Static error coefficients are used as a measure of the effectiveness of closed-loop systems for specified input signals. These coefficients provide information about the system's ability to accurately track a desired reference signal or reject disturbances. In this particular case, the question asks about the effectiveness of closed-loop systems for specified input signals, and the correct answer is option 'D', which states that the static error coefficients are used for all types of input signals including acceleration, velocity, and position.

Static Error Coefficients:
Static error coefficients are mathematical parameters that quantify the steady-state error characteristics of a control system. They are obtained by analyzing the system's response to a step input or a ramp input, which are common types of input signals used to evaluate the performance of closed-loop systems. There are three main static error coefficients:

1. Position Error Constant (Kp):
The position error constant, Kp, measures the steady-state error of a closed-loop system in response to a step input signal. It represents the ratio of the steady-state error to the magnitude of the step input. A larger Kp value indicates a smaller steady-state error, indicating better tracking of the desired reference signal.

2. Velocity Error Constant (Kv):
The velocity error constant, Kv, measures the steady-state error of a closed-loop system in response to a ramp input signal. It represents the ratio of the steady-state error to the slope of the ramp input. Similar to Kp, a larger Kv value indicates better tracking performance.

3. Acceleration Error Constant (Ka):
The acceleration error constant, Ka, measures the steady-state error of a closed-loop system in response to a parabolic input signal. It represents the ratio of the steady-state error to the acceleration of the input signal. Again, a larger Ka value indicates better tracking performance.

Effectiveness of Closed-Loop Systems:
By evaluating the static error coefficients, we can assess the effectiveness of closed-loop systems in terms of their ability to accurately track a desired reference signal. When the static error coefficients are small or negligible, it indicates that the closed-loop system can closely follow the reference signal without significant deviation. On the other hand, larger static error coefficients imply larger steady-state errors, indicating a less effective closed-loop system.

Conclusion:
Static error coefficients are essential measures of the effectiveness of closed-loop systems for specified input signals. They provide valuable information about the system's ability to accurately track a desired reference signal, regardless of whether it is an acceleration, velocity, or position input. The correct answer to the given question is option 'D', as static error coefficients are applicable to all types of input signals.