Xylem H-4280 - Manual (Page 26)

3-14 SDI-12 Command and Response Protocol H-4280
3.11 Extended Read/Write Offset and Read/Write Slope
The H-4280 processes the measurement data and computes the output value with a y=mX+b
linear equateion. 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 monitor or change
the Slope and Offset terms. The Slope is set to 1.0 and the Offset to 0.00 at the factory. With the
factory defaults the output will be in units of Volts. The new settings 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 "XRSn" or “XROn”
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
"aXRSn!" “a0011" Read Slope
"aXROn!" “a0031" Read Offset
"aXWSn ddd!" “a0031" Write Slope
"aXWOn ddd!" “a0031" 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
n is the channel number (0-7)
ddd is the new slope or offset value (For example: 20.0, 195 etc)
(Note: there must be a space between the n and ddd arguments)
Example of a H-4280 Extended "Read Slope" command:
Command Response Time Values Description
"aXRS5!" "a0011" 1 sec 1 Read channel 5 Slope
Subsequent Command Response Description
"aD0!" "a+1.00" Slope for channel 5 is 1.00
Example of a H-4280 Extended "Write Slope" command:
Command Response Time Values Description
"aXWS5 1.234!" "a0011" 1 sec 1 Write channel 5 Slope
Subsequent Command Response Description
"aD0!" "a+1.234" Slope for channel 5 is 1.234