Infrared spectrophotometer is the core equipment for measuring petroleum substances in water quality monitoring, which is based on infrared spectroscopy to achieve rapid quantitative analysis. The following are common types of faults and targeted solutions in practice:
1、 Abnormal light source system
Phenomenon: Insufficient energy alarm or generally low absorbance.
Cause: Aging of silicon carbide rods or halogen lamps after long-term use; Unstable power supply leads to fluctuations in output power; Misalignment of optical path collimation (such as loosening of mirrors).
solve:
-Replace the light source components with the same model, and preheat the new light source for at least 30 minutes to ensure stable output;
-Use a regulated power supply with good grounding to avoid electromagnetic interference;
-Open the instrument cover and use a special tool to fine tune the angle of the reflector to focus the beam on the monochromator entrance slit.
2、 Pollution or leakage of colorimetric pool
Typical manifestations: Failure of blank correction, poor repeatability, or appearance of abnormal absorption peaks.
Root cause analysis: Oil film or particulate matter adhering to the inner wall of the quartz colorimetric cell; The aging of the sealing O-ring causes leakage of carbon tetrachloride solvent; Residual impurities in the injection valve block the flow path.
Handling measures:
-Remove the colorimetric cell and ultrasonically clean it with acetone and anhydrous ethanol for 10 minutes, then blow dry with nitrogen;
-Replace the deformed or hardened fluororubber O-ring, and apply a small amount of vacuum grease to enhance the seal during installation;
-Execute automatic flushing program (supported by some models) to remove residual samples from the injection needle and tubing.
3、 Baseline drift or severe fluctuations
Feature: Baseline tilt or sawtooth jitter across the entire wavelength range.
Cause investigation: The environmental temperature exceeds the working range of the instrument (15-30 ℃); High humidity in the sample room leads to fogging of optical components; The reference solution has deteriorated or contains suspended solids.
Response strategy:
-Start the air conditioning to control the room temperature, and equilibrate the sample to ambient temperature before testing;
-Blow the sample chamber with a dry nitrogen stream and replace the desiccant filter element;
-Re prepare the reference solution (pure carbon tetrachloride needs to undergo dealromatization treatment), and use a 0.45 μ m organic phase filter membrane as the filter head.
4、 Abnormal data collection
Specific symptoms: missing characteristic peaks in the spectrum, low acceptance rate, or negative values.
Key checkpoint: detector response value saturation; Poor contact of AD conversion module; Software parameter settings are incorrect (such as too short integration time).
Repair plan:
-Reduce the sample concentration to within the range (recommended ≤ 80% transmittance);
-Turn off the power and restart the instrument, then unplug and plug in the data acquisition cable again;
-Enter the system settings and adjust the integration time to 0.5-2 seconds per time, and set the scanning frequency to 16 or more times to take the average.
5、 Calibration failure
Judgment criteria: The correlation coefficient of the standard oil curve is less than 0.995, and the measured value deviates from the expected value by more than ± 10%.
Core reason: The concentration gradient of the calibration standard solution is unreasonable; The optical path length of the colorimetric cell is inconsistent with the calibration; Interference filter center wavelength offset.
Correction process:
-Configure a standard series with at least 5 gradients according to national standards (such as 0-80mg/L);
-Replace the matching optical path gasket with the optical path indicated on the nuclear contrast color pool certificate (usually 1cm or 5cm);
-Contact the manufacturer for wavelength calibration of the optical system to restore the 2930cm ⁻¹ characteristic absorption peak position.
6、 Mechanical motion malfunction
Multiple locations: automatic sampler jamming, improper switching of filter wheel.
Disposal method:
-Clean the injection valve guide rail and apply an appropriate amount of clock oil;
-Loosen the fixing screw of the filter wheel, manually rotate it until smooth, and then tighten it again;
-If the stepper motor loses step, the driver board needs to be replaced or the firmware program needs to be upgraded.
The key points of daily maintenance include: ① replacing desiccants every month; ② Clean the injection system with blank samples every week; ③ Perform optical system calibration annually. Establishing instrument logs to record fault phenomena and handling processes can help quickly diagnose similar problems. Complex faults (such as motherboard damage) require contacting professional engineers for repair, and blind disassembly of optical components should be avoided.