Page 32 · 685 Series
ComboPak
User’s Manua
l
Cool
Fan is turned on whenever the TEC output is on and cooling, off
otherwise.
Heat
Fan is turned on whenever the TEC output is on and heating, off
otherwise.
For more details, see the TEC:FAN command in the
Computer Interfacing
Manual
.
Resistive Heaters and Heat/Cool Only Modes
The
ComboPak
supports temperature control using resistive heaters instead of
Peltier coolers. With resistive heaters, cooling is obviously not possible, and the
ComboPak
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
ComboPak
to operate in
a cool-only mode. This is only possible with Peltier coolers, as resistive heaters
will heat regardless of the direction of current.
To change the cooling mode use the TEC:HEATCOOL command.
Gain Control and the PID Loop
The
ComboPak
supports a fully configurable PID loop, allowing full
customization of the PID control parameters. To simplify control, eight standard
gain settings are 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
(specifically, 1, 3, 5, 10, 30,
50, 100, 300) and set 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 use the TEC:PID command to set the
individual P, I, and D values.
The PID parameters function within a mathematical formula as described below:
+
+
=
dt
d
D
dt
I
P
Output
*
*
*
Where
is the error in the system, expressed as:
= Target - Actual