Split Range Control Calculator
In split range control one controller output drives two valves, for example heating and cooling. See each valve’s opening for any controller signal and split point.
- Valve A works over 4 to 12 mA, valve B over 12 to 20 mA
- Calibrate positioner A for 4 to 12 mA and positioner B for 12 to 20 mA
Valve openings across the signal range
| Signal | Output | Valve A | Valve B |
|---|---|---|---|
| 4 mA | 0 % | 100 % | 0 % |
| 6 mA | 13 % | 75 % | 0 % |
| 8 mA | 25 % | 50 % | 0 % |
| 10 mA | 38 % | 25 % | 0 % |
| 12 mA | 50 % | 0 % | 0 % |
| 14 mA | 63 % | 0 % | 25 % |
| 16 mA | 75 % | 0 % | 50 % |
| 18 mA | 88 % | 0 % | 75 % |
| 20 mA | 100 % | 0 % | 100 % |
Split Range Scaling
Valve B: xB = (I − Isplit) ÷ (20 − Isplit)
Each valve’s positioner is calibrated to its own part of the 4 to 20 mA range; reverse action is set in the positioner or by the valve design.
Worked example
With a 12 mA split, valve A closing and valve B opening as signal rises, a 9 mA output gives valve A 37.5 % open and valve B shut.
Frequently Asked Questions
What is split range control?
One controller output operates two or more final elements in sequence, for example a heating valve on the lower half of the signal and a cooling valve on the upper half.
How do I calibrate positioners for split range?
Set the zero and span of each positioner to its part of the signal, for example 4 to 12 mA and 12 to 20 mA.
Can the split point be other than 12 mA?
Yes. Unequal splits are used when the two valves have different capacities or the process gains differ.
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