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2.11.3 Tuning a Closed Loop PID Controller 51
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2.11.3 Tuning a Closed
Loop PID Controller There has been a lot written about tuning closed loop control systems and specifically
PID control loops. This section does not attempt to compete with control theory
experts. It describes a few basic rules of thumb to help less experienced users get
started. This technique will not solve every problem, but it has worked for many oth-
ers in the field. This section assumes the user has worked through the operation sec-
tions of this manual and has a stable temperature reading from the control sensor. It
is also a good idea to begin at the center of the temperature range of the cooling sys-
tem (not close to its highest or lowest temperature).
2.11.3.1 Setting Heater Range
Setting an appropriate heater output range is an important first part of the tuning
process. The heater range should allow enough heater power to comfortably over-
come the cooling power of the cooling system. If the heater range will not provide
enough power, the load will not be able to reach the setpoint temperature. If the
range is set too high, the load may have very large temperature changes that take a
long time to settle out. Delicate loads can even be damaged by too much power.
FIGURE 2-5 Examples of PID control