198 SAMPLED-DATA CONTROL SYSTEMS 
digitally controlled system is the one using the bypass digital controller, 
in which failure of the latter produces no serious effect other than 
degraded performance. 
Digital controllers can be used with systems that are normally continu- 
ous. In such cases a sampling operation is deliberately introduced, and 
the sampled data so derived are applied to a digital controller. In this 
way, the advantages of this form of system can be applied to systems 
which are not sampled normally. On the other hand, where the data are 
normally in sampled form anyway, digital control is a natural means for 
processing the data and compensating the system in which they occur. 
Practical digital controllers need not be complex devices, and their use in 
the field is practical. 
