Arroyo Instruments TECPak 585 Series, User Manual

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TECPak User’s Manual · Page 25
Resistive Heaters and Heat/Cool Only Modes
The
TECPak supports temperature control using resistive heaters instead of
Peltier coolers. With resistive heaters, cooling is obviously not possible, and the
TECPak must be configured to not attempt to cool the output, or a run-away
condition will occur when the cooling current actually causes additional heating.
If your application requires, you can also configure the
TECPak to operate in a
cool-only mode. This is only possible with Peltier coolers.
To change the cooling mode, change Heat/Cool Mode setting in the
Settings…
dialog in Arroyo Control , or use the TEC:HEATCOOL command.
Gain Control and the PID Loop
The
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