When carrying out adjustments with the Modbus protocol, note that certain Modbus-specific adjustment requirements apply to GMP250 Series probes. Review the requirements before carrying out adjustments.
Modbus adjustment requirements
- CO2 measurement can be calibrated and adjusted in 1 or 2 points. Note that you must write an empty (NaN) value in all fields for any unused adjustment points. This prevents any possible earlier values left in those points from affecting the adjustment you are carrying out.
- Adjustment points must be populated starting from point #1 (leaving point 1 empty is not allowed).
- All CO2 adjustment points must contain two values: reference value (after) and measured CO2 (before).
| NOTICE
At the end of the sensor life cycle, the sensor can no longer be adjusted to the specified accuracy and must be replaced. For more information, see return code -4 in Adjustment function return codes. The probe will reject adjustments that are too large (maximum adjustment: 1000 ppm + 25 % of the probe’s uncorrected reading). If the probe appears to need such a large correction, repeat the adjustment procedure and make sure the measurement has stabilized and the reference environment is reliable. If the required adjustment is still too large, the probe needs to be serviced by Vaisala. |
Adjustment recommendations
For further information and instructions on probe adjustment, including general adjustment recommendations and requirements such as recommended reference flow rates, see GMP251 and GMP80 User Guide (M211799EN) and GMP252 User Guide (M211897EN). The probe documentation also describes the wiring, communication settings, and Modbus implementation of the probes.