Xylem SDI-12 RADAR - Manual (Page 6)

iNTroDUCTioN
4
Built-in LCD Display
The radar sensor has a built-in LCD
display which normally shows Distance
(distance from the radar unit to the
water). The display has three buttons and
can be used to monitor or edit the radar
unit configuration. The LCD display has
a short cord and can be detached from
the radar housing for convenience.
Communications
The radar sensor is a stand-alone
instrument that provides an SDi-12
output for communications with a
datalogger. The sensor is supplied with
Fast mode Data Logging
The radar response to an “am!” command is “0044” (4-seconds, 4-parameters). The actual
measurement completes very quickly and the service request is sent within 530ms. The reported
4-second value allows time for retries when troubleshooting the internal connection between the
SDi-12 interface and the radar unit. Unfortunately most data loggers cannot sustain a 1-second
logging interval even if the sensor responds within 500mS. For making measurements at a
sustained 1-second measurement interval two options are available as explained below.
a liquid-tight fitting and two 6- foot cables. one cable is convenient for making connections to
your data logger, the second cable used to connect to a laptop computer when using the TofTool
configuration and diagnostic program.
“Noaa” mode measurement
The radar supports the “am1” measurement. The H-3611 internally performs the following
measurement sequence.
1. makes 181 measurements at a precise 1 second interval.
2. Computes the standard deviation for the data set.
3. multiplies the standard deviation by 3 to obtain a High and Low outlier threshold.
4. Sifts through the data set and discards data points above and below the outlier thresholds.
5. Computes the standard deviation again for the data set with the outliers removed.
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