User guide

H-3521 SDI-12 Command and Response Protocol 5-11
5.10 Extended Read/Write Offset and Read/Write Slope
The H-3521 processes the pressure sensor input and computes Pressure in PSI units. Stage is
computed with a Stage = m * Pressure + b equation. The Slope (m) and Offset (b) terms are
programmable, allowing the user to scale the reading into other engineering units. These
commands allow the user to read or write (change) the Slope and Offset terms. The slope is set to
2.3067 and the offset to 0.00 at the factory. With the factory default (2.3067) the Stage will be in
units of water depth (in feet). The new values are 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 these settings any other time, use the "XRS" or “XRO” commands. This command takes
001 seconds to complete and places 1 value in the data buffer. Use the “aD0" command to collect
and view the new slope or offset.
Command Response Description
"aXRS!" “a0011<cr><lf>" Read Slope
"aXRO!" “a0011<cr><lf>" Read Offset
"aXWSddd!" “a0061<cr><lf>" Write Slope
"aXWOddd!" “a0061<cr><lf>" Write Offset
Where: a is the sensor address ("0-9", "A-Z", "a-z", "*", "?").
XRS are upper case characters.
XRO are upper case characters.
XWS are upper case characters.
XWO are upper case characters.
ddd is the new slope or offset value (For example: 20.0, 195)
Example of a H-3521 Extended "Read Slope" command:
Command Response Time Values Description
"aXRS!" "a0011<cr><lf>" 1 sec 1 Read Slope
Command Response Description
"aD0!" "a+1.00<cr><lf>" Slope is 1.00
Example of a H-3521 Extended "Write Slope" command:
Command Response Time Values Description
"aXWS1.234!" "a0061<cr><lf>" 6 sec 1 Write Slope
Command Response Description
"aD0!" "a+1.234<cr><lf>" Slope is 1.234