Forced Recalibration of MultiSensor CO2 Sensor

| Overview

The 75F Multi Sensor can sense Temperature, Humidity, Occupancy, and CO2. It uses a really delicate optical system for the CO2 sensing. The physical properties of this type of optical system are prone to change under mechanical stress. These changed physical properties affect the calibration of the sensors, leading to inaccurate sensor values or sometimes significantly inaccurate readings.

The above scenario is especially true for the CO2 sensors.

Factory set calibration often tends to vary, and when the device is put to use in a building environment, it could read inaccurate CO2 values or values that vary from the actual CO2 in the space.

| Forced Recalibration

To solve the mentioned above use case a forced recalibration method is introduced in the 75F system. This forced recalibration sets the CO2 sensor calibration so it can start sensing the expected CO2 values.

| Forced Recalibration Process

The Forced Recalibration (FRC) process marks three key steps.

• Initiating from the Physical Device
• Forced Calibration (FRC) Routine
• FRC Success/Failure

| Initiating from the Physical Device

The figure above depicts a device operating in Normal Mode

The LED powered ON for every 1 second.

The below table provides more details on the same.

• Press and hold the pair button on the Multi Sensor for 20 seconds to initiate the FRC trigger.

The figure above depicts a device with an FRC trigger

The LED in the Multi Sensor is powered OFF, reporting the start of the FRC routine.

Note: For a CO2 sensor recalibration to be successful, the process will have to be carried out in a large open room with a good supply of fresh air. This is where the CO2 levels are assumed to be 400 the default threshold set for the sensor.

| Forced Calibration (FRC) Routine

The FRC routine comprises two steps.

• Periodic Measurement
• Sensor Calibration

Periodic Measurement

This step is mandatory for any sensor calibration to be successful. The Multi Sensor starts the periodic measurement of CO2 During this time the LED is powered ON for every 2 seconds for 3 minutes.

The figure above depicts a device with an active FRC

The below table provides more details on the same.

Note: No more than a Multi-Sensor should be in the BUS for the periodic measurement to be successful.

Sensor Calibration

The sensor calibration occurs after the periodic measurement for 3 minutes.

| FRC Success/Failure

Based on whether the FRC was successful or not, the LED on the Multi Sensor is powered ON and OFF at different frequency intervals.

FRC success

For a successful FRC, the LED is powered OFF before it gets back to a normal sensing state.

Device in Normal Mode

The LED powered ON and OFF for every 1 second.

The below table provides more details on the same.

FRC Failure

For a failed FRC, the LED is powered ON and OFF for every 200 milliseconds, until power is cycled for it to get back to the normal sensing state.

The figure above depicts a device with a failed FRC

The below table provides more details on the same.

| Feature Release Version

• The Forced Recalibration support for the CO2 on the Multisensor is available from the Multi Sensor version 0.10.0 and above.