Internal PAR Sensor (General)

The clear-topped chambers, LED light sources, and the LCF all have a sensor for measuring the PAR in the chamber. Each of these is discussed in subsequent sections, but there is an offset adjustment that is available that is common to all.

Zeroing the ParIn Signal

Some instruments, at various times and for various reasons, might exhibit a slight offset in the ParIn signal. That is, when the sensor is in the dark, the ParIn_μm reading will not be exactly zero. If this is a problem, you can work around the situation by applying an offset to the measurement to correct it.

The way to do this is "ParIn zero..." in the Calib Menu (Figure 18‑22).

To zero the light sensor, press Zero (f1) when you are sure the chamber is completely darkened. The offset value will be retained (it will simply be the raw signal at the moment you pressed f1), and subsequently applied. (The equation for the final value is (14-17) on page 14-10 in the instruction manual.) The offset value is retained in the /dev/.user file. The offset value can be also be viewed in New Measurements mode in Diganostic Screen E (page 6-27 in the instruction manual).