Instruction manual

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• Select when/how often the temperature compensation is to be done. You can operate manually
anytime by pressing the MANUAL button whenever you want a temperature measurement and
correction (if necessary) made. Alternatively, you can select AUTO and set the frequency of automatic
temperature measurement and correction to be made. Most people will select a rate of about one
correction per minute (the correction will not actually be made unless the calculated motion exceeds
the dead zone).
• The FIRST time a reading is made in Manual or Auto the result before correction is written into the
session record. The commanded correction is then written into the session record as the second entry.
Thus, the first entry always tells you the starting point of the session.
• Each time a temperature measurement is made, it will be entered into the “latest data” boxes on the
screen. The temperature will also be automatically entered into the compensation formula, which will
compute the best-fit position using the data set. Finally, if a movement correction is actually made, the
data will be added to the session record in the window.
• When operating temperature compensation, changes to the dataset are locked out.
• A log is made automatically of each operating session. Measurements that result in focus motions are
written to the file RFTRACK.LOG (use Explorer to find it, usually in the same folder as the program).
Up to 1000 items in a session are allowed. The file is a simple ASCII file that can be inspected,
renamed, or moved into a spreadsheet or graph as described above. Any old file is converted to
RFTrackOld when you open the temperature compensation window (and the preexisting RFTrackOld
is erased).
• You can Clear the session record at any time using the Clear item on the file menu. Session data will
still remain in the log.
Note: when you close the temperature compensation window the temperature compensation operation will
cease. Normally you will want to minimize the window during your observation session, which will leave
the compensation running.
Operational Issues
Data Set Issues. The key to proper temperature compensation is to have a reasonable data set. Under most
applications, the dataset does not have to be of very high quality; however, it must span a reasonable
amount of temperature change covering or near your operating temperature.
Most operating problems arise from using a data set taken under one set of optical conditions and applying
it to another setup. In general, any change in your setup that changes the f/ratio will change the correction
coefficient. While the software will force the operating stepsize to the correct value (matching the dataset),
it cannot compensate automatically for changes in the position calibration unless you use the Relative
temperature compensation mode.
Direction Reversal. A more subtle error can be that you might have reversed the sense of the motion after
you took the dataset. If you look at the position calculator formula, you will see the form
A+B*(temp)=Position. B is the slope, i.e., the number of steps per temperature count that the scope focus
will change. You may have taken the data with one direction (giving for example -6.97 slope), but if you
change the RF reference direction, the -6.97 will be in the wrong direction. If that occurs, you could
develop a new dataset (which will show about +6.97) but the easier solution is to reverse the RF direction
setting using the manual buttons (see ch.3 setup instructions).
Thermal Tracking. As noted above, the standard temperature sensor is mounted inside the controller. In
most cases, this is sufficiently accurate (especially if you use duty cycle set to zero as we recommend);
however, you may wish to use a separate optional sensor on the scope itself (this is available as an option).
How accurate is the internal sensor in the RoboFocus control unit as a measuring device for the scope
temperature? The answer to that is complex:
• There may be systematic temperature differences in the observatory between the scope and the
controller