SR50AT-Series Sonic Ranging Sensors
12
SR50AT may reject a reading if the target distance changes at a rate of 4
centimeters per second or more.
The SR50AT completes a measurement and output the data typically in 1
second. In RS-232 and RS-485 serial modes, the data is completed within one
second for baud rates of 9600 bps and above. The total time for an SDI-12
measurement can exceed 1 second due to the long communication times
associated with the 1200 bps data rate.
If the SR50AT rejects a reading or does not detect a target, zero will be output
for distance to target or –999 for depth values.
8.1 Quality Numbers
Measurement quality numbers are available with the output data; these
numbers indicate the measurement certainty (TABLE
). Quality numbers
have no units of measure and typically vary from 152 to 600. Numbers that are
between 152 and 210 indicate good quality measurements. Zero indicates that
the reading was not obtained. Numbers greater than 300 indicate a degree of
uncertainty in the measurement. Causes of high numbers include:
•
sensor is not perpendicular to the target surface
•
target is small and reflects little sound
•
target surface is rough or uneven
•
target surface is a poor reflector of sound (extremely low density
snow)
TABLE 8-1. Quality Number Description
Quality Number Range
Quality Range Description
0
Not able to read distance
152 to 210
Good measurement quality numbers
210 to 300
Reduced echo signal strength
300 to 600
High measurement uncertainty
Although not necessary, quality numbers provide useful information such as
surface density in snow monitoring applications. Please note that quality
number values may increase during snowfall events consisting of low-density
snow.
8.2 Temperature Compensation
The SR50AT version of the sensor includes a temperature sensor to
compensate the speed of sound for variations in air temperature. The
temperature sensor is incorporated into the SR50AT Cable as shown in