Xylem H-3521 - Manual (Page 46)

5-16 SDI-12 Command and Response Protocol
H-3521
5.15 Extended Read Mean_Count and Write Mean_Count
The H-3521 makes multiple raw sensor measurements, discards the high and low values,
integrates (averages) the measurement data and computes Pressure (PSI). The number of raw
sensor measurements made for each SDI-12 measurement sequence is programmable. When
measuring turbulent water, tides or other special applications Mean_Count can be changed to
increase or decrease the number of pressure measurements made during the SDI-12 measurement
sequence.
The H-3521 makes 7.5 pressure measurements per second (133ms/ measurement). The ttt field in
the SDI-12 sensor response is computed by the H-3521 and indicates how much time the H-3521
will require to complete the measurement sequence. The ttt field will automatically change if
Mean_Count
is changed.
The H-3521 comes from the factory with Mean_Count set to 16. The factory default ttt field is
computed internally by the H-3521 as follows:
Raw Measurements: +2.13 sec (0.133 sec/measurement X 16 measurements)
Math Overhead:
+0.3 sec
Round Upwards +1.0
- - - - - - -
ttt 3.0 Seconds
The “aXRMC!” and “aXWMC!” extended commands allow the number of raw sensor
measurements for each SDI-12 measurement sequence to be monitored or changed.
Once a new Mean_Count value is written, a copy is sent to the sensor data buffer for verification.
This data can be viewed by using a subsequent "D" command. To read or verify the value any
other time, use the "XRMC" command.
Command Response Description
"aXRMC!" “a0011<cr><lf>" Read Mean_Count
"aXWMCn!" “a0011<cr><lf>" Write Mean_Count
Where: a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").
XRMC are upper case characters.
XWMC are upper case characters.
n is the number of raw measurements wanted
This command takes 001 seconds to complete and places 1 value in the data buffer. Use the
“aD0" command to collect and view the current value.