Pressure measurement Bourdon tube

Pressure and differential-pressure measurement. Bourdon tubes of weld-sealed. 347 stainless steel are used for pressure transmission in the HRE-2. Most suitable for reactor use are units contained within secondary pressure housings, such as the 2500-psi pressure transmitter shown in Fig. 8-21. Baldwin cells have been widely used for accurate pressure measurement in loops. 

An example of a pneumatic PI controller is shown in Fig. 8-64 7. This controller has two stages of pneumatic amphfication and a Bourdon tube input element that measures process pressure. The Bourdon tube element is a flattened tube that has been formed into a cui ve so that changes in pressure inside the tube cause vertical motions to occur at the ungrounded end. This motion is transferred to the left end of the beam, as shown. 

The indicator element measures the signal from the weighing element, and converts it into a readable form. It may be any of several different types, eg, the graduated beam of Figure 3, a Bourdon tube pressure gauge, or a numeric display device. Today (ca 1997), with the increase in automation, the indicator element may not display the weight but may instead transmit it electronically to a controller. 

Linear-Variable-Differential-Transformer and Reluctive Pressure Transducers. In ahnear-vatiable-differential-transformer (LVDT) pressure transducer, the pressure to be measured is fed to a Bourdon tube or diaphragm. The motion of this element is transferred to the... 

Elastic-Element Methods Elastic-element pressure-measuring devices are those in which the measured pressure deforms some elastic material (usually metallic) within its elastic limit, the magnitude of the deformation being approximately proportional to the applied pressure. These devices may be loosely classified into three types Bourdon tube, bellows, and diaphragm. 

Conditions of Use Bourdon tubes shoula not be exposed to temperatures over about 65°C (about 150°F) unless the tubes are specifically designed for such operation. When the pressure of a hotter fluid is to be measured, some type of hquid seal should be used to keep the hot fluid from the tube. In using either a Bourdon or a diaphragm gauge to measure gas pressure, if the gauge is below the... 

For measuring pressures of corrosive fluids, slurries, and similar process fluids which may foul Bourdon tubes, a cfiemical gauge, consisting of a Bourdon gauge equipped with an appropriate flexible diaphragm to seal off the process fluid, may be used. The combined volume of the tube and the connection between the diaphragm and the tube is filled with an inert liquid. These gauges are availabTe commercially. 

Good-quality Bourdon tube test gauges are highly suitable for pressure measurements of more than 20psi. They should be calibrated against a... 

The receiving gauge in the control room works on the transmitted pneumatic pressure, 15 psi giving full scale, but has its dial calibrated in terms of the plant pressure that it is indicating. The Bourdon tube of such a gauge is capable of withstanding only a limited amount of overpressure above 15 psi before it will burst. Furthermore, the material of the Bourdon tube is chosen for air and may be unsuitable for direct measurement of the process fluid pressure. 

It may be noted that the pressure measuring devices (a) to (e) all measure a pressure difference AP(— Pj — P ). In the case of the Bourdon gauge (0, the pressure indicated is the difference between that communicated by the system to the tube and the external (ambient) pressure, and this is usually referred to as the gauge pressure. It is then necessary to add on the ambient pressure in order to obtain the (absolute) pressure. Even the mercury barometer measures, not atmospheric pressure, but the difference between atmospheric pressure and the vapour pressure of mercury which, of course, is negligible. Gauge pressures are not. however, used in the SI System of units. 

We measured flow rate with a Varlan P/N 29-000086-00 Soap Bubble Meter. The pressure gauges were Heise bourdon-tube type with 0.1 psla divisions. The column was 16 feet of 1/4 inch copper tubing packed with Carbowax 20M loaded to 20% on Fluoropak 90. 

Pressure gauges, Part 1 Pressure gauges with Bourdon tubes, dimensions, measurement technology, requirements and testing 2/97... 

Those that are based on the measurement of the distortion of an elastic pressure chamber (mechanical pressure gauges such as Bourdon-tube gauges and diaphragm gauges)... 

The pressure is usually measured with the use of Bourdon tube gauges or transducers. 

Filled-System Thermometers The filled-system thermometer is designed to provide an indication of temperature some distance removed from the point of measurement. The measuring element (bulb) contains a gas or liquid that changes in volume, pressure, or vapor pressure with temperature. This change is communicated through a capillary tube to a Bourdon tube or other pressure- or volume-sensitive device. The Bourdon tube responds so as to provide a motion related to the bulb temperature. Those systems that respond to volume changes are completely filled with a liquid. Systems that respond to... 

Bourdon gauges are used on gas cylinders and are also considered a type of aneroid gauge. These devices have a coiled tube (shown in Figure 3.5) and are used to measure the pressure difference between the pressure exerted by the gas in a cylinder and the atmospheric pressure. The coiled tube is mechanically coupled to a pointer (shown in red). As a gas at a pressure above atmospheric pressure enters the coiled tube, it causes it to slightly uncoil, kind of like those New Year s Eve paper noisemakers. This causes the pointer to move over a numerical scale, thereby indicating the gauge pressure in the tank. 

A much more convenient method of direct pressure measurement involves the deflexion of a sensing element (e.g. a tensioned diaphragm made of a suitable metal or ceramic or a Bourdon tube) which separates... 

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