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Hi, I’m the Industrial Control Assistant. Every day, I share a little piece of knowledge related to industrial control. In the previous installment, we discussed the working principle of mass flow meters; today, we’ll give a brief overview of the principle behind volume flow meters. Let’s take a look together. In principle, a PDF is a hydraulic engine that absorbs a small amount of energy from the fluid; this energy is used to overcome the friction resulting from the rotation of the flow measurement element and its accessories, while simultaneously creating a pressure drop at the inlet and outlet ends of the instrument. Let the \"cyclic volume\" of the flow meter be υ, and let the number of rotations of the gear within a certain time period be N. Then the volume of fluid that passes through the flow meter during that time is V. The rotation of the elliptical gear is transmitted to the counter via a magnetic seal coupling and a transmission reduction mechanism, which then indicates the total amount of fluid that has passed through the flow meter. By attaching a transmitting device and combining it with an electrical display instrument, it is possible to transmit either the instantaneous flow rate or the cumulative flow rate. Although there are many segmentation methods to create PDFs in various formats, most of them share similar basic characteristics. The main cause of errors in PDF is the leakage volume through the gap between the moving measuring element that divides individual fluid volumes and the stationary measuring chamber. One of the reasons for leakage is to overcome the frictional resistance of moving parts ； The second is the effect of pressure drop caused by the hydraulic resistance of the instruments. The block diagram of the structural gear flowmeter is shown in Figure 2. The flow meter consists of two main parts: the measuring unit and the accumulation unit; optionally, an automatic temperature compensator, an automatic pressure compensator, a transmitter, and high-temperature extension (heat dissipation) components can be added. 2) Transmission mechanism: The transmission mechanism includes a magnetic coupling (or mechanical sealing device) and a speed reduction and adjustment mechanism. The speed adjustment mechanism is composed of a \"gear pair\". 4) Automatic temperature compensator: It continuously and automatically compensates for changes in the temperature of the medium being measured; there are both mechanical and electrical/electronic types available. 6) Transmitter: Transmitters come in various forms, including contact and non-contact types. Well, that’s all for today’s content. If there’s anything you’d like to know or discuss, feel free to leave a message anytime. New updates will be posted regularly, so please stay tuned.