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IOTA - Setup of Reflectometer
Notes from
MGL
and
RMG;
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.
Hardware Setup
![[reflectom.gif - Reflectometer setup]](reflectom.gif)
-
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.
Procedure
-
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 [3] into lamp opening [1]
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 [1] into fixture opening [2] and [3] into [4],
adjust feet to get maximum signal, and record current meter
(Ir).
-
Put [3] into specular outlet [5] and record current meter output
to monitor lamp output change with orientation (Iref).
-
Move lamp & photo-diode assembly into holder [6]
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 [6],
put detector [3] into [1]
and record current output for direct illumination (Ii).
-
Then:
Reflectivity = Ir / Ii
Paper is a few percent - most of the light diffused;
fresh aluminum is 91% at 550nm.