POWER PLANT INSTRUMENTATION & CONTROL

split range control is which the output of a controller is 
split to two or more control valves. For eg,
For 0% controller output,valve A fully open & B fully 
closed.
For 25%, Valve A 75% open,B 25% open
For 50%, Valve A& B- 50% open,
For 75%, Valve A 25%open, B-75%open..
For 100%, Valve A fully closed & valve B Fully Open..

Like this, the controller output action can be set depending 
upon the application.

as well as in split range control the control signal is split in two 
ranges according to the application .for eg,4-20MA.signal 
can be used as 4-12 MA. FOR VALVE A OPEN i.e.50%.& 12-20MA 
for vlv B open.vice-versa.