The following is a professional description of the debugging process for gas sensing transmitters, covering core steps and key details:

1、 Preparation work before debugging

1. Equipment inspection

-Confirm that the sensor model matches the type of gas being detected (e.g. NDIR principle for CO ₂, commonly used electrochemical formula for H ₂ S).

-Check if the IP rating of the casing meets the working conditions (Ex certification is required for explosion-proof areas), and ensure that there are no signs of corrosion on the wiring terminals.

-Measure whether the power supply voltage is within the allowable range (typical value of DC 12-30V) before powering on, to avoid reverse connection and circuit burnout.

2. Standard gas preparation

-Select standard gas cylinders calibrated by the metrology institute, covering the lower limit (LEL), upper limit (UEL), and alarm threshold of the concentration coverage range.

-Equipped with pressure reducing valve and flow meter (accuracy ± 1% F.S.), control the ventilation flow rate within the range of 0.5-1.5L/min.

-High purity nitrogen is used for zero calibration, and the mixed gas cylinder needs to be labeled with an expiration date (generally ≤ 12 months).

2、 Core debugging steps

1. Hardware connection and initialization

-Electrical connection: Shielded cable with single end grounding, kept away from interference sources such as frequency converters/motors. RS485 communication requires terminal resistance matching.

-Preheating operation: After stable startup for ≥ 30 minutes, observe the temperature drift value (high-quality sensor<± 0.5% FS/℃). Record the initial zero current (4mA corresponds to 0ppm).

2. Zero Calibration

-Apply 99.999% N ₂ and perform zeroing operation after the reading fluctuation is less than ± 1% FS.

-Special scenario handling:

-High temperature environment requires load cooling to room temperature before zeroing;

-When cross sensitive gases are present, enable the 'background compensation' algorithm.

3. Span Calibration

-Inject 50% LEL/50% VOL standard gas and adjust the gain potentiometer to accurately correspond the output to 20mA (or digital full range).

-Multi point calibration method: Select at least low/medium/high points (such as 0%, 50%, 90% FS) and draw a fitting curve. Nonlinear error should be less than ± 2% FS.

4. Response time test

-T90 time measurement: the time required from exposure to the display value reaching 90% of the target concentration.

-Diffuse sensor:<30 seconds

-Pump suction system:<15 seconds

-Recovery time test: The time it takes to fall back to within 10% FS after removing the gas.

3、 Advanced feature verification

1. Temperature compensation verification

-Place the sensor in a constant temperature chamber and test the indication error at -20 ℃, 25 ℃, and 60 ℃ respectively.

-Example: Within the range of 0-50 ℃, the total error should be<± 3% FS.

-Devices that enable automatic temperature compensation function require manual calibration to be turned off.

2. Correction of humidity impact

-Verify the deviation caused by a 10% change in relative humidity using a NaCl saturated solution (75% RH) and a dry air generator.

-Typical humidity coefficient of electrochemical sensors: -0.1% FS/% RH.

3. Anti interference capability test

-Cross sensitivity test: Introduce non target gas (such as CO when measuring O ₂) to ensure interference<± 1% FS.

-Electromagnetic compatibility (EMC): Apply 1V/m RF field strength and observe the amplitude of output jitter.

4、 Common problem solutions

-Excessive zero drift: Clean the sensor filter membrane; Check the sealing of the gas path; Update firmware version.

-Slow response: Increase the flow rate of the sampling pump; Replace the aging catalyst; Optimize the diffusion aperture.

-Communication interruption: Check for Modbus address conflicts; Increase terminal resistance; Isolate power supply noise.

5、 Maintenance suggestions

-Periodic tasks:

-Monthly: Appearance inspection+functional self check

-Quarterly: Standard gas re calibration

-Every year: sent to the metrology institute for traceability verification

-Storage conditions: Power off and store at -20~60 ℃, relative humidity<85% RH.