Absolute Distance Meter (Adm) - Leica AT500 User Manual

2.5.4
Description
Measurement
modes
Atmospheric influ-
ence
Additive constant
Reflector constant
34

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
reflector while still ensuring the highest accuracy. The ADM supports meas-
uring stationary points, as well as continuous measurements of a moving
reflector at speeds of up to 100 Hz.
The following measurement and modes are available:
Target Measurement Mode
Reflector Stationary
Continuous
B-Probe Stationary
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 influences 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 field the additive
constant can be verified 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 reflectors like the Tooling Ball (TBR) have an internal reflector
constant, which causes an apparent increase in the distance measurement.
This reflector constant is indicated on the accompanying Producer Certificate.
Please note: Hollow Corner Cube Reflectors (RRR) do not have a reflector
constant.
Measurement Profile
Fast
Standard
Precise
Continuous time
Continuous distance
Standard
Description of the System