4
AR2700
User’s Manual
1.3.4
Alarm Signal
Quick suggestion: connect the Alarm 1 signal wire (brown) to a 1K resistor in series
with an LED, anode to the resistor, cathode to ground (blue).
The default action is: Alarm will go active (LED lights) if a target is measured at a
distance greater than 1m.
1.4
General Description
The AR2700 is a laser diode based distance measurement sensor for ranges up to
230 feet (70 m) on regular surfaces with as little as 10% reflectivity and up to 885 feet
(270 m) using a reflective target. Contact Acuity for these targets. The accuracy is
generally specified with an absolute linearity of +/- 2.36 inches (60 mm) and a 1 sigma
repeatability of +/- 0.98 inches (25 mm). Linearity will vary depending on sample
averaging, temperature and surface reflectivity of the target surface. Measurement
noise to a stationary target of 50% reflectivity was reduced to 3 mm at 100 Hz sampling
speeds. The AR2700 internally compensates for temperature changes, but does not
have an on-board heater for use in cold environments.
1.5
Principles of Operation
The AR2700 uses the time of flight of light to measure distance. The laser beam is
projected from the
housing’s aperture and shines on a target surface, where it creates a
small infrared spot. From there the laser light is reflected back to the sensor. A collection
lens is located in the sensor to the side of the laser aperture. It collects a portion of the
reflected light, which is focused on an avalanche photodiode and converted to an electrical
signal. The signal is amplified and symbolizes a shift in phase. This phase is compared to
a reference signal to determine the amount of shift and hence a change in distance.
