Calibration-related Modbus registers and functions - GMP251

Modbus calibration registers (writable)
Register number	Address	Register description	Data format	Unit/Valid range
8193	0x2000	Calibration mode passcode	16-bit integer	1300 = calibration mode enabled Any other value = calibration mode disabled
8194	0x2001	Calibration year	16-bit integer	These 3 registers must be written in a single transaction. It is not possible to change only year/month/day alone; such an attempt will be ignored.
8195	0x2002	Calibration month	16-bit integer
8196	0x2003	Calibration day	16-bit integer
8197	0x2004	Calibration text	Text	Text string in UTF-8 encoding, maximum 15 bytes. When writing a new calibration text, all Modbus registers in this range must be written, even if the text is shorter. The written text must be filled with NUL bytes so that it is exactly 8 registers long. Any write attempts not writing all these registers in one transaction will be ignored.
	0x2005
	0x2006
	0x2007
	0x2008
	0x2009
	0x201A
	0x201B
8205	0x200C	Calibration interval	16-bit integer
8206	0x200D	Calibration expiry year	16-bit integer	These 3 registers must be written in a single transaction. It is not possible to change only year/month/day alone; such an attempt will be ignored.
8207	0x200E	Calibration expiry month	16-bit integer
8208	0x200F	Calibration expiry day	16-bit integer
8209	0x2010	Calibration reminder on/off	Boolean	When enabled, the calibration reminder only sends a notification message when the probe is connected to Insight PC software or an Indigo transmitter or Indigo handheld. In plain Modbus use, the calibration reminder function is not active and the Modbus client needs to track the calibration expiry date by itself.
User CO₂ adjustment
8449	0x2100	Reference CO₂ value, point 1	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8449	0x2101	Reference CO₂ value, point 1	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8451	0x2102	Measured CO₂ value, point 1	32-bit float	Any ppmCO₂ value can be entered as the measured value (also outside of the measurement range).
8451	0x2103	Measured CO₂ value, point 1	32-bit float
8453	0x2104	Reference CO₂ value, point 2	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8453	0x2105	Reference CO₂ value, point 2	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8455	0x2106	Measured CO₂ value, point 2	32-bit float	Any ppmCO₂ value can be entered as the measured value (also outside of the measurement range).
8455	0x2107	Measured CO₂ value, point 2	32-bit float
CO₂ adjustment data
8961	0x2300	Reference CO₂ value, point 1	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8961	0x2301	Reference CO₂ value, point 1	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8963	0x2302	Measured CO₂ value, point 1	32-bit float	Any ppmCO₂ value can be entered as the measured value (also outside of the measurement range).
8963	0x2303	Measured CO₂ value, point 1	32-bit float
8965	0x2304	Reference CO₂ value, point 2	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8965	0x2105	Reference CO₂ value, point 2	32-bit float	GMP251: 0–200000 ppmCO₂ GMP252: 0–30000 ppmCO₂
8967	0x2306	Measured CO₂ value, point 2	32-bit float	Any ppmCO₂ value can be entered as the measured value (also outside of the measurement range).
8967	0x2307	Measured CO₂ value, point 2	32-bit float

Modbus function registers (writable)
Register number	Address	Register description	Data format	Unit/Valid range
Functions
8457	0x2108	Activate CO₂ adjustment	16-bit integer	When writing to register: 1 = Activate CO₂ adjustment.
8458	0x2109	Restore factory CO₂ adjustment	16-bit integer	When writing to register: 1 = Restore factory CO₂ adjustment.

Adjustment function return codes
Value	Meaning
0	Adjustment successful
-1	Adjustment failed, calibration locked
-2	Adjustment failed, possible device error
-3	Adjustment failed, incomplete adjustment point data
-4	Adjustment failed, cumulative correction too large ¹
-5	Adjustment failed, invalid adjustment point values

¹ This code may indicate that the sensor is at the end of its life cycle and must be replaced. If adjustment attempts repeatedly produce this return code, consider replacing the sensor. Before replacing the sensor, ensure that no mistakes have been made in the adjustment (for example, rule out possible issues caused by insufficient stabilization time or quality of adjustment reference). See probe documentation for adjustment requirements.

Calibration-related Modbus registers and functions - GMP251 - GMP252

Calibrating and adjusting GMP251 and GMP252 probes using Modbus Technical Note