Xylem H-3311 - Manual (Page 21)

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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 position into other
engineering units. These commands allow the user to read the current slope and offset terms.
The slope is set to 0.005 and the offset to 0.000 at the factory. The H-3301/3311 has a mechanical
position resolution of 200 counts per revolution. When used with a pulley 1.0 feet in circumference:
0.005 feet/count x 200 counts/rev. = 1.0 feet/rev. The slope term can be changed for other pulley
diameters or for other units such as inches or meters.
Command Response Description
“aXRS!” “a0011<cr><lf>” Read Slope
“aXRO!” “a0011<cr><lf>” Read Offset
Where:
a is the sensor address (“0-9”, “A-Z”, “a-z”, “*”, “?”).
XRS are upper case characters.
XRO are upper case characters.
This command takes 001 seconds to complete and places 1 value in the data buffer. Use the “aD0”
command to collect and view the slope or offset.
Read User Offset and Read User Slope Commands
example of an extended “read user units slope” command:
Command Response Time Values Description
“aXRS!” “a0011<cr><lf>” 1 sec 1 Read Slope
Command Response Description
“aD0!” “a+0.005<cr><lf>” Slope Reading is 0.005
Pulley Circumference Units Slope
12in ft 0.005
18in ft 0.0075
375mm m 0.001875
750mm m 0.00375