Ronan X96S MASS FLOW GAUGE - Manual (Page 7)

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Theory
Theory of Radiation Gaging
Radiation gauges operate on the principle of radiation absorption and transmission.
A beam of gamma radiation is directed from the source holder, through the process material and housing, 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 density and flow of process material in the pipe while the transmitted radiation is
inversely related to the flow and density of process material in the pipe.
Therefore, an increased process mass flow results in a decrease of transmitted radiation.
Since the radiation that's not being absorbed is being transmitted, the process mass flow 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
condition.
When the process density is low the detector is exposed to a maximum amount of radiation which produces a HIGH output of
counts. When the process density is high the process material "shields" the detector and prevents radiation from reaching the
detector, producing a LOW output of counts.
The X96S displays the output measurement range in the selected user units. The "zero" of the measurement range represents the
lowest mass flow of interest, while the "span" of the measurement range represents the highest mass flow 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 gauge 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.