The maintenance of gas analyzer sensors is the core link to ensure their measurement accuracy, extend their service life, and ensure the safe operation of equipment. The maintenance details of different types of sensors (such as electrochemical, infrared, catalytic combustion, thermal conductivity, etc.) vary, but the core logic can be summarized into four stages: "regular inspection - cleaning calibration - status assessment - fault handling". The following are the specific operational steps for a general maintenance framework and typical sensors:
1、 Preparation before maintenance: Safety and tool readiness
Before starting any maintenance operation, it is necessary to prioritize safety and prepare specialized tools to avoid sensor damage or personnel risks caused by improper operation.
safety protection
If the detection medium is toxic, flammable and explosive gases (such as hydrogen sulfide, methane), the gas source should be cut off first, and the analyzer and pipeline should be purged with inert gas (such as nitrogen) to prevent residual gases from causing danger.
Wear personal protective equipment (PPE): such as nitrile gloves (to avoid hand grease contamination of sensors), goggles (to prevent liquid or dust splashing), anti-static wristbands (for sensitive sensors).
Preparation of tools and consumables
Basic tools: Phillips/Phillips screwdriver, wrench (matching analyzer housing bolts), lint free wiping cloth (such as lens paper), compressed air tank (cleaning dust, pressure ≤ 0.3MPa).
Special consumables: standard calibration gas (concentration must meet the sensor range, such as 99.99% nitrogen+20.9% oxygen mixture for oxygen sensors), sensor protective cover (if the original cover is damaged), electrolyte (only electrochemical sensors need to be regularly replenished).
Equipment status confirmation
Record the basic data of the analyzer before maintenance, including measurement values, zero drift, and response time, to facilitate comparison of performance after maintenance.
Turn off the power of the analyzer, unplug the power plug, and ensure that the device is completely powered off (some online analyzers need to switch to "bypass mode" to avoid interrupting gas monitoring).
2、 General maintenance operation steps (applicable to all types of sensors)
Step 1: Appearance inspection and cleaning of sensors
Open the analyzer casing, locate the sensor installation position (usually clearly marked, such as "O ₂ Sensor" or "COSensor"), and observe the appearance of the sensor:
If there is dust, oil stains, or condensed water on the surface of the sensor: gently blow with a compressed air tank (maintain a distance of 10-15cm), and for stubborn stains, use a lint free cloth dipped in a small amount of anhydrous ethanol (only wipe the outer shell to avoid penetrating the inside of the sensor) to wipe. Wait until completely dry before proceeding to the next step.
Check whether the sensor connection wires (such as signal wires and power wires) are loose, aged, or damaged. If so, replace them with wires of the same specifications (pay attention to the polarity of the positive and negative poles to avoid reversing and burning the sensor).
Check the sensor protective cover/filter membrane (such as dust-proof filter membrane, waterproof breathable membrane): If the filter membrane is clogged or discolored (such as the catalytic combustion sensor filter membrane being contaminated with oil), it is necessary to replace it with a new filter membrane (ensure sealing during replacement to prevent external impurities from entering the sensor chamber).
Step 2: Zero calibration (core maintenance step, eliminating drift errors)
Zero point calibration is the benchmark value for sensors to recognize "no target gas", usually performed every 1-3 months (shortened to 2 weeks for high concentration or high humidity environments).
Connect the zero point gas (such as high-purity nitrogen gas with a purity of ≥ 99.99% for measuring toxic gases, and anaerobic nitrogen gas for measuring oxygen) to the calibration interface of the analyzer, and adjust the gas flow rate to the required range of the sensor (usually 50-200mL/min, refer to the equipment manual).
Start the "zero calibration" mode of the analyzer (some devices require automatic calibration, while others require manual triggering), and wait for the sensor response to stabilize (usually 5-15 minutes, until the displayed value tends to be constant).
Confirm that the zero point value meets the requirements (such as the zero drift of the electrochemical sensor should be ≤ ± 1% FS). If it does not meet the requirements, repeat the calibration 1-2 times; If multiple calibrations still fail to meet the standard, it is necessary to check whether the sensor is malfunctioning.
Step 3: Span calibration (ensuring measurement accuracy and matching range)
The span calibration uses a standard gas of known concentration to calibrate the measurement upper limit of the sensor, synchronized with zero point calibration.
Turn off the zero point gas, connect the span standard gas (recommended concentration is 70% -80% of the sensor range, such as for CO sensors with a range of 0-1000ppm, use 700ppm standard gas), and adjust the flow rate to the specified value.
Activate the "span calibration" mode, wait for the sensor response to stabilize (slightly longer than zero calibration, about 10-20 minutes), and observe whether the displayed value is consistent with the standard gas concentration.
If the deviation of the displayed value exceeds the allowable range (such as ± 2% FS), adjust the "span factor" through the device button or software interface until the displayed value matches the standard value, and save the calibration data.
Step 4: Sensor Performance Test
After calibration is completed, it is necessary to verify the response performance of the sensor to ensure maintenance effectiveness:
Response time test: After introducing standard gas, record the time required for the sensor to rise from the initial value to 90% of the standard value (e.g. electrochemical sensor response time should be ≤ 30 seconds, infrared sensor ≤ 10 seconds). If it exceeds the time limit, it may be due to sensor aging or gas path blockage.
Stability test: Continuously introduce standard gas for 30 minutes and observe whether the displayed value fluctuates by ≤± 1% FS. If the fluctuation is too large, it may be due to gas leakage or internal component failure of the sensor.
Recovery time test: Switch back to zero gas and record the time required for the sensor to drop from the standard value to 10% of the zero value, ensuring that the sensor can quickly recover to the reference state.