Pressure measurement liquid level gauges

Power was supplied from a dc generator located externally to the area. Temperatures were measured with a Rubicon potentiometer with a range of 0.01 to 100,000 jlv in conjunction with a Leeds and Northrup galvanometer. Pressure was controlled in the dewar with automatic pressure control valves and was measured with a 12-in. laboratory test pressure gauge. Liquid level was indicated with a resistor-type liquid level gauge. 

Liquid level measuring devices are classified into two groups (a) direct method, and (b) inferred method. An example of the direct method is the dipstick in your car which measures the height of the oil in the oil pan. An example of the inferred method is a pressure gauge at the bottom of a tank which measures the hydrostatic head pressure from the height of the liquid. 

The pressure in a vessel is measured with a pressure gauge or a manometer (shown at left). The unknown pressure Punknown is applied to one side of a U-shaped tube and a known reference pressure is applied to the other. Pknown may be another vessel or the atmospheric pressure that is determined with a barometer. The difference in liquid levels / may be converted to a pressure (e.g., 760 mm mercury=1 atm). If the liquid... 

When distillation is performed at atmospheric pressure it is necessary to read the barometer, from time to time, so that boiling points may be corrected to 760 mm (see section 4.13). A reliable mercury barometer should be used [32]. The one after Gay-Lussac or that after Schrodt-Kiefer is often used in the laboratory. For an accuracy of d O.l mm the vernier should be employed in reading the mercury level. The liquid pressure gauges developed by Nickel [32] make allowance for the surface tension of the measuring liquid and enable corrections for zero deviations such a.s those caused by temperature changes. 

Plasticizer level indicators are essential to protect storage tanks from overflows. Differential pressure gauges and floating type indicators are used for the measurement of tank levels. It is possible to calibrate level gauges in volumetric units or to indicate depth of liquid. Level indicators can also have transmitters and these may be related to high level... 

Gauge gaj [ME gauge, fr. ONE] (15c) (gage) n. (1) Any instrument that measures and indicates such quantities as thickness, pressure, temperature, or liquid level. (2) The thickness of a plastic sheet or film, usually given in mils or mm. (3) Any of the standard wire and sheet-metal scales in which the gauge numbers are inversely related to wire diameter or sheet thickness. (4) The number of wales per inch in a knit fabric. (5) On spinning or twisting frames, the distance from the center of... 

All vessels were fitted with external wall thermocouples (3 mm, stainless steel, sheathed type K). Interior fluid temperatures, vapor and liquid, were measured on several levels at a single, near-eentral, vertieal position eorresponding to the fill-level gauge connection with similar, though 1.5-mm diameter, thermocouples. Both vapor and liquid pressures were determined from remote ealibrated pressure transducers. The target tank was mounted on a frame supported on four fire-proteeted load cells these were used to determine the variation in propane mass with PRV aetion. 

Level gauging instruments measure the liquid level in the tank. Pressure transmitters measure the hydrostatic pressure of the liquid column. Both level and pressure are primary functions for the calculation of volume and mass, respectively. Hybrid sj stems, such as HIMS, use both inputs in one system. Conversions from volume to mass or vice versa are made using density and temperature as secondary inputs. The density input may be obtained from an outside source, such as a laboratory, or may be measured in the tank by using pressvue transmitters or servo density. The temperature input is obtained from a temp ature-measuring system in the tank. 

Although a pressure gauge is more commonly used to measure the pressure inside a laboratory vessel, a manometer is sometimes used (Fig. 4.5). It consists of a U-shaped tube connected to the experimental system. The other end of the tube may be either open to the atmosphere or sealed. For an open-tube manometer (like that shown in Fig. 4.5a), the pressure in the system is equal to that of the atmosphere when the levels of the liquid in each arm of the U-tube are the same. If the level of mercury on the system side of an open manometer is above that of the atmosphere side, the pressure in the system is lower than the atmospheric pressure. In a closed-tube manometer (like that shown in Fig. 4.5b), one side is connected to a closed flask (the system) and the other side is vacuum. The difference in heights of the two columns is proportional to the pressure in the system. 

There are two basic ways for a vacuum gauge to read a vacuum direct and indirect. For example, say that on one side of a wall you have a known pressure, and on the other side of the wall you have an unknown pressure. If you know that a certain amount of deflection implies a specific level of vacuum, and you can measure the current wall deflection, you can then determine the pressure directly. This process is used with mechanical or liquid types of vacuum gauges. On the other hand, if you know that a given gas will display certain physical characteristics due to external stimuli at various pressures, and you have the equipment to record and interpret those characteristics, you can infer the pressure from these indirect measurements. This indirect method is how thermocouple and ion gauges operate. 

Example 2.1. A manometer of the type shown in Fig. 2.4 is used to measure the pressure drop across an orifice (see Fig. 8.19). Liquid A is mercury (density 13,590 kg/m ) and fluid B, flowing through the orifice and filling the manometer leads, is brine (density 1260 kg/m ). When the pressures at the taps are equal, the level of the mercury in the manometer is 0.9 m below the orifice taps. Under operating conditions, the gauge pressuret at the upstream tap is 0.14 bar the pressure at the downstream tap is 250 mm Hg below atmospheric. What is the reading of the manometer in millimeters ... 

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