Page 20 · 5235
TECSource
User’s Manual
The typical setting is 100
μ
A, but your application will determine the actual
needs.
The Steinhart-Hart Equation
As can be seen from the temperature versus resistance graph above, resistance
varies inversely with temperature in a non-linear fashion. This relationship can be
accurately modeled by polynomial equations, and one such being the Steinhart-
Hart equation:
3
)
ln(
*
)
ln(
*
1
R
C
R
B
A
T
+
+
=
The coefficients A, B, and C can usually be obtained from the thermistor
manufacturer. The
TECSource
defaults to the coefficients for the BetaTHERM
10K3A1 thermistor (A = 1.12924x10
-3
, B = 2.34108x10
-4
, C = 0.87755x10
-7
). You
can change the coefficients under the
Sensor Coeffs
menu.
Resistive Heaters and Heat/Cool Only Modes
The
TECSource
supports temperature control using resistive heaters instead of
Peltier coolers. With resistive heaters, cooling is obviously not possible, and the
TECSource
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
TECSource
to operate in
a cool-only mode. This is only possible with Peltier coolers.
To change the cooling mode, adjust the
H/C Mode
setting to
Heat/Cool
,
Heat
Only
, or
Cool Only
, as appropriate.
Gain Control and the PID Loop
The
TECSource
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
menu setting. 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 will be available as settings in the menu.
Summary of Contents for Arroyo 5235
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