Note on Analog and Digital System

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Analog and digital systems:

The analog system is used to sense the continuous time and continuous amplitude signal and the processing unit also processes continuous time and continuous amplitude signal. In contrast, Digital system consists of an analog transducer, but the signal processing unit consists of an analog-to-digital converter(ADC),processing the discrete/digital signal and the display units are of numeric display devices viz. A digital computer, seven segment display, Digital multimeter etc.

Analog and digital instrumentation systems are briefly explained below:

1.Analog instrumentation system

It is used to measure and process the continuous time and continuous amplitude signal. The functional block diagram of Analog instrumentation system is given below.

analog Instrumentation system
Analog Instrumentation system

Various elements of Analog instrumentation system are:

a.The Primary element/Input element(Transducer):

The input element receives the quantity whose value is to be measured and converted into its proportional electrical signal such as voltage ,current ,inductance ,capacitance etc, which is done by Transducer.

b.The Secondary element/Signal processing unit:

The output of the transducer is provided to the signal processing unit. It processes the signal into a suitable form so that it is acceptable in the output unit. This unit may consist of devices like amplifiers,filters,attenuators ,modulators etc.

c.Output(Indicating) unit:

The output of the signal processing unit is fed to the Indicating unit. In this unit, the signals are measured and value is indicated to the user/reader in readable form. The indication may be either through an indicating instrument, CRO, computers , chart recorders and so on.

2.Digital instrumentation system

In addition to the all functional parts used in the analog instrumentation system, Analog-to-digital converter(ADC) is used in a digital instrumentation system, thereby processing discrete (digital data) by the signal processor. The functional block diagram of Digital instrumentation system is shown below.

Digital instrumentation system
Digital instrumentation system

Various elements of Digital instrumentation system are:


It is the element that converts all the physical input parameters like temperature,pressure,displacement,velocity,force etc into its proportional electric signal.

b.Signal conditioning unit:

In this unit, Signals are integrated,differentiated,subtracted etc as per requirement to fed it to Scanner/multiplexer. It includes all the balancing circuits and calibration element along with it.


Multiple analog signals are received by this unit and are sequentially provided to Signal converter.

d.Signal converter:

It is used to convert the signal coming from Scanner/multiplexer into the form acceptable by an analog-to-digital converter.

e.Analog to digital converter(ADC):

The analog signal is converted into its proportional digital signal by this unit. The output of the ADC is fed to a digital display.

f.Digital recorder:

It is basically a digital storage device like oscilloscope or computer. For non-recording scheme , it may be a decimal display or any other numeric display.


1.S.morris.alan(2001). Measurement and Instrument principle(3 ed.).A division of Reed Educational and Professional Publishing Ltd

  • Analog instrumentation system is used to sense the continuous time and continuous amplitude signal and the processing unit also processes  continuous time and continuous amplitude signal
  • Digital instrumentation system is o sense and processes the discrete time and discrete amplitude signal.
  • The transducer,signal processing unit, and output unit are the elements of Analog instrumentation system.
  • Transducer,Signal conditioning unit,Scanner/multiplexer,Signal converter,Analog to digital converter(ADC),Digital recorder are the elements of Digital instrumentation system.

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