What are the main classifications of positive displacement meters? What are the measurement principles?

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1. Practical principles and operating steps of pipettes

Practical principles and operating steps of pipettes The working principle of pipettes is mainly divided into two categories according to the working principle: gas piston pipettes and external piston pipettes. Air push: The working principle is to push the piston through the expansion and contraction of the spring, remove some air, use atmospheric pressure to suck in liquid, and then push the air out of the liquid delivery body by the piston. There is an air column between the liquid and the piston, which is suitable for conventional aqueous solutions. External piston type pipette (Positive separation): The working principle is to extract and dispense liquid through the continuous movement of the piston inside the pipette or suction head. The piston comes into direct contact with the liquid without an air column. This design is not only suitable for conventional aqueous solutions, but also particularly suitable for problematic liquids such as high viscosity, volatility, and foaming. The operation steps of a pipette include selecting the appropriate pipette tip: The pipette tip and pipette tip are equally important, and only high-quality pipette tips can fully reflect the accuracy of the pipette. It is recommended to use the manufacturers original suction head to ensure smooth and flawless tip and uniform height, thereby ensuring the reproducibility of experimental results. Choose a pipette that is suitable for the range: The optimal range for using a pipette is 30% to 100% of its maximum range. Using within this range can ensure the accuracy and precision of pipetting. Assembly of pipette tip: Insert the pipette tip vertically into the pipette tip, gentl

y press and tighten, do not knock up and down or shake left and right to avoid damaging the internal parts of the pipette. A pipette with elastic suction nozzle function can reduce the force required to assemble/detach the suction head, while ensuring the airtightness of the suction head assembly and improving the uniformity of the pipette. Adjusting the scale: Rotate the scale adjustment knob to achieve better accuracy when adjusting from a large range to a small range; When adjusting from a small range to a large range, it is best to first adjust it slightly larger and then return to the desired scale. Ensure accurate scale adjustment for precise pipetting operations. Liquid suction: Ensure vertical suction to avoid the pipette being tilted and causing a larger volume. Try to submerge the suction head shallowly to prevent liquid from remaining on the surface of the suction head; But at the same time, it should be submerged deep enough to prevent the absorption of air. Pre wet at least 3 times to fill the air column with saturated liquid molecules, especially when removing volatile liquids. The suction and discharge of liquid should be slow and uniform to improve the accuracy of pipetting. It is recommended to use an electric pipette to reduce human error. After suctioning the liquid, stay for a while, especially for large range pipettes, to ensure that the liquid completely enters the pipette tip. Liquid dispensing: When dispensing, the tip of the pipette should be placed against the inner wall of the container (especially for volumes below 20 μ L), and the angle of the pipette should be maintained between 20 ° and 45 °. When the volume is less than 10 μ L, directly pour the liquid to the bottom of the container. Ensur

What are the main classifications of positive displacement meters? What are the measurement principles?

1. Practical principles and operating steps of pipettes

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