Signal Conditioning | Signal Conditioning Block Diagram

What Is Signal Conditioning

Usu­al­ly mea­sur­and is a phys­i­cal quan­ti­ty. It is mea­sured by a stage called detec­tor trans­duc­er. This stage will act as the first part of the instru­men­ta­tion sys­tem. ‘The out­put of the first part is not sig­nal con­di­tion­ing but is changed by the sec­ond stage called intermediate 

The last part of the mea­sure­ment sys­tem con­sists of ele­ments or con­trol ele­ments such as indi­cat­ing, record­ing, dis­play­ing, data processing 

Cal­cu­lat­ing dynam­ic phys­i­cal quan­ti­ties requires a real­is­tic ana­log or dig­i­tal out­put, avail­able from the inter­me­di­ate stage of sig­nal conditioning 

Sig­nal con­di­tion­ing equip­ment is required to per­form lin­ear oper­a­tions such as ampli­fi­ca­tion, atten­u­a­tion, inte­gra­tion, dif­fer­en­ti­a­tion, addi­tion and subtraction 

Also requires oth­er non-lin­ear oper­a­tions such as mod­u­la­tion, demod­u­la­tion, sam­pling, fil­ter­ing, clip­ping and clamp­ing, lin­eariz­ing or multiplication 

DC SIGNAL CONDITIONING 

The trans­duc­er con­verts the mea­sur­and (phys­i­cal scale) into an equiv­a­lent elec­tri­cal sig­nal. The out­put of the trans­duc­er must be increased suf­fi­cient­ly to per­form the func­tions of con­ver­sion, pro­cess­ing, indi­cat­ing and record­ing properly

Pas­sive trans­duc­ers require exci­ta­tion because such trans­duc­ers do not auto­mat­i­cal­ly gen­er­ate volt­age but cur­rent. The trans­duc­er acts as an arm of the bridge net­work. A sep­a­rate DC source is used to excite it 

The bridge is bal­anced by a poten­tiome­ter. By which its unbal­ance con­di­tion is cal­cu­lat­ed. The DC ampli­fi­er ampli­fies the sig­nal ade­quate­ly. It should have qual­i­ty ther­mal and long last­ing stability 

Fol­low­ing the DC ampli­fi­er is a low pass fil­ter. It is used to remove high fre­quen­cy com­po­nents and noise in the data signal 

DC sig­nal con­di­tion­ing is used in com­mon resis­tance trans­duc­ers such as poten­tiome­ters and resis­tance strain gauges 

Ac Signal Conditioning 

Defects in DC sig­nal con­di­tion­ing are elim­i­nat­ed in car­ri­er type AC sig­nal conditioning 

The trans­duc­ers used are vari­able induc­tance trans­duc­ers. The car­ri­er oscil­la­tor pro­duces car­ri­er fre­quen­cies rang­ing from 50Hz to 20KHz. Car­ri­er fre­quen­cies are 5 to 10 times larg­er than sig­nal frequencies 

Trans­duc­er para­me­ter changes mod­u­late the ampli­tude of the car­ri­er fre­quen­cies at the bridge ouput. Also the wave­form is ampli­fied and demodulated 

The demod­u­la­tion that takes place in this is phase sen­si­tive. There­fore the polar­i­ty of the DC out­put indi­cates the direc­tion of the para­me­ter change at the bridge output 

Active fil­ters are used to elim­i­nate unwant­ed fre­quen­cies and to pre­vent over­load­ing of the AC ampli­fi­er. The phase sen­si­tive demod­u­la­tor fil­ters the car­ri­er fre­quen­cy com­po­nents in the data signal 

AC sys­tems are used in vari­able reac­tance trans­duc­ers. Longer cables are also used to trans­mit sig­nals where trans­duc­ers are con­nect­ed to sig­nal con­di­tion­ing equipment 

Once the phys­i­cal dimen­sions have been con­vert­ed by the trans­duc­ers to the cor­re­spond­ing ana­log elec­tri­cal prop­er­ties, they must be ampli­fied to the appro­pri­ate volt­age and cur­rent lev­el. Such process­es are car­ried out with elec­tron­ic circuits