What is a Peak Flow Meter?

Flowmeter tube is a kind of equipment. Due to the unique structural design inside the flowmeter, it is suitable for measuring liquids and gases. It is an all-metal structure, with indication type, electric remote transmission type, corrosion resistance type, high voltage type, jacket type, explosion-proof type.

Aiming at the difficulty of detecting the adhesion of the Coriolis flowmeter in the tube of the Coriolis flowmeter, a method for detecting the adhesion of the Coriolis flowmeter in the tube based on density measurement was proposed. First, on the basis of analyzing the relationship between the vibration frequency of the vibrating tube and the density of the liquid in the tube, a phase-matching-based algorithm is used to track the frequency, and whether the tube is attached according to the change in frequency. The relationship between the density and the density, the relative error of the density measurement is less than 0.3%; finally, an adhesion detection experiment was performed by dripping solder. ^[1]

Due to the unique structural design of the flowmeter, welding needs to be performed inside the flow tube. The biggest difficulty is that the welding process is not observable and non-destructive testing is not possible. Therefore, a large number of tests on the welding process are needed to ensure mass production It was able to obtain qualified and consistent welds. Using Minita's DOE (Design of Experiments) method, it successfully achieved the selection of the optimal process parameters and passed the process evaluation. ^[2]

Selection of key elements of flowmeter tube

First list the key factors that affect the quality of the weld, then analyze the scores one by one, and finally select the four most important key factors:

(1) Tungsten electrode position: the horizontal distance from the root of the pipe joint to the center of the tungsten electrode. Because the thickness of the tube is very different, if the tungsten electrode is facing the joint, the thinner flow tube may be burned through, so the tungsten electrode needs to be offset to the thicker side by a certain distance.

(2) Peak current: The current at the peak when the pulse is used.

(3) Pulse frequency: The frequency of the pulse is determined by the peak time and the base time.

(4) Tungsten pole angle: the angle formed by the tip of the tungsten pole. ^[2]

Flow tube root penetration

Set 3 levels of range for 4 key elements, set the upper and lower limits of each element, and enter Minitab software to automatically assign the test sequence to be performed. A total of 11 groups of tests will be performed.

Minitab Flowmeter tube Minitab analysis results

After analysis by Minitab software, the main effect = 0.036 and the interaction effect = 0.015. Both the main effect and the interaction effect value are less than 0.05, which proves that the results are reliable.

Define the tungsten electrode position as A , the peak current as B , the pulse frequency as C , the tungsten electrode angle as D , and the root penetration as Y , then:

Y = -141.484 + 83.3023 A +0.981667 B +1.96737 C +0.468 D -0.570833 AB -0.983685 AC -0.2875 AD .

Test the optimal results again and optimize them to get the final optimal parameters.

Macro metallography obtained with optimal welding process parameters. It can be seen that the weld completely meets the requirements of the welding process, with an average penetration depth of 0.98mm, which is a qualified weld. ^[2]

Relationship between peak current of flowmeter tube and tungsten electrode position

Twelve sets of experiments were carried out, and a large number of macroscopic metallographic diagrams were obtained. Through the analysis of the penetration depths of these metallographic diagrams, the following two-dimensional relative relationship between the peak current and the tungsten electrode position and the change trend of the weld can be obtained.

When the tungsten electrode position is very close to the joint: when the current is small, the penetration depth is shallow, and there is a risk of not being welded; when the current is large, the penetration depth is large, but at the same time the supporting depth on the back is also very large, because there is no filler material, so There is a risk of undercuts on the back side, resulting in substandard welds. When the tungsten electrode is far away from the joint: if the current is small, the penetration depth is shallow, and there is a risk of not being welded in the depth direction, and at the same time, there is a risk that the weld is misaligned and not welded to the joint; when the current is large, the penetration is deep Large, but the deepest penetration is not at the joint, which proves that the penetration is not visible, there is no risk of undercutting on the back, but in the width direction, there is still the risk that the weld is misaligned and not welded to the joint.

That is, the four corners are connected into a large rectangle, and the optimal parameter obtained is probably at the center of the rectangle. Therefore, when the peak current and the position of the tungsten electrode change around the optimal parameter in a small range, a qualified weld can still be obtained. , Illustrates the inclusiveness and stability of the process. ^[2]

Appearance and gas protection effect of flowmeter tube weld

(1) In order to make the larger rectangular box larger, try to add a small welding gun swing based on the optimal parameters.

(2) Appearance of welding seam: The gas shielding effect should make the welding seam color reach the level above 5 in AWSD 18.2. The comparison of welding seam color under different pre-inflation time and the test result of oxygen analyzer will finally determine the gas protection. time. Combined with the main points of the process, the control of gas protection, with the extension of the pre-inflation time, the protection effect of the weld is gradually improved. The final pre-inflation for 3 minutes or more can reach the level of 2 to 3 in AWSD 18.2, which meets the requirements. ^[2]