PLC Setpoint Ramp Rate Calculator
Build a setpoint or output ramp in a PLC: from the ramp rate and the task time, find the increment to add each scan and the time the ramp takes.
- Increment = rate ÷ 60 × Ts = 5 ÷ 60 × 0.1 s = 0.008333
- Ramp time = |end − start| ÷ rate = 12 min
- Each scan: SP = SP ± increment, clamp at end value
Ramp Formulas
Ramp time = |end − start| ÷ ramp rate
Ramp rate is in engineering units per minute, Ts the fixed task time in seconds. Run the ramp in a cyclic task with a known interval; in a free running scan, multiply the rate by the measured cycle time instead.
Worked example
Ramping a temperature setpoint at 5 °C/min in a 100 ms task adds 0.00833 °C each scan; going from 20 to 80 °C takes 12 min (7200 scans).
Frequently Asked Questions
Why ramp a setpoint?
To avoid thermal shock, pressure surges or large controller outputs when the setpoint changes, and to follow product recipes.
Where should the ramp run?
In a fixed interval cyclic task, so the increment per execution gives a known rate.
How do I stop overshoot of the end value?
Limit the ramped value so it never passes the target, then set it exactly to the target.
Learn more on the blog
Why 24 volts is used in PLC systems
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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