Page 26 ·
586
TECPak
User’s Manual
Gain Control and the PID Loop
The
586
TECPak
supports a fully configurable PID loop, allowing full
customization of the PID control parameters. To simplify control, eight standard
gain settings are also defined, and many applications can achieve acceptable
performance with these predefined gain settings, eliminating the need to
understand and adjust the PID loop.
The predefined gains are numbered
1
through
300
, and set using the Gain
setting in the
Settings…
dialog in
Arroyo Control,
or by using the TEC:GAIN
command. Increasing the gain value will increase the speed of the control loop.
For full access to the PID parameters, change the gain setting to
PID
, and the
individual P, I, and D values can be set with the TEC:PID command.
The PID parameters function within a mathematical formula as described below:
PID Formula:
dt
d
D
dt
I
P
Output
*
*
*
Where
is the error in the system, expressed as:
= Target - Actual
The controller can calculate ideal PID values using the AutoTune function,
discussed in detail in the next section.
To manually adjust the PID, start by changing the I and D values to zero, and
adjust the P value so that it reaches the set point as quickly as possible without
overshooting the set point an unacceptable amount. Gradually increase the I
value until the set point is achieved without oscillation. In many systems, the D
term is not needed and may be left at zero.
For additional information on PID loop tuning, consult online resources such as
Wikipedia (http://en.wikipedia.org/wiki/PID_controller) or search for terms such
as “Ziegler-Nichols method”, or “PID Loop”.
Using the AutoTune Function
The
586
TECPak
is capable of automatically determining PID parameters for
most applications. Using a form of the Ziegler-Nichols method, the
TECPak
will
step through a process to determine the thermal response of the mount, which
can then be used in a mathematical model to calculate the PID parameters.
