Study on a New Method for Online Calibration of Flowmeters
Time:2022-11-09 Read:689
Reading guide: Flowmeter is a measuring instrument used to measure flow, which is widely used in industrial and agricultural production, energy measurement, national defense construction, environmental engineering, transportation, people's life, and other fields, and plays an important role in the measurement field.

Online Calibration of Flowmeters

In order to adapt to different applications on different occasions, there are various types of flowmeters. The flowmeter used in the railway locomotive maintenance system is mainly used for the metering and statistics of the fuel injected into diesel locomotives and the fuel supply in the oil depot. It is a volumetric liquid flowmeter.

Verification status of flowmeter

As a measuring instrument, the flowmeter needs periodic verification to ensure the accuracy and reliability of the measured value. The verification basis of the positive displacement liquid flowmeter is the verification regulation of JJG667-2010 Liquid Positive Displacement Flowmeter. At present, Beijing Bureau Group mainly uses the volume method for on-site online verification to determine the metering accuracy of the flowmeter. The standard instrument is a standard metal measuring instrument, commonly known as the standard tank (generally 100L). Connect the flow meter to the oil filling port of the standard tank through a hose. 

During calibration, open the flowmeter stop valve, inject the oil into the standard tank through the measured flowmeter, and record the flowmeter reading. When the standard tank is full, close the stop valve. At this time, read the flowmeter again. Finally, the calibrator reads the reading of the standard measuring tank and compares it with the cumulative flow value of the flowmeter to be measured. The difference obtained is the indication error of the flowmeter to be measured. The verification method has the following problems in the actual verification process.

Online Calibration of Flowmeters manufacturers

Few inspection points

According to the verification regulation of JJG667-2010 Liquid Volumetric Flowmeter, the flowmeter with an accuracy level of no less than 0.5 shall have at least 5 verification points, including the maximum flow point and the minimum flow point. However, in actual verification, due to the large size and bulkiness of the standard tank, the 100L standard tank is 1.26m high and 0.8m in diameter. The verification unit can only carry two vehicles at most each time, and the large capacity standard tank can not be carried at all. Therefore, only common points can be verified on-site, and the 5 verification points of the flowmeter cannot be covered.

Short running time

The regulation requires that after the flowmeter is installed on the calibration device, the calibration test can be carried out after the flowmeter runs for (1-5) min under the maximum flow. Each calibration point shall be operated for at least 5min for calibration. However, taking the LC50 flowmeter as an example, the maximum flow is 24m3/h, namely 400L/min; The minimum flow is 2.4m3/h, i.e. 40L/min. At the maximum flow rate, it is full within 15s, and even at the minimum flow rate, it is full within 2.5min. The running time cannot meet the requirements of the regulations.

Deviation easily caused by verification conditions

The flow meter and the standard tank are temporarily connected with rubber pipes. Due to environmental factors, sometimes the distance between them is more than 10 meters. After the standard tank is filled with a closed stop valve, there is still residual diesel oil in the rubber hose. The flow of this oil is included in the flowmeter but not in the standard tank. The rubber tube is calculated as per the inner diameter of 50mm. In this case, the amount of oil left in the rubber tube is about 20L, with obvious deviation. In order to solve this problem, the rubber tube is often filled before verification on-site, but it is impossible to determine whether the residual amount is equal each time during subsequent verification, so this deviation is reduced but still exists.

Online Calibration of Flowmeters wholesale

Serious waste of oil products due to difficulty in the oil return

When the standard tank is used for inspection, the tank shall be emptied for the next inspection after the oil is filled. However, due to the limitation of on-site equipment, the drained oil cannot be discharged back to the oil depot at all, and can only be temporarily stored in waste oil drums for other purposes. Each verification point on the site shall be verified at least three times, excluding the test run before verification. Therefore, no less than 500L of waste oil generated each time cannot be discharged back to the oil depot. If the diesel oil is calculated as 5 yuan/L, the verification of one flowmeter will consume 2500 yuan of diesel oil. This will not only create potential safety hazards but also cause serious waste.

The actual verification work is difficult to operate

In order to facilitate the refueling of locomotives, most of the refueling equipment is distributed in the middle of the two lines, and vehicles loaded with standard tanks cannot enter the site, so the standard tanks must be manually unloaded from the vehicles and transported to the verification site. As the standard tank is very heavy, at least 2 strong laborers are required to carry it in place. In order to drain oil into the oil drum, we should also try to raise the standard tank. During the calibration, if the refueling of the locomotive is encountered, it will be forced to stop. It often takes several hours to calibrate a flowmeter, which is time-consuming and laborious.

A New Method for Online Calibration of Flowmeters

In order to improve the current verification method of the flowmeter of the Group Company, the portable ultrasonic flowmeter can be used for online calibration.

Online Calibration of Flowmeters factory

Principle and method of online calibration of portable ultrasonic flowmeter

The ultrasonic flowmeter is generally the time difference method, and its working principle is that the ultrasonic beam emitted by the transmitter probe travels through the pipe and shoots into the fluid at a certain angle, refracts through the pipe many times, and passes through the fluid, and then is received by the receiving probe. In the process, the instantaneous average velocity of the fluid is calculated according to the linear formula through the different propagation times of the ultrasonic wave in the forward and reverse flow of the fluid. The fluid flow can be measured by combining the cross-sectional area of the pipe and other known parameters.

In recent years, ultrasonic flowmeter has been used more and more in pipeline flow measurement. The portable ultrasonic flowmeter can realize non-contact measurement by clamping the ultrasonic probe onto the pipe. The method is to take the ultrasonic flowmeter as the standard meter, clamp it on the pipeline to be measured, and then read the cumulative value between the ultrasonic flowmeter and the flowmeter to be measured in a specific time period.

Advantages of portable ultrasonic flowmeter

The portable ultrasonic flowmeter has obvious advantages in practice: the equipment is small in size and easy to carry; the External clip probe, is easy to install; It can realize non-contact measurement with small pressure loss; It can be applied to different types of flow meters and is widely used; It can be used for different mediums and pipe diameters of different sizes, and is adaptable to the temperature range (- 20 ℃ to 55 ℃); It can be tested while refueling the locomotive, and there is no oil return problem.


The future development trend of measurement is calibration, especially online calibration. For flowmeter, online calibration has obvious advantages. The author thinks that the application of a portable ultrasonic flowmeter to online calibration of the flowmeter is a feasible method, which can greatly reduce the workload of flowmeter calibration, reduce energy and capital consumption, and should be popularized.