Operating Manual of Model 721N Visible Spectrophotometer 1
Table of Contents 1. Chief uses... 3 2. Working Conditions... 3 3. Main Specifications...3 4.Operating Principles...4 5. Optical design...4 6. Installation, Operation and Maintenance...5 7. Calibration and Troubleshooting... 7 8. Standard Package... 8 9.Storage and Warranty period...8 2
1. Chief uses Model 721N visible spectrophotometer, an analytical instrument commonly used in physico-chemical laboratories to make quantitative and qualitative analysis of specimen materials in the near ultra-violet, visible spectral range, finds much scope for its service in such fields as medicine, clinical examination, biochemistry, petro-chemical industry, environmental protection and quality control. 2. Working Conditions 2.1 The instrument should be installed in a dry room with the temperature kept between 5 and 35, and relative humidity under 85%. 2.2 While in use, the instrument should be placed on a solid, smooth working table, free from shocks or vibrations. 2.3 Strong illumination and direct exposure to sunlight should be avoided. 2.4 No airflow, e.g., produced by an electric fan, should be directed straight towards the instrument. 2.5 Keep the instrument far away from any high-intensity magnetic field, electric field or electrical equipment that produces high-frequency waves. 2.6 Power supply for the instrument should be AC 220V ± 22V,50Hz ± 1Hz,with good ground connection. To increase the anti-interference performance, it is recommended to use AC regulated power supply, either an electronic AC voltage stabilizer or an AC constant voltage regulator with a capacity of 1000W or above. 2.7 Do not use the instrument in a place where there is hydrogen sulfide, fluorine sulfite or other corrosive gases. 3. Main Specifications 3.1 Optical system: single beam, diffraction grating 3.2 Wavelength coverage: 360nm 1000nm 3.3 Light source: 12V 20W tungsten-halogen lamp 3.4 Receptor: photocell 3.5 Wavelength accuracy:±2nm 3.6 Wavelength reproducibility: 1nm 3.7 Spectral bandwidth: 4 nm 3.8 Stray light: 0.15%τ at 360nm 3.9 Transmittance accuracy: ±0.5%τ 3.10 Transmittance reproducibility: 0.2%τ 3.11 Stability: light current 0.5%τ/ 3 min., Dark current 0.2%τ/ 3 min. 3.12 Power supply: AC 85 V-242V 3.13 Overall dimensions: 570mmⅹ400mmⅹ260mm 3.14 Net weight: 14kg 3
4.Operating Principles The 721N spectrophotometer works on the colorimetry principle/ Beer s law. The substance in the solution, excited by the light irradiation, produces an effect of light absorption. Each kind of substance has its own absorption spectrum distinct from others because of its absorption selectivity. When a monochromatic light is transmitted through the solution, the light energy decreases as it is absorbed, in proportion to the concentration of the substance. τ= I / I Log I / I= KCL A=KCL In the above: τ--- transmittance I --- intensity of the incident light I ---- intensity of the transmission light A ---- absorbance K ---- absorption coefficient L ---- length of light travel through the solution C ---- concentration of the solution L I0 CCBBBBBNB I It can be inferred from the formula that when the intensity of the incident light, absorption coefficient and length of light travel through the solution remain invariant, transmission light varies according to the concentration of the solution. 5. Optical design The optical system of auto-collimating dispersion grating and single-beam light path is adopted for 721N visible spectrometer. The optical diagram 4
is shown below. Light emitted by the tungsten-halogen lamp, after passing through the filter, gathers at the collecting mirror and is directed to the entrance slit of the monochromator. Reflected by the reflective mirror on to the collimator, it becomes parallel and is transmitted to the dispersion and diffraction grating, producing a continuous monochromatic spectrum. The spectrum travels back to the collimator, and then focuses at the exit slit. The monochromatic light of a given band width selected by the exit slit then goes through the condensing lens to the center of the sample. The light transmitted through the sample is finally received by the photocell. 1 2 4 5 3 6 12 11 10 9 8 7 1---- collecting mirror 2 --- filter 3 --- tungsten-halogen lamp 4 --- entrance slit 5 --- reflective mirror 6 --- collimator 7 --- grating 8 --- exit slit 9 --- condensing lens 10 --- sample holder 11 --- shutter 12 --- photocell 6. Installation, Operation and Maintenance 6.1 Installation 6.1.1 Before installation, check the safety of the instrument, the voltage of the power supply and the ground connection. 6.1.2 Calibrate the instrument before it is put to use, as the wavelength accuracy may be affected by handling in transportation. 6.2 Operation Turn on the power switch and preheat the instrument for 30 minutes. The four keys on the keyboard are 1) A/T/C/F key, 2) SD key, 3) / 0% key and 4) / 100% key. 6.2.1 The A/T/C/F key is used to switch between A, T, C and F modes. 5
A --- Absorbance T --- Transmittance C --- Concentration F --- Factor 6.2.2 The SD key has two functions: a) to be used in RS232 serial interface and data transmission ( one-way transmission from the instrument to the computer ) b) when in F mode, to confirm the current F value, and to switch automatically to C, whose value will be calculated (C=F* A) 6.2.3 The /0% key is used: a) to set zero. It is effective only in T mode. Uncover the sample compartment, press the key, and it will show 000.0. b) as the descending key. When in F mode, press the key and the F value will decrease by 1. Holding the key will speed up the decrease. When the F value reaches 0, a press on the key will change the value to 1999. 6.2.4 The /100% key has the following two functions: a) When in A or T mode, close the sample compartment, press the key and it will read 0.000 or 100.0. b) To be used as the ascending key (effective only in F mode). Press the key and the F value will increase by 1. A long press will speed up the increase. When the F value reaches 1999, another push of the key will change it to 0. And still another push it will increase by 1. Example: Let the F value be 1500. Method Ⅰ a) Press the A/T/C/F key to set it at F mode. b) If the current F value is 1000, press the Δ/100% key until it goes up to 1500. c) Press the SD key, and the current F value shows 1500. Then C mode automatically appears. Suppose the A value measures 0.234, then the C value reads 0.351. Method Ⅱ a) Press the A/T/C/F key to switch it to F mode. b) If the current F value is 1000, press the Δ/100% key until it reaches 1500. Press the A/T/C/F key again to go to C mode. If the A value measures 0.234 then the C value reads 0.351. 6.3 Maintenance 6.3.1 To ensure the steady operation of the instrument, it is recommended to use an AC voltage stabilized power source. 6.3.2 After operation, turn off the power and cut off the power supply. 6
6.3.3 Put a dusk cover with some desiccants over the instrument when it is not in use, to keep it clean and dry. 6.3.4 After months of operation or after it is moved, the instrument should be checked for its wavelength accuracy. 7. Calibration and Troubleshooting After a long time of use, the instrument needs calibrating or repairing, as its performance index may have changed. Here are some tips. 7.1 Replacement of tungsten-halogen lamp Put on a clean pair of working gloves before you replace the lamp. Be sure the power is off. Loosen the two clamping screws on the lamp bracket with a wrench. Remove the damaged lamp and fix the new one. Set the wavelength of the instrument at 500nm. Switch on the power. Move the lamp up and down and from side to side, until its focus falls exactly on the entrance slit. Observe the reading in T mode without adjusting the Δ/100% key. Readjust the lamp to make the reading at its maximum. Finally, tighten the two screws. Caution: The two clamping screws serve as the voltage output end of the tungsten-halogen lamp. Be sure that short circuit never occurs when the lamp is turned on. 7.2 Calibration of wavelength accuracy Spectrophotometer 721N is checked for its wavelength accuracy by a point-to- point method against the two characteristic absorption peaks of a didymium filter 529nm and 808nm. In case the point-to-point measurement shows a wavelength different from the peak wavelength of the didymium filter (maximum permissible error is ± 2nm), remove the wavelength knob, loosen the three positioning screws on the wavelength dial, adjust the dial pointer to the characteristic absorption peak wavelength value, and tighten the screws. 7.3 Troubleshooting Troubles Causes Remedies 1 No functioning after 1Power supply not connected 1Check power line power is on 2Power fuse melted 2Replace fuse 3Loose contact of power 3replace power switch switch 2 Unstable display 1Insufficient warm-up time 1Ensure 20 minutes 2Excessive vibration, warm-up time strong air current 2Improve working near light source,or conditions strong external light 3Check power 3Unstable voltage voltage 4Poor grounding 4Check ground connection 7
3 Unable to set zero 1Shutter blocked 1Repair shutter 2Amplifier failure 2Repair amplifier 4 Unable to set 100% 1Tungsten-halogen lamp 1Check or repair not lit lamp power circuit 2Inaccurate light path 2Readjust light path 3Amplifier failure 3Repair amplifier 5 Concentration incor- 1Display board out 1Repair or replace rectly calculated of order display board 8. Standard Package 1) 1 main set 2) 1 power supply cable 3) 1 accessory kit 4) 5 fuses (3A) 5) 1 filter (for use from 330nm to 371nm) 6) 1 operating manual Note: If there is any change in this package, an accessories & spare parts list attached should be referred to as final. 9.Storage and Warranty period 9.1The instrument should be stored in its original manufacturer s packaging in a room where the ambient temperature is kept between 5 and 35, relative humidity no more than 85%, and the air contains no harmful, corrosive substance. 9.2 The manufacturer will repair the product free of charge if, during the period of twelve months from the time of its original purchase, this product proves defective under normal handling, use and service due to defective materials or workmanship (easily worn parts excluded).. 8