Radiation based density sensor.pptx
Transcript of Radiation based density sensor.pptx
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RADIATION BASED DENSITY SENSGamma
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PRINCIPLES OF OPERATION
Gamma-based density gauges consist of a sealed source in a source holder and a
detector. The source holder is mounted on the side of a pipe or chute with the detethe opposite side. A focused beam of gamma radiation is transmitted from the sourthe pipe and process material to the detector.
As the density of the material in the pipe changes, the amount of radiation reachingdetector changes. The greater the density of the material, the lower the radiation fidetector; the lower the density of the material, the higher the radiation field at the d
When the radiation strikes the scintillation crystal, pulses of light are emitted which a
detected by a photomultiplier tube. The photomultiplier tube outputs a signal propothe number of light pulses received. The electronics monitors this signal and generascaled 4 to 20 mA or other useable process signal
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TECHNICAL APPLICATIONS
PROCESS TEMPERATURE COMPENSATED DENSITYWith input from a temperature probe, the density can be calculated to a refeprocess temperature.
PERCENT SOLIDS MEASUREMENT
When the carrier fluid remains stable, nuclear density gauges provide highly ameasurement of percent solids for most slurries.
MASS FLOW MEASUREMENT
When used in conjunction with a flow meter, nuclear density gauges providemass flow monitoring.
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INDUSTRIAL APPLICATIONS
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SCINTILLATION DETECTOR
Radiation interaction in scintillator produces light (may bvisible range)
Quantification of output requires light amplification anddetection device(s)
This is accomplished with the: Photocathode
Photomultiplier tube
Both components are placed together as one unit
optically coupled to the scintillator
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SCINTILLATION DETECTOR
Gamma rayScintillationevent
Reflector housing
Fluor crystal NaI (Tl)
Photocathode
Photoelectrons
Dynodes
Photomultiplier tube
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SCINTILLATION DETECTOR
Main components - Photocathode material
Dynodes electrodes which eject additional electrons after being struck by an electron
Multiple dynodes result in 106 or more signal enhancement
Collector accumulates all electrons produced from final dynode
Resistor collected current passed through resistor to generate voltage pulse
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SCINTILLATION DETECTOR
Scintillation material with a high light outputis preferred for all sapplications.
Emission wavelength should be matched to the sensitivity of thdetection device that is used (PMT of photodiode).
Scintillation light pulses (flashes) are usually characterized by aof the intensity in time (pulse rise time) followed by an exponendecrease.
Decay timeof a scintillator is defined by the time after which tthe light pulse has returned to 1/e of its maximum value.
Most scintillators are characterized by more than one decay tiusually, the effective average decay time is given
The decay time is of importance for fast counting and/or timin
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SCINTILLATION DETECTOR
NaI(Tl) is one of the most important scintillants. Can only be used in hermetically se
Material Density [g/cm3]Emission
Max [nm]
Decay
Constant (1)Refractive Index (2)
Conversion
Efficiency (3)
NaI(Tl) 3.67 415 0.23 ms 1.85 100
CsI(Tl) 4.51 550 0.6/3.4 ms 1.79 45
CsI(Na) 4.51 420 0.63 ms 1.84 85
CsIundoped 4.51 315 16 ns 1.95 4 - 6
CaF2 (Eu) 3.18 435 0.84 ms 1.47 50
6LiI (Eu) 4.08 470 1.4 ms 1.96 35
6Li - glass 2.6 390 - 430 60 ns 1.56 4 - 6
CsF 4.64 390 3 - 5 ns 1.48 5 - 7
(1) Effective average decay time Forg-rays.
(2) At the wavelength of the emission maximum.(3) Relative scintillation signal at room temperature forg-rays when coupled to photomultiplier tube with a B
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SCINTILLATION DETECTOR
Oscilloscope
Scaler
Multi-
Channel
Analyzer
DiscriminatorAmplifierPre-
Amp
High
Voltage
Detector
(Crystal &
Photomultiplier)
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SCINTILLATION DETECTOR
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GAMMA RADIATION SOURCES
Radioactive isotopes are used as gamma radiation soulevel, density and interface measurement as well as for limit detection.
The gamma source radiates equally in all directions. Forradiometric measurements, however, only radiation pasthrough the tank or pipe is of interest.
All other radiation is superfluous and must be shielded othis reason, the radioactive source is mounted in a specsource container which affords the necessary protectioproviding a defined, practically unattenuated, narrow bin one direction only.
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GAMMA RADIATION SOURCES
Features and Benefits Point source in special source container ensures simple
handling and easy installation
Specially constructed source capsule conforms to strictsafety requirements, Class 66646 to ISO 2919
Choice of source type and activity ensures optimized dfor your application
The radioactive sources, both 137Cs and 60Co, are sealed in a double-walled, weldesteel capsule. The encapsulation corresponds to Performance Class C 66646 as per ISOproviding maximum protection against temperature, external pressure, impact, vibratpuncture.
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GAMMA RADIATION
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GAMMA RADIATION SOURCEShttp://www.end
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SENSOR SET UP
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SENSOR SET UP
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