UV-Visible Spectrophotometer Common Faults

one. Light source part:

(1) Failure: Tungsten light is off;

Cause: Tungsten filament burned (highest probability of this type);

Check: There is working voltage at both ends of the tungsten lamp, but the lamp is not bright; take off the tungsten lamp with multimeter resistance file detection.

Disposal: Replace the new tungsten lamp;

(2) Fault: Tungsten light is off;

Reason: No lighting voltage;

Check: The fuse is blown;

Disposal: Replace the fuse, (if you replace it again and then blow it, check the power supply circuit);

(3) Failure: The Xenon light is off;

Reason: The lifetime of the xenon lamp expires (the reason for this is the highest);

Check: filament voltage, anode voltage, filament may not be broken (red filament can be seen);

Disposal: Replace the lamp;

(4) Failure: The Xenon light is off;

Cause: The xenon lamp starts to fail;

Inspection: In the process of starting up the xenon lamp, the filament is usually warmed up for a few seconds, then the anode and cathode of the lamp can start to glow, if the lamp flashes or flashes continuously in the beginning of the starting light. After moving and replacing the new xenon lamp, it is still possible that there is a failure in the starter circuit, and the probability of damaging the high-power transistor for lamp current adjustment is the highest.

Disposal: need professional repair;

two. Signal section:

(1) Fault: No detection signal output;

Reason: No light beam hits the sample chamber;

Check: Set the wavelength to 530nm, slit as far as possible to the widest gear, and place a white paper on the exit of the light window of the sample chamber in a dark environment, observe whether there is a green spot image on the white paper;

Disposal: Check if the light source mirror is turned to position? Does the tangential motor of the double beam instrument rotate (the ear can hear the sound of motor rotation)?

(2) Failure: In the absence of any object in the sample chamber, the baseline noise in the full wavelength range is large;

Cause: The position of the light source mirror is incorrect, and the quartz window surface is sputtered with a sample;

Check: Observe that the light source is shining into the center of the entrance slit? Is there any contamination on the quartz window?

Disposal: Readjust the position of the light source and clean the quartz window with ethanol.

(3) Failure: In the absence of any object in the sample chamber, only the baseline noise in the UV region is large;

Causes: Deterioration of xenon lamp, deterioration of mirror surface of optical system, and crystal appearing in filter;

Inspection: The baseline of the visible area is relatively flat. After the power is turned off, the monochromator and cover of the instrument are turned on. The naked eye can observe that the surface of the grating and the reflector has a white mist covering the surface; if the optical system is normal, the greatest possibility is The aging of the xenon lamp can be judged by the energy check or the replacement of the new lamp.

Disposal: Replace the xenon lamp, stick the dirt on the mirror surface with fire gum or grind the filter with the abrasive paste (Note: This kind of technique needs to be carried out by someone with certain maintenance experience);

(4) Failure: Baseline memory after the sample chamber is put into the vacancy, the noise is large, especially in the ultraviolet region;

Cause: The surface or interior of the cuvette is contaminated, the glass cuvette or blank sample is used to absorb the ultraviolet spectrum too strongly, making the amplifier beyond the calibration range;

Check: Set the wavelength to 250nm, zero the first thing without putting any items, then insert the empty cuvette into the side of the sample path. At this time, the absorbance value should be less than 0.07Abs; if it is greater than this value, it may be The cuvette is not clean or a glass cuvette is used; the same method can also determine the absorbance value of the vacant solution;

Disposal: Clean the cuvette and replace the vacant solution;

(5) Failure: Absorption results appear negative (most common);

Reason: No vacancy memory, sample absorbance value is less than vacant reference solution;

Check: Know the position of the reference solution and the sample solution;

Disposal: Make vacant memory, exchange reference solution or configure sample solution with reference solution;

(6) Failure: poor reproducibility of sample signal;

Cause: Excluding the reason of the instrument itself, the biggest possibility is the unevenness of the sample solution. In a simple single-beam instrument, the sample cell holder is generally push-pull type, and sometimes repeated push-pull is not in the same position;

Inspection: Replace a stable sample determination;

Disposal: take the correct sample configuration; repair the push-pull sample holder positioning the ball;

(7) Failure: When doing a baseline scan or sample scan, the baseline or signal has a large negative pulse;

Reason: Scanning speed is set too fast, the signal is read, mistakenly read the filter or light source switch as a signal;

Check: change the scanning speed;

(8) Failure: When doing a baseline scan or sample scan, the baseline or signal has a long period of negative or full screen noise;

Reason: The filter feeder motor "out of step", resulting in stall misalignment, especially domestic-made motor;

Check: It may be possible to recover from a reboot, or turn on the monochromator to check the relative position of the wavelength and the filter to check (note that the detector should be protected from strong light when the monochromator is turned on);

Disposal: Replace the feeding motor;

(9) Failure: The peak position of the sample is not correct;

Cause: The wavelength transmission mechanism generates displacement;

Check: Determine whether the wavelength is correct by using the deuterium lamp's characteristic spectrum of 656.1nm.

Disposal: For high-end instruments, the processing method is relatively simple, and the instrument's inherent auto-correction function can be used. For relatively simple instruments, this adjustment requires specialized staff to perform the adjustment.

(10) Failure: The resolution of the signal is not enough. The concrete manifestation is that small peaks that should be superimposed on a large peak cannot be observed;

Cause: The slit is too narrow and the scanning speed is too fast, which causes the detector to respond to a lower speed and loses the signal to be measured. According to common sense, a certain slit width must correspond to a certain range of scanning speeds; or slits. Set too wide to reduce the resolution of the instrument and merge the small peaks in the big peak.

Check: Slow down the scanning speed or look at the slit;

Disposal: Fit the scan speed, slit width, and time constant into an optimal condition;

(11) Failure: When the wavelength of the instrument is fixed at a certain wavelength, the signal of the absorbance value swings up and down, especially the simple instrument that converts the measurement mode into a key switch type;

Cause: The contact of the switch contacts due to long-term oxidation;

Check: When the air pressure is pressed by hand, the absorbance value changes.

Disposal: Use metal activator to clean the key contacts;

(12) Fault: The zero drift of the instrument is mainly reflected in simple instruments;

Reasons: In simple instruments, the zero point is often adjusted by potentiometers. Such potentiometers are generally made of carbon film resistors, and they often cause poor contact when used for a long time.

Disposal: Replace the potentiometer;