Chapter 4 Temperature Controller Module Operation 51
4.4.3.4.2 Constant Resistance/Reference Mode (Const R/Const v/Const i)
This mode operates identically to the Const T mode, but the sensor input is not
converted to temperature, but is displayed in unconverted form. Likewise, the set
point is used directly, not converted from temperature. Thermistor and RTD sensors
use resistance (Const R mode, “
R
SET
=
” and “
R=
” variables), LM335 sensors use
millivolts (Const v mode, “
v
SET
=
” and “
v=
” variables), and AD590 sensors use
microamps (Const i mode, “
i
SET
=
” and “
i=
” variables).). Const R, Const v, and
Const i are primarily intended for users who know a sensor set point in “sensor”
units, not in ºC. I
TE
current is also displayed in these modes. Const v and Const i
modes are not supported on dual or combination TECs, as the sensors required for
these modes are not supported.
4.4.3.4.3 Constant Current Mode (Const I
TE
)
Unlike the modes above, the Const I
TE
mode allows the operator to explicitly set the
amount and direction of current flow through the TEC, using “
I
SET
=
” and “
I
TE
=
”
variables. If a sensor has been selected, the TEC temperature will be displayed.
Although temperature is not a factor in the amount or direction or current flow, the
high and low temperature limits are observed, and will shutdown the output if
exceeded, in Const I
TE
mode if a sensor is selected. For no temperature limits, set the
sensor type to “None.” Use caution when limits are not active, as the temperature
may exceed your TEC or Laser’s thermal limits. Const I
TE
mode is not supported on
dual or combination TECs.
4.4.3.4.4 Effects of Calibration on TEC modes
On startup, the 8300/8600 performs an auto-calibration to eliminate most of the error
in ADC and DAC values. After this auto-calibration, each sensor type supported by
the module has an offset calibration, while the I
TE
set point and read back has a two
point calibration. These calibration constants are then used to calibration a set point
or read back value. This includes “cross-mode” values, such as displaying actual
current while in constant temperature mode. While the current
set point
calibration
has no effect in Const T mode, the
read back
calibration is used to more accurately
display the actual current.
4.4.3.5 Limits
4.4.3.5.1 TE Current Limit (Limit I
TE
)
This sets the maximum drive current the module will allow. This maximum applies to
all modes (constant I
TE
/R/T).
4.4.3.5.2 Temperature Limits (Limit T
HI
and Limit T
LO
)
The 8300/8600 supports both a low and high temperature limit, and can be
programmed to turn the TEC output off in the event those limits are exceeded
(default state). The temperature limits are monitored regardless of the mode of the
module. This has the added safety feature of shutting down the module in Const I
TE
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