Introduction to Industrial Automation

Figure 6.24  Determination of the cyclic operation time of an analog input module.

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  Introduction to Industrial Automation

If it is desired to have a greater accuracy of a control action, then another A/D converter should be 

selected that will have 10 bits, and thus a corresponding resolution of 1 step in 1024 steps of the 

full scale. More specifically:

 

◾

8-bit converter: Resolution = 256 different digital values between the minimum and maxi-

mum of the range, thus 0.004 (2

–8

=0.004) step of the full scale

 

◾

10-bit converter: Resolution = 1024 different digital values between the minimum and max-

imum of the range, thus 0.001 (2

–10

=0.001) step of the full scale

 

◾

12-bit converter: Resolution = 4096 different digital values

 

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14-bit converter: Resolution = 16384 different digital values, and so on

Thus, the bigger the resolution of an A/D converter, the more accurate the digital representa-

tion of an analog signal is. For example, if an analog input signal is varying from 0 to +10 V, the 

step size of the accuracy, in the case of an 8 bit and 10 bit, the A/D converter is defined as:

 

◾

8-bit A/D converter: 10/256 = 39.1 mV per step or 25.6 steps per volt of the voltage input 

signal

 

◾

10-bit A/D converter: 10/1024 = 9.76 mV per step or 102.4 steps per volt of the voltage input 

signal