Understanding PressureSensor 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 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 4 D w y e r I n s t r u m e n t s , I n c .

Understanding Pressure Sensor Accuracy

New Accuracy Equation

1% RMS ≠ 1% RSS ≠ 1% SUM ≠ 1% TEB

Why is Accuracy Important?E ffi c i e n c y a n d Q u a l i t y

E ffi 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

Why is Accuracy Important?Ac c u r a c y v s . P r i c e

%

$

Accuracy StandardsW 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 .

Accuracy StandardsI E C D e fi n i t i o n o f Ac 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 fi 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 fi e d c o n d i t i o n s a n d b y a s p e c i fi e d

p r o c e d u r e .

Accuracy StandardsI E C 6 1 2 9 8 - 2 S t a n d a rd

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.

Accuracy FactorsN 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 ff 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 .

Accuracy FactorsH y s t e re s i s

T h e m a x i m u m d i ff 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 fi 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 .

Accuracy FactorsN 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 fi 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

Accuracy FactorsB e s t Fi t S t r a i g h t L i n e v s . Te rm i n a l Po i n t

Calculating AccuracyW h a t a re t h e d i ff e re 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 Fa c t o r s

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

Calculating AccuracyRo o t o f t h e M e a n S q u a re d M e t h o d

𝑹𝑴𝑺=√ ( 𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 )𝟐+(𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 )𝟐+(𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚 )𝟐

𝟑

Calculating AccuracyRo o t o f t h e S u m S q u a re d M e t h o d

𝑹𝑺𝑺=√ (𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 )𝟐+(𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔 )𝟐+( 𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚 )𝟐

Calculating AccuracyS u m o f t h e Fa c t o r s M e t h o d

𝑺𝒖𝒎=𝑵𝒐𝒏−𝑳𝒊𝒏𝒆𝒂𝒓𝒊𝒕𝒚 +𝑯𝒚𝒔𝒕𝒆𝒓𝒆𝒔𝒊𝒔+𝑵𝒐𝒏−𝑹𝒆𝒑𝒆𝒂𝒕𝒂𝒃𝒊𝒍𝒊𝒕𝒚

Calculating AccuracyTo t a l E r ro r B a n d ( @ 2 1 ° C )

Calculating AccuracyAc 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%

Pressure Sensor Technology

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 - fi 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 )

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

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

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 ff 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

Capacitive( Fi 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

Hall Cell( G ro 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

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