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Definition of scientific term
Chinese name:
Analytical Balances
English name:
Analytical balance
definition:
The weighing range and reading capacity are suitable for a general term for a variety of analytical balances.
Applied discipline:
Mechanical Engineering (a subject); laboratory instruments and devices (two subjects); balance instrument - name of the balance (three subjects)
Before weighing, check whether the balance is normal, whether it is in the horizontal position, whether the lifting ear and the circle code are off, whether the glass frame is clean inside or outside. The analytical balance is an indispensable instrument in the quantitative analysis work, generally refers to the accurate weighing to 0.0001. Balance of grams (0.1 mg).
classification:
There are many types of analytical balances: mechanical, electronic, manual, semi-automatic, fully automatic, and so on.
Features
Analytical balances are more accurate weighing instruments than platform scales and can be accurately weighed to more than 0.0001g (ie 0.1mg). There are many types of analytical balances, but the principles and methods of use are basically the same.
principle
The mechanical balance is based on the principle of leverage. When the balance is balanced, the mass of the object is equal to the mass of the weight.
Electroanalytical balances use electromagnetic balancing methods. Because the weight is weighed, calibration is needed to eliminate the effects of gravitational acceleration.
Precautions:
(1) The action should be slow and light: the lifting pivot slowly opens and opens to the maximum position, and slowly rotate the circle code to prevent the circle code from falling off or being misplaced.
(2) The weighing object cannot be placed directly in the weighing pan. According to the different properties of the weighing object, it can be placed in a paper sheet, a surface dish or a weighing bottle. Can not be called the object that exceeds the maximum weight of the balance.
(3) The balance cannot be replaced during the same weighing process to avoid relative error
How to use the electronic analytical balance:
1. Check and adjust the balance to the horizontal position.
2. Check the power supply voltage beforehand (if necessary, configure the voltage regulator), and warm up to the required time according to the requirements of the instrument.
3. After preheating for a sufficient time, the balance switch is turned on and the balance automatically performs sensitivity and zero adjustment. After the stability mark is displayed, formal weighing can be performed.
4. When weighing, place the clean weighing bottle or weighing paper on the weighing pan, close the side door, press the peeling button lightly, the balance will automatically check the zero point, and then gradually add the substance to be weighed until the required weight.
5. The weight of the substance is the actual value displayed on the display when the “→†mark appears in the lower left corner of the display.
6. At the end of weighing, the weighing bottle (paper) should be removed in time, the side door should be closed, the power supply should be cut off, and the usage registration should be completed.
Mechanical analysis balance method:
1. Slowly turn the lifting pivot button, open the balance, and observe the swing range of the pointer. If the pointer swings to one side, adjust the zero adjustment screw on the balance beam.
2. Put the material to be weighed from the left door into the center of the left plate. Press the first name on the balance of the tray and take the appropriate weight with the tweezers. Put the appropriate weight from the right door to the center of the right plate and slowly raise it with the left hand. Lifting pivot button (Because the difference in mass between the two sides of the balance is too large, the full lift lifting button may cause the lifting lug to fall off. Damage the cutting edge), depending on the deviation of the pointer, the weight is reduced from large to small. After the gram group weight is tested, add the game code adjustment. In the process of adjusting the balance of the balance code, the right door must be closed. At this time, the lifting pivot button can be raised all the way. After the pointer swings to stop, the scale indicated on the label should be at or near zero.
Weighing method:
(1) Direct weighing method: If the solid sample is not hygroscopic and stable in the air, direct weighing can be used. First accurately weigh the quality of the clean container on the balance, then use a spoon to take a proper amount of the sample into the container and weigh its total mass. The values ​​of the two masses are subtracted to give the mass of the sample.
(2) Reduction method: The weighing method is generally used for weighing on the analytical balance. The exact mass of the sample and the weighing bottle is first weighed, and then the sample in the weighing bottle is poured into a container of the drug to be held, and the estimated amount is close to the amount obtained. After filling the medicine, cover the weighing bottle and place it on the balance to accurately weigh its quality. The difference between the two masses is the mass of the sample. If too many medicines are poured into the container at one time, the weight must be discarded and never returned to the weighing bottle. If the sample to be poured is not enough, it can be added once more, but the number is less.
(3) Designation method: For samples with stable properties, sometimes for the purpose of calculation, samples of the specified quality may be weighed. When weighing by the specified method, place a watch glass on each side of the balance plate (their mass is as close as possible), adjust the balance point of the balance to the center scale, and then add a fixed mass weight to the left balance pan. Add the sample to the right balance pan (this is convenient to pick and place the sample) until the equilibrium point of the balance reaches the original value. At this time, the mass of the sample is the specified mass.
4. When using the analytical balance, in addition to the relevant operating rules of the pallet balance, it should also be noted that: when adding the weight, picking up the scale or other reasons, the balance beam should be supported first, otherwise the knife edge will be damaged. Use the most important one of the balance rules. The balance door should be closed every time it is weighed. When the balance is turned on after the weight is added, the pointer swing should be controlled between 2 and 4 grids. The sample is weighed and weighed in a clean and dry weighing bottle or watch glass. The weighing bottle should not be taken by hand and should be taken with a filter paper strip. At the end of the weighing, check whether the balance beam is supported, whether the weight is complete, whether the medicine is scattered into the balance, whether the balance door is closed, and whether the cloth cover is covered. After the balance has been used for a period of time, it must be sent to the metrology department for verification and adjustment. The overall cleaning of the balance should be carried out twice a year.
Major manufacturer
At present, the common electronic analytical balances are: Sartorius, Germany, METTLER, Japan, Shimadzu, Japan, AND, Shanghai, Shenyang, etc.
Operating procedure
1. The use of the rotary switch must be opened and closed slowly and evenly. If the switch is too fast, the blade will be damaged, and the measurement error will occur due to excessive shaking.
2. At each weighing, the balance should be closed. Never increase or decrease the weight when the balance is opened, or place the weighing object in the weighing pan.
3. When weighing, you should first estimate the added weight first, then turn on the balance, observe the pointer offset, then increase or decrease the weight, and then turn the balance back on until the reading in the projection screen reaches 10mg.
4. When the object is below 10mg, it can be read directly on the projection screen.
5. The indoor temperature of the balance should be kept at 20±2°C to avoid sun exposure and eddy current attack or single-sided cold and heat. The silicon germanium desiccant should be placed in the frame cover. Do not use acidic liquid as a desiccant.
6. The object to be weighed should be placed in the center of the weighing pan and must not exceed the maximum weighing of the balance.
7. Objects that are too hot and cold and contain volatile and corrosive substances should not be weighed in the balance.
8. After the balance is used, the brake should be closed and the weight index should be hovered to zero, and the balance should be covered with a cover.
9. When the entire balance is to be moved, the beams, left and right weighing pans, ring weights, lifting lugs and other parts must be carefully removed and placed in the box. Other parts cannot be removed at will.
Main Specifications
1. Maximum weighing: 200g
2. Minimum division value: 0.1mg
3. Mechanical plus code range: 10mg~199.99g
4. Optical reading range:
5. Differential scale full value: 10mg
6. Each small scale value: 0.1mg
7. Weighing pan diameter: 7.5cm high 15.5cm
8. Transformer: Input 220V output 6.2V 50Hz
9. Balance appearance: length 39 × width 30 × height 44 (cm)
10. Net weight: 18Kg
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