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