What Is a Photometer?

A spectrophotometer, also called a spectrometer, is a scientific instrument that decomposes light with complex components into spectral lines. The measurement range generally includes the visible light region with a wavelength range of 380 to 780 nm and the ultraviolet light region with a wavelength range of 200 to 380 nm. Different light sources have their own unique emission spectra, so different luminous bodies can be used as the light source of the instrument. Tungsten lamp emission spectrum: Spectral light with a wavelength of 380 to 780 nm emitted by a tungsten lamp light source is refracted by a triangular prism to obtain a continuous chromatogram consisting of red, orange, yellow, green, blue, indigo, and violet; this chromatogram can be used as visible light The light source of the spectrophotometer.

Spectrophotometer operation method

1. Turn on the power, turn on the instrument, open the cover of the sample chamber, and warm up for 10 minutes.

2. Set the sensitivity switch to 1 (If the zero adjuster cannot be adjusted to 0, you need to choose a higher gear.)

3. Turn the wavelength selector according to the desired wavelength.

4. Pour the blank solution and measurement solution into the cuvette 3/4 respectively, wipe the outer wall with a lens cleaning paper, put it into the sample chamber, and align the blank tube with the light path.

5. With the cover of the dark box open, adjust the zero adjuster so that the pointer of the reading dial points to t = 0.

6. Close the cover of the dark box and adjust the "100" adjuster so that the blank tube has t = 100. After the pointer is stable, gradually pull out the sample slide bar, read the optical density values of the measuring tubes and record them.

7. After the color comparison, turn off the power, take out the cuvette and wash it, and clean the sample room with a soft cloth or paper.

Precautions

1. The instrument should be placed in a dry room and placed on a sturdy and stable workbench. The indoor lighting should not be too strong. In hot weather, you cannot use an electric fan to blow air directly to the instrument to prevent the bulb filament from shining brightly and unstable.

2. Before using the instrument, the user should first understand the structure and working principle of the instrument, and the functions of each control knob. Before the power is turned on, the safety performance of the instrument should be checked. The power wiring should be firm and the power should be good. The starting position of each adjustment knob should be correct, and then press the power switch.

3 When the instrument is not powered on, the meter pointer must be on the "0" engraved line. If this is not the case, you can use the calibration screw on the meter to adjust it.

Routine maintenance

Analytical instrument workers need to understand the daily maintenance of the instrument and simple test methods for the main technical indicators. They often perform maintenance and testing on the instrument to ensure that the instrument works in the best state.
First, temperature and humidity are important factors affecting the performance of the instrument. They can cause the corrosion of mechanical parts, reduce the smoothness of the metal mirror surface, cause errors or performance degradation of the mechanical parts of the instrument; cause the aluminum film of the optical components such as gratings, reflectors, focusing lenses to rust, resulting in insufficient light energy, stray light, Noise, etc., even the instrument stops working, which affects the life of the instrument. It should be calibrated regularly during maintenance. There should be an instrument room with four seasons constant humidity, equipped with constant temperature equipment, especially a laboratory located in the southern region.
Second, the dust and corrosive gas in the environment can also affect the flexibility of the mechanical system, reduce the reliability of various limit switches, buttons, and photoelectric couplers, and it is also one of the reasons for the corrosion of the aluminum film of the required components. Therefore, it must be cleaned regularly to protect the environment and the indoor sanitary conditions of the instrument, and to prevent dust.
3. After a certain period of use of the instrument, a certain amount of dust will accumulate inside. It is best to open the instrument cover regularly to perform dust removal work under the guidance of a maintenance engineer or under the guidance of the engineer. The sealed window of the box is cleaned, the optical path is calibrated if necessary, the mechanical part is cleaned and necessary lubrication, and finally, it is restored to the original state, and then necessary inspections, adjustments and records are performed.

Spectrophotometer maintenance

As a precision instrument, the spectrophotometer will inevitably undergo certain changes in its technical conditions during operation due to the working environment, operating methods and other reasons, which may affect the performance of the equipment and even induce equipment failures and accidents. Therefore, the analyst must understand the basic principles and instructions of the spectrophotometer, and be able to find and eliminate these hidden dangers in time, and repair the failures in time to ensure the normal operation of the equipment.

1) If the test wavelength is changed drastically, please wait for a while. After the lamp is thermally balanced, recalibrate the "0" and "100%" points. Then measure again.

2) When the pointer instrument is not powered on, the pointer of the meter must be on the zero scale. If this is not the case, a mechanical zero adjustment is required.

3) After using the cuvette, immediately rinse it with distilled water, and wipe off the water traces with clean and soft gauze to prevent the surface finish from being damaged and affect the light transmittance of the cuvette.

4) The operator should not move the light bulb and reflector light easily, so as not to affect the light efficiency.

5) Type 1900 Spectrophotometer, because its photoelectric receiving device is a photomultiplier tube, it is characterized by a large magnification, so it can be used to detect weak photoelectric signals, but not to detect strong light. Otherwise, it is easy to generate signal drift and decrease sensitivity. In view of the above characteristics, when repairing and using such instruments, care should be taken not to expose the photomultiplier tube to light for a long time. Therefore, when preheating, open the cuvette cover or use a light blocking rod to avoid prolonged exposure Performance drift causes unstable operation.

6) After the sensitivity of the amplifier is shifted, it must be re-zeroed.

7) The matching of cuvettes. The cuvette must be used together, otherwise the test results will be meaningless. Comparisons should be made before each test. The specific method is as follows; inject the same solution into the two cups to be tested, place the instrument at a certain wavelength, quartz cuvette; 220nm, 700nm filled with distilled water, glass cuvette: 700nm filled with distilled water, Adjust the transmittance of one cell to 100%, measure the transmittance of other cells, record the difference between the displayed value and the direction of light transmission. If the difference of the transmittance is within the range of ± 0.5%, it can be used in combination. If it exceeds this range Its effect on test results should be considered.

Several typical faults easy to appear in the spectrophotometric scoring operation and their troubleshooting methods:

1) The instrument cannot be zeroed. possible reason:

a) The light door cannot be completely closed. Workaround: Repair the light door assembly to completely close it.

b) The transmittance "100%" is turned to the end. Solution: Re-adjust the "100%" knob.

c) The instrument is severely wet. Solution: Open the photocell cassette, blow it with a hair dryer for a while, and change the desiccant.

d) Circuit failure. Solution: send it to the repair department to repair the circuit.

2) The instrument cannot be adjusted to "100%". possible reason:

a) Insufficient light energy. Solution: Increase the sensitivity ratio, or replace the light source lamp (although the lamp is still on).

b) The cuvette rack is not in place. Solution: Adjust the cuvette holder to place it.

c) The photoelectric conversion part is aging. Solution: Replace parts.

d) Circuit failure. Solution: Adjust the circuit.

3) During the measurement, the "100%" point often changes. possible reason:

a) The cuvettes are placed in different positions in the cuvette rack, or there are droplets on the surface. Solution: Wipe the surface of the cuvette clean with mirror paper, then place it on the left side of the cuvette, and use the positioning clip to locate it.

b) Circuit failure (voltage, photoelectric receiving, amplifying circuit). Solution: send for repair.

4) Digital display is unstable. possible reason:

a) Insufficient warm-up time. Solution: Extend the warm-up time to about 30 minutes (some instruments may also be unstable when working for a long time due to aging and other reasons).

b) The desiccant in the photocell fails, making the microcurrent amplifier damp. Solution: Bake the circuit and replace or bake the desiccant.

c) Excessive environmental vibration, large air velocity near the light source, strong external light exposure, etc. Solution: Improve the working environment.

d) Photocells, circuits and other reasons. Solution: send for repair. ^[2]