In-Situ Aqua TROLL 400 Modbus and SDI-12 Reference Guide - Manual (Page 54)

7.3.2 ORP Measured Value
The measured value is derived as follows:
ORP = m
orp
× mV + b
orp
Where:
mV is the measured sensor millivolts
m
orp
and b
orp
are slope and offset respectively
ORP is the calculated value
7.4 Calibration Procedure—pH
1. Write the Calibration Mode On command (0xE000) to the Sensor Command
register.
2. Place the pH sensor into one or more pH standards.
3. Read the pH mV and temperature parameters at each pH standard.
4. Calculate new pH calibration values and write these values to their
corresponding registers.
5. Write the Calibration Update command (0xE001) to the Sensor Command
register. The sensor sets the Last User Calibration Date to the current date and
sets the Next User Calibration Date to zero (none required).
6. Optionally, read the Last User Calibration Time register, add the next calibration
interval, and write the result to the Next User Calibration Time register.
7. Write the Calibration Off command (0xE002) to the Sensor Command register to
place the sensor in normal operation.
7.5 Calibration Procedure—ORP
1. Write the Calibration Mode On command (0xE000) to the Sensor Command
register.
2. Place the ORP sensor into a standard.
3. Read the ORP mV and temperature parameters of the standard. Reading the
ORP parameter in the calibration will return raw ORP millivolts, without the
current calibration applied.
4. Calculate new ORP calibration values and write these values to their
corresponding registers.
5. Write the Calibration Update command (0xE001) to the Sensor Command
register. The sensor sets the last user calibration date to the current date and
sets the Next User Calibration Date to zero (none required).
6. Optionally, read the Last User Calibration Time register, add the next calibration
interval, and write the result to the Next User Calibration Time register.
7. Write the Calibration Off command (0xE002) to the Sensor Command register to
place the sensor in normal operation.
7.5.1 Sensor Command Timeouts
Both the Sensor Cal Defaults command (0xE003) and the Restore Sensor Defaults command
(0xE004) require a response timeout of 1000 milliseconds.
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