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Second, the design principle As the name suggests, the differential pressure type liquid level meter's measurement result is the pressure difference, but because the oil tank is often cylindrical, the area S of its cross section circle is the same, then, the weight and the height are in direct proportion relation. That is, as long as the P value is accurately detected, the inventory G of the actual oil product can be obtained. From the formula, the density is also inversely proportional to the height h. When the temperature changes, the actual liquid level rises despite the volume expansion or contraction of the oil. Or lower, the detected pressure is always the same. If the user needs to display the actual liquid level, media temperature compensation can also be introduced to resolve.
Third, the actual application of differential pressure transmitter in Wenzhou New Century Oil Depot project, the author applies this idea to the actual design. Design conditions: 2000m3 oil tank, diameter d = 14.5m, height h = 14m.
A table: Use ZD-1151LT flanged type explosion-proof differential pressure transmitter from Wenzhou Zhongda Automation Instrument Co., Ltd. The flange type is used to prevent sedimentation of the bottom of the tank and block the pressure tube. The transmitter range is 0～140kPa. .
The second time table: The XWP-T803 series intelligent light column display alarming instrument of Zonda Corporation was selected. The universal signal input can change the measuring range arbitrarily. The light column is used to display the liquid level and the number of oil products is displayed in numbers. Taking 6# tank as an example, the height is 14m.
At the top of the oil tank, a set of liquid level alarm device is designed to prevent the oil from overflowing and serve as double insurance. In the application, since the measured value is directly the tonnage, the oil tank can be stored regardless of the type of oil. The value displayed in the secondary table is the tonnage of the oil in the tank, which avoids the need to determine the density for conversion.
In general, the oil products entering and leaving the warehouse are often pumped through the oval gear flow meter. Because the accuracy of the flow meter is limited, the highest is only 0.2, and the density must be calculated. The results are often inconsistent, resulting in measurement disputes. Now because the results of the tank measurement are tons, and the accuracy can reach 0.2 or even 0.1, the measurement results are more accurate than the volumetric flowmeter. Although the absolute error of the measurement result is relatively large due to the resolution when a small quantity of oil is put in and out of the warehouse, the higher accuracy and the smaller relative error of the large amount of oil when entering and leaving the warehouse are other. Unmatched by measurement methods, it is particularly suitable for monthly, quarterly and annual inventory. Practice has shown that its main advantages are: 1 simple and convenient installation and maintenance; 2 intuitive and clear readings directly read the inventory of oil products; 3 exemption from the determination of density and conversion.
Fourth, pay attention to the problem (1) design and installation should take into account the pressure at the bottom of the tank to open as low as possible to eliminate the error caused by temperature changes, if necessary, the introduction of temperature compensation.
(2) In the case of tank tanks with horizontal cross-sections that are not equal (as small as above), compensation measures should be considered. If the second table selects XWP-C803 series level-capacity controller.
(3) In order to achieve a certain accuracy, if there is a breather valve at the top of the tank, a differential pressure transmitter must be used instead of a pressure transmitter. When open tanks or precision requirements are not high, pressure transmitters can be used directly to facilitate installation.
(4) As far as possible, the secondary meter uses a smart meter, which can easily change the range and achieve temperature compensation.
(5) When installing the differential pressure transmitter negative pressure chamber to install the water collector, and often to sewage, so as not to affect the accuracy of accumulated water.
Application and Solution of Differential Pressure Level Transmitter in Oil Tank Metering
The industry application and solution of differential pressure level transmitter in oil depot metering I. INTRODUCTION In the current measurement and design of oil tank oil level, it is more popular to use radar level gauge or float ball, buoy, steel. Band level gauges, etc. Although the radar level gauge has high precision but the cost is high, buoys, floats and other liquid level gauges are troublesome to install and maintain. The differential pressure level gauge is widely used in closed vessels such as boiler steam drums, but the measurement result is not a true liquid level. Therefore, there is little application for the measurement of liquid level in oil tanks. In fact, the precise liquid level of the oil tank is not very important. The actual level of understanding is not the liquid level. Instead, the actual level (ie tons) of the oil in the tank can be known by measuring the liquid level to prevent flooding. Therefore, it is also a good choice to use the differential pressure method to measure the liquid level (actually tons). Because the current application of differential pressure transmitter is very mature, such as differential pressure transmitter 1151,3051 and EJA, the technology is very complete, the precision can reach 0.075 level, and the price dropped sharply, the performance price is higher.