Here you can control periodic error management functions, focus positioning, reticle brightness, and mount backlash.
PEM ON: Press this button to turn on the mount’s periodic error correction logic. Before doing this you should do a PEM Record on a night of steady seeing. Once pressed the Last Sent edit box will be updated.
PEM OFF: Press this button to turn off the mount’s periodic error correction logic. Once pressed the Last Sent edit box will be updated.
PEM Record: Press this button to start a PEM record. Typically you will want to wait until a night with relatively steady seeing for your area. Have a CCD camera autoguiding on a relatively bright star (mag 6+) near the meridian and declination 0. Once pressed the timer is activated. Once you are sure the PEM is done (7-8 minutes is adequate) then click the Stop Timer button. PEM is ready to use by clicking PEM ON.
To use this function, you must have an electric focus motor (available from JMI, Meade and others) plugged into the GTO Control Panel. If so you can control the in and out focus movement with this control panel.
First, select the rate, fast or slow then press the + or – button to adjust the focus. Focus will move while the button is pressed. The selected rate will override the keypad’s rate once one of the buttons is pressed.
You can adjust the brightness of an illuminated reticle with this control. First, plug the cord of the reticle into the connector on the GTO Control Panel. Press the + button to increase reticle brightness and the – button to reduce brightness. One click of the button will change the brightness by one level up to the maximum or minimum brightness.
This command sets the amount of backlash compensation employed each time a servo motor axis reverses direction.
Set Dec: Clicking this button sets the Dec backlash of the mount.
Set RA: Clicking this button sets the RA backlash of the mount.
Click the Backlash Tests button to bring up three tests suggested by Roland Christen to test the health of your declination axis. Roland posted some tests that you can run on your AP mount to see if it has a potential problem with Dec movement.
IMPORTANT: Before running tests 1 and 2 set the mount’s backlash to 0. Also while performing the tests do not try to auto-guide.
Dec Backlash Test 1
Before starting Test 1 set up your camera control program (e.g. MaximDL, CCDOps, etc.) to do a 100 second exposure (but do not autoguide). You can also set up an auto-dark exposure, but make sure that you start the test when the camera control software is exposing the light image.
Once you start the exposure press the Start Test 1 button. With the default settings (recommended) the entire procedure will take about 90 seconds.
Test 1 will move the scope in this manner: East - pause - West - pause - East to center - North - pause - South - pause - North to center.
The stars in the resulting exposure should look something like the image to the right. The scale might be different but you should see what looks like many plus signs in the image.
If you take the image near Dec=0 the height and width will be about the same. Although not shown in this particular image the East and West points will be slightly brighter than the North/South points. This will make it easy for Roland to establish the orientation of the camera.
Dec Backlash Test 2
You will run Test 2 three times, once for each of the guide rates. Before starting this test set up your camera control program (e.g. MaximDL, CCDOps, etc.) to do a 25 second exposure but do not try to autoguide. You can also set up an auto-dark exposure, but make sure that you start the test when the camera control software is exposing the light image.
Start by setting the Guide Rate to 1x. Once you start the exposure press the Start Test 2 button. With the default settings (recommended) the entire procedure will take about 16 seconds.
Although the scale might be different, the stars in the resulting exposure should look something like the image shown.
For reference the actual movement in Test 2 is: North+West - South+West - West only (the pause setting) - North+West.
Now you will need to repeat the tests at 0.50x and 0.25x. The star patterns will look similar but smaller because the movement rate is slower. Here are two examples taken with my Traveler:
AFTER RUNNING TESTS 1 AND 2
If you see star patterns different from the above images then crop a bright star in each of the four images and save them as a high-quality JPEG. Please make sure to “stretch” each image appropriately so that it is not too dim or overexposed. If you do not know how to stretch and create a jpeg then save the cropped image in FITS format.
Then send the 4 files (preferably zipped to save bandwidth) to Astro-Physics via email (check their web page for latest contact email: http://www.astro-physics.com.
After submitting these tests AP will advise you if anything appears anomalous and if so what can be done about it.
Dec Backlash Test 3
This test moves the declination motor at regular intervals to check that the gears move properly.
To do this test you will need to remove the cover from the declination motor housing (contact AstroPhysics for directions if you need).
The Guide Rate combo-box has 4 choices: 0.25x, 0.50x, 1.00x, and Cycle. You can choose a specific rate or Cycle to have PulseGuide repeat the test at each rate.
While watching the uncovered declination gears click the Start Test 3 button. PulseGuide will send 5 pulses spaced 2 seconds apart (or however many you entered in the Pulses edit box). Each pulse will be of the same duration – that which you enter in the Pulse Duration edit box. 133 milliseconds is the default. Watch carefully to make sure the pulses look evenly timed and that the fastest moving gear moves equally each time.
Once all pulses have been sent in one direction, an equal number of pulses are sent in the reverse direction. It is normal on reversal of direction that there is a slight delay in movement because of backlash. If this happens you may wish to increase the pulse count.
If you see erratic movement please contact AstroPhysics for instructions.