Ronan X96S DENSITY GAGE - Manual (Page 7)

Density Gage Manual 012407 3
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 pipe (or vessel) and its process material, and onto the
surface of the detector.
Some amount of radiation is absorbed by the material through which it passes, and some of the radiation 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 (or mass) of process in the pipe while the transmitted radiation is inversely
related to the density (or mass) of process in the pipe.
Therefore, an increased process density results in a decrease of transmitted radiation.
Since the radiation that's not being absorbed is being transmitted, the process density 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
density.
When the process is light (low density) the detector is exposed to a maximum amount of radiation which produces a HIGH output
of counts. When the process is heavy (high density) the process material "shields" the detector and prevents radiation from
reaching the detector, producing a LOW output of counts.
Ronan’s Density Monitor is used to replace the lab sampling process since the gage output, when accurately calibrated, will
correlate to the density values of process taken from samples near the gage location.
The X96S Microprocessor converts the detector signal to user's measurement units of SGU, percent solids, Baume H, Baume L,
API, or percent steam. The X96S Microprocessor is capable of simultaneously displaying density in two different sets of units.
These different representations of the density value are called density 1 and density 2.
The X96S displays the output measurement range in the selected user units. Channel 1 and Channel 2 can be set independently.
For both channels, the "zero" of the measurement range represents the lowest density of interest, while the "span" of the
measurement range represents the highest density 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 density (SpG) into user-selected units
• Measurement Range – 4-20 mA output defined by the user-selected range in user-selected units.