INSTRUMENTATION by Ralph H. Müller
Bulk Moisture Analysis System 'T'HE
RAPID AND coNTiNixnjs
MEAS-
•*- UKEMENT of moisture in bulk m a terials is a continuing problem. Of the various methods which have been used, such as t h e measurement of dielectric constant, great care h a s t o b e taken in filling t h e measuring cell in a reproducible m a n n e r . Although n e u t r o n techniques were suggested some years ago, Nuclear-Chicago h a s come u p with a new a n d ingenious system which provides a direct readout in terms of water content in per cent b y weight. According to a recent announcement, Nuclear-Chicago of 359 E a s t H o w a r d Ave., D e s Plaines, 111., manufactures the Qualicon 507 Bulk Moisture Gauge. T h e moisture measurement is made by t h e use of t w o different kinds of nuclear radiations, neutrons and gamma rays. A beam of high energy neutrons
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is directed from t h e gauge t o t h e m a terial. Some of the neutrons a r c r e flected backward. These reflected neutrons lose some of their energy a n d become " m o d e r a t e d . " Such low energy neutrons a r e measured by a n e u t r o n detector in t h e 507 head. Although all materials serve as a n e u t r o n moderator t o some extent, hydrogen is b y far the most efficient. Where most of the hydrogen in a system is associated with water, t h e determination of t h e n u m b e r of moderated neutrons r e flected from t h e material provides a measurement of the a m o u n t of moisture in t h e material per unit volume. If there were no density variations in bulk materials, this measurement would suffice. However, studies of density variations in granular materials on a conveyor have shown deviations t o be as great as ± 1 0 % and almost never
less t h a n ± 2 % on a long t e r m basis. T h e density measurement in t h e 507 is m a d e b y simultaneously directing a beam of gamma rays into t h e material. T h e n u m b e r of gamma rays reflected by the material or t r a n s m i t t e d through the material is an inverse function of its density. These independent signals a r e t r a n s m i t t e d t o an electronic unit, where they are scaled t o pounds p e r cubic foot, and presented simultaneously t o .a simple ratio computer. This ratio signal is presented continuously in terms of per cent water b y weight (Fig. 1 ) . A plutonium-béryllium source with an o u t p u t of about 3 X 10 e high-energy neutrons p e r second is in t h e gauge head. T h e g a m m a rays are provided b y a cesium-137 source containing from 50 t o 200 m c . of isotope. T h e complete measuring system consists of
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MOISTURE
CO
DENSITY
MOISTURE PER UNIT WEIGHT
Figure 1 Response of t h e Qualicon 5 0 7 to moisture changes per unit volume
Response changes
of the 5 0 7 to
density
Combined response in terms of moisture per unit weight VOL. 3 5 , N O . 1 , JANUARY 1 9 6 3
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INSTRUMENTATION CABLE TO MEASURING AND RECORDING INSTRUMENTS
DETECTION HEAD FAST NEUTRON SOURCE THERMAL NEUTRON DETECTOR \
GAMMA RAY DETECTOR
SCRAPER PLOW GAMMA ' RAY SOURCE
thing to
remember...
high resolution microanalysis of
amino acids now resolves
MATERIAL
FLOW
CONVEYOR
Figure 2. Measuring head of Nuclear-Chicago Bulk Moisture Gauge mounted over a conveyor belt
a measuring head and an electronic unit which may be located several hundred feet from the point of meas urement. The electronic unit provides direct meter display of the per cent moisture by weight, plus a proportional voltage signal which may be used to drive a recorder and water control system. A schematic of the system, as mounted over a conveyor belt is shown in Fig. 2. The measuring head is con tained in a rectangular steel box weigh ing 600 lb. and measuring 20 X 20 X o7 inches. In some installations, the gamma source is located in a separate unit centered beneath the conveyor belt in a container 9 X 7 X 36 inches. The electronic amplification used in both measuring channels makes use of a vibrating-reed electrometer. The vi brating reed converts the d.c. signal from the radiation detector to an a.c. signal for amplification. This system provides unusual stability for process control instrumentation and eliminates frequent adjustment due to zero drift. In conveyor belt installations where the material bed is not relatively smooth, a scraper plow or self-clearing roller is mounted just ahead of the measuring head to provide bed-leveling. A special measuring head is available for mounting on the side of a surge bin. In this type of installation, pre cautions must be taken to provide smooth flow of the material through the bin without buildup on the bin wall. This may be done by lining the wall with smooth plastic such as Teflon sheet or by installation of a bin vibrator. The sample volume, which the neutrons and gamma rays penetrate, must be relatively large. The mini mum sample on a conveyor belt is ap proximately 16 inches wide and 2 inches
over 8 0 ninhydrin positives from 1 ml untreated urine
. . . readability to 0.01 micromoles
Figure 3. Moisture probe used in batch testing. Readings require one minute thick. When a gage is mounted on the side of a bin, the sample beina; measured continuously is approximately 1 cubic foot in volume. When a circu lar gage head is mounted around a pipe, the minimum pipe diameter is usually S inches. The accuracy of the Qualicon 507 Bulk Moisture Gauge is influenced by the nature of the measured product and the type of installation. In gen eral, an accuracy of better than 0.2% may be obtained over a moisture range of 2% to 80% for materials which con tain a relatively fixed percentage of bound hydrogen. The measurement be comes somewhat less precise with ma terials having larger variable amounts of bound hydrogen. If the per cent moisture is less than 2%, a larger time constant should be used to maintain high accuracy. The same instrument in the form of a probe is shown in Fig. 3 and is in tended for batch testing.
N o w . . . from ten times less samplc.Tcchnicon offers Amino Acid Chromatograms of even higher resolution and sensitiv ity . lYo^iJlOWJΐSJol·TO_0;l_JTlic2r> mole of each amino acid with out electronic amplification... readability 0.01 micromoles,, e.g. : over 80 ninhydrin positive substances resolved in 22 hours from 1 ml of untreated urine. How's it done? Simple... re duce column size from 9mm to 6mm, use our new close frac tionated Chromobead* resin, and our new tubular flow cells. (More than 20 times as efficient as our standard flow cuvette.) This new Technicon single column, 22 hour micro-system outdates even the latest con ventional apparatus. Write for details and a folio of chromato grams today! |
Trode me.k
T E C H N I C O N ®
AutoAnalyzer
®
TECHNICON CHROMATOGRAPHY CORP. Research Park · Chauncey, N e w York Circle No. 134 on Readers' Service Card
VOL 35, NO. 1, JANUARY 1963
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