Xylem SDI-12 RADAR - Manual (Page 26)

SDi-12 CommaND & reSPoNSe
24
example of an “am2!” command:
Command response Time Values Description
"am2!" “a0013” 1 sec 3 make measurement.
Subsequent Command response
"aD0" a+aa.aaa+BB.BBB+CC.C
where:
aa.aaa = Stage (feet, inches, meters etc.)
BB.BBB = Standard Deviation (feet, inches, meters etc.)
CC.C = Power Supply Voltage (Volts)
The radar only supports the”am3” measurement command when the Power mode = 1. Data
values generated in response to this command are stored in the sensor’s buffer for subsequent
collection using “D” commands. The data will be retained in the sensor until another “m”, “ C”, or “V”
command is executed.
when Power mode = 0, the radar returns “a0000” signifying the command is not supported in this
mode.
when Power mode = 1, the radar averages the data collected from the previous fifteen seconds
and returns the mean and standard deviation
The standard deviation is computed as follows:
1. Compute the mean for the data set
2. Compute the deviation by subtracting the mean from each value
3. Square each individual deviation
4. Divide by one less than the sample size
5. Take the square root
Command response Description
“am3!” “atttn” initiate measurement
where:
a is the sensor address (“0-9”, “a-Z”, “a-z”, “*”, “?”).
m is an upper-case aSCii character
ttt is a three digit integer (000-999) specifying the maximum time, in seconds, the sensor
will take to complete the command and have measurement data available in its buffer.
n is a single digit integer (0-9) specifying the number of values that will be placed in the
data buffer. if “n” is zero (0), no data will be available using subsequent “D” commands.
“am3” 15 Second average measure Command