Understanding Setpoint Ramping and Ramp/Soak Temperature Control
What is Setpoint Ramping?
Many temperature controllers have the facility to ramp their effective setpoint towards the final target value at a predefined rate. A deviation alarm is often used with this feature to check that the process is closely following the ramp. When the setpoint reaches the top of the ramp, a “soak period” begins where the setpoint is maintained at this value.
Why Use Setpoint Ramping in Temperature Control Processes?
Ramping protects a process from rapid changes in the setpoint and the resulting thermal shock as the controller tries to force the process variable to follow. This is especially useful if there is a power-cut, because it guides the rise back to the target setpoint when power is restored.
Setpoint Ramping Example
If you set the ramp rate to 1000°F/hr and the setpoint to 750°F, and the current temperature is 200°F at power-on, the effective setpoint starts a 200°F and rises towards 750°F at 1000°F per hour. A similar process occurs when switching back to automatic mode from manual control.
The exact implementation of setpoint ramping varies depending on the controller model. Different functions include:
- implementing a ramp whenever the setpoint value is adjusted
- only implementing a ramp when the active setpoint is changed (e.g. from local setpoint 1 to local setpoint 2)
- an adjustable time for the soak, after which the control outputs are disable
- an indefinite soak following the ram
How Do Ramp/Soak Segments Work?
There are a number of different types of profile segments as well as the commonly referred to, Ramp and Soak. Profile Segments can be ramps, dwells (soak) or steps. Additional special segments may also be possible, such as holds, ends, loops or joins.
- Step Segment increases or decreases the setpoint value instantaneously
- Ramp Segment increase/decreases the setpoint over a set time, or at a defined rate.
- Soak Segment (also called Dwell Segment) maintains the value of the previous segment for a defined time.
- Hold Segment maintains the value of the previous segment until the profiler is given an instruction to move to the next segment.
- Loop Segment sends the profile back to a previous segment to run that part of the profile more than once.
- Join Segment ends the current profile and start another one.
- End Segment stops the current profile.
Profilers usually have options for one or more segment event outputs.
Learn more about how programmable temperature controllers work with segments.
Want to learn more? Watch Ian Parnell, head of Technical Support at West Control Solutions discuss setpoint ramping and ramp/soak functionality in more detail.
