There are many factors affecting the calibration results of the densitometer. This paper analyzes the influence of the main standard, supporting equipment, calibration environment, calibration method and personnel proficiency on the calibration results of the densitometer, and points out the correct operation method. Through the calibration of the density meter with the China Institute of Metrology, the calibration results are accurate and reliable.
Densitometer is the most commonly used instrument for measuring liquid density. It has been widely used in industrial and agricultural production, scientific research, medical and defense, and national defense. With the rapid development of various industries such as petrochemical, food industry, medical and health, there are clear requirements for the accuracy of density values in controlling production processes, ensuring product quality, trade, etc. Whether the value of the density meter is accurate or not Reliable, directly affects the accuracy of liquid density measurements, so it must be calibrated.
The accuracy of the densitometer calibration results is influenced by a number of factors, not only related to the technical level of the main standard, density test solution and technicians, but also to the method of operation. Based on years of experience in density measurement work, the author puts forward some insights on the problems in density meter calibration. By analyzing various factors affecting the density meter calibration, the correct operation method of density meter calibration is pointed out.
1, The working principle of the density meter
The direct comparison method is used to carry out the density meter calibration according to the requirements of the verification procedure. The densitometer and the standard densitometer are simultaneously immersed in the same test solution, and the indication values on the index table are directly compared. If the calibration liquid is different from the liquid actually used by the calibration densitometer during calibration, the capillary constant correction is performed, and finally After a series of calculations, the correction value of the calibration meter is obtained.
2. Densitometer calibration process
2.1 Density meter cleaning
Before calibration, the standard density meter, the calibrated densitometer, the calibration cylinder, the agitator, etc. are washed and dried, and then placed in the calibration room. The cleaned glass instrument should not be covered with water drops. The cleaned density meter should not be touched by hand. The stem of the ruler. If the appliance is not clean, it will not only contaminate the density fluid, but also cause the densitometer stem to be exposed to too much liquid, introducing errors into the measurement results.
2.2 Density meter density liquid preparation
Carefully pour the density solution into the test cylinder and stir evenly. Adjust the density liquid to within 2 scales of the calibration point of the standard density meter. Otherwise, the measurement result will have a large error.
2.3 Density meter visual inspection
At present, the quality of densitometers on the market is uneven. Some manufacturers of density meters are driven by interests, ignoring the quality of products. Some enterprises even do not obtain the “production measurement instrument license” and privately produce density meters. Therefore, a visual inspection must be performed before calibration. There shall be no fog, nodules or cracks in the density meter, and the ballast chamber shall not be loose. If one item does not meet the requirements, it shall be judged as unqualified and no indication calibration shall be performed.
2.4 Density meter calibration
Lightly lift the standard and the top of the dry tube of the densitometer by hand, that is, the left and right hands should pinch the upper end of the densitometer main pipe, do not pinch it to the dry pipe scale, and slowly immerse it in the density liquid, and then slowly approach the equilibrium position. Let go, otherwise, the density meter will fluctuate up and down, and the dry tube is filled with liquid, which increases the quality of the densitometer and makes the measurement result low.
Therefore, when calibrating, be sure to operate proficiently so that it fluctuates within the three scale values of the calibration point and stabilize for 1~3min. This is especially true for viscous liquid such as sulfuric acid aqueous solution or ethyl hydrogen sulfate or potassium iodide-imidium iodide. Important, especially potassium iodide and mercury iodide. In addition, the densitometers do not collide or adsorb together, and they cannot adhere to the inner wall of the verification cylinder. Otherwise, due to the presence of supporting force, the buoyancy is increased correspondingly, which brings errors to the calibration results.
For the liquid to be fully stirred, so that the liquid temperature in the cylinder is even and stable, and at the same time, attention should be paid not to generate bubbles. Because of the presence of bubbles, the inside of the liquid is not uniform, and the bubbles can also adhere to the densitometer, so that the volume of the densitometer increases, resulting in Value error.
Differential pressure densitometers have been widely used in the industrial field, so how to choose a suitable density meter has become one of the major concerns of manufacturers and customers. When users want to buy a density timer, we must make clear the following questions:
1. The user should use a densitometer to measure what medium is used, and whether the measured medium is corrosive. Corrosive and non-corrosive manufacturers choose different linings when they are manufactured, so we must know this problem;
2. Choose whether to install the pipe or the tank during installation. If it is installed in the pipeline, it should be clear how much the pipe diameter is. If it is installed in the tank, you should know whether to choose side or top loading;
3. Know what the thermometer is working for;
4. What is the approximate range of variation of the measured liquid density;
To figure out the above problems, it is absolutely necessary for the user to choose a differential pressure densitometer. Only by clarifying all the problems, the manufacturer can make a density meter that satisfies the user according to the needs of the customer.
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