User's Manual

2.5.4 Absolute Distance Meter (ADM)
The Absolute Distance Meter module of the AT500 uses a modulated and
polarised infrared light beam, which allows a dynamic lock-on to a moving
reector while still ensuring the highest accuracy. The ADM supports meas-
uring stationary points, as well as continuous measurements of a moving
reector at speeds of up to 100 Hz.
The following measurement and modes are available:
Target Measurement Mode Measurement Prole
Reector Stationary Fast
Standard
Precise
Continuous Continuous time
Continuous distance
B-Probe Stationary Standard
The accuracy of the measured distance is primarily dependent on the accur-
acy of the determination of:
•
The ambient air temperature
•
The air pressure
A change or a deviation in the atmospheric parameters affects the distance
measurement accuracy as follows:
•
±1 °C results in a change in distance of approximately 1 ppm.
•
±4 hPa result in a change in distance of approximately 1 ppm.
•
The air humidity inuences the distance measurement if the climate is
hot and damp, therefore ±30% relative humidity results in a change in
distance of approximately 1 ppm at 40 °C, approximately 0.3 ppm at
20 °C and approximately 0.1 ppm at 0 °C ambient temperature.
For an absolute distance measurement the following values must be known:
•
The additive constant (ADM Offset)
•
The scale factor
These values are precisely determined in the factory. In the eld the additive
constant can be veried through a sensor check or compensation process.
☞
Refer to the Tracker Pilot Reference Manual on details of the
ADM check and compensation process.
Glass prism reectors like the Tooling Ball (TBR) have an internal reector
constant, which causes an apparent increase in the distance measurement.
This reector constant is indicated on the accompanying Producer Certicate.
Please note: Hollow Corner Cube Reectors (RRR) do not have a reector
constant.
Description
Measurement
modes
Atmospheric inu-
ence
Additive constant
Reector constant
34 Description of the System