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AECL-5378
ATOMIC ENERGY (W£*& L'ENERGSE ATOMIQUEOF CANADA LIMITED I f i j DU CANADA LIMITEE
CALIBRATOR FOR TRITIUM-IN-AIR MONITORS
by
R.V. OSBORNE and A.P. PRINi
Chalk River Nuclear Laboratories
Chalk River, Ontario
JULY 1976
ATOMIC F:M;RGY OF CAN AIM LI.MI ill)
CALIBRATOR FOR TRITIUM-IN-AIR MONITORS
bv
R.V. Osborne and A.P. Prim"
Chalk River Nu;lear LaboratoriesChalk River, Ontario
July 1976
AECL-5378
Calibreur pour les moniteurs de tritium dans l'air
par
R.V. Osborne et A.P. Prini*
* Adresse actuelle: Division de génie mécaniqueConseil National de Recherches. Ottawa
Résumé
Ce calibreur est un contenant thermiquement isolé dans lequel de l'eau tritiée estmaintenue à ±0.03°C près dans une température choisie entre 8°C et 1 2°C. La vapeur d'eautritiée dans l'air peut être prélevée à des débits d'air allant jusqu'à 8 E/min. La concentrationdu tritium dans l'air est prévisible pour une gamme de conditions ambiantes à ±3.5% près.La perte du contrôle de température est signalée à la fois visuellement et électriquement.
Le rapport contient des détails sur le concept, les procédures de mise en service, lefonctionnement, le calibrage et l'entretien du calibreur et sur les moyens de diagnostiquerses défauts de fonctionnement.
L'Energie Atomique du Canada, LimitéeLaboratoires Nucléaires de Chalk River
Chalk River, OntarioKOJ 1J0
Juillet 1976
AECL-5378
ATOMIC 1 NI .RGY ()[• C A N A D A L1MITI.I)
I H R A T O R I OR T R I T I l l M - I N - A I R M O N I T O R S
bv
R.V. O s h o r n e :ind A.P. Prini*
S U M M A R Y
I he ca l ib ra to r is ;i thermal ly insulatccl c o n t a i n e r in which t r i t ia tcd wate r is ma in ta ined
wiihin tO.O.^ ' ( ' DI a selected t e m p e r a t u r e be tween <S"( and 1 2°C. Tr i t ia ied w a t e r v a p o u r in
air may he w i t h d r a w n at air How rates up to S t / m i n . Flic c o n c e n t r a t i o n of t r i t ium in air is
p red ic tab le to within ± 3 . 5 ' ' for a range of ambien t cond i t ions . Loss of t e m p e r a t u r e con t ro l
i>. signalled bo :h visually and electr ical ly.
Included in the repor t are deiai ls of the design, p rocedure s for commiss ion ing ,
opera t ing , cal ibrat ing a i d servicing '.he ca l ibra tor and for d iagnosing faults in its ope ra t i on .
^Present address : Mechanical Hngineering Division,
Nat ional Research Counci l . O t t a w a .
Chalk River Nuclear Labora to r ies
Chalk River, On ta r io
July 1976
AECL-5378
CALIBRATOR FOR TRITIU.YJ-IN-AIR MONITORS
1.
4.5.
(,.
VPPENDICES
CONTENTS
Introduclion(iencral designTheoryPerformance
AcknowledgementReferences
Page
A. Specifications y
1. Tritiatcd water vapour output y2. Operating conditions y
3. Supplies y4. Temperature controller characteristic jO5. Indicators 10t\ Signal output ]07. Connections Flectrical 10< S . Connections Mechanical 10l). Controls I'lectrical 10
10. Controls Mechanical 1 11 1. Dimensions ] ]
B. Circuit Description 12
1. Bridge amplifier 122. Pulse-width modulator 123. Frigistor driver 12
4. Fault detector 14
5. Frigistor heat-exchanger temperature sensor 16
C. Operating Procedures 17
1. Choice cftritiated water concentration 172. ''sing the calibrator |73. Routine check-out of calibrator 18
CONTI-.NTS Con"i P:«ge
I). Fault Diagnosis Il>
1. Initial diagnosis Il>2. Persistant blowing ol fuse i t ' I 1"'3. Persistent coolant fault indication l l )
4. Control fault indication 205. Output concentrat ion ol tritialed water vapour high 21(i. Output concentrat ion ot Iritiated water vapour low 227. Output concentrat ion of lriliale.il water vapour not steadx 23
H. Commissioning. Calibration and Servicing Procedures 24
1. Commissioning ^4
2. Calibration ^73. Adjusting the temperature set point 30
4. Servicing ; Q
F. Mechanical Assembly of Calibrator 31
G. Llccliical Assembly 34
Frontispiece - Tritium calibrator AEP 5284.
CALIBRATOR FOR TRITIUM-IN-AIR MONITORS
1. Introduction
1 he cal ibra t ion ot i n s t rumen t s thai measure the c o n c e n t r a t i o n in air of t r i t ia ted wate r
\ a pour (II IO) nia\ he 'hecked hy sampl ing from a known source of I1TO. Dry air may he
sa tura ted with water vapour hy t.impK bubbl ing th rough waler . However this approach
presents se \e ia l p rob lems . The sa tu ra t ion vapour dens i ty will he that co r re spond ing to ti.e
l e i n p e i a i u i e of ihe water . l o r an un insu la ted eon ia ine r the sa tu ra t ion t e m p e r a t u r e will be
below ainhienl because of the evaporat ive cool ing. If t r i t ia ted wa te r is used then Ihe
c o n c e n l r a l i o n of I ITO in Ihe effluent air will similarly d e p e n d upon the b u b b l e r
l e m p c r a l u r e . Also ihe con rcntni t ion of I I ' l l ) in air will depend on iso topic f rac t ionat ion in
the change of phase. Under equi l ib r ium c o n d i t i o n s the speci l ic act ivi ty of I ITO in the
wipoui phase varies with t e m p e r a t u r e and is less than that in the liquid phase. This
f;;icli»i);iiioi) JJ.NO varies in the non-equ i l ib r ium p r a c t i c e s i t ua t ions will] the .sampling How
rate and geome t ry and may differ from the equi l ib r ium value1 .
A n o t h e r practical p rob l em is tha t , when using air that is nearly s a tu ra t ed wi th t r i t i a ted
water vapour , adsorp t ion on tub ing and ins t rumen t su i^ .ces is apprec iab le , and small
t e m p e r a t u r e d e c r e m e n t s be low the t e m p e r a t u r e in the bubb le , result in c o n d e n s a t i o n .
By using ;, bubb le r that is con l ro l l eu at a fixed t e m p e r a t u r e be low ambien t these
p r o b l e m s arc reduced . AKP-5284 is such a device which has been designed specifically for
inco rpo ra t i on in the t r i t ium m o n i t o r A 5 - P - 5 2 7 5 * - ' bu t which m a y be used separa te ly for
providing a k n o w n c o n c e n t r a t i o n of t r i l ia ted wa te r vapour .
2. Genera l Design
The buhhle r . an insulated c o p p e r cell con ta in ing i r i t ia ted wa te r , is cooled by a
fVigisfor. ;[» elecuicully driven device iliul transfers heal by mains of tho Peltier effect. The
heat is dissipated through a water-cooled heat exchanger.
The fronlispiece shows the complete calibrator, and the assembly is shown in FigureI. l'he top of the insulated container is removable to allow access to the capped filling tube.The electrical control circuit and power supplies are packed at ihe side of the insulatedcontainer. All the connections, controls and indicators are on the front panel. The calibratoris free standing. | Detailed drawings are given in Appendix F. ]
The temperature of the surface of the copper cell is sensed by a thermistor whichconstitutes a resistive arm of a bridge circuit. The variation of resistance generates a voltasiesignal that is used to control the frigistor power. Figure 2 illustrates the control circuit inblock form. Rather than use a linear amplifier to drive the frigistor which wouldnecessitate providing capability for heat dissipation in the output stages similar to that ofthe frigistor itself a variable-duty saturating switch is used.
The amplified signal from the thermistor bridge modulates the width of pulses from aconstant frequency clock. These pulses drive the output transistors into saturation: the heatdissipated by them is therefore very much less than that dissipated by the frigisior. Thefluctuations in the voltage across the frigisior at the clock frequency are reduced by
1
c a p a c i t i x e s m o o t h i n g . I h i s i s n e e d e d b e c a u s e p u k e d d r i v e o f f r i g i s i o r s i s i n e l l i c i e n l . I l i e
a v e r a g e v o l l a g c d r i v e l o 1 h e f r i g i s t o r i s p r o p o r t i o n a l l o t h e d u t \ c y c l e ' i . e . . l l i e p u h c
w i d i h ' c l u c k p e r i o d ) .
I h e b r i d s i c a m p l i f i e r h a s a g a i n o f 1 1 ) 0 1 ) a n d ' h e d \ n a m i e t e m p e r a t u r e s e n s j u \ ' i \ a ! i t s
i n i i p u l i s 4 5 \ ' ' C . I h e d u l y c y c l e i s v a r i e d f r o m 5 I " x t l I n i ^ w i n g • > ! i ..' \ .
c o r r e s p o n d i n g i<> ( ) . 2 ' > ( .
' 1 1 K c o n t r o l s y s t e m i n c l u d e s t w o l i m i t m o n i t o r s . I n l l i e l i r s t . a w i n d o w c o m p a r a t o i
s e n s e s I h e o u t p u t v o l t a g e a I t h e b r i d g e a m p l i f i e r o n I p u t . \ V h e n e v e r t h e v< i l l a g e i s o u t s i d e t i e
n o r m a l o p e r a t i n g r a n g e , a l a t i l t s i g n a l i s g e n e r a t e d . I n t h e s e c o n d , ( h e v o l i a g c a c n i s v .<
( h e m i i s l o r s e n s i n g d i e t e m p e r a t u r e o f I h e i i e a t e x c h a n g e r i s m o n i t o r e d b \ a l a t c h i n g
c o m p a r a t o r m a t i s I r i p p e d w h e n t h e h e a l e x c h a n g e r t e m p e r a t u r e h a s e x c e e d e d 3 . ^ ( . \
l i g l i t - e m i t t i n g d i o d e i n d i c a l e s i b i s s t a t e . I h e d r i v e t o t h e t r i g i s i o r i s a l s o s h u t d o w n l o a v o j d
p o s s i b l e d a m a g e . B e c a u s e o f t h e l o s s o f c o o l i n g t h e f i r s ! f a u l t c i i M i i l w i l l b e a c t u a t e d a m ! t h e
f a u l l s i g n a l w i l l b e g e n e i ' a l e i l . R e s c u i n g o f t h e l a l c h e d c o m p a r a t o r i s n e e d e d , b e b i r e n o r m . ! !
o p e r a l i o n c a n b e r e s t o r e d .
A n o i i i p u t o \ ' t r i l i a l e d w a t e r \ a p o u r i s o b t a i i K d I n s u p p h . i n g a i r t o l i v e i : i l c i a t a H o w
r a i e u p t o N {
j). Theory
The mass ol water M in unit volume of air leavins: a bubbler will be i;i\en b\
M =c (I ' .i.C,). h( 1 )
where t is the I'raclion of I he ingoing (dry) air that is saturated by moisture and isdependent upon the air How rate F. a temperature 1 and the particular geometryrepresented here by the variable ( i : and h is the saturated vapour density and is a functionof temperature T.
The concentration C. of tritium in air when the water in the bubbler is tritiated atspecific activity S is given by
C = M. a< P\r .G). S
where a is the ratio of the specific activity of tritiated water in the gas phase to that in thewater phase which depends here on the variables noted above.
The greatest variation with temperature will be in the saturated vapour density hwhich, approximately, is proportional to the temperature in degrees Celsius in thistemperature range. For one design of calibrator. G is fixed. Hence, assuming that thetemperature can be controlled to within a small fraction of a degree the concentration oftritium in air in the calibrator will be given by
C = e ( F ) a ( F ) h ( T ) . S.
If the pressure at which the concentration (per unit volume) is measured differs fromthat within the calibrator, then an additional term, 7. mis t be added to this expressionwhere 7 = (measurement pressure) ^ (calibrator internal pressure) so that C = ecryhS.
l(a) Assembly of Iritinni calibrator f'igure l(b) Assembly of tritium calibrator
Krilialcc! walcr container). (control circuits).
r
t
Block diagram of temperature control system.
I he description of the calibrator must therefore include the extent of the variation ofoutput concentrat ion with How rate and the effecl of ambient condit ions un tiutemperature. The actual average temperature in the calihraior may differ from the set pointtemperature because of the temperature distribution within the container resulting fromheat losses to the outside through insulation. This wiii also be affected by the heat influxwith the air and evaporative cooling. This "heat How1' may be analysed as lollows:
with
I" the input air How rateAT tii1.1 air ami a m b i e n t t e m p e r a t u r e minus the c o n t r o l t e m p e r a t u r eQ the heat of evaporation of water
p tiie density of airc the specific heat capacity of air (at constant pressure i
h tin; saturated vapour density of the effluent air
X the heat flux into the container with unit temperature difference
across the insulation
then tlie net rate (11) at which heat has to be dissipated by the frigistor is given by
1! = X.AT + F .c .pAT F.Q.h
Taking Q = 2.441) MJ/kg
;j = 1.185 kg/nr1
c = 1.012 kJ/fkg.K)h = : ) . 4 g / n r ' at 2S3 K (10°C)
(hen
H = XAT+ ! .20x HP1 AT.F 2 . . V \ K r 2 F i \
with X in J/(s.K) and F in e m ' / s .
The maximum value required for F is about 100 cnvVs. If AT ~ 20 K (20 cC). the lasttwo terms nearly cancel. Hence the heat gain from the incoming air can offset theevaporative heat loss, thereby reducing the demand on the cooling device. The heat gain byconduction should be reduced so (hat it is the same order (or less) as the maximumout-of-balance of the last two terms a few watts. For styrofoam insulation with thermalconductivity ~ 30 m\V/(m.K), about 5 cm thickness is needed for a 1 litre container.
Figure 3 shows the heat gain by such a system for various How rates and airtemperatures. Figure 4 shows the minimum temperature differential between set point andambient for cooling to be needed at various air flow rates, i.e.. for control to be maintainedin a cooled system. For example, at 67 cm 3 / s (4 C/min) the set point must be at least 5 K(5°C) below the ambient temperature.
H i u i i v 3 H e a t g a i n b v i n s u l a t e d c o n t a i n e r a t v a r i o u s a i r f l o w r a t e s . I l i e e f f e c t i v e
s u r f a c e a r e a i s a s s u m e d t o b e 0 . 3 5 m 2 .
f i g u r e 4 M i n i m u m t e m p e r a t u r e d i f f e r e n c e b e t w e e n a i r a n d s e t p o i n t v a l u e f o rc o o l i n n t o h e n e e d e d .
T h e c o n c e n t r a t i o n o f t r i t i u m MI a i r l e a v i n g t h e c a l i b r a t o r w i l l v a r y w i t h t h e t o t a lv o l u n i o f a i r p a s s e d t h r o u g h . A s w a t e r e v a p o r a t e s f r o m t h e c a l i b r a t o r , i ' l e s p e c i f i c a c t i v i t y o ft i i e r e m a i n i n g w a t e r w i l l c h a n g e b e c a u s e t h e s p e c i f i c a c t i v i t y o f t h e v a p o u r d i f f e r s f r o m t h a to f t h e l i q u i d ( i . e . a ^ I !. A s s u m i n g t h a t d r y a i r i s i n t r o d u c e d i n t o t h e c a l i b r a t o r , t h e s p e c i f i c
a c t i v i t y o f the wa te r w i l l he sziven b y ' 'h.F. t
S = S O ( 1 w
a 1
u h e r e S o a n d \ V ( ) a r e t h e i n i t i a l s p e c i l " : a c t i v i t y a n d i n i t i a l m a s s o f w a t e r i n t h e c a l i b r a t o ra n d t is t h e l i m e f o r w h i c h a i r H o w s a t r a t e F . T h e v a r i a t i o n o f S S ( 1 ( a n d h e n c e ( ( " o ) w i l lt h e r e f o r e d e p e n d u p o n t h e v a l u e o f a f o r t h e p a r t i c u l a r b u b b l e r u s e d h e r e .
4. Performance
The output concentration of tritium in air is t-.iven by
(' = 7tahS from Section 3.
where 7 i*. the ratio of pressure at which concentration is measured to that in thecalibrator
f is the fraction of air saturated by the calibratora is the ratio of specific activity of HTO in the vapour phase to that in the
liquid phaseh is the saturated vapour densityS is the specific activity of the calibrator water.
The values of the coefficients in the relation between output concentration andspecific activity were determined on the prototype calibrator using the apparatus shown inFigure 5. The value of 7 is close to unity. The measured value of e. the saturated fraction, iswithin 4'V of unity and its variation with flow rate relative to the value at 4 fc/min is shownin Figure 0. The isotope coefficient, a. was determined to be 0.78 at a flow rate of 4 V/minand its variation with How rate relative to this value is also shown in Figure 6.
The range of e relative to the value at 4 t/min is from 101.2'/ at 1 t'/min to 99.8" at 8fc'/min: the similar relative range of a is from 1 02 r ' at 1 C/min to 99" at 8 !i/min. Hence, forthe set temperature of IO°C (h = 9.4 g/m3 ), the output is given by
C=750S(MPC) a
where S is in Ci/kg and the internal and external pressures are equal. The error is less than±3.5'; for a flow rate range 1 - 8 8/min as is shown in Figure 7 by the line labelled"tritium". This is the product ea estimated from Figure 6.
The variations above are for an ambient air temperature of" 23° C at which, as isobscrved from Figure 3, the evaporative heat losses nearly balance the heat gain from theincoming air.
The effective temperature of the water in the bubbler is affected by the ambienttemperature, and. to a lesser extent by the frigistor cooling water temperature. Thecorresponding variation in saturated vapour density (and, approximately in tritium outputconcentration for low flow rates) is 0.1 27(1°C variation of ambient air temperature in therange 1 3°C to 35°C and 0.07"/°C variation of cooling water temperature up to 35°C.
The measured rise time constant for flow rates greater than 1 C'min is less thar '0 s.i.e.. 99.7" of the steady output is attained in I minute. In an extended run of 3 hours, theconcentration kept within 1.3" of a mean value.
The concentrations in output air for repeated on/off measurements had a standarddeviation of 0.2" over a period of 2 hours.
The specific activity of the water in the calibrator increases with air volume passed,approximately at 0.4"/nr\ At 4 E/min air flow, the change is 0. ]'",/h.
—-tXf-r —
7 y..A1- A
HX -©
l- ' iL' i i iv 5 . \ p | i ; i r ; i l i i s l o r d e t e r m i n i n g t h e c h ; i I L K i c r i s l i L s o f t h e c a l i b r a t o r . '1 he w a t e r
Ir;ip--. arc l o p r e v e n t c ross c d i ) I ; j m i n ; i t i o n o ! c c j i i i p n i c n l s h o u l d l l o w ra tes o r p ressu res
he a l l o w e d l o range h e \ o i u l a c c e p t a b l e l i m i t s . The t r i t i u m m o n i t o r w a s a p o r t a b l e
i o n i / a l i o n c h a m b e r t y p e A l l 1 521 5 1 " ' 1 . The ! 1 T ( ) t r a p s w a t e r h u b ' o l e r s e o l l e e t e d
i a t e d w a t e r \ a p o u r e m i t t e d b y t h e e a l i h r a t o r .
I— 1 r ~i r
I
I
1-iL'ure (i \ a r i a t i o n o t ' i / and a w i t h How- rate. A m b i e n t a i r t e m p e r a t u r e is 23° ( " .
[ T h e read ing e r ro r o f the dew p o i n t m e t e r used t o m o n i t o r the o u t p u t c o r r e s p o n d e d
l o i l ) . . ^ ' • in i-: i ha t o | the t r i t i u m m o n i t o r c o r r e s p o n d e d t o ± 0 . 1 ' ' i n t he p r o d u c t ac. T h e
'.al l ies o f a were e s t i m a t e d f r o m the measured ae and the values o f a de r i ved f r o m the i i ne
T i l led l o the measured a values. The e r r o r bars s h o w n c o r r e s p o n d o n h t o the read ing
iU >
102
01
00
99
98
\
i
i 1 i i i 1 1
\
3 4 5 6
R F L O . - . R i - T E : L I T R E S P E R M I N U T E
Figure 7 Variation (if humidity output (e) and tritium (uilpui (cai with How rate.
5. Acknowledgement
We appreciate the assistance of B.A. MacOonald in producing the engineering drawingsfor this calibrator.
6. References
1. R.V. Oshorne. Sampling for Tritiated Water Vapour, p.1428-1433 in "Proceedings of
I lie Third International Congress of the International Radiation Protection Associa-
tion, September 9 14. /W,"( '0NF-730907.
2. R.V. Osborne, Central Tritium Monitor ("or CANDU Nuclear Power Stations. 1HEETrims. Nucl. Sci. \S-22.
R.V. Oshorne and A.S. Coveart. A Portable Monitor for Tritium in Air. Nucl. Instr.
Methods I Of). 1X1-187, 1973.
Al.
A3.
AI'PKNDIX A
SPECIFICATIONS
Tritialed VV:i(er Vapour Output
( oneentratiou in output air
Reproilucibilily
Variation of concentration inair with flow rate
Variation of concentration inair with total How
Variation of humidity in
air with How rate
Specific activity o I water
vapour relative to water
A2. Operating Conditions
Air How rate range
Inpul air humidity
Water in calibratorControl temperature set pointAir pressure drop across calibrator
Ambient temperature range forspecified set point
Supplies
Cool inn water: pressurequalityflow rate
Proportional to concentration
of tritium in vatcr to within ±3.5 ' ;
for operation under specified conditions
0.2';
+ 2'' at 1 V/min to
I'"' at 8 t/min relative
to value at 4 t/min
+0.4 ' ' /nr 1
+ 1.2'' at i (.'/min to1.2'' at ?! t'/min relative
to value at 4 v'min
0.78
1 8 v/min
Dew point < 25' C
300 500 g
10"C± 2°C
< 100 Pa ( < 5" I! : O)
18°C 35°C
<1 M P a ( < t 50 psi)Domestic service water adtquute< 1 cm3 ,'s
Power 115 V. 60 Hz. 100 W
A4. Temperature Controller Characteristic
Deviation from nominal set pointlor particular specified thermistor
Adjust nent ol' temperature control
Temperature control stability
Automatic shutdown of controller
\ 5 . Indicators
Power
laull
Aft. Signal Output
Fault
A7. Connections — Electrical Isee Figure Al )
I ine
I a u l t
AS. Connections — Mechanic.il (see Figure Al )
Dry air inlet
I Vitiated water vapour outlet
Cooling water in
Coolimi water mil
+ O.U.V'C
I leal exchangertemperalur • >15
On when line supplied and
main fuse intact
On when temperature notbeine controlled
MS V to +1 V level change when
temperature not being controlled
A9. Controls - Electrical (see I'igure Al
Power on/otT
luse l l I'l )
luse ( I : L : 2 I
Reset
3 pin (Bendix PTO2A 12 3P)
2 pin (Bendix PTO2A S 2S)
'-i" polyllo
' j " poly Ho
1 a" polyllo
V polyllo
Switches line to calibrator
2 A. protects complete unit
0.5 A. protects control system only
Resets cooling watertemperature sensing and drivecircuits
A10. Controls Mechanical (see Figure A I )
inlet shi't-ol'l valve V,
Outlet sh:n-olT valve V2
A l l . Dimensions
( abinel si/e
Connec t s dry air inlet t o
bubb le r
Connec t s t r i t ia ted wa te r
vaoour ti- ou; le t
47 cm high x ?H cm wide x 23 cm deep
( I X ' : " x 1 5 " x T l
15 km'-33 I hi
I'isiuiv A 1 Conlrol and connector panels.
APPENDIX 15
CIRCUIT DESCRIPTION
B1. Bridge Amplifier (Figure BI )
Thermis to r T i l l senses the cal ibrator cell t empera tu re . The signal voltage at thejunct ion of T i l l and R13 is amplified ami inverted by A2. 1 he reference voltage at thejunction of R2 and R5 is amplified hy At and is summed with the inverted signal voltage byamplifier A3 with a max imum gain of i 000 . Diode ( R2 limits the negative swing of A3 toprotect the following circuit. Capaci tor C4 limits the bandwid th of amplifier stage.
Resistors R4 and RX may be set to the value of the thermis tor T i l l at the desired
opera t ing t empera tu r e and subs t i tu ted tor T i i l by switch SW1. P o t e n t i o m e t e r R 14 enables
the out-of-balance signal to be zeroed at this set point .
Ihe rate of change of ou tpu t voltage with t empera tu re from A3 at m a x i m u m gain is
0 .022 ( "V . The span of 0 12 V therefore cor responds to a variation of 0 .2d°C in
thermis to r t empera tu re .
B2. Pulse-width Modula tor (Figure B2i
( lock (IC2) produces negative going pulses 7 jus wide at f requency 5 0 0 Hz deter-mined by R 3 3 . K34 and C3 . Tliese pulses trigger 1(1 on the negative going transi t ion.Ihe pulse width from IC1 is modula ted by the error voltage from the bridge amplif ier suchthat the du ty cycle of the I(T ou tpu t varies from a few percent to grea ter than 80rV asshown on Figure B3. This fixed frequency, variable duty-cycle signal is applied to thefrigistor drive circuit .
Loss of adequa te cooling for the frigistor results in the connec t ion at C'3 and R 3 4being g rounded . This shor ts out the timing capaci tor ("3 s topping IC2 oscil!a<ing andshut t ing off pulses to the frigislor drive circuit .
B3. Frigistor Drive (Figure B4)
The variable duty-cycle pulses from the pulse-width m o d u l a t o r are amplified by theDarlington pair 0 3 . Ol to drive the frigistor.
When the drive pulse is high, both 0 1 and 0 3 sa tura te and supply power to thefrigistor and reservoir capaci tor ( ' ! . When the drive pulse is low, Q l and Q3 are tu rned off.leaving the charge on Cl to supply current to the frigistor for this interval. The effectivetime constant of the parallel combina t ion of Cl and the frigistor ( 1 4 jus) is much longer thanthe clock period.
lle.it dissipation in the drive circuit is decreased by this switching technique . Theaverage voltage across the frigistor is p ropor t iona l to the duty cycle ot the drive pulses.
12
NON-INVERTING AMPLIFiEROUTPUT TO
C 4 PULSE-WIDTH
MODULATOR
BRIDGESUMMING AMPLIFIER
INVERTING AMPLIFIER
•"igurc Bl Temperature sensing bridge inui amplifier circuit.
MODULATED MONOSTABLE CLOCK
SIGNAL VOLTAGE FROM
BRIDGE AMPLIFIER —
R 3 3
2I NEL55S
J_- C l
R 3 4
T-i
TO F R I G I S T O R D R I V E C I R C U I T SHUT DOWN S I G N A L FROM HEAT EXCHANGER
TEMPERATURE S E N S I N G C I R C U I T
Fieun.1 B2 Pulse-width modulutor circuit.
80 —
?0 —
bO —
2 1 b 6 10 12
SI GtJOL VOLTDGE FROI' BRIDGE fiMPLIcIER
Figure B3 Variation of pulse-width modulator duty cycle and frigistor current withsignal voltage.
B4. Fault Detector (Fi«ure B5)
The output voltage from the bridge amplifier is monitored by a window comparatorA5. A6. The potential divider R2S. R2<> and R30 establishes the reference voltages +1 1.8 Vat the inverting input of amplifier A6 and +0.6 V at the non-inverting input of amplifier A5.If the bridge output voltage is between 0.6 and ! \.H V. then the output of A6 is low and isisolated from A5 and the output of A5 is low. The base of Q4 is held at approximately 0.6V and the monitor output is high.
If the bridge voltage is less than 0.6 V, then A5 output goes high, turning on 04 andholding the monitor output close to ground. Similarly, if the bridge voltage is greater than13.5 V. A6 output goes high taking A5 output high and turning on Q4.
Hence when the control circuit is hard on or hard off. indicating loss of control, thefault detector output is low.
14
5.5V
SIGNALPULSES
IN
FRIGISTOR
Fisuire B4 I1'ritiistor drive circuit.
S I G N A L V O L T A G E FROM B R I D G E A M P L I F I E R
-15V
WINDOW COMPARATOR
FAULT SIGNAL
i-itiure B5 Fault detector circuit.
RESET
SV 2
/̂ |
f v W M !
--{X—! N 4 4 I
SHUTDOWN SiGNAL
TO CLOCK
FAULT INDICATOR
Figure Bd Frigistor heat-exchanger temperature-sensing circuit.
B5. Frigistor Heat-exchanger Temperature-sensor (Figure B6)
The- temperature of the heat exchanger is sensed hy thermistor Til2. Temperatureexcursions above .^"C result in a decrease in thermistor resistance sufficient to trigger avoltage comparator.
Normally, the output of amplifier A4 is low and the non-inverting input of A4 is heldnegative with res pec I to the inverting input by the potential divider R21 and TH2. Theinverting input voltage is set by the potential divider R15. R18. When the temperature of1112 goes beyond 35°C. the voltage at the non-inverting input goes positive with respect tothe other input and A4 output latches high. 01 is turned on and shorts out the timingcapacitor in the pulse-width modulator, thereby shutting off the drive to the frigistor. Q2 isalso turned on. energizing the light emitting diode LED-1.
When adequate cooling water hax been restored to the heat exchanger, the circuit canbe reset by SW2. operation of which momentarily increases the voltage at the invertinginput of A4 above that at the positive input, thereby driving the output low. A reset is alsoneeded when the device is initially turned on.
Triggering of the circuit and the resulting loss of drive to the frigistor will also activatethe fault detector circuit since the bridge amplifier output will go out of the normaloperating range.
APPENDIX C
OPERATING PROCEDURES
C'l. Choice .)(' [Vitiated VV;iler Concentnition
T h e o u t p u t c o n c e n t r a t i o n ( ' in a i r is g i v e n a p p r o x i m a t e l y b y
C - 7 5 0 - y s ( M P C ) . , ( s e e S e c t i o n 4 in n m i i i t e x t I
w h e r e S is t h e w a t e r c o n c e n t r a t i o n in ( i k g . 7 is t h e r a t i o o l p r e s s u r e a t t h e o u t p u t t o p r e s -s u r e wi t h i n t h e c a l i b r a t o r a n d ( h e c o n s t a n t o f p r o p o r t i o n a l i t y h a s t h e u n i t s 1 f j"5 k g m '
a n d 1 < MPC ' ) . f = l ( ) / j ( ' i m \ d e f i n e d f o r s t a n d a r d t e m p e r a t u r e a n d p r e s s u r e .
H e n c e , f o r a c a l i b r a t i o n c o n c e n t r a t i o n in a i r o f ( ( M P C I w i t h 7 = 1
Approximately 500 g of tritiated water at this specific activity is needed in thecalibrator.
If the specific activity of the tritiated water in the calibrator needs to be changed then
the cell shouid be thoroughly dried before adding the new tritiated water. The filling cap
must be closed i'irmly before the calibrator is used.
The speeif'ie activity and quantity of tritiated water in the calibrator should be notedon the outside and the appropriate 'radioactive material' label affixed.
The actual output concentration should be confirmed by following the calibrationprocedure F2.
C2. Using (he Calibrator
2.1 The output air is tritiated; the calibrator must therefore be used in a closed system orin a suitably ventilated room.
2.2 I he calibrator control system should have been set up following procedures inAppendix I: I and the output concentration should have been verified followingprocedures in Appendix F2.
2..} Follow the routine check out as given in Appendix (S3.
2.4 Connect a dry air supply to the calibrator inlet via a flow regulating valve and flowmeter (V3 and I:l 1 in Figure CI ).
2.5 Connect the outlet to the system to be calibrated.
2.(i If the calibrator has been disconnected from line power, reconnect, turn on and resetthe fault circuit. Leave to reach thermal equilibrium. From ambient temperature, anovernight wait is recommended.
17
. afCUR OUT
l i g u r e ( I C o n n e c t i o n s to the Cal ibra tor .
2.~i ( l o s i . 1 i V L i i i k i t i i i i : v a l v e V , , o p e n \ ' , . o p e n V , a n d s l o w l y o p e n V , t o g i v e a flow r a t e
wilhin the lanue I-S l!/min th rough the ca l ibra tor . The nomina l value of 4 f n i i n is
r e c o m m e n d e d .
C'.?. Routine Check-Out of Calibrator
Before each use the following should be con f i rmed :
3.1 Inlel and out le t valves are closed, the filling cap is secure and the the rma l insulat ion is
in place.
3.2 Cool ing wate r is c o n n e c t e d and is ( lowing. If the wa te r supply is c o n n e c t e d but wa t e r
does not flow Hi rough, check that the supply pressure is at least 10 kPa above ambien t
( 1.5 psigl. If so . inspect the wate r lines for b lockage and clear as needed .
. \ 3 The ambien t t e m p e r a t u r e is within the specified l imits . 18 C 35 C.
3.4 1 lectrical power is c o n n e c t e d , is swi tched on and is indica ted by the ' p o w e r on" l amp .
If the lamp is not on . d i sconnec t the line cord and inspect line fuse I -1 ' I : replace if
needed. If the fuse blows a second t ime, fol low fault diagnosis p r o c e d u r e \)2.
} . ^ Coolant fault circuit is not a c tua t ed and fault ind ica tor . I .HD-1. is not on . If Lhl)-1 is
on a l though cool ing wate r is suppl ied , reset the fault circuit (SW2). If the circuit will
not reset or the indica t ion repea ls immedia te ly or after power has been suppl ied for
several minu te s , measure the inlel wa te r t e m p e r a t u r e which should be < 3 0 ° C and
the flow ra te which should be > 1 0 0 g /min . If these cond i t i ons are met and the
coolant fault indicat ion persists after resets, follow the fault diagnosis p r o c e d u r e D3 .
3.(i Cont ro l fault signal is 'high1 (—15 V) indica t ing that the t e m p e r a t u r e is within 0.2"'C
of the set poin t . If" the set point has just been changed or the unit filled u p o r swi tched
on. then a ' l ow ' (^-1 V) signal will persist until the t e m p e r a t u r e is wi th in 0 .2°C of the
set point . If the l o w ' signal persists after the ca l ib ra tor has been on for several hou r s .
then follow the fault diagnosis p r o c e d u r e 1)4.
1 s
AITFNDIX I)
I AULT DIAGNOSIS
i) 1. Inili;il Diagnosis
fc i i " ; n i \ f ; i u l t . the p r o c e d u r e fo r r o u t i n e check out o l I he m o n i t o r . A p p e n d i x ( J .
s h o u l d be f o l l o w e d be fo re the p r o c e i lures in th is .Append ix . I he tai l I Is l o r w h i c h gu idance in
d iagnos is is g iven a ' c :
D2 Persistent b l o w i n g o l I use I I ' I
1).^ Persistent coo lan t fau l t i n d i c a t i o n
1)4 ( o n t i o l fau l t i n d i c a t i o n
1)5 O u t p u t c o n c e n t r a t i o n o f t r i t i a t e d wa t e r v a p o u r h igh
\)<i Output concentrahon of tr i t iated water vapour low
D"1 Output concentration o f tr i t iated water vapour not steady.
1)2. Persistent Blowing of Fuse I-U 1
fau l t in :
1. 01 and frigistor circuit
2. Power supply PSI or wiring
1.2. D isconnec t the lead a! the pos i t i ve o u t p u t o f PSI .
Replace the fuse and sw i t ch on Schemat i c <i I
1. I f the fuse remains i n t a c t , the lau l t is
in the f r ig is to r c i r c u i t , e i t he r the
f r ig i s to r . 0 1 . ( 1 o r the i n c o n n e c t i o n .
2. I f the fuse b lows again, inspect the w i r i n g
to PSI and I P I . I f i n tac t and l .Pl is not
s h o r t e d , the faul t is in P S I .
D.i. Persistent Coolant Fault Indication
( omplele Procei' ire (.'?>.
Fault in :
1. Sensing assembly2. 1 led rical circuit
1.2. Disconnect ine wires to 1112 at terminals I B 1-5 Schematic ( I i
and T B I - d and measure the resistance o f TM2. Assembly F l
I. I f the resistance is less than 4.5 kf>. then
the sensing assembly is defective. Inspect
the wir ing and mechanical assembly for
faults. Assembly ! :2
I')
if the resistance is greater than 40 k£2. (henthe thermistor circuit must lie open.
If the resistance is within the range 40k£2 4.5 k!2. then the conlrol circuit is faults.Check the voltages associated with the Schematic G2A4 circuit lo locate the defective component. Appendix P>5
1)4. Control Fault indication
Complete Procedure C3
Fault in:
1. Inconnections
2. Power supply3. Window comparator4. Bridge amplifier5. Pulse width modulator(>. Frigistor7. Sensing thermistorX. Control loop win
1. Inspect the readily accessible wiring of
TB1 and PC 2 for breakage. Assembly HI
2. Measure the power supply voltages on PC2 at Schematic (11terminals C ( + 15 V). D (-15 V). G (Ground) Assembly (.3and M (+5.5 V). If an incorrect voltage is observed.
check the connection to the power supply. If intact,disconnect the power supply from all circuits andremeasure the output voltage(s) for a 5 fi. 5 W loadon PSi. a 1 50 ft 2 W load on PS2. If the supplies arecorrect, the fault must be on PC2 or the frigistordrive circuit. Check for overheated components.
3. Measure the voltage at terminal .1 on PC2. Schematic G2if it is between 0.6 and 1 1.8 V. the system is Appendix B4controlling. The fault must be in the window
comparator circuit, A5. A6. Check the voltagesto locate the faulty component.
4 7. If the voltage at terminal J is outside 0.6-1 1.8 Schematic G2V. the circuit is not controlling. Assembly G3Switch SW! on PC2 to CALIB and measure the Appendix Blvoltage at terminal J on PC2.
4. If the voltage at J is not within the range0.6-1 1.8 V, the bridge amplifier is incorrectlyset up or is faulty. Check voltage': associated
with A I, A2 and A3 to locate the faulty components.Follow the commissioning procedure HI to set up. Procedure HI
20
5. 11" the voltage al J is within the range 0.6-1 l.N Appendix B2
V. observe the waveforms on an oscilloscope at Waveshapes H2
pins 3 and (i on 1C1 and IC2. If any are incorrect
replace the appropriate K".
(•>. if the waveshapes in 5 are correct observe the
waveshapes at terminal 1. on PC 2 and thenegative terminal ol 'CI . J Coil her is incorrect.the wiring to the I'rigistor stage o r Q 3 . Q l . Schematic CA
(\ or the I'rigistor is faulty.
7.X If the waveshapes in 5 and 6 are correct thesensing thermistor Till is probably faulty or thecontrol loop gain is too high. Measurethe resistance from terminal B to te-minal A on PC2(SW1 in CALIB position). This should be 2.2-2.6 kfiat I()°C to 1.3 kfi at 25°C. A fault in TH1 may beverified by setting the voltage at terminal J onPC2 to 10 V by adjusting the calibrate control R4and observing thai an increase in resistance of'J'Hldoes not occur, indicating that the increasedcooling is not being sensed. Return R4 to previousset points.
X. If the TH I value is correct, reduce the loop gain by an
anticlockwise adjustment of R25 by a maximum of 10turns, l! this adjustment stabilizes Hie controlthen the thermal coupling between the cooler andthe sensor has deteriorated and should beinspected as soon as practicable: operation withreduced gain gives poorer control of thelemperature. If the reduction in gain does notstabilize the control system then the thermalcoupling her ween the sensing thermistor and thecopper can should be inspected.
1)5. Output Concentration of Triliated Water Vapour High
Complete Procedure ('3.
Fault in:
1. Air How-rale
2. Calibrator internal pressure3. Water in outlet tubing4. Temperature set point5. Specific activity of tritiated water
1. Check lhat the airflow rate is not grea ter
tlian Kl'/min. (It" a higher How has been IKCII.
w;iior may have been blown in to the out le t
tubing am! the eonevn t r a t i on may c o n t i n u e
high.)
2. Check lhat the pressure in the ca l ib ra tor is correc t .
( Nole the o u t p u t c o n c e n t r a t i o n varies wiili abso lu te
pressure in the ca l ibra tor . |
3. Sinn off the How through the ca l ibra tor by
closing V I . V2. A d o p t i n g p recau t ions a p p r o p r i a t e
to the c o n c e n t r a t i o n of i r i i ia led wate r used,
replace the lulling c o n n e c t e d t o Ihe ca l ib ra to r
ou t l e t . Retest Ihe o u t p u t , leaving the air
flowing Tor ~ 30 minu te s to remove any wa te r
d rop l e t s in the internal tub ing .
4 .5 II the high c o n c e n t r a t i o n persists, measure
the dew point of the out le t air. if this is
also high then dry ing is not c o m p l e t e or the
set point is high. ( N o t e t i n t the normal set
point ad jus tment can only vary ihe o u t p u t
c o n c e n t r a t i o n by 20 ' <'.)
5. If the dew point is correct then the specific
activi ty of the t r i t ia ted wa t e r is high. Change
the wa te r following the p r o c e d u r e C l . A p p e n d i x C
1)6. Output Concentration of Trilinled Wnler Vapour Low
Complete Procedure C3.
I'iiult in:
1. Air How rates
2. Calibrator internal pressure
3. Specific activity
4. Level ot water in cell
1. Check that air is flowing out of the
calibrator at the required How rale.
2. Check internal pressure in the calibrator. A high
ratio of internal pressure to external pressure
results in a low measured external concentration.
3. Measure the (.lew point of the outgoing
air. If this is correct, then the
specific activity of the tritiated
water is incorrect. Change as appropriate. Appendix C
4. II the dew point is low. replenishthe water in the cell, using tntiutedwater of the same specific activity.
1)7. Output Concentration of Tritiated Water Not Steady
Complete Procedure C3.
Follow Diagnosis 1)5. faults 1.2.
Diagnosis 1)6. fault 3.
APPENDIX K
COMMISSIONING. CALIBRATION AND SERVICING PROCEDURES
El . Commissioning
1.01 Equipment and drawings needed:
.1 1/2 digit multimeter. 0.1 mV resolution
Oscilloscope. 100 kHz hand-width minimum
Thermometer for ambient temperature, ±0.1 °C
Drawings: G l , General schematic
G2. Temperature control board schematicG3, Temperature control board assembly
Tritiated water. 500 g at required specific activity (see Appendix C'l )
1.02 Complete the assembly of the calibrator.
1.03 Make sure that the whole unit is at ambient temperature i.e. power has not been
applied within the last few hours.
1.04 Set SW1 to CAL1B and determine the sensing thermistor resistance at ambienttemperature by measuring the resistance from terminal A to terminal B on PC2.
1.05 Measure the ambient temperature to ±0.1°C.
1.06 Determine from Figure El the multiplying factor for this ambient temperature.
1.07 Multiply the measured thermistor resistance by this factor. The result is the resistancethat the thermistor will have at 10°C. (Note, because of the tolerances in thermistorparameters the actual set point may be up to ±2°C from this value. If a more preciseset point is required then paragraph E.i should be followed.)
1.08 Switch SW1 on PC2 to SET.
1.01' Measure the resistance from terminal A to the switch end of R8 (i.e. R4 + RS).Adjust K4 so that the combined resistance R4 + R.S equals the value of resistance ito+ i n (determined in 1.07.
1.10 Turn the power on (SW1) on the front panel (see Figure G l ) and verify the suppliedvoltages at terminals (' ( + 15 V), D(-1 5 V) and M (+5.5 V) on PC2.
1.1 1 Switch SW1 on PC2 toCALJB.
1.12 Measure the voltages from pin ft of Al and pin 6 of A2 to ground terminal G (seeFigures G l , G3 i. Adjust RI4 so that these voltages have equal magnitude (butopposite polarity) to within 1 mV.
1.13 Set R25 to maximum value (maximum clockwise) and adjust R27 so that the outputvoltage of A3. measured at terminal J. is between 4 V and 5 V.
24
2.OF
1 .9 —
1 .8 -
1.7 1.
L I I | I I | | | | I | I | | I | I | | I | | I | I I I I I I ) | I I I I I I I I I I I I I I I I ' I I " I I I I I
1 P h . .. .I ,. . .I ... . I . . . . I • ... I ... . I . . . . I15 16 17 18 19 20 21 22 23 24 25 26 27
AMBIENT TEMPERATURE °C
Figure HI Multiplying factor for the control thermistor resistance at the set-pointtemperature.
1.14 Supply cooling water at a temperature below 30°C and a flow rate of at least 100g/niin.
1.15 Press reset SWj on front panel.
l . l d Ve r i f y that the waveshapes in the pu lse-w id th m o d u l a t o r and f i i g i s to r dr ive are as
shown in Figure \2. 1 he c lock per iod shou ld be 1.9 + 0.3 ms and the c lock pulse
width 7.5 .+• 1.0 fj\.
1 . 1 7 S w i t c h S W I o n P C ' 2 t o S I ; T a n d v e r i f y t h a t t h e d u l y c \ c l c o f t h e w a v e f o r m a t p i n 3
o f 1 ' C I i n c r e a s e s s o t h a t t h e ' h i g h ' l e v e l i s m a i n t a i n e d f o r g r e a t e r t l v . n i ( ) ( ) ' • ' o f t h e
l i m e . . A t t a c h a v o l t m e t e r b e t w e e n t e r m i n a l .1 a n d g r o u n d ( t e r m i n a l ( I ) , s w i t c h S W I t o
" C A I I H " a n d b y v a r y i n g R I 4 v e r i f y t h a t t h e d u t y c y c l e v a r i e s f r o m - 1 0 : t o - S O as
t h e v o l t a g e a l .1 v a r i e s f r o m — 0 V t o - 1 3 V .
I . I S ( h e c k t h e f a u l t a l a r m c i r c u i t as f o l l o w s : . A t t a c h t h e v o l t m e t e r a l t e r n a t e ! ) b e t w e e n
t e r m i n a l k o n P C 2 a n d g r o u n d a n d t e r m i n a l .1 a n d g ; > . u n d a n d v e r i f y t h a t t h e \ o l i a < j e
a l k is r e l a t e d t o t h e v o l t a g e a t .1 as s h o w n b e l o w ( R I 4 i s u s e d t o a d j u s t t h e v o l t a g e a t
.1) .
.1 K
> ! V j > I 4 V
--.10 V \
<0.5 V
> 1 2 V
1.1') Reset R U s o t h a t the voltage al .1 is between 4 V and 5 V.
1.20 Cheek the coolant fault circuit as fol lows:
per te rm ina l I I to te rm ina l i on PC2 and ve r i l y that I.I-.DI ( F A U L T ) is energized
and that the voltage at te rm ina l 1 is reduced to less than 0.3 V . Sw i t ch SWI to SHT
ami tu rn power o f f .
1.21 A d d 500 g o f t r i t i a ted water o f the requi red speci f ic ac t i v i t y (see A p p e n d i x C l )
tak ing I lie precaut ions appropr ia te for that ac t i v i t y o f t r i t i u m .
1.22 T u r n the power o n . press the Rl-SI-.T (SW2 OP f ron t panel) and leave overn ight to
reach a stable tempera tu re .
l .2. i l u r n o f f the coo l i ng water supp ly . V e r i f y that a f ter a few m inu tes the coo lan t faul t
i nd i ca to r 1.1 D I is energized and that the fault a larm is also act ivated ( < 1 V at
te rmina l K. on l 'C2).
1.24 Turn coo l i ng water on and press RFS I T (SW2) .
1.25 The o u t p u t f r o m the ca l ib ra to r shou ld n o w be checked f o l l o w i n g the ca l ib ra t ion
procedure l '2 .
(a )
Figure L2 Waveforms observed with vertical V/cm and horizontal s/cm oscilloscopesellings as shown at:
a. Pin 3 of IC2
K Pin f i o l ' K ' 2
c. Pin 5 of IC!
Upper, w i th voltage at J = 1 V
Lower, wi th voltage at J = I OV
d. Upper, terminal L on PC 2
Lower, negative connection of ("1 and frigistor.
E2. Calibration
2.01 This method allows the output from the calibrator to be established with respect to aliquid scintillation counting standard. The equipment required is as follows:
Dry air supply: dew point <-25°C
How rate 4 t/min minimum
pressure < 20 kPa gauge
27
Air control valve and How meter for air at 4 t min.
Two-way change over stopcocks (V4. V5)
Fight. 250 cm3 gas-washing bottles ( huhhlcrs 151 BM
Wet test meter, accuracy ±3 ' ;
Six volumetric flasks. 250 c m '
Six pipel tes. 1 c m '
f 'tilling. I !4" polyelhlene. as rctjuirccl
Distilled water as required
Liquid scintillation counter with known calibration.
2.02 The commissioning procedure (Appendix I: I I or the routine check-out of the
calibrator (Appendix ('?•) should have been completed.
2.03 Connect Hie calibrator as shown in Figure H3. The calibrator should be allowed tostabilize overnight if the power has been recently turned off for more than a lew-minutes.
2.04 Turn stopcocks V4 and V5 so that bubblers B1 and B2 are open and B3 and B4 are
closed oil'.
2.05 Open V2 and VI .
2.0(i Open V3 to allow 4 t/miii air How rate through the calibrator and note the time.Confirm by liming that the flow rate at the wet test meter (WTM) is the same, withinthe meter accuracies, as that indicated on the flow rale meter. If it is not. locate theleak(s) in the interconnections, taking the precautions appropriate for the specificactivity of tritium being used in the calibrator.
2.07 Approximately 10 minutes after opening V3. watch the volume reading on the WTM
and, at a convenient scale point, rapidly valve out 131 and B2 and valve in B3 and B4.
Note the WTM reading at this change-over.
2.0S Replace Bl and B2 with B5 and Bd. each containing 200 cm3 distilled water.
2.01) When 30 lilies of air have passed through the WTM, valve in B5 and B0 and valve out
B3 and B4.
2.10 Repeal 2.OS. 2.0<) will) B7. B.S.
2.1 1 Repeal 2.OS. 2.0l>. inserting Bl and B2 for the final change-over.
2.12 Close V3. VI and V2.
2.13 Transfer qualitatively the contents of B3-BS to six labelled 250 cm3 volumetric flasks
and top up these to 250 em 3 .
2.14 Withdraw 1 cm3 from each flask for liqii'd scintillation counting. Note: the activity in1 enr1 from the B3, B5 and B7 bubblers may be greater than desirable for directinsertion into a counter, depending upon the calibrator content and normal counterapplication. For guidance the table below gives the extra dilution that such a I cm3
sample requires to give a I c m ' sample containing ~~ 2 x 104 disintegration per
T a b l e F l : D i l u i i o n o f I a n ' s a m p l e f r o m 2 5 0 t i n ' w a t e r c o n t a i n i n g a c t i v i t y c o l l e c t e d f r o m
M) l i t r e s o f a i r f r o m c a l i b r a t o r .
W a t e r A c t i v i t y
C i ' k »
0.1
0.01
ApproximateAir Concentration
<MPC)a
700
70
7
Dilution
100
10I
Dilute as required and determine the sample counting rales.
2.15 Calculate the activity collected in eacn bubbler from the observed count ing rate, the
calibration factor of the liquid scintillation counter , and the total dilution of the
sample which is 250 x the extra factor as determined in 2.14. For example , for
sample B3. with.
N , min"1 = counting rate from B3
N . niin"' per disintegialion min"1 = calibration factor for this kind of sample in the
counter as derived from a standard
and I ) , = 250 x the factor as determined in the table in 2.14 for this sample.
then
Activity- col lected (A3) =
N , '
N..I ) , min ' .
2.1 6 Calcula te the average d is in tegra t ion rale per unit air vo lume from.
A =A , + A4 A s + A() A 7 + A,
V 7 K
min ' litre '
where V , 4 is the air volume passed through B , . B 4 , e tc , nominally 30 litres in this
series.
2.1 7 Calculate the calibrator ou tpu t (C) in (MPC) from:
C = A (MPCL
I UMI'O. = 10
D R Y A I R
I N P U T
" 2
CALIBRATOR
AEP 5284
-o
l i ^ t i r e I . ; A p p a r a t u s f o r m e a s u r i n L ! I h o o u t p u t f r o m i h c c a l i b r a t o r .
I.i. Adjusting I he Temperature Sol Poinl
T h e o u l p u t c o n c c n l r a t i o n and h u m i d i t y m a \ l ie ad jus ted up I " * ! ( ) ' • b\ c h a n y i n i : the
\ a l u e o f l i i o re fe rence rcs is lo rs . 1^5 -t K 1 4 on P C I . T h e percen la t i c ch ;mgo in o u l p u l
I ' l i i K o n l r j i i on nv l i u m i d i l y is a p p r o x i m a t e l y 1.5x the peivenla jze c lmngo in re fe rence
iv^ is io i - - . i.e.. i l l l ie e o n i h i n c d va lue o l K5 + R 1 4 is i iK ' iv ; isod by (>'•' the o u t p u t
e o i K Y i i i n i i i o p . w i l l he deeieased h>' l ^ ' - . i This is de r i ved f r o m the l l i o r m i s t o r ( en ;pe ra l i i r e o f
eoe 'T ie ien i l i t ' 4..^i ' ' ' '( and the I n i m i d i l v eoe lT iL ient J ! 1 (J ( " o l ' d . 4 ' - ( '. i
1 4 . Serv ie in t ;
4 . 0 ! 1 his prneed ' .ne s l u u i l d Ix- f o l l o w e d j f l e r "- I n : i r ' o! ' ;, ir has t l o w o d : l i ro t : i . ' l i . o r
. l i m n , i l l \ . w h i e h e \ o r eomes t ' i rs l .
4 . i ! . 1 R e m m e i l i e eover am i I l l l i n j ! eap I ron) the eel ! and w i t h a su i tab le p r o b e and t a k i n g
p r e e a u l i o n s a p p r o p r i a t e t o I he ael i v i l y in the ea l ib ra t o r . de l e r m i n e the d e p t h ot w a t e r
\v. the ee l l . I f the d e p t h is less than " \ 5 em l .^") t hen rep len ish t o a d e p t h o\' ! 2.5 em
i 5 " . - 5(10 ti t o t a l ) .
4 . ( l . i ( o m p l e t e the r o u t i n e c h e e k - o u t of the c a l i b r a t o r ( A p p e n d i x C3 ) .
4 . 0 4 C o m p l e t e the c a l i b r a t i o n c h e c k ( A p p e n d i x H 2 ) .
APPENDIX F
MECHANICAL ASSEMBLY OF CALIBRATOR
( L P I ';
"ASIUGFLOK HINGED L I D
A / ( 4C CF S S Tc * STE P/ ' C O N T i ^ F P )
r'LED 1
! J l )
• D n n Dn n n n• • • • •
HINGED /SIDE D O O R /
ACCESS TOELECTRONICS)
•
•
•
D•
•
•
••
•
•
•••
•
••
•
i i
- BALL
VALVES
S M G E L O K
Figure Fl Complete calibrator assembly, front view.
AIR CONNECTIONS
. " SWAGELOK
.." SWAGELOK
WATER CONNECTIONS
HEAT EXCHANGER
FILLER CAP
FRIGISTOR SOLDEREDTO CONTAINER ANDHEAT EXCHANGER WITHINDIUM-TIN EUTECTICSOLDER
COMPLETE ASSEMBLY WRAPPEDWITH PIPE INSULATING TAPE
Figure F2 Cell ussemhlv.
I N S U L A T I O N
P O S E R S U P P L YB O A R D P C I
H M P E R A T U R F C O N T R O LCI R C U I T B O A R D PC 2
H E A T S I N K
P 0 W F R S U P P L YP S
P I P E I N S U L A T I N G T A P E
I N S U L A T I O NC H I P S
I N S U L A T I O N
I N S U L A T I N G
0 1 V I O E R
Figure I;3 Complete calibrator assembly, inside view.
: \
APPENDIXG
ELECTRICAL ASSEMBLY
'L~,L^ _ Z C - B 5
• C M •
Figured General schematic.
R 2 7
* 1 " a I
O 6 A A
ON 0 ° °V33
o
M o L o G o D o ( -C2- ^ KCO O 4
Figure Ci2 Temperature control board assembly (PC2).
4-15 V
C4 415V
4-4.25V __L 7 6 w -15V R 2 2
E O vA/V*I k -12.81V CR4
I S k ^ t l 5 V
Au\_ RESISTORS. 3 W UNLESS OTHCEWISE. NOTED
SETTiflNTT
C 4 -H5V
+• i i . a v
J
TYPICM_ VOLTAGES SHOWN
W UNI_E.SS NOTED• * IMOICATE.^ Mi&u STABIUTT
S E C T I a N 2Figure G3 - Temperature control board schematic
35 -_
r
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