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1. Understanding Pressure
Sensor Accuracy
and Sensor Technology
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 f i 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 .

2. New Accuracy Equation
1% RMS ≠ 1% RSS ≠ 1% SUM ≠ 1% TEB

3. Why is Accuracy Important?
E f f i c i e n c y a n d Q u a l i t y
 E f f i c i e n c y
 I m p r o v e o p e r a t i o n s
 R e d u c e o p e r a t i n g c o s t
 Q u a l i t y
 R e d u c e s c r a p
 I m p r o v e y i e l d s

4. Why is Accuracy Important?
A c c u r a c y v s . Pr i c e
%
$

5. Accuracy Standards
W h o i s t h e I E C ?
 F o u n d e d i n 1 9 0 6 , t h e I E C ( I n t e r n a t i o n a l E l e c t r o t e c h n i c a l
C o m m i s s i o n ) i s t h e w o r l d ’s l e a d i n g o r g a n i z a t i o n f o r t h e
p r e p a r a t i o n a n d p u b l i c a t i o n o f I n t e r n a t i o n a l S t a n d a r d s f o r a l l
e l e c t r i c a l , e l e c t r o n i c a n d r e l a t e d t e c h n o l o g i e s
 T h e I E C i s t h e l e a d i n g g l o b a l o r g a n i z a t i o n t h a t p u b l i s h e s
c o n s e n s u s - b a s e d i n t e r n a t i o n a l s t a n d a r d s

6. Accuracy Standards
I E C D e f i n i t i o n o f A c c u r a c y
( I n t e r n a t i o n a l E l e c t r o t e c h n i c a l C o m m i s s i o n )
 A c c u r a c y i s m a x i m u m p o s i t i v e a n d n e g a t i v e d e v i a t i o n f r o m t h e
s p e c i f i e d c h a r a c t e r i s t i c c u r v e o b s e r v e d i n t e s t i n g a d e v i c e u n d e r
s p e c i f i e d c o n d i t i o n s a n d b y a s p e c i f i e d p r o c e d u r e

7. Accuracy Standards
I E C 6 1 2 9 8 - 2 S t a n d a r d
 A c c u r a c y m u s t i n c l u d e H y s t e r e s i s ,
N o n - R e p e a t a b i l i t y a n d N o n - L i n e a r i t y

8. Accuracy Factors
N o n - Re p e a t a b i l i t y
 T h e m a x i m u m d i f f e r e n c e
i n o u t p u t w h e n t h e s a m e
p r e s s u r e i s a p p l i e d ,
c o n s e c u t i v e l y, u n d e r
t h e s a m e c o n d i t i o n s a n d
a p p r o a c h i n g f r o m t h e
s a m e d i r e c t i o n

9. Accuracy Factors
H y s t e r e s i s
 T h e m a x i m u m d i f f e r e n c e i n
s e n s o r o u t p u t a t a p r e s s u r e
w h e n t h a t p r e s s u r e i s f i r s t
a p p r o a c h e d w i t h p r e s s u r e
i n c r e a s i n g a n d t h e n
a p p r o a c h e d w i t h p r e s s u r e
d e c r e a s i n g d u r i n g a f u l l
s p a n p r e s s u r e c y c l e

10. Accuracy Factors
N o n - L i n e a r i t y
 T h e m a x i m u m p o s i t i v e o r n e g a t i v e d e v i a t i o n b e t w e e n t h e a v e r a g e
c u r v e a n d t h e s e l e c t e d s t r a i g h t l i n e , e x p r e s s e d i n p e r c e n t o f
i d e a l o u t p u t s p a n a n d i s i n d e p e n d e n t o f n o n - r e p e a t a b i l i t y a n d
h y s t e r e s i s
 T h r e e N o n - L i n e a r i t y M e t h o d s ( d e f i n e d b y I E C )
 Te r m i n a l P o i n t N o n - L i n e a r i t y
 B e s t F i t S t r a i g h t L i n e N o n - L i n e a r i t y
 Z e r o B a s e d N o n - L i n e a r i t y

11. Accuracy Factors
B e s t F i t S t r a i g h t L i n e v s . Te r m i n a l Po i n t

12. Calculating Accuracy
W h a t a r e t h e d i f f e r e n t m e t h o d s ?
 R o o t o f t h e M e a n S q u a r e d
 R o o t o f t h e S u m S q u a r e d
 S u m o f F a c t o r s
 To t a l E r r o r B a n d ( @ 2 1 ° C )

13. Calculating Accuracy
Ro o t o f t h e M e a n S q u a r e d M e t h o d
𝑹𝑴𝑺 =
𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 𝟐 + 𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 𝟐 + 𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚 𝟐
𝟑

14. Calculating Accuracy
Ro o t o f t h e S u m S q u a r e d M e t h o d
𝑹𝑺𝑺 = 𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 𝟐 + 𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 𝟐 + 𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚 𝟐

15. Calculating Accuracy
S u m o f t h e F a c t o r s M e t h o d
𝑺𝒖𝒎 = 𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 + 𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 + 𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚

16. Calculating Accuracy
To t a l E r r o r B a n d ( @ 2 1 ° C )

17. Calculating Accuracy
A c c u r a c y Va r i a n c e B a s e d o n M e t h o d
 N o n - L i n e a r i t y – 0 . 5 % B F S L
 N o n - R e p e a t a b i l i t y – 0 . 0 5 % F. S .
 H y s t e r e s i s – 0 . 1 % F. S .
𝑹𝑴𝑺 =
𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 𝟐 + 𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 𝟐 + 𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚 𝟐
𝟑
= 𝟎. 𝟑𝟎%
𝑹𝑺𝑺 = 𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 𝟐 + 𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 𝟐 + 𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚 𝟐 = 𝟎. 𝟓𝟏%
𝑺𝒖𝒎 = 𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 + 𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 + 𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚 = 𝟎. 𝟔𝟓%

18. Pressure Sensor Technology

19. Major Sensor Technologies
 S t r a i n M e a s u r i n g E l e m e n t s
 B o n d e d ( S i l i c o n o r F o i l G a u g e s )
 D e p o s i t e d ( T h i n o r T h i c k - f i l m )
 S i l i c o n P i e z o r e s i s t i v e ( M o u n t e d o n s u b s t r a t e )
 D i s p l a c e m e n t M e a s u r i n g E l e m e n t s
 H a l l - C e l l ( G r o s s M o t i o n )
 C a p a c i t i v e ( F i n e M o t i o n )

20. Bonded Strain Gauges
 S i l i c o n S t r a i n G a u g e – S i l i c o n s t r a i n g a u g e b o n e d t o m e t a l
s u b s t r a t e
 F o i l S t r a i n G a u g e – F o i l s t r a i n g a u g e b o n e d t o m e t a l s u b s t r a t e
B o n d e d S i l i c o n
G a u g e

21. Deposited
 T h i c k F i l m - F o r m e d b y t h e d e p o s i t i o n o f l a y e r s o f s p e c i a l
a d h e s i v e s o n t o a n i n s u l a t i n g s u b s t r a t e o n a d i a p h r a g m
 T h i n F i l m - S t r a i n g a u g e s a r e a t t a c h e d t o a m e t a l l i c b a s e e l e m e n t
u s i n g a s p u t t e r i n g p r o c e s s .
T h i n F i l mT h i c k F i l m

22. Silicon Piezoresistive
( M o u n t e d o n S u b s t r a t e )
 S i l i c o n P i e z o r e s i s t i v e - R e s i s t a n c e e l e m e n t s d i f f u s e d i n
c r y s t a l l i n e o r p o l y c r y s t a l l i n e S i l i c o n
Silicon Piezoresistive

23. Capacitive
( F i n e M o t i o n )
 C a p a c i t i v e – D i a p h r a g m m o v e m e n t b e t w e e n p l a t e s d e t e r m i n e s
c a p a c i t a n c e
d
h
a
Diaphragm
Substrate
Detect Electrode
Source Electrode
Guard Electrode
Glass
Ceramic CapacitiveMetal Capacitive

24. Hall Cell
( G r o s s M o t i o n )
 H a l l - C e l l - M a g n e t s t r e n g t h d e t e r m i n e s H a l l c u r r e n t

25. Pressure Sensor Ranges
B o n d e d S t r a i n G a u g e
0 1 B a r ( a ) 1 0 B a r ( a ) 6 0 B a r ( a ) 6 0 0 B a r ( a ) 2 0 0 0 B a r ( a )
Pressure Range
T h i n - F i l m
C e r a m i c T h i c k F i l m
S i l i c o n P i e z o r e s i s t i v e
C e r a m i c C a p a c i t i v e