Data Sheet
MaxBotix
®
Inc.
Copyright 2005 - 2013 MaxBotix Incorporated
Patent 7,679,996
HRUSB-MaxSonar
®
-
EZ™
Series
Page 3
Web: www.maxbotix.com
PD12141h
MaxBotix Inc., products are engineered and assembled in the USA.
Serial Output Format
The sensor output is provided over the COM port (or equivalent) in an ASCII character format. If a target is detected at
480 millimeters the output appears as follows: “R0480 <carriage return>”. The output is an ASCII capital “R”, followed
by four ASCII character digits representing the range in millimeters up to a maximum of 5000 millimeters. This is
followed by an ASCII space and a carriage return.
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Sensor Operation
When operating in free run mode, the HRUSB-MaxSonar-EZ sensors are designed to be used in a variety of indoor
environments. Most range readings are accurately reported. If the range readings are affected, the effect is typically less
than 5 mm. This allows users to employ real-time ultrasonic distance sensing without the need for complicated user
software.
Many acoustic noise sources will have little to no effect on the reported range of the HRUSB-MaxSonar-EZ sensors.
However, users are encouraged to test sensor operation in the operating environment.
Sensor Operation from 30-cm to 50-cm
Because of acoustic phase effects in the near field, objects between 30-cm and 50-cm may experience acoustic phase
cancellation of the returning waveform resulting in inaccuracies of up to 5-mm. These effects become less prevalent as the
target distance increases and has not been observed past 50-cm. For this reason, industrial users that require the highest
sensor accuracy are encouraged to mount the HRUSB-MaxSonar-EZ from objects that are farther than 50-cm.
Target Size Compensation
Most low cost ultrasonic rangefinders will report the range to smaller size targets as farther than the actual distance. In
addition, they may also report the range to larger size targets as closer than the actual distance.
The HRUSB-MaxSonar-EZ sensor line compensates for target size differences. This means that, provided an object is
large enough to be detected, the sensor will report the same distance, typically within 2%, regardless of target size.
Smaller targets can have additional detection noise that may limit this feature. In addition, targets with small or rounded
surfaces may have an apparent distance that is slightly farther, where the distance reported may be a composite of the
sensed object(s).
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Internal Temperature Compensation
The speed of sound in air increases about 0.6 meters per second, per degree centigrade. Because of this, each
HRUSB-MaxSonar-EZ is equipped with an internal temperature sensor which allows the sensor to apply a compensation
for speed of sound changes.
The self heating (15mW at 5V, or 8mW at 3.3V) will change the temperature of the sensor by about 1 degree Celsius.
The amount of self heating is dependent upon user mounting.
Most importantly, the actual air temperature of the path between the sensor and the target may not match the temperature
measured at the sensor electronics. Sensors mounted in vertical applications, or applications where the environmental
temperature gradient is severe, may experience a large temperature measurement error which will effect the sensor
accuracy. For example, buildings with a height of 2-meters can have floor to ceiling temperature variations of 5°C or
more. Because of these temperature effects, users desiring the highest accuracy output are encouraged to use a properly
mounted sensor or to manually account for this measurement error.