Stabilizing the Antenna

warningWARNING In no event shall Vaisala be liable for any damage to the antenna/pedestal system that may occur during stabilization configuration performed by the customer.

After the initial power-up and cabling is complete, align the antenna. A suggested sequence is given below, based on the assumption that none of the parameters are yet correct.

For information on modifying parameter values, see Using TTY Setup Menus.

Most of this configuration is made through the RCP8 chat interface.

You can access this by running RCP8 with rcp8 -int shell command.

When the host computer interface is correctly configured, you can also access this through the antx program on the controlling host.

  1. Disable host computer control until the positioning is stabilized by answering No in the site host section of the Process incoming servo control packets question.

    While you are there, setup the rest of the host computer interface questions.

  2. If this is a shipboard system, disable the platform stabilization until the basic antenna control is tuned by answering No to the first question in the INU section.
  3. Use the axis command to define most of the fixed information for each axis, particularly the angle source.
  4. Temporarily set the elevation shutdown limits 15° short of mechanical stops, leaving enough distance for the antenna to coast to a stop in case of errors.
  5. Disable soft limits. These only work when the position servo is configured.
  6. Set the limit switch options and polarity.
  7. Use the RCP setup utility to configure the Interface to RCP section to match the other corresponding configurations.

    Once this is done, the Antx and Antenna utilities should work.

    Verify that the displayed angles match the RCP8 front panel.

  8. On the azimuth axis, do the following:
    1. Set the maximum output drive voltage to +/-10 V and do the following:
      • Verify that a drive of 0 cannot move the antenna.
      • Set the drive sign correctly.
      • If you have a high-gain servo, it may go at full speed at a lower voltage, and it may move with a 0 drive (because of a small A/D offset voltage). In this case, you must add an external resister divider to lower the drive voltage. If the voltage needs to be lowered a small amount use the drive voltage question. Vaisala recommends the voltage divider below about 5 V.
    2. Adjust the tachometer voltage range using the gain potentiometers on the back of the CP.

      The potentiometers closer to the end of the CP controls elevation. The T units are displayed in RCP8 in a range of +/-100.

      The goal is that the maximum velocity of the antenna should be within the measured limits. Be aware that this speed may exceed the maximum velocity requested by RCP8. Use the monitor command to watch this, then give drive commands like ad 10 to give small drives.

      Bring the speed up to 25 % of the maximum you expect, then adjust until the T display is below 25.

    3. Calibrate the tachometer by getting the sign and offset correct. Then enter level and speeds in the axis command.

      Set the Tach zero- delay-smoother window to a short (0.05 second) value.

    4. Determine the motor starting drives, the nominal drive slope, and the maximum angular velocity.

      Determine the drive sign, then set the drive slew rate fairly short (0.10 second). Set the velocity feedback dead zone to 0.3, and the feedback slope to 25.

      The velocity servo should now be stable.

    5. Set up the position servo parameters to achieve a stable motion between 2 positions that are separated by an angular distance.

      Make sure that both steps of 1° and of 10° perform quickly with no overshoot.

  9. Repeat 8 for the elevation axis.
    For most of the elevation axis stabilization, keep the antenna in the middle of the range, away from the stops.
  10. Set the final elevation shutdown limits approximately 0.2° short of the mechanical stops.
  11. Enable the elevation soft limits, and set them approximately 0.5° short of the shutdown limits.

    In setup RCP section set the elevation limits to the same soft limits.

  12. If this is a shipboard system, enable the data from the INU section.

    See Aligning the Pedestal for Shipboard Use.