10. Troubleshooting#
This section provides general troubleshooting guidelines for the air quality sensor. If the sensor does not operate as expected, always start with basic checks such as power supply, wiring, communication settings, airflow path, filter condition, and installation environment. Many issues can be caused by incorrect connection, blocked filters, unstable power supply, or improper communication configuration.
Before performing any troubleshooting activity, disconnect the sensor from the power supply unless the procedure specifically requires the sensor to be powered. Troubleshooting should be carried out only by qualified personnel familiar with the installation, electrical connections, and safety requirements.
Sensor does not power on#
If the sensor does not start, first check the power supply voltage and polarity. Make sure that the power supply is within the specified operating range for the sensor. Verify that all cables are correctly connected and that there are no loose wires, damaged connectors, corrosion, or water ingress. Check the fuse, power protection, datalogger power output, or external power supply if used. If the sensor is powered from a solar system or battery, verify that the battery is charged and that the power output is enabled. If the sensor still does not power on after these checks, disconnect it from the system and contact technical support.
The Instrument Does Not Connect To The PC Application Over RS-232 Connection#
Make sure that the cable is properly connected to the instrument. Check that the cable M12 circular connector is firmly connected and screwed to the instrument. It is not sufficient to simply attach the cable connector to the instrument connector, the cable connector must be screwed into the instrument connector.
Check power supply. Make sure that the power is being supplied to the instrument. A direct-current voltage, between 9 and 27 Volts must be connected to brown (+) and white (-) wires of the instrument cable. The power supply must be able to deliver at least 500 mA of current.
Check RS-232 connector. The yellow, green, and grey wires from the instrument cable must be properly connected to the serial port on the computer. Make sure that the grey wire (signal ground) is connected – the RS-232 connection will not work if the signal ground is not connected. Also, make sure that the yellow (device Rx) and green (device Tx) are properly connected. If you are using a standard DB9 type connector on the PC computer.
Make sure that you are using the correct COM port. If there are multiple COM ports available on your computer, make sure that you are selecting the correct COM port in the PC application. If you are not certain which COM port number is assigned to the COM port that is being used to establish a connection with the instrument, try setting up the connection with each COM port available in the system, until the connection is established.
Make sure that the COM port is not already open. Only one application may use a single COM port in the system. Make sure that no other open application uses the same COM port that you are trying to open.
Try restarting the application and/or the computer. Close and reopen the configurator application and try to establish the connection again. Restart your computer and try to establish the connection to the instrument again.
The Instrument Does Not Respond Over Modbus (RS-485) Interface#
Make sure that the cable is properly connected to the instrument. Check that the cable M12 circular connector is firmly connected and screwed to the instrument. It is not sufficient to simply attach the cable connector to the instrument connector; the cable connector must be screwed into the instrument connector.
Check power supply. Make sure that the power is being supplied to the instrument. A direct-current voltage, between 9 and 27 Volts must be connected to brown (+) and white (-) wires of the instrument cable. The power supply must be able to deliver at least 500 mA of current.
Check RS-485 connector. Make sure that the RS-485 lines on the instrument cable are properly connected to the RS-485 connector. The dark red wire should be connected to A+ line, and the orange wire should be connected to B- line. Make sure that the A+ and B- lines are not swapped. Make sure that you have correctly identified and connected the dark red wire, as there is also a bright red wire that is not used. It is possible to misidentify the wire and to connect the bright red wire to A+ instead of dark red wire.
Check that you are using the correct slave device ID. The default Modbus device ID is 1. The Modbus device ID can be changed by connecting the instrument to the PC application (over RS-232 connection). Connect the instrument to the PC using RS-232 connection. Open the Geolux Instrument Configurator application and establish a connection between the instrument and the PC. Then check the Device ID parameter and make sure that it is the same as the slave device ID used in issued Modbus requests.
Make sure that there are no two devices on the bus with the same Device ID. Modbus allows to have multiple devices connected on the same bus simultaneously. Each device must have a unique slave device ID assigned, so that the bus master can distinguish between the devices. If two or more devices are assigned the same slave device ID, a bus conflict will happen and prohibit the master to correctly communicate with the slave devices. To resolve this problem, change the instrument’s slave device ID to a unique number through the Geolux Instrument Configurator PC application.
Check that you are using the correct Modbus connection parameters (baud rate, parity, stop bits). The default Modbus connection parameters are 9600 bps, even parity, 1 stop bit. These parameters can be changed by connecting the instrument to the PC application (over RS-232 connection). Connect the instrument to the PC using RS-232 connection. Open the Geolux Instrument Configurator application and establish a connection between the instrument and the PC. Then check and verify that all Modbus connection parameters are correct.
Unstable or incorrect measurements#
If the measured values appear unstable, incorrect, or unrealistic, inspect the sensor installation and airflow path. Make sure that all filters are clean and that the air inlets and outlets are not blocked by dust, insects, spider webs, leaves, snow, ice, or other contamination. The sensor has two filters: one for the particle measurement module and one for the gas measurement module. If either filter is blocked, the airflow through the corresponding measurement module may be reduced, which can affect measurement accuracy. Clean the filters only by gently blowing them with dry compressed air. The maximum allowed air pressure is 3 bar. Do not use water, solvents, brushes, cloths, or mechanical cleaning tools. Also check the installation location. The sensor should not be installed too close to exhaust outlets, ventilation openings, walls, corners, heat sources, or other objects that may disturb airflow or create local pollution effects. Avoid locations where water can drip directly onto the sensor or where the sensor can be exposed to excessive dust, steam, or chemical vapours outside the specified operating conditions.
Particle measurements are too high or too low#
If particulate matter values are unexpectedly high, check for local contamination sources such as construction dust, road dust, smoke, nearby exhausts, insects, or dirt inside the particle filter area. A blocked or contaminated particle filter can cause incorrect readings. If particulate matter values are unexpectedly low, check whether the particle measurement filter or inlet is blocked. Reduced airflow through the particle measurement module can result in lower measured values. After cleaning, allow the sensor to operate for a stabilization period and compare the readings with expected environmental conditions or a reference instrument, if available.
Gas measurements are unstable or drifting#
Gas sensors can be influenced by temperature, humidity, cross-sensitivity to other gases, and environmental changes. If gas readings are unstable, first check that the gas measurement filter is clean and that the airflow path is not blocked. Make sure the sensor has been powered long enough to stabilize after installation, cleaning, or restart. Some gas sensors require a warm-up or stabilization period before readings become stable. If the values continue to drift or remain outside expected limits, calibration or service inspection may be required. Do not attempt to clean or touch internal gas sensing elements.
Condensation or moisture detected#
If condensation, moisture, or water ingress is suspected, disconnect the sensor immediately. Do not operate the sensor while moisture is visible around connectors, filters, or inside accessible parts of the housing. Allow the sensor to dry naturally in a safe, dry environment. Do not use heat guns, ovens, open flame, or direct high-temperature air to dry the sensor. After drying, inspect the connectors, cables, seals, and filters. If there are signs of corrosion, water ingress, or damaged seals, the sensor should be inspected by authorized service personnel before being returned to operation.
Sensor readings do not change#
If the sensor readings remain constant for a long period, check whether the sensor is communicating correctly and whether new measurements are being requested by the datalogger or control system. Verify that the measurement interval is correctly configured. Also check that the sensor is not in sleep mode, service mode, or another operating mode that prevents continuous measurement. Inspect the filters and airflow path. If airflow is completely blocked, the sensor may not respond properly to changes in air quality.
Frequent communication errors#
Frequent communication errors may be caused by long cables, poor grounding, incorrect shielding, electrical noise, wrong serial settings, or unstable power supply. Check cable routing and avoid running communication cables close to high-power electrical cables, motors, pumps, relays, or radio transmitters. For RS-485 installations, use suitable twisted-pair cable and proper termination if required by the installation. Also verify that only one device on the bus uses the same Modbus or SDI-12 address. Address conflicts can cause intermittent or complete communication failure.
Maintenance after troubleshooting#
After any troubleshooting or cleaning activity, check that all filters, covers, connectors, screws, and seals are correctly installed. Reconnect the sensor and verify normal operation. It is recommended to record all troubleshooting actions in the maintenance log, including the date, sensor serial number, installation location, observed problem, actions taken, and final result. This information can help identify recurring issues and support further technical analysis. If the problem cannot be resolved on site, contact authorized technical support. When contacting support, provide the sensor serial number, firmware version if available, installation photos, wiring diagram, power supply information, communication settings, error messages, and a description of the observed behaviour.