Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site
LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC :
https://nrc-publications.canada.ca/eng/view/object/?id=ca8de769-5251-4424-a71d-367f0399f3f0
https://publications-cnrc.canada.ca/fra/voir/objet/?id=ca8de769-5251-4424-a71d-367f0399f3f0
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Calibration of humidity sensors at DBR/NRCC, Saskatoon
Ser
THP
/
'r"
;-
N21
d
no,
1304
National Research
Conseil national
c,
2
Council Canada
de rechmhes Canada
BLDG
Division of
Division des
Building Research
recherches en biitiment
Calibration of Humidity Sensors at
DBR/NRCC, Saskatoon
by C.P. Hedlin and R.G. Nicholson
Reprinted from
Proceedings of the International Symposium on
Moisture and Humidity
Washington, D.C., April 15-18, 1985
p. 395
-
399
(DBR Paper No. 1304)
Price $1.00
NRCC 24731
La Station rbgionale des Prairies de la Division des recherches
en bbtiment du Conseil national de recherches du Canada emploie
deux dispositifs pour gtalonner les capteurs d'humiditg.
Un
systsme
3
deux temperatures permet d'etalonner les capteurs aux
tempbratures de point de rosee allant jusqu'a environ 20°C; un
deuxibe petit systeme 3 deux tempbratures pouvant Btre plange
dans un liquide pour prevenir la condensation dans les
conduites est utilise regulierement pour des temperatures de
point de ros6e allant jusqu'a 65OC.
MOISTURE
AND
HUMIDITY
-
Proceedings of
the
International Symposium on
Moistu
Washington,
L C ,
April 1
1985
i
Humidity
CALIBRATION
OF
HUMIDITY SENSO
r
DBRSN RCC, SASKATOON
C. P.
Hedlin
R.
G.
Nicholsan
O ISA, 1985
C.P. Hedlin and R.G. Nicholson P r a i r i e R e g i o n a l S t a t i o n D i v i s i o n of B u i l d i n g Research Saskatoon, Saskatchewan, Canada
S7N OW9
ABSTRACT
Two d e v i c e s a r e used t o c a l i b r a t e humidity s e n s o r s a t t h e P r a i r i e R e g i o n a l S t a t i o n , D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council of Canada. A two-temperature system p r o v i d e s f o r c a l i b r a t i o n f o r dew-point t e m p e r a t u r e s up t o a b o u t 20°C; and a small two-pressure system t h a t can be immersed i n a l i q u i d b a t h t o a v o i d condensation i n t h e l i n e s i s used r e g u l a r l y f o r dew-point
t e m p e r a t u r e s up t o 65OC. INTRODUCTION
Excess m o i s t u r e u n d e r l i e s many common problems i n b u i l d i n g s , i t s e f f e c t s e v i d e n c e d i n a m u l t i t u d e of ways
--
s t a i n i n g , r o t t i n g , mould growth, i c e l e n s i n g , b r i c k s p a l l i n g , e t c . The importance of i n t e r i o r humidity a s a s o u r c e of m o i s t u r e i n t h e f a b r i c of b u i l d i n g s h a s l e d t h e D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research Council o f Canada, t o s e t up a f a c i l i t y a t t h e P r a i r i e Regional S t a t i o n (PRS) i n Saskatoon t o c a l i b r a t e humidity s e n s o r s .Two d e v i c e s a r e c u r r e n t l y used f o r c a l i b r a t i o n work: a two-temperature "Atmosphere Producer," and a t w o - p r e s s u r e system. The two-temperature s y s t e m was developed i n t h e l a t e 1950s (1). B r i e f l y , two g l y c o l - f i l l e d b a t h s p r o v i d e independent t e m p e r a t u r e c o n t r o l f o r a s a t u r a t o r chamber and a c a l i b r a t i o n chamber. The l i q u i d i s s t i r r e d and t e m p e r a t u r e c o n t r o l l e d by on-of f h e a t e r s and r e f r i g e r a t i o n . The t e m p e r a t u r e of t h e b a t h i s measured w i t h wire-wound p l a t i n u m
r e s i s t a n c e thermometers* and a Mueller b r i d g e ( F i g u r e 1).
These t e m p e r a t u r e s a r e t a k e n t o be e q u a l t o t h o s e
F o f t h e c a l i b r a t i o n chamber a n d s a t u r a t o r chamber. A i r i s pumped round a loop; i t p a s s e s o v e r w a t e r i n t h e s a t u r a t o r chamber, moves t o t h e c a l i b r a t i o n chamber and t h e n back t o t h e s a t u r a t o r . Thus, by r e p e a t e d p a s s a g e through t h e s a t u r a t o r chamber t h e a i r i s brought e f f e c t i v e l y t o s a t u r a t i o n a t s a t u r a t o r t e m p e r a t u r e . Heat e x c h a n g e r s b r i n g t h e
I
* C a l i b r a t e d a g a i n s t a n o t h e r wire-wound platimum r e s i s t a n c e thermometer c a l i b r a t e d a t t h e Applied P h y s i c s D i v i s i o n , N a t i o n a l R e s e a r c h C o u n c i l of Canada. a i r t o t h e t e m p e r a t u r e o f t h e b a t h b e f o r e i t i s d i s c h a r g e d i n t o t h e s a t u r a t o r o r c a l i b r a t i o n chamber. The l o o p i s c l o s e d e x c e p t f o r a p i n h o l e provided t o a l l o w t h e system p r e s s u r e t o f l u c t u a t e w i t h b a r o m e t r i c p r e s s u r e .Two manometers measure t h e d i f f e r e n c e between t h e p r e s s u r e s i n t h e two chambers and b a r o m e t r i c p r e s s u r e . The d i f f e r e n c e between t h e two v a l u e s i s t h e d i f f e r e n c e between t h e c a l i b r a t i o n and s a t u r a t o r chamber p r e s s u r e s . A c o r r e c t i o n i s a p p l i e d t o a c c o u n t f o r t h e consequent d i f f e r e n c e i n w a t e r vapour p r e s s u r e . A n a l y s i s of t h e p r o b a b l e e r r o r s i n t h e s y s t e m was c a r r i e d o u t . On t h e b a s i s of t h i s s t u d y i t was e s t i m a t e d t h a t t h e maximum u n c e r t a i n t y i n r e l a t i v e h u m i d i t y ranged from 0.03% RH a t 10% RH t o 0.40% RH a t 100% RH. The system was i n t e n d e d i n t h e f i r s t i n s t a n c e f o r c a l i b r a t i o n o f Dunmore-type s e n s o r s . Up t o 20 of them can be mounted i n s o c k e t s on a c a n t i l e v e r beam t h a t i s t h e n s e a l e d i n s i d e t h e c a l i b r a t o r chamber. The r e s i s t a n c e of e a c h s e n s o r can be checked by a s y s t e m t h a t , i n t u r n , b r i n g s t h e s e n s o r s i n t o a c i r c u i t l e a d i n g t o a r e s i s t a n c e b r i d g e .
A t h i g h r e l a t i v e h u m i d i t i e s t h e r e was some l e a k a g e i n t h e l e a d s t o t h e s e n s o r s ; i . e . , open c i r c u i t r e s i s t a n c e s a s low a s 5 megohms might o c c u r , producing a n e r r o r i n t h e measured r e s u l t . A f i x e d r e s i s t o r i s p l a c e d i n one of t h e 20 s o c k e t s f o r u s e a s a r e f e r e n c e t o warn when t h i s problem o c c u r s . Normally t h e t e m p e r a t u r e of t h e
c a l i b r a t i o n chamber i s s e t a t t h e d e s i r e d v a l u e , e.g., 20°C. The t e m p e r a t u r e of t h e s a t u r a t o r chamber changes by s t e p s t o produce a s e r i e s of dew-point t e m p e r a t u r e s ( r e l a t i v e h u m i d i t i e s ) i n t h e c a l i b r a t i o n chamber. About 314 h i s r e q u i r e d a t each new humidity l e v e l t o change t h e
t e m p e r a t u r e of t h e b a t h and a l l o w t h e s e n s o r t o r e a c h e q u i l i b r i u m .
TWO-PRESSURE SYSTEM
I n t h e two-pressure system ( 2 ) a vacuum pump i s u s e d t o draw room a i r through a s a t u r a t o r chamber, a t h r o t t l i n g v a l v e , and t h e c a l i b r a t i o n chamber a t a r a t e of a b o u t 0.05 L / s ( F i g u r e 2). Flow r a t e s much i n e x c e s s of 0.05 L / s cause s u r g i n g i n t h e a i r flow. The r e l a t i v e h u m i d i t y i s g i v e n by t h e
r a t i o of t h e t o t a l p r e s s u r e s i n t h e c a l i b r a t i o n chamber and t h e s a t u r a t o r . The t h r o t t l i n g v a l v e i s a d j u s t e d t o produce t h e r e q u i r e d v a l u e . It i s h e a t e d a few d e g r e e s ( w i t h a 5 W h e a t e r ) t o a v o i d c o n d e n s a t i o n from t h e a d i a b a t i c c o o l i n g t h a t accompanies sudden r e d u c t i o n i n p r e s s u r e .
The humidity s e n s o r s a r e p l a c e d i n s o c k e t s mounted i n t h e c o v e r p l a t e of t h e c a l i b r a t i o n chamber. E l e c t r i c a l l e a d s t o t h e o u t s i d e a l l o w measurement o f r e s i s t a n c e . The whole assembly, i . e . ,
s a t u r a t o r chambers, c a l i b r a t i o n chamber, t h r o t t l i n g v a l v e , a n d i n t e r c o n n e c t i n g p i p i n g , i s immersed i n a l i q u i d b a t h s o t h a t t h e t e m p e r a t u r e o f t h e s y s t e m c a n be r a i s e d above room t e m p e r a t u r e w i t h o u t danger of c o n d e n s a t i o n i n t h e l i n e s . The d e v i c e i s r e g u l a r l y u s e d f o r c a l i b r a t i o n a t 6S°C and h a s been used a t h i g h e r t e m p e r a t u r e s a s w e l l . There was some concern t h a t a i r bubbled t h r o u g h w a t e r i n t h e s a t u r a t o r s would e n t r a i n w a t e r d r o p l e t s o r , a l t e r n a t i v e l y , t h a t i t would n o t r e a c h s a t u r a t i o n . It was t h e r e f o r e compared w i t h t h e Atmosphere Producer, u s i n g Dunmore s e n s o r s a s t r a n s f e r r e f e r e n c e s . Various d e p t h s o f beads were
p l a c e d above t h e w a t e r s u r f a c e t o e x t r a c t d r o p l e t s , and h u m i d i t y coming from t h e s a t u r a t o r was measured. The r e s u l t s s u g g e s t t h a t t h e
s a t u r a t o r was working a s r e q u i r e d . Agreement between t h e two c a l i b r a t i n g systems was w i t h i n a b o u t 1% RH.
CALIBRATION PROCEDURES
A v a r i e t y of t y p e s of humidity d e v i c e s were c a l i b r a t e d , i n c l u d i n g Dunmore t y p e s e n s o r s , h e a t e d e l e c t r i c a l , dew-point, and aluminum o x i d e
hygrometers. It i s sometimes n e c e s s a r y t o d e v i s e ad hoc p r o c e d u r e s f o r c a l i b r a t i n g equipment t h a t d o e s n o t f i t normal methods. For example, t h e s e n s i n g component of dew-point d e v i c e s i s o f t e n b u i l t i n t o t h e body of t h e measuring s y s t e m and cannot be p l a c e d i n t h e c a l i b r a t o r chamber of e i t h e r t h e Atmosphere Producer o r t h e two-pressure system. E i t h e r may be used a s t h e s o u r c e of a i r of known humidity. A i r i s t a k e n from one o r o t h e r and s u p p l i e d t o t h e dew-point s e n s o r . With t h e Atmosphere Producer, t h e a i r must be r e t u r n e d t o
i t t o m a i n t a i n closed-loop o p e r a t i o n . C o r r e c t i o n s have t o be made f o r p r e s s u r e changes.
Equipment i s n o t c e r t i f i e d . The t e s t s a r e c a r r i e d o u t and t h e u s e r i s p r o v i d e d w i t h t h e r e s u l t s , b u t t h e c a l i b r a t i o n procedure does n o t conform t o any e s t a b l i s h e d s t a n d a r d . The emphasis i s p l a c e d o n p r o v i d i n g a p r a c t i c a l s e r v i c e t o u s e r s of humidity equipment. N a t u r a l l y e v e r y e f f o r t i s made t o a c h i e v e a c c u r a c y , and no t e s t would be c a r r i e d o u t w i t h o u t c o n f i d e n c e t h a t r e l i a b l e r e s u l t s would r e s u l t . Humidity s e n s o r c a l i b r a t i o n (and humidity measurement) i n v o l v e s a measure of a r t a s w e l l a s s c i e n c e . The o p e r a t o r must be aware of t h e f o i b l e s of t h e c a l i b r a t i n g equipment and be s e n s i t i v e t o any v a r i a t i o n s i n t h e d a t a t h a t might i n d i c a t e a m a l f u n c t i o n i n g system. OPERATIONAL DETAILS 1 ) Sensors a r e normally c o n d i t i o n e d f o r a p e r i o d o f t i m e , e.g., Dunmore s e n s o r s r u n t o t h e t o p of t h e i r RH range. 2 ) Water i n t h e s a t u r a t o r o f t h e two-temperature system i s changed p e r i o d i c a l l y , a l t h o u g h t e s t s of "used" w a t e r w i t h a c o n d u c t i v i t y m e t e r have shown no s u b s t a n t i a l accumulation of c o n t a m i n a t i n g m a t e r i a l . The s a t u r a t o r i s charged w i t h t r i p l e - d i s t i l l e d water. 3 ) Heated e l e c t r i c a l h y g r o m e t e r s may be p l a c e d i n t h e c a l i b r a t i o n chamber of t h e Atmosphere Producer. It g i v e s o f f some h e a t , b u t t h i s is n o t a m a t t e r f o r concern s i n c e i t i s a dew-point t e m p e r a t u r e s e n s o r r a t h e r t h a n a r e l a t i v e h u m i d i t y s e n s o r .
4 ) Output i s monitored u n t i l i t i s judged t o have reached e q u i l i b r i u m b e f o r e c a l i b r a t i o n d a t a a r e t a k e n .
5 ) L a b o r a t o r y r u b b e r h o s e s i n t h e two-pressure system d e t e r i o r a t e a t h i g h t e m p e r a t u r e s and must b e r e p l a c e d a p p r o x i m a t e l y once a y e a r .
6 ) S i l i c o n e g r e a s e i s used t o e n s u r e t h a t t h e g a s k e t s e a l s t h e c o v e r o f t h e two-pressure u n i t t o t h e body of t h e c a l i b r a t i o n chamber. The s e a l i n g method h a s proved t o be v e r y e f f e c t i v e . On o n l y one o c c a s i o n i n n e a r l y 20 y e a r s d i d a l e a k o c c u r t h a t damaged s e n s o r s . 7 ) Two-pressure s a t u r a t o r chambers a r e f l u s h e d o u t p e r i o d i c a l l y w i t h h o t w a t e r t o remove contaminants.
CALIBRATION OF DUNMORE-TYPE SENSORS
The m a j o r i t y of t h e c a l i b r a t i o n work h a s been done o n D u n m o r e t y p e h u m i d i t y s e n s o r s , which c o n s i s t o f a p a i r of e l e c t r o d e s mounted on a p l a s t i c b a s e , e i t h e r wound o n a c i r c u l a r t u b e o r mounted o n a f l a t s u r f a c e . They a r e covered w i t h a t h i n f i l m o f p o l y v i n y l a l c o h o l . The l a t t e r i s p r e p a r e d w i t h v a r i o u s c o n c e n t r a t i o n s of l i t h i u m c h l o r i d e t o make s e n s o r s f o r d i f f e r e n t r a n g e s o f humidity. Any g i v e n s e n s o r c o v e r s o n l y a l i m i t e d r a n g e of h u m i d i t y , e.g., 8 0
- loo%,
70- 85%, e t c .
Ten t o twelve i n d i v i d u a l s e n s o r s a r e normally r e q u i r e d t o c o v e r t h e f u l l range. The a c t i v e m a t e r i a l g a i n s o r l o s e s m o i s t u r e a s t h e r e l a t i v e humidty r i s e s o r f a l l s , and i t s e l e c t r i c a l r e s i s t a n c e v a r i e s o v e r a n o p e r a t i n g r a n g e of a b o u t 3 decades. C a l i b r a t i o n a t PRS i s done by exposing s e n s o r s t o a range of h u m i d i t i e s a t f i x e d t e m p e r a t u r e s , t h e n measuring t h er e s i s t a n c e . I n e a c h c a l i b r a t i o n a minimum of t e n p o i n t s are p r o v i d e d
--
f i v e f o r s t e p w i s e r e d u c t i o n i n humidity and f i v e f o r i n c r e a s i n g humidity. Some h y s t e r e s i s e x i s t s . A s e t o f s u c h c a l i b r a t i o n d a t a i s shown i n F i g u r e 3, u s i n g a l o g a r i t h m i c p l o t .I n 1965 a n arrangement was s e t up t o meet t h e needs o f a g r o u p o f u s e r s who must c o n t r o l humidity c a b i n e t s a t t e m p e r a t u r e s up t o 65'C and
( s i r m l t a n e o u s l y ) r e l a t i v e h u m i d i t i e s u p t o 98%. C a l i b r a t i o n s a r e c a r r i e d o u t t w i c e a n n u a l l y a t PRS o n s u b m i t t e d s e n s o r s s i n c e d r i f t o r damage may cause changes i n t h e i r c a l i b r a t i o n . Simultaneous c a l i b r a t i o n o f g r o u p s o f s e n s o r s r e d u c e s t h e c o s t t o e a c h u s e r i n t h a t r e p e t i t i o n of t h e c a l i b r a t i o n p r o c e d u r e i s avoided.
Using t h e d a t a and a second o r d e r r e l a t i o n l o g RH = A
+
B l o g R+
C l o g R~ ( 1 a v a l u e of RH was found a t R = 1 megohm f o r e a c h c a l i b r a t i o n c a r r i e d o u t a t 25OC (1 megohm RH = I @ ) .S i n c e t h e arrangement was e s t a b l i s h e d some s e n s o r s have been r e t u r n e d f o r c a l i b r a t i o n a number of t i m e s and t h e r e h a s been a n o p p o r t u n i t y t o o b s e r v e d r i f t i n c a l i b r a t i o n caused by u s e and aging. Twenty s i x s e n s o r s have been c a l i b r a t e d f o u r o r more t i m e s i n p e r i o d s s p a n n i n g 3 t o 19 y e a r s . These r e p r e s e n t two r a n g e s of humidity. Range I , c e n t e r e d a t a b o u t 8 5
-
88% RH ( 1 megohm), and Range I1 c e n t e r e d a t a b o u t 75% RH. Sensors i n o t h e r r a n g e s have been c a l i b r a t e d b u t a r e n o t i n c l u d e d i n t h i s r e p o r t . Data a r e shown i n F i g u r e 4 f o r f i v e of t h e 26 s e n s o r s . Each i s p l o t t e d a g a i n s t a range of RH v a l u e s a p p r o p r i a t e t o i t s behaviour. They were s e l e c t e d t o i l l u s t r a t e s h o r t , medium and long-term s t a b l e o p e r a t i o n and, i n one c a s e , a l a r g e d e p a r t u r e from t h e normal l-megohm range. Over t h e p e r i o d of o b s e r v a t i o n , f o u r of t h e 26 s e n s o r s changed by between 5 and 18% RH. The remaining 22 d e v i a t e d by l e s s t h a n a b o u t 2.5% RH from t h e a v e r a g e o f t h e i r high-low v a l u e s . The l a t t e r d i d n o t show a c o n s i s t e n t t r e n d , b u t u s u a l l y f l u c t u a t e d up o r down i n a n e r r a t i c manner. T h i s v a r i a t i o n c o u l d have been o c c a s i o n e d by a c t u a l changes i n t h e s e n s o r s , b u t c a l i b r a t i o n e r r o r may a l s o be a f a c t o r .The s e n s o r s may be d i v i d e d i n t o two c a t e g o r i e s , t h o s e t h a t performed c o n s i s t e n t l y w i t h i n f 2 + % RH and t h o s e t h a t d i d n o t . It seems l i k e l y t h a t t h e l a t t e r were damaged i n some way. It i s s u g g e s t e d t h a t i f d e s t r u c t i v e c i r c u m s t a n c e s c o u l d be avoided, t h e s e s e n s o r s might o p e r a t e f o r l o n g p e r i o d s of time w i t h i n a +2$% RH range. SUMMARY
1) Two d e v i c e s , a two-temperature system and a two-pressure system, a r e u s e d t o c a l i b r a t e humidity s e n s o r s . The Atmosphere Producer i s l i m i t e d t o a dew-point t e m p e r a t u r e r a n g e of about
-40 t o +20°C. The two-temperature system i s o p e r a t e d a t dew-point t e m p e r a t u r e s of 65°C and, on o c c a s i o n , h i g h e r .
2 ) As a v a r i e t y o f t y p e s o f humidity-sensing d e v i c e a r e c a l i b r a t e d , s p e c i a l measures must sometimes be t a k e n t o connect them t o t h e c a l i b r a t i n g f a c i l i t i e s .
3 ) Dunmoretype s e n s o r s have been c a l i b r a t e d a t r e g u l a r i n t e r v a l s f o r i n d u s t r i a l u s e , and some i n d i v i d u a l s e n s o r s have been r e - c a l i b r a t e d a number of times. The r e l a t i v e h u m i d i t i e s c o r r e s p o n d i n g t o t h e i r l-megohm r e s i s t a n c e s a t 25°C were c a l c u l a t e d . I n a few c a s e s , p o s s i b l y d u e t o p h y s i c a l damage, t h e c a l i b r a t i o n changed by a l a r g e amount. I n about 85% of t h e c a s e s
1-megohm r e l a t i v e h u m i d i t i e s remained w i t h i n a ?24% RH band. P e r i o d s of o b s e r v a t i o n ranged from about t h r e e t o 19 y e a r s . These were f o r t h e h i g h humidity range, i . e . , f o r measuring 70% RH o r higher. S e n s o r s i n lower r a n g e s may be more s u b j e c t t o d r i f t . ACKNOWLEDGEMENT The a u t h o r wishes t o e x p r e s s t h a n k s t o t h e f o l l o w i n g f i r m s f o r a l l o w i n g u s e of c a l i b r a t i o n r e s u l t s f o r t h e i r humidity s e n s o r s : Bach-Simpson L t d . , B e l l N o r t h e r n R e s e a r c h , Canadian Marconi Company, Croven C r y s t a l s L i m i t e d , Murata E r i e North America L t d . , P h i l l i p s E l e c t r o n i c s , Q u a l i t y E n g i n e e r i n g , C.R. Snelgrove Co. Ltd., Varian A s s o c i a t e s of Canada Ltd. T h i s paper i s a c o n t r i b u t i o n from t h e D i v i s i o n of B u i l d i n g Research, N a t i o n a l Research C o u n c i l of Canada, and i s p u b l i s h e d w i t h t h e a p p r o v a l of t h e D i r e c t o r of t h e D i v i s i o n . REFERENCES
1. T i l l , C.E., and Handegord, G.O., Proposed humidity s t a n d a r d , T r a n s a c t i o n s , American S o c i e t y of H e a t i n g , R e f r i g e r a t i n g and Air-Conditioning E n g i n e e r s , Vol. 66, 1960, p. 288-308. 2. Hedlin, C.P., A d e v i c e f o r c a l i b r a t i n g e l e c t r i c a l h u m i d i t y s e n s o r s , M a t e r i a l s Research and S t a n d a r d s , Vol. 6, No. 1, 1966, p . 25-29.
RECORDER
1
I
SENSOR-
S A T U R A T O R C H A M B E R B A T H C A L I B R A T I O N C H A M B E R B A T H A TEMPERATURE CONTROLLER E LIQUID W M P
B HEAT EXCHANGER F HEATER
C RESISTANCE THERMOMETER G CALIBRATED PLATINUM D REFRIGERATION UNIT RESISTANCE THERMOMETER
F I G U R E 1
S C H E M A T I C I L L U S T R A T I O N O F T W O - T E M P E R A T U R E A T M O S P H E R E PRODUCER
MERCURY
MANOMETER MANOMETER ELECTRICAL LEADS ( A P , ) ( A P2)
f
- NINE SENSORS - ONE THERMOCOUPLE SATURATOR CHAMBERS - (2) EACH 135 mm HIGH x 3 5 mm DIA F I G U R E 2 S C H E M A T I C I L L U S T R A T I O N O F TWO-PRESSURE S Y S T E M F O R H U M I D I T Y S E N S O R C A L I B R A T I O N7 0 8 0 9 0 1 0 0 R E L A T I V E H U M I D I T Y . % F I G U R E 3 T Y P I C A L P L O T OF H U M I D I T Y S E N S O R C A L I B R A T I O N D A T A - l o g R V S l o g R H . V A L U E S A R E FOR A S E N S O R C A L I B R A T E D A T 2 5 ° C . DOTTED L I N E S H O W S B E S T F I T F I G U R E 4 P L O T S OF R E L A T I V E H U M I D I T I E S A T 1 m e g o h m A T 25°C F O R F I V E H U M I D I T Y S E N S O R S . V A L U E S A R E FOR C A L I B R A T I O N BETWEEN 1 9 6 5 A N D 1 9 8 4 . THE T O P F O U R S E N S O R S R E M A I N E D W I T H I N A '3% R H B A N D . THE 1 m e g o h m R H F O R THE B O T T O M S E N S O R C H A N G E D B Y A B O U T 14%. P O S S I B L Y D U E TO P H Y S I C A L D A M A G E
