PXI-668x Not Completing Self Survey and Blinking Amber GPS LED

Updated Jan 3, 2023

Reported In

Hardware

  • PXI-6683
  • PXI-6682

Driver

  • NI-Sync

Issue Details

  • I have a PXI-6682(H) or PXI-6683(H) timing and synchronization module installed in my PXI(e) chassis, and I have set the Time Reference as GPS. The Self Survey runs, but it never fully completes. I notice this either in the GPS tab of the NI MAX Test Panel, by reading the Percent Complete of Self Survey NI-Sync property, or having a blinking amber GPS light on the module. How can I troubleshoot this issue?
  • I have a PXI-6683(H) module in my PXI(e) chassis that will not complete it's Self Survey. It continuously gets stuck at 99% for several hours. How can I fix this?

Solution

The first thing to verify is that the GPS antenna is detecting at least 4 satellites. You can determine this by looking at the Number of Satellites Available field in the MAX Test Panel or by querying the Satellites Available property with the NI-Sync Property Node. If you are not seeing at least 4 satellites, try moving your antenna to a different location.

Once at least 4 satellites have been found, the GPS receiver performs a Self Survey. The Self Survey is the process of performing measurements of the visible satellites once per second and averaging those measurements so that the current position can be determined as accurately as possible. Once an accurate position is determined, time data received from the GPS satellites can be precisely applied. 

If the Self Survey is not completing, the following are some things to check: 
  • The Self Survey may take 10-20 minutes to complete. Make sure you have waited at least this length of time.
  • If mobile mode is enabled, it is expected that the Self Survey will not complete because the Self Survey is only performed when mobile mode is disabled.
    • Note: Using mobile mode with a stationary antenna will degrade the accuracy of the onboard GPS receiver. Only enable mobile mode if the antenna will be moving while the device has power.
  • Ensure that the antenna is connected properly.
  • Ensure that the cable length is not preventing an accurate signal from being acquired. Refer to the Maximum Cable Length section of the PXI-6682 or PXI-6683 user manual for more information on calculating the cable length requirements for your application.
  • Relocate the antenna to an area with a clear line of sight to the sky.
    • The antenna requires a straight line of sight to the sky in all directions, with a 30 ° angle to the ground.
    • The antenna should be placed away from high buildings or trees to reduce the amount of signal reflections. Note: some buildings may act as a Faraday cage, which will hinder signal integrity. Therefore, if the antenna is indoors, place it outside.
Figure 1: GPS LED indicator colors and meaning