Chapter 3
Theory of Operation
P/N 57150002, Revision 5.0 3 - 67 Trimble S, VX, SPS & RTS Service Manual
F
The reference pulse is measured very accurate so the shape of the pulse is known. By knowing the
shape of the reference pulse the received external target pulse can be identified because the shape is
identical.
The time difference between the reference and external target pulse is measured and converted into
a distance.
Fig. 3-61 Functional diagram for the DR300+ / DR PLUS distance unit
The transmitter unit includes a 5 meter fibre bundle and the receiver unit a 10-meter fibre bundle to
reduce disturbances and separate the reference pulse and external pulse in time. This makes it
possible to measure at shorter distances.
The internal light path is named as the reference path and is connected to the same receiver diode as
the receiver fibre. A glass reflector will divert a part of the transmitted signal into the reference path.
The receiver diode (APD) amplification is set by a procedure in the service software were the
reference greywedge is adjusted.
Measuring sequence, detailed:
Transmitting of an IR light pulse
The transmitter diode sends light pulse to a target.
Measuring of reference pulse - calibration
A process to identify the shape of the pulse is started. The shape of the pulse will later be used to
identify the returned external pulse.
Search for external (reflected) pulse - coarse measurement
To speed up the measuring process a coarse time measurement is made to identify the external pulse
within a shorter time interval.
Motor
Targe t
Transmitter
diode
Receiver
diode
Grey-
wedge
Light pulse
Reference path
DR 300+ distance unit
10 m fibre bundle
5 m fibre bundle
Reference
greywedge
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