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15 Questions about Laboratory Analytical Balance(Part 3)

Date:2020-11-10

Question 14. How to check the accuracy of electronic balance?

The electronic balance is one of the routine laboratory instruments and is a precision electronic instrument. Therefore, the accuracy of the electronic balance should be checked before using it. Then how to test the balance before use, let me introduce you specifically:

1. Inspection of mechanical parts

(1) Check the switch (whether it is too tight, too loose, or the eccentric shaft does not rotate to the lowest point or exceeds the lowest point);

(2) Partial inspection of the column (verticality of the column, level, base plate);

(3) Check the beam part of the electronic balance (whether the agate knife edge is worn, whether the sensing weight and balance weight are slippery, whether the pointer is perpendicular to the beam);

(4) Check the suspension system (whether the lifting lugs are stuck, tilted, or not, whether the dampers are stuck or not, or whether the scale is tilted);

(5) Whether the adder is stuck;

2. Inspection of optical system

(1) Whether the bulb is not bright, the brightness is not enough, or whether it is a permanent light;

(2) Whether the light screen is normal (no light, weak light, black-red light or strip light);

(3) Whether the scale is normal (whether the scale is clear, can't see the scale, the scale is inclined, the marking line is curved);

3. Inspection of measurement performance

(1) Whether the zero point of the empty scale has changed;

(2) Whether the empty scale and full scale are consistent;

(3) Use two full weights to try to compare the balance deviation. After the two full weights are exchanged, eliminate the weight difference and calculate the deviation from the balance;

(4) Put the same small weight on the left and right plates respectively, and compare the difference in sensitivity between the two plates, which is called "partiality".

3. Inspection of measurement performance

(1) Whether the zero point of the empty scale has changed;

(2) Whether the empty scale and full scale are consistent;

(3) Use two full weights to try to compare the balance deviation. After the two full weights are exchanged, eliminate the weight difference and calculate the deviation from the balance;

(4) Put the same small weight on the left and right plates respectively, and compare the difference in sensitivity between the two plates, that is, "partiality".

Electronic Balance

 

Question 15: Analysis of the adjustment method of the electronic balance

Lab electronic balances will produce measurement errors due to uneven placement during the weighing process. The higher the weighing accuracy, the greater the error. For this reason, most electronic balances provide the function of level adjustment.

There is a level bubble behind the balance. The level bubble must be located in the center of the liquid chamber, otherwise the weighing is not accurate. After adjustment, try not to move it, otherwise, the vial may shift and need to be readjusted.

Electronic balances generally have two leveling bases, which are generally located at the back and some at the front. You can adjust the level of the balance by rotating these two leveling bases.

The specific adjustment method is as follows:

1. Rotate the left or right to level the base and adjust the level bubble to the center line of the liquid cavity.

Rotating a left or right leveling base alone is actually adjusting the inclination of the balance, and the level bubble can definitely be adjusted to the center line. The key is to adjust which leveling base. Beginners can judge like this: first manually tilt the balance to make the leveling bubble reach the center line, and then look at the leveling base, which one is higher or lower, adjust the height of one of the leveling bases to move the leveling bubble to the center line.

Note: The next step can be taken after reaching the central line

2. Rotate the two leveling bases at the same time, the amplitude must be the same, both clockwise or counterclockwise, so that the level bubble moves on the center line, and finally moves to the center of the liquid cavity. If the leveling base rotates clockwise or counterclockwise at the same time, the inclination of the balance remains unchanged, so that the vial will not deviate from the center line. As long as there is no problem with the direction of rotation, it can definitely reach the center of the liquid chamber. Rotate clockwise or counterclockwise at the same time: Rotate and level the base at the same time with both hands (one hand to the chest, one hand to the chest, in the opposite direction, generally rotating the base clockwise or counterclockwise at the same time).

3. Direction problem: It is not easy for beginners to judge the direction. You can manually raise the base or another support to move the blisters to the center, and then observe the position of the leveling base to see if it needs to be raised or lowered. Note that in the second step, the amplitude of both hands must be the same. If they are inconsistent, the drop will shift from the center line. If it shifts, just start again from the first step. After proficiency, the level bubble of an electronic balance can be leveled in 1-2 minutes.