Signal Conditioning Circuits

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SignalConditioning

Circuits Bilal Alabwini Mohammad AL-

Qaisi


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Introduction

• a basic measurement system consists mainly

of the three blocks: sensing element, signalconditioning element and signal rocessingelement !

• "he sensing element con#erts the non-electrical signal$ into electrical signals !

• signal conditioning element is to con#ert the#ariation of electrical signal into a #oltagele#el suitable for further rocessing!

• signal rocessing element! %t takes the oututof the signal conditioning element andcon#erts into a form more suitable for

resentation !


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Unbalanced D.C. Bridge

To illustrate the properties of unbalanced d.c.bridge, let u consider the circuit shown in g


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• R2: ariable resistance can be considered tobe a sensor

• e ! : The output oltage which aries with

the change of the resistance "#R$R%&'

• p: The ar( ratio of the bridge

• ): the e*citation oltage


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•1-e& #s ' Characteristics is nonlinear (since x is resentin the

denominator as well as in the numerator(.

2-Maximum sensitivity of the bridge can be achieved forthe arm ratio p=1.

)- Nonlinearity of the bridge decreases with increase in thearm ratio p, but the sensitivity is also reduced. "his fact

can be #eri*ed by lotting ( e&+ .S / for di0erent p

4 !or unity arm ratio "p=1#, and for small x, we can obtainan approximate linear relationship as 1e& 2 (/+34 5!


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6ush-ull Con*guration

• "he characteristics of an unbalanced wheatstone bridgewith single resisti#e element as one of the arms can greatlybe imro#ed with a ush-ull arrangement of the bridge,comrising of two identical resisti#e elements in twoad7acent arms: while the resistance of one sensor

decreasing, the resistance of the other sensor is increasingby the same amount, as shown in *g!

• adantage of using push+pull conguration :

8- 9irst of all, the nonlinearity in the bridge outut can be

eliminated comletely

- the sensiti#ity is doubled comared to a single sensorelement bridge


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Unbalanced .C. Bridge with -ush+pull Conguration

• %; (a and (b shows the schematicarrangements of unbalanced A!C! bridge withinducti#e and caaciti#e sensors resecti#ely

with ush-ull con*guration!


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Amli*ers


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.Aarently, both the two amli*ers are caable ofdeli#ering any desired #oltage gain, ro#ided the hasein#ersion in the *rst case!the inut imedance of the in#erting amli*er is *niteand is aro'imately >8, while a nonin#erting amli*erhas an in*nite inut imedance! =e*nitely, the secondamli*er will erform better!


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Di/erential (plier


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• "here are se#eral criteria are used for 7udging the erformance of an amli*er:

8- inut imedance- gain and bandwidth

)-common mode re7ection ratio (CM>>!

44CM>> is a #ery imortant arameter forinstrumentation circuit alications and it is desirableto use amli*ers of high CM>> when connected toinstrumentation circuits!!

Ad is the di0erential mode gain!

Ac is the common mode gain of the amli*er!


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%nstrumentation Amli*er

• ?sing to amlify a small di0erential #oltagefew hundred times in instrumentationalications !

•

A single stage di0erential amli*er is notcaable of erforming this 7ob e@ciently,because of

8- the inut imedance is *nite

- the achie#able gain in this singlestage amli*er is also limited


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• "he ma7or roerties are

• (i high di0erential gain (ad7ustable

u to 8&&&• (ii in*nite inut imedance,

• (iii large CM>> (& dB or more, and

(i# moderate bandwidth!


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Signal Conditioning Circuits

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