CIRAS-3 Operation Manual V. 1.09 54 support@ppsystems.com
recorded from all PLCs by pressing the R key and parameters can be toggled on the LCD by pressing the
S key.
PLC3 Temperature Control
All PLC3s include temperature control as standard. Each PLC includes a built-in Peltier heating/cooling
module which allows a wide range of temperature control. Optimal control depends on the ambient air
temperature due to power requirements to heat or cool the cuvette or leaf to temperatures that are much
different than ambient. With full power available you can usually control cuvette temperature (Tcuv) from
approximately 10 °C below ambient to 15 °C above ambient, but within the absolute temperature range of
0 to 45 °C. Note that slight differences are expected between sensor-based and calculation-based
methods. Automatic control of “leaf temperature” is heavily influenced by the following 3 variables:
1. Leaf transpiration in the cuvette
2. Light (incident radiation)
3. Size and construction of the PLC window
At lower light intensities, leaf temperature control is wider and at high light intensities it is much tighter.
We recommend that when using “Set leaf temperature” as the Temperature Control Type under Settings
(F2) that you do so maintaining leaf temperature (Tleaf) at or near ambient levels especially at high light
intensities and transpiration rates. Although all PLC3s include temperature control as standard, there are
some key differences between each type as follows:
Temperature Measurement
PLC3 Universal – Includes an IR sensor for accurate, non-contact measurement of leaf temperature and
energy balance for calculation of leaf temperature. We recommend IR thermometry as long as the entire
cuvette window is covered with leaf material. If the cuvette window is not covered 100% with leaf
material, you must select energy balance.
PLC3 Narrow and Conifer – Includes a leaf thermistor for direct measurement of leaf temperature and
energy balance for calculation of leaf temperature. We recommend the energy balance method.
Temperature Control Type
PLC3 Universal – Five control options are available:
• Set leaf temperature
• Track leaf to ambient
• Cuvette temperature
• Track cuvette to ambient
• Disable temperature control
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