Walz MINI-PAM-II, Manual, Page: 21 / 130

Components and Setup Chapter 4
15
Essential optoelectronic elements of this micro-quantum-sensor
are:
- A 3 mm ∅ diffusing disk.
- High stability silicon photovoltaic detector with filter set for
PAR correction, magnetically attached to 2035-B Leaf Clip
Holder.
- Cosine response characteristics (Angular dependence: Error
< 3 % for angle between -30 ° and +30 ° from normal axis).
The sensor is factory calibrated and calibration factors are stored
in the internal memory of the 2035-B leaf clip. The stability of cal-
ibration depends on keeping the diffuser clean. It is advisable to
check calibration regularly by comparison with a standard quan-
tum sensor. Any deviation can be corrected by entering a recali-
bration factor in WinControl-3 or on the touch screen. A substan-
tial increase of the calibration factor from its original value indi-
cates dirt-deposition on the diffuser, which may be reversed by
gentle cleaning using a cotton tip applicator, moistened with
some diluted ethanol.
Thermocouple
A NiCr-Ni thermocouple is mounted in the Perspex tube on which
the leaf area is resting. The thermocouple is forming a loop that
gently presses against the lower surface of the leaf. This ar-
rangement results in effective temperature equilibration between
leaf and thermocouple, and protects the thermocouple from di-
rect sun radiation.
The reference couple is located on the circuit board, in close
proximity to the thermovoltage amplifier, enclosed in the bottom
part of the holder. The relationship between thermovoltage and
temperature is almost linear. With decreasing temperatures there
is a small decline of ΔV/ C. Calibration was performed at 25 °C.