Basics of Split Range Control

Split range control is a control strategy in which one tries to control a process parameter (say pressure) by adjusting more than one manipulated variable.

in this you may have single controller and more than one final control elements (say control valve. in the case of one controller controls 2 CV,

we can do it like this:-

Normal control sognal ranges from 4~20 mA, one can set the zero of 1st control valve as 4mA and 12mA as span of the same, the second one’s zero may be set 12 mA and span 20 mA. in practical the first valve will start open a signal above 4mA and and will be fully open at 12mA after that the Second one starts open and reaches its maximum at 20 mA.

More info