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IOTA - Setup of Reflectometer
Created: July 2004
Courtesy of Bill Kindred at MMTO,
IOTA occasionally uses their reflectometer
to test the reflectivity of the siderostats.
The following notes compile information
on how to set up and use the reflectometer.
Note: For a given power supply setting,
current reading from the detector depends on
orientation of the lamp
(due to sagging of the filament),
especially at lower currents.
Note: Cord motions can cause short term currents;
vibrations can be a problem.
Filters: 310nm, 380nm, 450nm, 550nm, 700nm
Items are not rotationally symmetric - check for lines and pins.
Turn on bulb power supply, set to a low voltage,
turn on current to bulb (orange switch on supply), and
increase voltage until current limited state (light over current on).
Put detector assembly  into lamp opening 
to adjust current meter scale for maximum sensitivity
without saturation, i.e., adjust current to give reading
near 1.999 in appropriate meter range.
Bulb voltage should be 5.4 to 6.6V, current around 3.3A.
Put  into fixture opening  and  into ,
adjust feet to get maximum signal, and record current meter
Put  into specular outlet  and record current meter output
to monitor lamp output change with orientation (Iref).
Move lamp & photo-diode assembly into holder 
clamped at same orientation as in 3.
Repeat measurement of 4.;
if current meter output is different (due to lamp orientation),
adjust "FINE" of power supply to recover same reading.
With the lamp left in place in holder ,
put detector  into 
and record current output for direct illumination (Ii).
Reflectivity = Ir / Ii
Paper is a few percent - most of the light diffused;
fresh aluminum is 91% at 550nm.