Datasheet
Page 4
Web: www.maxbotix.com
PD11500c
MaxBotix
®
Inc.
Copyright 2005 - 2012 MaxBotix Incorporated
Patent 7,679,996
HRXL-MaxSonar
®
-
WR/WRC
™
Series
MaxBotix Inc., products are engineered and assembled in the USA.
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 HRXL-MaxSonar-WR 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 1%
1
, regardless of target size
1
.
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). Compensation for target size is applied to all range outputs: pulse width, analog voltage, and serial
format output by the sensor.
Supply Voltage Droop and Charge Compensation
During power up, the HRXL-MaxSonar-WR sensor line will calibrate itself for changes in supply voltage. Additionally,
the sensor will compensate if the supplied voltage gradually changes.
If the average voltage applied to the sensor changes faster than 0.5V per second, it is best to remove and reapply power to
the sensor.
For best operation, the sensor requires noise free power . If the sensor is used with noise on the supplied power or ground,
the readings may be affected. Typically adding a 100uF capacitor at the sensor between the V+ and GND pins will correct
most power related electrical noise issues.
_______________________________________________________________________________________________________________________________________
HRXL-MaxSonar®-WR™ Temperature Compensation
On Board – Internal Temperature Compensation
The speed of sound in air increases about 0.6 meters per second, per degree centigrade. Because of this, each
HRXL-MaxSonar-WR is equipped with an internal temperature sensor which allows the sensor to apply compensation for
speed of sound changes.
The actual air temperature of the path between the sensor and the target may not match the temperature measured at the
sensor electronics. Sensors can be mounted in vertical applications, or applications where the environmental temperature
gradient is severe. These users may experience a large temperature measurement error which will affect the sensor
accuracy. For example, buildings with a height of 3-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
external temperature sensor or to manually account for this measurement error.
HR-MaxTemp, an External Temperature Sensor
Although the HRXL-MaxSonar-WR has an internal temperature sensor; for best accuracy, users are encouraged to use the
optional external temperature sensor. On power-up, the HRXL-MaxSonar-WR will automatically detect an attached
HR-MaxTemp temperature sensor and begin to apply temperature compensation using the external temperature sensor.
The external temperature sensor allows for the most accurate temperature compensation, by allowing temperature
readings to be taken that better reflect the composite temperature of the acoustic ranging path. For best results users are
encouraged to connect the temperature sensor midway between the HRXL-MaxSonar-WR and the expected target
distance.
Notes:
1
Refer to section that compares WR to WRC on page 11