SunScan User Manual v 1.05
Appendices
••••
75
B. Logging the Beam Fraction sensor
You can log the Beam Fraction sensor in a similar manner, using the (optional)
special logging cable for it. Two outputs are available, corresponding to the Total
incident PAR and Diffuse PAR photodiode readings.
Be aware that the shade ring elevation may need readjustment after an hour or two.
Also, that separately logged incident PAR readings cannot at present be merged
with probe readings of transmitted PAR to give LAI estimates using the SunScan
mathematical model.
Wiring connections
The Beam Fraction sensor logging cable plugs into the BFS cable connector, giving
up to 12 metres distance from the logger. If you need more length, simply join on
extra screened multicore cable of a similar type. Make sure the joint is weatherproof.
The cores of the BFS logging cable have the following functionality:
Core
Function
Logger Connection
orange
V+ Power supply positive
Sensor power positive (switched for warm-up)
green
0V Power supply negative
Sensor power negative (0V)
brown
HI Total PAR signal output
positive
Input c, for Total PAR
grey
LO Common signal output
negative
Input channels - common negative
blue
HI Diffuse PAR signal output
positive
Input c, for Diffuse PAR
braid
Screen
Frame earth, or 0V
Note: the grey and green are connected internally in the BFS case. The braid is not
connected to any other core.
Output
•
The output signals are the Total and the Diffuse PAR irradiance.
•
The millivolt outputs are linear, with a sensitivity of
1 mV = 1
µµµµ
mol.m
-2
.s
-1
.
Maximum output is dependent on the supply voltage, and can exceed 2500 mV.
Logger requirements
•
The BFS requires a voltage supply of 5-15 V dc (unregulated), at about 1 mA
current.
Warning! Pre-Release Beam Fraction sensors require a regulated voltage supply of
5 V dc (
±±±±
0.25 V). Refer to Delta-T if you are uncertain about this.
•
Configure two logger channels for voltage input, with the above sensitivity.
•
Use a "warm-up" time of 1 second (the logger must apply the power 1 second
before taking its reading). Outputs will be stable after 10 ms.
