Weighing methods and use rules of common analytical balance

01

Direct weighing method: if the solid sample is not hygroscopic and stable in the air, the direct weighing method can be used. First accurately weigh the mass of the clean container on the balance, and then use a spoon to take an appropriate amount of sample and add it to the container, and then weigh its total mass. The mass of the sample can be obtained by subtracting the two mass values.

02

Attenuation method: generally, the subtraction method is used for weighing on the analytical balance. First weigh the exact mass of the sample and the weighing bottle, and then pour part of the sample in the weighing bottle into the container of the drug to be filled until the estimated quantity is close to the required quantity. After pouring the medicine, put the weighing bottle on the back cover and put it on the balance to accurately weigh its mass. The difference between the two masses is the mass of the sample. If too many drugs are poured into the container at one time, the weight must be discarded and the weighing bottle must not be put back. If the poured sample is not enough, it can be added again, but the number of times should be less.

03

Designation method: For samples with relatively stable properties, sometimes in order to facilitate calculation, samples of designated quality can be weighed. When weighing with the specified method, place a watch glass on both sides of the balance plate (their mass shall be as close as possible), adjust the balance point of the balance to about the middle scale, and then add a fixed mass weight to the left balance plate, and add a sample to the right balance plate (it is convenient to take and place the sample) until the balance point of the balance reaches the original value. At this time, the mass of the sample is the specified mass.

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04

Designation method: For samples with relatively stable properties, sometimes in order to facilitate calculation, samples of designated quality can be weighed. When weighing with the specified method, place a watch glass on both sides of the balance plate (their mass shall be as close as possible), adjust the balance point of the balance to about the middle scale, and then add a fixed mass weight to the left balance plate, and add a sample to the right balance plate (it is convenient to take and place the sample) until the balance point of the balance reaches the original value. At this time, the mass of the sample is the specified mass.

The weighing bottle shall not be held by hand, but shall be clamped with filter paper strip. After weighing, check whether the balance beam is properly supported, whether the weights are complete, whether there are drugs scattered into the balance, whether the sky level door is closed tightly, and whether the cloth cover is well covered. After a period of use, the balance should be sent to the metrological department for verification and adjustment. The overall cleaning of the balance should be carried out twice a year.

Analytical balance is a type of balance, and it is more and more widely used in daily life. Do you know the structure of analytical balance? What are the types of analytical balance?

There are many types of analytical balance: mechanical, electronic, manual, semi-automatic, fully automatic, etc.

Calibration method of analytical balance: it can be divided into internal calibration type and external calibration type. The so-called internal calibration means that the electronic balance is equipped with internal calibration weights, which can be easily retrieved at any time and calibrated with one button. For external calibration, press the calibration key to manually calibrate the weight from the outside.

Electronic balance

1. Check and adjust the balance to the horizontal position.

2. Check whether the power supply voltage matches (if necessary, configure the voltage stabilizer) in advance, and power on and preheat to the required time according to the instrument requirements.

3. Turn on the balance switch after preheating for enough time, and the balance will automatically adjust the sensitivity and zero point. After the stability sign is displayed, formal weighing can be carried out.

4. When weighing, place the clean weighing bottle or paper on the weighing plate, close the side door, press the lower key lightly, the balance will automatically calibrate the zero point, and then gradually add the material to be weighed until the required weight.

5. The weight of the weighed substance is the actual value displayed on the display screen when the "→" sign appears at the lower left corner of the display screen.

6. After weighing, the weighing bottle (paper) should be removed in time, the side door should be closed, the power should be cut off, and the use situation should be registered.

Mechanical balance

1. Slowly turn the lifting pivot knob, 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. Place the material to be weighed from the left door into the center of the left panel, clamp the appropriate weight from the right door into the center of the right panel with tweezers according to the initial weight measured on the tray balance, and slowly lift the lifting pivot knob with the left hand (because the weight difference between the two sides of the balance is too large, the lifting lug may fall off and damage the blade), and add or subtract the weight from the large to the small according to the deviation of the pointer.

3. After the weight of the gram group is tested, add the traveling weight for adjustment. In the process of balance adjustment by adding a traveling weight, the right door must be closed. At this time, all the lifting pivot buttons can be raised. After the pointer swing stops, the scale indicated on the label should be at or near zero.