For large antennas it may be necessary to measure well over 1000 points, which then have to be re-measured at least five more times. The large number of measurements and repetitive measuring task is where the motorized TDM5000 will save EMS valuable time, while assuring that no point is missed.
At an average time to acquire each point manually of 30 seconds, the motorized TDM5000 could easily reduce this acquisition time by 50% and save five hours per sequence! Using a rate of $100 per man-hour, the total savings for this job could be $3000. This doesn’t include the time savings due to the reduced likelihood of missing points on subsequent measurements and the associated troubleshooting.
With the introduction of the TDM5000 motorized theodolite, having its incorporated distance meter accurate to 0.5mm, EMS decided that an investment in the TDM5000 would yield a good return in saved time and money while improving the quality service EMS gave to its customers.
EMS recently completed a seven-week alignment job on Kwajalein, a South Pacific island. Kwajalein’s Ground-Based Radar Prototype (GBR-P) antenna is contracted to Ratheon as part of the U.S. Ballistic Missile Defense System for the US Government. The octagon phased array antenna is 14 meters in diameter. EMS was hired to manage the installation and alignment of the electronic array elements into a flat plane and to measure the gravity deformation of the flat surface as it is rotated from horizon to zenith. Using a TDM5000 a total of about 200 points were measured on the array’s mounting surface. This set of 200 points was re-measured about 15 times during the course of aligning the antenna, adding up to 3000 pointings. The instrument was controlled using proprietary EMS software.
"The motor feature is the best single thing about the TDM5000", Michael Brenner says. "As the target locations are nominally known I don’t have to search for the targets. During repetition measurements the program controls the pointing of the theodolite to the next target and I only have to fine tune to a center mark. I even can leave my glasses off during this operation as I don’t have to search for the targets. All together this procedure will speed up the measurement by a factor of two."
During all the measurements, the TDM5000 communicates with a Personal Computer through the RS232 data link. Once the point data are recorded, EMS analyses the coordinates. Reference points are used to create a part frame, a plane is fit to the target points and the adjustment needed to optimise the plane is calculated. In the end the surface flatness was aligned to an RMS error of 80 microns.
The targeting used for these antenna alignment tasks generally consists of 10mm and 20mm square reflective targets, placed above screw adapters. Often, a Leica right angle eyepiece is used to allow for steep shots (up to 90 degrees). A 12V transformer connected via a Y-cable usually powers the TDM5000.
EMS has stated that, depending on future needs, they would be willing to further invest in a theodolite capable of centering on a tape target.