Digital instruments are becoming more and more popular because of their inherent advantages over analog instruments,such as,greater speed,increased accuracy,better resolution,reduction in operator errors and the ability to provide automatic measurement in system application.
Digital instruments use logic circuits and techniques for carrying out measurements of quantities.Any digital instrument may be viewed as an arrangement of logic gates that change states at very high speeds in the process of carrying out a measurement.
The major advantage of digital instruments is the readability of the measurement result because of the digital read-out.In analog instruments,the user performs the function of an analog-to-digital converter(ADC).The user must read the analog scale properly,process some skill in interpolation,be able to use mirrored scales and in general,have a good eye.
The second major advantage of digital instruments over analog instruments is the accuracy.In general,digital instruments are more accurate than analog ones.For example,a low-cost digital multi meter.
Digital instruments provide better resolution than analog instruments. A typical values of resolution of a digital instrument may be one part in 1 µV can be read on the 1 -V input range.
The digital instruments also have greater speed.The maximum speed of reading and period of sampling is interrelated.
The digital voltmeters may have sampling rate from a few sample per second to 1000 samples per second.However,input capacitance and filter limits the sampling speed to 100 or below.Also,it is impossible to read out at high reading speed.
A digital instrument is quite different from an analog instrument with digital read-out.The circuit required for measurements in a digital instrument is of analog instrument with analog read-out,except that digital display is unambiguous and can be read more quickly.
Virtually all digital instruments provide a digital display of the measurand.A fixed number of pulses proportional to the measurand are entered in a digital counter and the counter actuates the digital display.So the counting circuits are vital parts of the digital instruments.
Digital instruments,particularly digital voltmeters of multi meters are employed for measurement of analog quantities.Conversion of an analog signal into an equivalent digital signal is,therefore,essential.Thus analog-to-digital converters (ADCs) are most important parts of digital instruments.
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