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Are two antennae better than one?


Things you should know before doubling up on your GNSS positioning sensors






When coming upon a 3D machine control system, the most immediate distinction is that of the number of masts on the blade.

Some have a single mast, some have two. -And for those who spend a lot of time among these systems, it's obvious that manufacturers seem to have a clear preference of one over the other.

When we speak about dozers, single vs dual mast systems become relatively easy to understand:

Dual-antenna-3D-machine-control-system

To get the 3D position for the entire cutting edge of the blade, a single GNSS antenna must be complemented with a blade slope sensor. This set-up requires the blade to be kept fixed to the direction of travel, though. If using a PAT blade, a rotation sensor must be added if correct cut/fill is to be generated.

Using two GNSS antennae dispenses of the blade slope and rotation sensors because the position, slope and orientation of the blade is instantaneously known.

In most dozer applications, single and dual-antenna systems perform equally well. However, the dual-antenna system has an advantage in applications where the machine does not point in the same direction in which it is traveling. An example will be when the dozer is working a steep slope and the tracks are slipping a bit. The machine will have a tendency to 'crab'.

Because a dual-antenna system measures the absolute positions of the corners of the blade vs a single-antenna system that includes the orientation of the blade vs the machine, the dual-antenna system will give correct cut/fill while the single antenna system will have somewhat incorrect cut/fill values.

Dual-antenna-GCS900-Trimble-machine-control-system
The user will have to determine if this benefit is enough to justify the higher cost of a dual-antenna system.

A dual-antenna system on a grader is easier to install than a single-antenna system. Similar to when on a dozer, the dual-antenna set-up dispenses of the blade-slope and rotation sensor.

In grader applications, the dual-antenna system has the advantage that the operator can articulate and sideshift the blade without losing cut/fill accuracy.

In a single-antenna system, on the other hand, the blade must be kept relative to the machine center so that the system can resolve the position of the entire cutting edge
A dual-antenna 3D machine control system from Trimble


of the moldboard from the single GNSS antenna, blade slope and rotation sensor.

Single-antenna systems, however, are basically a GNSS antenna added to a conventional grader machine control system. This means the GNSS antenna can be removed and the system can still be used as a fully-functional blade slope and cross slope machine control system.

If just one of the GNSS antennas in a dual-antenna system is damaged or removed, the 3D machine control system ceases to function.

A dual-mast system is not more accurate than a single-mast system. How you are planning to use the system should be the determining factor as to which type you buy.

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