Chapter 3
Theory of Operation
Trimble S, VX, SPS & RTS Service Manual3 - 74 P/N 57150002, Revision 5.0
F
EDM offset
The Trimble High Precision / DR Standard / DR instrument has the same offset when measuring in
EDM mode (to reflector) and DR mode (to DR target). This offset is measured in Offset
determination in PASS.
EDM offset
Determination to four prisms between 10 - 100 meter and verification to one prism between 10 - 100
meter. Totally five prisms.
Determination to one DR target between 2,4 - 2,6 meter and to one DR target between 15 - 50 meter.
Totally two DR targets.
Short distance correction
No short distance correction exist for the High Precision distance unit, only for the DR300+ / DR
PLUS distance unit.
Difference between DR mode and reflector mode
The difference between the two modes is that in reflector mode the filter motor close to only allow
measurements to prisms. In DR mode the filter motor is open for DR measurements. The filter motor
includes a filter that reduces the signal.
Description of the transmitting signal from transmitter to receiver
The transmitting signal from the transmitter laser diode for the internal path is decoupled from a
reference mirror in front of the transmitter laser diode.
In reflector mode the transmitting signal is sent through a filter to reduce output power. This filter is
controlled by a filter motor and in DR mode this filter is removed from the transmitting signal.
Next the signal will reflect through a transmitter prism and the front lens on the way to the target
(reflector or DR).
The returned target signal will reflect back through the front lens and via two reflectors and then into
the receiver fibre.
The amplitude of the received target signal is controlled by a greywedge. The greywedge is driven
by a step motor. A reflex coupler on the transceiver board indicates the open greywedge position.
The measurement is divided in an internal and an external part to compensate thermic drift. The
internal path comes from the transmitting signal decoupled from a reference mirror. The switching
between internal and external path works with a paddle on the switch motor.
The receiver diode receives the target signal and calculates a distance in the transceiver board. The
distance information is sent to the IPC board.
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