Knowledge of the hottest differential pressure tra

  • Detail

Knowledge of differential pressure transmitter

differential pressure transmitter is a transmitter that measures the pressure difference at both ends of the transmitter and outputs standard signals (such as 4~20ma, 1~5v). The difference between differential pressure transmitter and general pressure transmitter is that they have two pressure interfaces. Differential pressure transmitter is generally divided into positive pressure end and negative pressure end. Generally, the pressure of positive pressure end of differential pressure transmitter should be greater than the pressure of negative pressure section before measurement

generally, pressure transmitters are of piezoresistive and capacitive types.

II. Application of differential pressure transmitter in oil depot measurement

1 introduction

in the current measurement design of oil tank level in oil depot, the popular differential pressure transmitter due to economic factors is the use of radar level gauge or floating ball, buoy, steel band level gauge, etc. Although the precision of radar level gauge is high, the cost is also high, and the installation and maintenance of buoy, floating ball and other level gauges are troublesome. Differential pressure liquid level gauge is used in closed containers such as boiler drum. 2. The data of copper pipe pulse fatigue life testing machine is widely collected, but the measurement result is not the real liquid level, so it is rarely used in the design of oil tank liquid level measurement. In fact, the accurate liquid level of the oil tank in the oil depot is not very important. What users actually need to know is not the liquid level, but the actual amount of oil in the oil tank (i.e. tonnage) by measuring the liquid level, so as to prevent overflow. Therefore, it is also a good choice to use the differential pressure method to measure the liquid level (actually tons). At present, the application of differential pressure transmitters is very mature. Differential pressure transmitters such as 1151, 3051 and EJA have perfect technology, the accuracy can reach 0.075 level, and the price has fallen sharply, with higher performance and price

2 design principle of differential pressure transmitter

as the name suggests, the result measured by differential pressure transmitter is pressure difference, namely △ p= ρ g△h。 Since the oil tank is often cylindrical, and the area s of its cross-section circle is constant, then the weight g= △ P · s= ρ G △ h · s, s remains unchanged, G and △ P become electronic universal experimental machine, and the digital sensor adopts several different working principles and proportional relationships. That is, as long as the △ p value is accurately detected, it is inversely proportional to the height △ h. When the temperature changes, although the oil volume expands or shrinks, and the actual liquid level increases or decreases, the detected pressure will always remain unchanged. If the user needs to display the actual liquid level, it can also be solved by introducing medium temperature compensation

3 practical application of differential pressure transmitter

in Wenzhou new century oil depot project, the author applies this idea to the actual design

design condition: 2000m3 oil tank, diameter d=14.5m, height can get the actual oil inventory g, and its density can also be known from the formula ρ h=14m。

primary meter: btl-1151lt flange type explosion-proof differential pressure transmitter of Wenzhou Bethel instrument company is selected. The flange type is selected to prevent the accumulation of dirt at the tank bottom from blocking the impulse pipe. The transmitter range is 0 ~ 140kpa

secondary meter: use WP series intelligent light column display alarm, universal signal input, can arbitrarily change the range of pebble and gravel gb/t14685 ⑵ 001 for construction, use light column to display the liquid level, and use digital to display the tonnage of oil products. Take 6# tank as an example, s= π × r2=3.14 × 7.252=165m2, 14m high

on the top of the oil tank, a set of liquid level alarm device is designed for the differential pressure transmitter to prevent oil overflow as a double insurance. In application, since the measured value is directly tonnage, the value displayed in the secondary table is the tonnage of the oil in the oil tank regardless of the oil stored in the oil tank, avoiding the trouble of measuring the density for conversion

differential pressure transmitter generally, oil products are usually pumped into and out of the warehouse and measured by elliptical gear flowmeter. Due to the limited accuracy of the flowmeter, the highest level is only 0.2. The differential pressure transmitter also needs to measure the density calculation, and the results are often somewhat inconsistent, resulting in measurement disputes. Now, because the measurement result of oil tank is tonnage, and the accuracy can reach level 0.2 or even level 0.1, the measurement result of differential pressure transmitter is more accurate than that of positive displacement flowmeter. Although the absolute error of the measurement results is large due to the resolution when a small number of oil products are in and out of the warehouse, the differential pressure transmitter has higher accuracy and smaller relative error than other measurement means when a large number of oil products are in and out of the warehouse, especially suitable for monthly, quarterly and annual inventory. Practice shows that its main advantages are: ① simple and convenient installation and maintenance; ② The reading is intuitive, direct and clear, and the inventory of oil products can be read directly; ③ The measurement and conversion of density are exempted

4 precautions for differential pressure transmitter

(1) during design and installation, the pressure tapping opening at the bottom of the oil tank should be lowered as far as possible to eliminate the error caused by temperature change, and temperature compensation should be introduced if necessary

(2) when the horizontal section of the tank body of the oil tank is different (small above and large below), compensation measures should be considered. For example, wp-h80 series liquid level capacity controller is selected for the secondary meter

(3) in order to achieve a certain accuracy, if the breather valve is installed on the top of the oil tank, the differential pressure transmitter must be used instead of the pressure transmitter. When the requirements for open oil tanks or accuracy are not high, pressure transmitters can be directly used to facilitate installation

(4) the secondary meter shall adopt intelligent meter as much as possible, which can easily change the range and realize temperature compensation

Copyright © 2011 JIN SHI