The accuracy of an electro hydraulic servo system depends on the system deadband and open-loop gain.
System deadband is the composite deadband of all the components in the system.
Deadband is defined as that region or band of no response where an input signal will not cause an output.
For example, with respect to a servo valve, no flow will occur until the electric current to the torque motor reaches a threshold minimum value.
This is shown in Figure 17-16,
which is obtained by cycling a servo valve through its rated input current range
and recording the output flow for one cycle of input current
The resulting flow curve shows the deadband region and hysteresis of the servo valve.
Hysteresis is defined as the difference between the response of the valve to an increasing signal and the response to a decreasing signal.