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STI S.r.l. – Via Dei Caravaggi 15, 24040 Levate (BG) – ITALY www.imi-critical.com
Manual 4054 – rev.00 02/2021 – DT2 - 21 -
Figure 12: Split range-operation with two positioners
12. TSUP: Set point ramp UP
13. TSDO: Set point ramp DOWN
The setpoint ramp is effective in automatic operation and limits the speed of alteration of the active setpoint. When
switching over from manual operation to automatic the active setpoint is adjusted to the setpoint on the positioner
with the setpoint ramp.
This bumpless manual/automatic switchover avoids excessive pressure increases on long pipelines.
In the position TSUP = Auto the slower of the two travel times determined during initialization is used for the
setpoint ramp. TSDO is then ineffective.
14. SFCT: Set point function
Non-linear valve characteristics can be linearized with this function and any flow characteristics simulated in linear
valve characteristics.
Four valve characteristics are stored in the positioner
• Linear (14.SFCT = LINE, factory setting)
• equal percentage 1:30 (14.SFCT=1:30)
• quick open 30:1 (14.SFCT=30:1)
• custom (14.SFCT=FREE)
15. SP00 to 35. SP20: Set point turning points
A flow parameter can be assigned to the respective set point turning value at an interval of 5 %. These points lead
to a polygon chain with 20 straight lines which therefore represents a projection of the valve characteristic.
The set point vertex values can only be input at 14.SFCT=FrEE. You may only enter a strictly monotonous
characteristic, and two consecutive vertex values must differ by at least 0.2 %.
36. YA: Manipulating variable limiting start
37. YE: Manipulating variable limiting end
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