Xylem H-3311 - Manual (Page 22)

20
SDI-12 COMMAND &
RESPONSE PROTOCOL
The H-3301/3311 processes the raw shaft encoder position with a mX+b equation. The slope (m)
and offset (b) terms are programmable, allowing the user to scale the encoder position into other
engineering units. This command allows the user to write (change) the slope and offset terms.
The new value is stored in non-volatile EEPROM within the sensor. Once the new slope or offset
value is written to the EEPROM, a copy is sent to the sensor data buffer for verification. This data can
be viewed by using a subsequent “D” command. To verify the Slope or Offset any other time, use the
“Read User Slope” or “Read User Offset” commands.
Command Response Description
“aXWSddd!” “a0011” Write Slope
“aXWOddd!” “a0011” Write Offset
Where:
a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”).
XWS are upper case characters.
XWO are upper case characters.
ddd is the new slope or offset value. The input format is very flexible. Some examples are
shown below.
20.0
0.195
-500
Write User Offset and Write User Slope Commands
example of an extended “write user units slope” command:
Command Response Time Values Description
“aXWS1.234!” “a0011” 1 sec 1 Write Slope
Command Response Description
“aD0!” “a+1.234” Slope verified at 1.234
This command tests the individual segments of the display by cycling through the numbers 0-9 in
each of the different positions on the display followed by displaying the numbers 100, 1000 and
10000 to test the decimal locations.
Command Response Description
“aXTD!” “a0200” Test Display
Where:
a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”).
XTD are upper case characters.
Test Display