Delta SS1-UM-1.05 User Manual download pdf (Page 52)

52 •

••

• Measurement options Document code: SS1-UM-1.05

You should not expect to have to do this very often. The photodiodes and light

measurement circuits are very stable.

The source of the apparent variability mentioned above is the not quite ideal cosine

and spectral response of the sensors.

Restoring the factory calibration

At any time after carrying out the

Recalibrate option you can restore the original

factory calibration. You do not have to set up the probe or BFS in uniform light.

♦ On the Workabout, simply access the

Calibrate procedure (∪

∪∪

∪+C) and select

Restore Factory calibration.

You will briefly see a message confirming that this has been done.

Effect of the shade ring on the BFS

If the above matching tests are carried out with the shade ring elevated (but not

actually casting a shadow on either BFS sensor), you will get different results.

The shade ring blocks about 7% of the diffuse sky light, and none of the direct beam.

In bright sun conditions it will have no significant effect on LAI readings. In

completely overcast conditions it might contribute a small error of up to 0.1 to the

LAI value.

Comparing the calibration with other PAR sensors

You can carry out matching comparisons between the probe and BFS and any other

PAR quantum sensor. You cannot reset the probe values to it, but you can annotate

the readings and retain the comparison information in the SunScan data files.

Routine maintenance and cleaning

The probe diffuser is Perspex. Clean it when necessary with a damp cloth, moistened

with mild detergent, or with IPA (iso propyl alcohol).

The BFS diffusers are also made of Perspex. Clean them very carefully, especially

the groove around the diffusers. Use a fine soft brush to remove any dirt or dust

from the groove - it could affect the accuracy of the cosine response of the sensors.

The "spread" measurement

The "spread" value is a measure of the relative variation of the light along the probe.

This is a useful parameter in light profiling measurements: it is the value of the

standard deviation of the 64 photodiode readings, divided by their mean.

You can check the probe uniformity of calibration at any time by taking a reading in

uniform light. The spread value should be 0.00 or 0.01.

1 2 ... 47 48 49 50 51 52 53 54 55 56 57 ... 85 86

No comments

Delta SS1-UM-1.05 User Manual Page 52