Copyright © Parallax Inc. PING))) Ultrasonic Distance Sensor (#28015) v2.0 2/4/2013 Page 3 of 9
Practical Considerations for Use
Object Positioning
The PING))) sensor cannot accurately measure the distance to an object that: a) is more than 3 meters
away, b) that has its reflective surface at a shallow angle so that sound will not be reflected back towards
the sensor, or c) is too small to reflect enough sound back to the sensor. In addition, if your PING)))
sensor is mounted low on your device, you may detect sound reflecting off of the floor.
a. b. c.
Target Object Material
In addition, objects that absorb sound or have a soft or irregular surface, such as a stuffed animal, may
not reflect enough sound to be detected accurately. The PING))) sensor will detect the surface of water,
however it is not rated for outdoor use or continual use in a wet environment. Condensation on its
transducers may affect performance and lifespan of the device.
Air Temperature
Temperature has an effect on the speed of sound in air that is measurable by the PING))) sensor. If the
temperature (°C) is known, the formula is:
m/sT0.6331.5C
Cair
The percent error over the sensor’s operating range of 0 to 70 ° C is significant, in the magnitude of 11
to 12 percent. The use of conversion constants to account for air temperature may be incorporated into
your program (as is the case in the example BS2 program given in the Example Programs section below).
Percent error and conversion constant calculations are introduced in Chapter 2 of
Smart Sensors and
Applications
, a Stamps in Class text available for download from the 28029 product page at
www.parallax.com.
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