Specifications

16
SECTION 5.0
TROUBLE-SHOOTING GUIDE
The following common problems and solutions have been collected over the years from our
customers and our attempts to solve their instrument problems. Before calling us, read through
these and relevant sections of this manual to see if an easy solution exist for your errant
photometer.
1) Unit has been turned on and left to warm up for the proper time but no display is seen
unless light is incident on the detector.
With a small screwdriver adjust the offset control pot on the front panel. (See Figure 2-7.) With no light incident on
the detector, rotate the control pot CCW for at least 20 turns to make sure a display value is seen and then rotate CW
until a count of 5 is obtained with the GAIN and TIME set for 1.
2) The dark count (no light on the detector) appears to drift with time and temperature
beyond what you have been accustomed to.
This could be a serious problem if the drift is due to a break in the moisture seal protecting the detector/electrometer
assembly. The unit should always be kept in a dry and warm environment when not used. Place the unit in a sealed
container with about 4 ounces of activated desiccant for a period of 48 hours. If desiccant is not available, use a 100-
watt spotlight placed about 2 feet from the unit for a similar length of time. Allow the unit to come to ambient
temperature before measuring the drift. If the problem does not disappear or reduce to acceptable levels, it will have
to be returned to Optec for repair.
3) The unit appears to give much higher than expected counts every once in a while.
If the unit is powered by the adapter, any surge in the power line may cause an increase in the number of counts for
the integration interval. Refrigerator, compressors, dome motors, and telescope position servos could easily be the
cause of this problem. Vibration and strong radio signals may also be the cause of the problem.
4) The night appears clear but the star count is diminishing with time faster than expected
due to changing extinction conditions.
A common problem especially with Celestron and Meade telescopes is that a nearly invisible film of condensed
water will develop on the corrector plate or main mirror during the night if the dew point is high enough. Usually
this fog film can only be seen when a strong light is projected down the front of the telescope and the optics carefully
inspected. A hair dryer is the only cure. "Dew-zappers", low wattage heaters designed to fit over the front cell, are
now commonly available to avoid this condensation problem.
5) As the star approaches the edge of the detector the count begins to fall but it looks as if the
star is still completely within the ring as seen in the eyepiece.
The stellar light profile (energy vs. radius from the center of the star) is much larger than what is seen. On a good
night a seeing disk could appear to be about 2 arc-second in diameter. However, to capture over 99% of the energy a
detector diameter (field aperture) of over 20 arc seconds is needed. A hazy night or a night with much greater
turbulence could increase the stellar profile many more times. Thus, care must be taken to keep the star from drifting
near the edge of the detector since some of the incident energy will be lost.