Problems with double-flange transmitters
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I’m just starting out in this industry, so I have a humble question. How do double-flange transmitters measure flow and level by detecting pressure? How is this distinguished? Is the conversion done at the control center? I saw that for measuring flow rate, pressure, and liquid level on-site, the same type of transmitter is used.
The liquid level difference is related to the pressure difference; it can be converted through range conversion in the DCS, or it may first go to a secondary meter for processing. If the flow rate is measured using a throttling device, it is also a pressure difference, so the pressure difference signal can be converted as well.
A double-flange type is called a differential pressure transmitter, I guess. There is also a orifice plate in the middle. A differential pressure flow meter operates on the principle of placing a flow resistance element in the pipeline; as the fluid passes through this element, a differential pressure is generated. There is a definite numerical relationship between this differential pressure and the fluid flow rate. By measuring this differential pressure, the fluid flow rate can be determined and converted into an electrical signal for output.
The pressure value can be converted into liquid level height; modern transmitters are capable of directly converting the liquid level, or the conversion can be carried out via an analog signal at the terminal.
Using the pressure formula ΔP=ρgh, a double-flange transmitter can determine the value of ΔP. Taking level measurement as an example, once the density ρ of the medium and the acceleration due to gravity g are known, the height of the medium can be determined. Of course, transmitters generally output a 4-20mA signal; by connecting it to a DCS and setting the appropriate range, it is possible to know the conditions at the site as well
P=ρGH → H=P/ρG. Liquid levels are generally expressed as percentages; the magnitude of pressure corresponds to the level of the liquid, and any change in pressure corresponds to a change in the liquid level. Setting the theoretical pressure value corresponding to the desired liquid level defines the range, and the percentage output represents the percentage of the liquid level.
Measure pressure separately at the high and low ends, perform calculations internally, and transmit the signals to the control center
Because all of these ultimate testing elements you mentioned are pressure or differential pressure values; it’s just a matter of using the appropriate calculation formulas to convert these measured pressures or differential pressures into intuitive display values within the control system, based on corresponding relationships.
Is this h the liquid level height? How is that traffic measured? ?
The friend above has already explained clearly the relationship between pressure and liquid level height. Measuring flow rate by differential pressure is known as differential pressure flow metering. In addition to a differential pressure transmitter, it also requires the use of a throttling device that operates on the principle of differential pressure, such as orifice plates, venturi tubes, average velocity tubes……there are many such devices. The throttle element is placed inside the pipeline; as flow passes through it, a pressure difference is generated. This pressure difference is measured by a transmitter, which then captures and outputs it. The simplest relationship is that there is a square-root relationship between differential pressure and flow rate; there are many posts on this topic