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Thermistor Temperature Sensors
T h e m a t e r i a l s i n c l u d e d i n t h i s c o m p i l a t i o n a r e f o r t h e u s e o f D w y e r I n s t r u m e n t s , I n c . p o t e n t i a l c u s t o m e r s a n d c u r r e n t e m p l o y e e s a s a r e s o u r c e o n l y . T h e y m a y n o t b e r e p r o d u c e d , p u b l i s h e d , o r t r a n s m i t t e d e l e c t r o n i c a l l y f o r c o m m e r c i a l p u r p o s e s . F u r t h e r m o r e , t h e C o m p a n y ’ s n a m e , l i k e n e s s ,
p r o d u c t n a m e s , a n d l o g o s , i n c l u d e d w i t h i n t h e s e c o m p i l a t i o n s m a y n o t b e u s e d w i t h o u t s p e c i fi c , w r i t t e n p r i o r p e r m i s s i o n f r o m D w y e r I n s t r u m e n t s , I n c .
© C o p y r i g h t 2 0 1 5 D w y e r I n s t r u m e n t s , I n c .
ThermistorsO v e r v i e w
D w y e r I n s t r u m e n t s o ff e r s m a n y t e m p e r a t u r e m e a s u r i n g p r o d u c t s t h a t u s e a t h e r m i s t o r a s t h e s e n s i n g e l e m e n t
D w y e r a l s o m a n u f a c t u r e s a w i d e v a r i e t yo f t h e s e t e m p e r a t u r e s e n s o r s
ThermistorsO v e r v i e w
T h e r m i s t o r s a r e b a s e d o n t h e p r i n c i p a l t h a t t h e e l e c t r i c a l r e s i s t a n c e o f s e m i c o n d u c t o r m a t e r i a l s i s a f u n c t i o n o f t h e t e m p e r a t u r e
T h e r m i s t o r ’ s w o r k w e l l o v e r s m a l l e r t e m p e r a t u r e r a n g e s w i t h b e t t e r a c c u r a c y t h a n RT D ’ s b u t a r e v e r y n o n - l i n e a r
T h e y a l s o g e n e r a l l y o ff e r b e t t e rr e s p o n s e t i m e s
T h e r m i s t o r s h a v e m u c h h i g h e r r e s i s t a n c e v a l u e s t h e n RT D ’ s w i t h r a n g e s t y p i c a l l y r a n g i n g f r o m 1 0 0 o h m s t o 1 0 0 m e g a o h m s
ThermistorsO v e r v i e w
T h e r e t w o m a i n t y p e s o f t h e r m i s t o r s b a s e d o n t e m p e r a t u r e r e s p o n s e : P T C a n d N T C
W i t h P T C , p o s i t i v e t e m p e r a t u r e c o e ffi c i e n t , t h e r e s i s t a n c e i n c r e a s e s w i t h i n c r e a s i n g t e m p e r a t u r e
P T C t h e r m i s t o r s a r e f o r m e d b y u s i n g s e m i c o n d u c t o r m a t e r i a l s a l o n g w i t h p o l y c r y s t a l l i n e c e r a m i c
A P T C t h e r m i s t o r h a s a n e x t r e m e l y l a r g e r e s i s t a n c e c h a n g e f o r s m a l l t e m p e r a t u r e c h a n g e s a n d h a s a c r i t i c a l s w i t c h t e m p e r a t u r e w h e r e t h e r e s i s t a n c e b e g i n s t o c h a n g e q u i c k l y a s s h o w n i n t h e g r a p h
T h i s b e h a v i o r m a k e s t h e m w e l l s u i t e d f o r o n - o ff u s e a s a s w i t c h .
ThermistorsO v e r v i e w
W i t h N T C , n e g a t i v e t e m p e r a t u r e c o e ffi c i e n t , t h e r e s i s t a n c e d e c r e a s e s w i t h i n c r e a s i n g t e m p e r a t u r e .
N T C t h e r m i s t o r s a r e f o r m e d w i t h s i n t e r e d m e t a l o x i d e s m a d e o f t r a n s i t i o n m e t a l s s u c h a s n i c k e l , m a n g a n e s e , c o p p e r , i r o n , a n d c o b a l t
T h e y c a n a l s o b e c o n s t r u c t e d o f s e m i c o n d u c t o r m a t e r i a l s o f s i l i c o n o r g e r m a n i u m
N T C t h e r m i s t o r s a r e c o m m o n l y u s e d t o m e a s u r e t e m p e r a t u r e o v e r a s p e c i fi c r a n g e
N T C ’ s a r e d e s i g n a t e d b y t h e i r r e s i s t a n c e v a l u e a n d t e m p e r a t u r e c u r v e s u c h a s a 1 0 K Ty p e 3
ThermistorsO v e r v i e w
T h e r m i s t o r s c o m e i n s e v e r a l s t y l e s o f c o n s t r u c t i o n d e p e n d i n g o n t h e a p p l i c a t i o n n e e d
T h e r m i s t o r s t y l e s i n c l u d e : r o d s , b e a d s , d i s c s , w a s h e r s , a n d fl a k e s
ThermistorsO v e r v i e w
S i n c e t h e r m i s t o r s h a v e s u c h h i g h r e s i s t a n c e r a n g e s t h e y a r e t w o w i r e d e v i c e s a s l e a d w i r e r e s i s t a n c e h a s a l i t t l e o r n o e ff e c t
T h e r m i s t o r s a r e w i r e d d i r e c t l y t o t h e m e a s u r i n g i n s t r u m e n t o r t h e y c a n b e e x t e n d e d w i t h i n s u l a t e d e l e c t r i c a l c o p p e r w i r e
S e n s o r w i r e s s h o u l d n e v e r b e r u n i n c o n d u i t w i t h p o w e r s o u r c e s o r t h e r e c o u l d b e n o i s e p r o b l e m s
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