Compensation – automatic compensation for the radioisotope decay

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Ronan X96S LEVEL GAGE Manuel d'utilisateur Page 8