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58
Chapter 5
Fast. The number actually defines the proportional loop gain. The slow/fast suffix
indicates the speed at which the integrator's output increases. The slow setting allows
for larger masses or greater distance between the sensor and the thermo-electric
cooler by slowing the speed of the integrator.
Both the proportional gain and the integration time must be matched to the thermal
characteristics of the TE cooler and sensor. If the settings are incorrect, the
temperature set point will take an excessive amount of time to settle, or it will
oscillate around the set point and never settle.
The Gain setting depends on the type of TE cooler that you are using, but we can
suggest guidelines for selecting the proper gain. Set the gain to 1 fast and increase it
until the actual temperature oscillates around the set temperature. Then reduce the
gain to the next lower value.
To read the Gain setting, go to the setup. The display will show the value of the Gain
setting. In Constant I
5.4.3.4
Limits
5.4.3.4.1
TE Current Limit (Limit I
This sets the maximum drive current the module will allow. This maximum applies to
all modes (constant I
5.4.3.4.2
Temperature Limits (Limit T
The TEC 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
when the temperature limit is exceeded (if the output off bits are enabled for this
condition).
Caution: these limits do not apply if the sensor type is set to "None."
5.4.3.4.3
Resistance/Reference Limits (Limit R
Like the temperature limits, the TEC also supports both a low and high
resistance/reference limit, and can be programmed to turn the TEC output off in the
event those limits are exceeded, although by default this is disabled. These limits are
monitored only while in Const R/v/i mode.
5.4.3.5
Tolerances (Tol Time and Tol Temp)
The Tol Time and Tol Temp elements are used for determining when the TEC is "in
tolerance," where the actual temperature has stayed within Tol Temp of the set point
for at least Tol Time seconds. The Tol Time value is expressed in seconds, and can
Temperature Controller Operation
mode the Gain setting has no effect.
TE
)
TE
/R/T).
TE
and Limit T
HI
)
LO
or Const R mode
TE
/v
/i
and Limit R
HI
HI
HI
/v
/i
)
LO
LO
LO
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