The resistance ratios of platinum resistance thermometers from different manufacturers are compared a t many temperatures below 375 K. These resistance ratios can be interrelated by a function with six coefficients determined from the defining fixed point calibrations by the method of least squares. We suggest that this single function could replace the four deviation functions of the IPTS-68. Non-uniqueness in the temperature scale resulting from the imperfections both of this new, and of the IPTS-68 deviation functions are discussed. An even simpler deviation function is used to calibrate thermometers in the range 90 to 273 K. Moderately precise secondary calibrations are obtained over the whole temperature range using this simpler function together with comparisons with a calibrated thermometer a t only four temperatures. We show one way of smoothing the reference function of the IPTS-68 to make it more nearly resemble a real thermometer. The new six-coefficient function is then used to relate all thermometers to this smoothed reference function.

ABSTUCT A p o r t a b l e s a l i n o m e t e r f o r u s e w i t h small b o t t l e samples i s described. I t i s based on the continuous flow principle used in our precision laboratory salinometer. Bowever, (I) i t i s not thermostatted, i n s t e a d i t has two c e l l s i n t h e same bath and Greasures t h e c o n d u c t i v i t y r a t i o of sample t o s t a n d a r d s e a w a t e r a t t h e same temperature; (2) t h e water is drawn from t h e s a m p l e b o t t l e by s u c t i o n i n s t e a d of d r i v e n by pressure; ( 3 ) t h e r e q u i r e d sample i s l e s s t h a n 1 / 1 0 t h a t of t h e l a b o r a t o r y model so that standard water can be used continuo u s i y a s r e f e r e n c e ; ( 4 ) t h e r e is no contamination of the rest of the sample, alnost the whole of which i s a v a i l a b l e f o r o t h e r m a s u r e s e n t s . The r e a d i n g c i r c u i t o p e r a t e s on 100-200 Hz square wave current and determines the ratio of conductivi t y of t h e measured sample t o s t a n d a r d s e a w a t e r a t t h e same temperature directly. Appropriate trims are provided to compensate fgr cell constant d i f f e r e n c e s and d e v i a t i o n of the standard seawater from exactly 35 O / o o S. IKTRODUCTION The l a b o r a t o r y s a l i n o a t e r i s t h e m a i n s t a y of a great mny ocean systems, either as a c a l i b r a t i o n device or for checking the performance of t h e CTD being used. Also i n many surveys large numbers of b o t t l e s a n p l e s a r e o b t a i n e d and t h e s a l i n i t y n e e d s t o be correlated with other measurements being c a r r i e d o u t on t h e same s a n y l e s . Most e a r l i e r s a l i n o m e t e r s s u f f e r e d from one o r more d e f i c i e n c i e s s u c h as: requirement for a l a r g e b o t t l e s a m p l e , p a r t i c u l a r l y i f t h e l a s t s a m p l e had r a d i c a l l y d i f f e r e n t s a l i n i t y ; r a p i d d r i f t of s t a n d a r d i z a t i o n r e q u i r i n g f r e q u e n t u s e of s t a n d a r d or substandard seawater reference; many and inconv e n i e n t c o r r e c t i o n s ; e r r o r s c a u s e d by bubble f o r m a t i o n , p a r t i c u l a r l y i f t h e s a m p l e w a t e r was c o l d ; r e l a t i v e l y s l o w o p e r a t i o n p a r t i c u l a r l y i f data processing time was included; and inaccurate compensation for temperature. Several years ago a p r e c i s i o n l a b o r a t o r y s a l i n ometer was developed a t NRC[ 11 i n which the use of d i s c r e t e s a s p l e s w i t h r e p e t i t i v e f l u s h i n g was replaced by a continuous flow systen with a h e a t exchanger and masuring cell i n s e r i e s and mounted i n a p r e c i s e l y t h e r m o s t a t t e d s t i r r e d b a t h . T h i s instrument is now commercially available* and has become t h e s t a n d a r d i n s t r u m e n t i n many l a b o r a t o r i e s a l l over the world. I t s chief advantages were a reduced number of c o r r e c t i o n s , e a ...

No abstract

No abstract