3.9 Steady-State Error and Error Constants 3.9 STEADy-STATE ERROR AND ERROR CONSTANTS In this section, we consider the unity feedback block diagram shown in Figure 3.14 subject to standard inputs and determine the associated tracking error in each case. The standard inputs considered are the sampled step, the sampled ramp, and the sampled parabolic. As with analog systems, an error constant is associated with each input, and a type number can be defined for any system from which the nature of the error constant can be inferred. All results are obtained by direct application of the final value theorem. From Figure 3.13, the tracking error is given by E ( z ) = R ( z ) 1 + G ZAS ( z ) C ( z ) R ( z ) = 1 + L ( z ) (3.40) where L(z) denotes the loop gain of the system.