These photos show you how to build a two-channel sun photometer with a built-in temperature sensor and connections to a digital panel meter. These are minimum instructions for use by those who already have some electronic construction experience. Note that not all connections on the board are used. Be sure to examine the photos carefully to make sure that you make connections as required!
|Components that must be oriented in a particular direction.
Note that the op-amp lettering is upside down in this view, but it is mounted correctly on the board.
|Components that can be oriented in either direction.
The resistor values may be different. The capacitors, especially the 220 pf capacitors, may look different from the photo.
|Other connections to pc board.
The yellow wire is for the temperature sensor.
|Solder pc board to DATEL panel meter. Be sure to observe orientation of panel meter and board. The label may be a stuck-on paper label or it may be printed directly on the side of the meter. Only 7 pins, as shown, need to be soldered to this board.|
|Case components I
||Case components II
|Final electronic assembly|
|Aligning your sun photometer|
On a day with an unobstructed view of the sun, turn the sun photometer on use the rotary switch to select the red or green channel. Point the sun photometer toward the sun so that a circle of sunlight shining through the front L-bracket falls on the paper face on the rear bracket. Move the instrument around a little, up and down and side to side, and observe where the panel meter signal is the highest. Hold that position and use a sharp pencil to mark a small dot in the center of the circle of light. Select the other channel and repeat. The dots should be in almost exactly the same place.
With a pencil, draw a light cross through the dot (or between two nearly coincident dots). Center a small colored adhesive dot over the cross and press it in place. Gently erase the pencil marks. Finally, wrap a piece of clear tape around the rear bracket to hold the paper and dot in place. When the alignment is completed, put a little super glue along the edges of the L-brackets where they are attached to the case to make sure they do not move.
Your instrument is now aligned and when you make a measurement, you should always center the circle of sunlight on this colored dot. Note that your instrument must be calibrated against a reliable standard before measurements can be used to calculate aerosol optical thickness. Contact IESRE for details.
It is possible that the gain on one or both channels will be too high, depending on the output from the LED detector. If the digital panel meter reads just "1" when the sun photometer is pointed at the sun on a clear summer day near noon, then the gain is too high. The way to fix this is to replace the gain resistors with smaller values. It may be possible to solder an additional resistor in parallel with the existing resistor — this will lower the gain. The resistors can also be removed (carefully!) and replaced. Your kit may include some extra resistors.