Figure 3-27 Example Set Point Profile - Honeywell VPR100 User Manual

output function block. In this light, tuning the overall cascade control configuration becomes the
considerably simpler matter of tuning a single control loop.
Set Point Profile Implementation
By definition, set point profiles are essentially user-specified plots of process values against time. These
plots are characterized by "segments" which are a series of intervals of varying time lengths that divide the
plots into several segments. Within each segment, process values are typically drawn as straight lines that
ramp up or down or stay constant at predetermined levels. An example of a simple five-segment set point
profile is shown in Figure 3-27. Set point profiles with up to 63 segments can be specified using the
instrument. Note that when a segment depicts the process value as sloping up or down, it is referred to as a
"ramp." The term "soak" is used to describe a segment when the process value is made to stay constant. In
Figure 3-27, segments 1, 3, and 5 are ramps while segments 2 and 4 are soaks.
PROCESS
VALUE IN
ENGINEERING
UNITS
To force a process value to vary linearly with time at various rates within successive time intervals is the job
of a set point profiler, another class of function blocks available within the instrument. Be advised that use
of set point profilers is typically observed in thermal or heat treat applications. For example, being able to
vary temperature in accordance with a set point profile is vital in the tempering of metal or ceramic parts.
Refer to the application of Figure 3-15 discussed at the beginning of this section. This application dealt
with controlling a furnace zone's temperature by means of a 4 to 20 mA gas valve actuator. If the furnace
zone temperature were to be manipulated so that it followed the ramps and soaks of a set point profile, the
first step would be to implement the function block diagram established in Figure 3-20. In general, the
control configuration that holds a process value to a local set point, must be programmed and on line before
allowing the process value to be characterized by a profile. With regard to the application at hand, a set
point profiler function block programmed with a user defined set point profile may be brought into the
configuration once the furnace zone's basic temperature control loop is operational. Note that the output of
the profiler function block will essentially be the set point profile.
From the cascade control strategy's explanation, recall that all control loop function blocks within the
instrument have a Setpoint #2 parameter that may be used as a remote set point input for connecting to the
profiler's output.
LP1 in the function block diagram of Figure 3-20 will make use of SP2's remote set point functionality so
that a set point profiler's time varying set point may be applied to it. Refer to Figure 3-28.
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Figure 3-27 Example Set Point Profile

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