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1.0: Pressure Instruments - Geosciences

1.0: Pressure Instruments - Geosciences


Atmospheric-pressure sensors are called barometers. Almost all barometers measure the pressure difference between atmospheric pressure on one side of the sensor, and a reference pressure on the other side. For most barometers, the reference pressure is a vacuum (zero pressure).

Aneroid barometers use a corrugated metallic can (the aneroid element) with a vacuum inside the can. A spring forces the can sides outward against the inward-pushing atmospheric-pressure force. The relative inflation of the can is measured with levers and gears that amplify the minuscule deflection of the can, and display the result as a moving needle on a barometer or a moving pen on a barograph (a recording barometer). The scale on an aneroid barometer can be calibrated to read in any pressure units (see Table 1-3)

Mercury (Hg) barometers (developed by Evangelista Torricelli in the 1600s) are made from a U-shaped tube of glass that is closed on one end. The closed end has a vacuum, and the other end is open to atmospheric pressure. Between the vacuum and the air is a column of mercury inside the tube, the weight of which balances atmospheric pressure.

Atmospheric pressure is proportional to the height difference ∆z between the top of the mercury column on the vacuum side, and the height on the side of the U-tube open to the atmosphere. Typical ∆z scales are millimeters of mercury (mm Hg), centimeters of mercury (cm Hg), or inches of mercury (in Hg). To amplify the height signal, contra-barometers (developed by Christiaan Huygens in the 1600s) use mercury on one side of the U-tube and another fluid (e.g., alcohol) on the other.

Because mercury is a poison, modern Torricelli (U-tube) barometers use a heavy silicon-based fluid instead. Also, instead of using a vacuum as a reference pressure, they use a fixed amount of gas in the closed end of the tube. All Torricelli barometers require temperature corrections, because of thermal expansion of the fluid.

Electronic barometers have a small can with a vacuum or fixed amount of gas inside. Deflection of the can is measured by strain gauges, or by changes in capacitance between the top and bottom metal ends of an otherwise non-conductive can. Digital barometers are electronic barometers that include analog-to-digital circuitry to send pressure data to digital computers. More info about all weather instruments is in WMO-No. 8 Guide to Meteorological Instruments and Methods of Observation.


1.0: Pressure Instruments - Geosciences

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No pressure: NSF test finds eliminating deadlines halves number of grant proposals

In recent years, the National Science Foundation (NSF) in Arlington, Virginia, has struggled with the logistics of evaluating a rising number of grant proposals that has propelled funding rates to historic lows. Annual or semiannual grant deadlines lead to enormous spikes in submissions, which in turn cause headaches for the program managers who have to organize merit review panels. Now, one piece of the agency has found a potentially powerful new tool to flatten the spikes and cut the number of proposals: It can simply eliminate deadlines.

This week, at an NSF geosciences advisory committee meeting, Assistant Director for Geosciences Roger Wakimoto revealed the preliminary results from a pilot program that got rid of grant proposal deadlines in favor of an anytime submission. The numbers were staggering. Across four grant programs, proposals dropped by 59% after deadlines were eliminated. “We’ve found something that many programs around the foundation can use,” Wakimoto told the advisory committee on 13 April.

The idea is one of several that NSF has tested for easing the strain on the merit review system. The no deadline idea began several years ago with a small grant program for instruments and facilities within the earth sciences division of the geosciences directorate. After making the switch in 2011, the program saw a more than 50% drop in proposals—and that number has stayed down ever since.

But many people doubted that NSF would see the same effect if officials dropped deadlines for one its regular science grant programs, says Alex Isern, the head of the surface Earth processes section. So she decided to test it out. She eliminated the twice-a-year deadlines for four of her grant programs, in geobiology and low-temperature geochemistry, geomorphology and land-use dynamics, hydrological sciences, and sedimentary geology and paleobiology. NSF sent out a notice about the change at the beginning of 2015, and after a 3-month proposal hiatus, the no-deadline approach began in April 2015. The number of proposals plummeted, from 804 in 2014 to just 327 in the 11 months from April 2015 to March.

Some NSF programs, such as those in the atmospheric and geospace sciences division, have always done without deadlines. But Isern believes this is the first instance where NSF has tracked the switch like a controlled experiment. So far, she says, there have been no effects on the demographics of who is applying, such as the age of the principal investigator or the type of university they are applying from. Because of a lag in decisions, she hasn’t yet measured the expected rise in success rates.

Feedback from scientists has been good so far, Isern adds. In a field where many scientists do field work, having no deadline makes it easier for collaborators to schedule time when they can work on a proposal. “I think they like the flexibility,” she says. “They’re able to be more thoughtful about it.” However, one scientist told Isern that he was very busy and couldn’t function without a deadline. Her response? “I’ve actually given you 365 deadlines.”

Paul Bierman, a geologist at the University of Vermont in Burlington, says the move is an “incredibly good idea” and expects success rates to go up. In October 2015, he and two collaborators resubmitted a previously rejected proposal to the geomorphology program: a $265,000, 3-year request to study the thinning of glaciers that retreated from New England within the last 20,000 years. Bierman thought it would only take the three of them a month or so to revise their proposal, but the lack of a deadline allowed them to buff the proposal to a shine over the course of several months. The extra polish apparently paid off: He received a notice of recommendation for funding this week.

The switch is “going to filter for the most highly motivated people, and the ideas for which you feel the most passion,” he predicts. When he sits on merit review panels, he finds that he can usually reject half of the proposals right away as being hasty or ill-considered. “My hope is that this has taken off the bottom 50%,” he says. “Those are the ones you read and say, ‘Did they have their heart in this?’”

Carol Frost, head of the earth sciences division at NSF, says that many other program managers are thinking about trying out the idea. “There’s an awful lot of talk across the foundation,” she says. She has one concern, however: When proposals go down, and success rates go up, programs could be punished for having higher success rates than their peers. “One of the arguments that has been made for increasing budgets has been, ‘Look, we have such proposal pressure, give us more money,’” she says. The experiment provides evidence that proposal pressure can be easily manipulated, she says. “It’s not a good metric to use to decide whether a certain program deserves to have an augmented budget.”


Liquid filled gauge

Ranges
Vacuum / Compound to 200 psi (16 bar)
Pressure from 15 psi (1 bar) to 15,000 psi (1,000 bar)
Pressure from 15 psi (1 bar) to 10,000 psi (700 bar) - 2” size or other equivalent units of pressure or vacuum

Working pressure
2 & 2½”: Steady: ¾ full-scale value
Fluctuating: 2/3 full-scale value
Short time: full-scale value

4”: Steady: full-scale value
Fluctuating: 0.9 x full-scale value
Short time: 1.3 x full-scale value

Operating temperature
Ambient: -40°F to +140°F (-40°C to +60°C) - dry
-4°F to +140°F (-20°C to +60°C) - glycerine filled
-40°F to +140°F (-40°C to +60°C) - silicone filled
Medium: +140°F (+60°C) maximum

Temperature error
Additional error when temperature changes from reference temperature of 68°F (20°C) ±0.4% of span for every 18°F (10°K) rising or falling.

Weather protection
Weather tight (NEMA 4X / IP 66)

Pressure connection
Material: copper alloy
Lower mount (LM) or center back mount (CBM) -
Lower mount (LM) or lo er back mount (LBM) - 4”
⅛” NPT, ¼” NPT or ½” NPT limited to wrench flat area ABS (2” & 2½”) and white aluminum (4”)

Bourdon tube
2” (50 mm) ≤ 870 psi (60 bar): C-shape copper alloy
2” (50 mm) > 870 psi (60 bar): Helical copper alloy
2½” (63 mm) ≤ 870 psi (60 bar): C-shape copper alloy
2½” (63 mm) > 870 psi (60 bar): Helical copper alloy
2½” (63 mm) > 6,000 psi (400 bar) : Helical stainless steel
4" (100 mm) ≤ 1,000 psi (70 bar): C-shape copper alloy
4" (100 mm) > 1,000 psi (70 bar): Helical stainless steel

Movement
Copper alloy

Dial
White ABS (2” & 2½”) and white aluminum (4”)

Pointer
Black aluminum

Case
304 stainless steel with vent plug and stainless steel crimp ring. Suitable for liquid filling.

Case connection sealed with O-ring, (O-ring material dependent on the case fill):


About us

BD | SENSORS is a medium sized family run company that sets great store by independence and sustainability.

What makes a family business strong? Or, in another way, what should a family business be based on? Because family is the foundation of a larger whole, a family business in particular must be measured upon its credibility and stability. When responsibly dealing with customers and employees, decisions have to be healthy and sustainable.

BD|SENSORS is this kind of family business!
With three generations working in the company, as well as being owner-managed, this is exactly what BD | SENSORS sees as a guarantee for stability. Although the company operates globally, it stands by its location in Upper Franconia in North Eastern Bavaria and focuses on the idea „Made in Germany“.
Our affiliate in the Czech Republic, as well as our subsidiaries in China and Russia all benefit from this company strategy.

At BD | SENSORS, we consider strategy before acting,
high regard before speculation and return before turnover.

In this spirit, we create customer-oriented solutions in pressure and level measurement technology.

The group of companies has a total staff contingent of around 300 located in four countries: Germany, the Czech Republic, Russia and China.


Flow Meters

Flow meters are sophisticated measuring devices that employ a range of technologies designed to quantify the rate or volume of a moving fluid, either liquid or gas, in an open or closed conduit. The type of flow meter used will vary by application, but coriolis, differential pressure, magmeter, electromagnetic, oval gear, thermal, paddlewheel, positive displacement and ultrasonic are the most commonly used technologies.

Accurate flow measurement is a critical component of many commercial and industrial processes. Flow meters are instruments designed to quantify the rate or volume of a moving fluid—either liquid or gas—in an open or closed conduit. Whether determining the proper concentrations of ingredients in manufacturing, measuring fuel usage, ensuring proper flow for cooling equipment, or monitoring municipal water and sewer services flow meters serve in a wide variety of applications. Because of this, a number of flow measurement technologies have been developed. Each of these technologies comes with particular advantages and disadvantages. Understanding the needs of an application is always the first step towards selecting the proper flow meter.

Flow Measurement

Flow measurement can be described in either of two ways:

Volumetric flow in which Q = AV, meaning that the volume of fluid passing through a flow meter (Q) is equal to the cross-sectional area of the pipe (A) times the average velocity of the fluid (V). The only flow meter technology that measures volume directly is the positive displacement flow meter, however, other types of flow meters measure the velocity of the flowing stream to determine the volumetric flow. Examples of flow meter technologies that measure velocity include electromagnetic, turbine, ultrasonic, and vortex flow meters.

Mass flow in which W = RQ, meaning that the mass flow of fluid passing through a flow meter (W) is equal to the fluid density (R) times the volume of the fluid (Q). Examples of flow meter technologies that measure mass flow include Coriolis mass and thermal flow meters.

Other types of flow meters, notably differential pressure and variable area flow meters, do not measure volume, velocity or mass, but rather measure flow by inferring its value from other measured parameters.

Flow Meter Technology

Coriolis Mass Flow Meters

Coriolis meters make direct mass flow measurements based upon the Coriolis effect: the deflection of moving objects when they are viewed in a rotating reference frame. Coriolis flow meters artificially introduce a Coriolis acceleration into the flowing stream. As the fluid is "deflected", the forces generated cause an extremely slight distortion or 'twisting action' of the measuring tube that is directly proportional to the mass flow rate. This distortion is picked up by special sensors and converted to an output signal.

Coriolis mass flow meters can provide flow (mass or volume), density, and temperature measurements of liquids and gases all within a single meter. Since the measurement principle is independent of the physical fluid properties, these meters typically have a very high accuracy. The lack of straight pipe requirements and moving parts makes them a very attractive alternative to other flow meters.

Differential Pressure Flow Meters

Differential Pressure flow meters measure the velocity of fluids by reading the pressure loss across a pipe constriction. These meters can contain laminar plates, an orifice, nozzle, or Venturi tube to create an artificial constriction. Highly sensitive pressure sensors measure the pressure before and after the constriction. According to Bernoulli's principle, the pressure drop across the constriction is proportional to the square of the flow rate. The higher the pressure drop, the higher the flow rate.

Differential pressure flow meters utilize a robust, time proven measuring technique for a wide range of clean liquids and gases. The meters are available in a wide range of line sizes with wide temperature and pressure ranges. Installation is relatively easy and the meters often offer temperature and pressure measurements as well, measurements of mass flow compensation . Care should be taken with highly viscous liquids, though, as accuracy can be adversely affected or not achieved.

Magmeters / Electromagnetic Flow Meters

Electromagnetic flow meters are volumetric flow meters that measure the voltage created when conductive liquids move through a magnetic field. According to Faraday's Law, the voltage induced across any conductor as it moves at right angles through a magnetic field is proportional to the velocity of that conductor. With magmeters, the liquid serves as the conductor and the magnetic field is created by energized coils outside the flow tube. Electrodes detect the voltage which is directly proportional to the flow rate.

Electromagnetic flow meters can measure corrosive liquids and slurries, and have the ability to measure flow in both directions with equal accuracy. A conducting fluid and a non-conducting pipe liner are required. Magmeters will generally not work with hydrocarbons, distilled water and many non-aqueous solutions. They are also ideal for applications where low pressure drop and low maintenance are required.

Positive Displacement Flow Meters

Positive displacement flow meters measure the volumetric flow rate of a moving fluid or gas by way of precision-fitted gears or rotors containing cavities through which precisely known volumes of fluid pass. A basic analogy would be holding a bucket below a tap, filling it to a set level, then quickly replacing it with another bucket and timing the rate at which the buckets are filled (or the total number of buckets for the "totalized" flow).

Positive displacement flow meters are very accurate and have high turndown. They work best with clean, non-corrosive, and non-erosive liquids and gases, although some models will tolerate some impurities. They require no straight runs of pipe for fluid flow stream conditioning though pressure drop can be an issue. They are widely used in custody transfer and are applied on residential home natural gas and water metering.

There are two common types of positive displacement flow meters. Nutating disk meters feature a circular disk mounted on a ball inside a precision fitted measuring chamber. As the liquid flows through the chamber, the disk rotates and wobbles upon the ball. Each rotation causes a predictable wobble which creates a cavity of a known size through which the liquid passes. By using an indicator or totalizer, the number of rotations can be counted and the flow rate determined.

Oval gear meters use oval shaped gear-toothed rotors that rotate within a chamber. As these rotors turn, they sweep out and trap a very precise volume of fluid between the outer oval shape of the gears and the inner chamber walls. The flow rate is then calculated based on the number of times these compartments are filled and emptied.

Rotameters / Variable Area Flow Meters

Variable area flow meters / rotameters are among the oldest and most mature principles in flow measurement. Based upon Bernoulli's theorem, these meters consist of a uniformly tapered flow tube, a float, and a measurement scale. As a gas or liquid is introduced into the tube the float rises, its weight supported by the fluid flowing underneath, until the entire volume of fluid can flow past the float. The position of the float corresponds to a point on the tube's measurement scale and provides an indication of the fluid's flow rate.

The operating principle of variable area meters is as simple as it is reliable. They are generally inexpensive, easy to install and feature low, nearly constant, pressure drop. However, concern for orientation of rotameters (floats) must be observed, as they must be mounted vertically and have moderate accuracy. Variable area flow meters are generally not suitable for low-flow applications.

Thermal Flow Meters

Thermal flow meters measure mass flow rate by means of measuring the heat conducted from a heated surface to the flowing fluid. Relying on the principle that a fluid flowing past a heated temperature sensor removes a known quantity of heat as it passes, thermal flow meters measure either how much electrical power is required to maintain the temperature of the heated sensor or the temperature difference between the heated sensor and the flow stream. Either of those values is directly proportional to the mass flow rate.

Thermal flow meters are used almost entirely for gas flow applications. Their design and construction make them popular for a number of reasons. They feature no moving parts, have nearly unobstructed flow path, require no temperature or pressure corrections, and retain accuracy over a wide range of flow rates. Straight pipe runs can be reduced by using dual-plate flow conditioning elements and installation is very simple with minimal pipe intrusions.

Turbine / Paddlewheel Flow Meters

Turbine or paddlewheel flow meters are mechanical meters that have a freely rotating turbine set in the path of a fluid stream. The flowing liquid or gas causes the turbine to spin upon its axis. The rate of spin will be proportional to the velocity of the flow. The simple and reliable design of turbine meters makes them popular choices for large commercial and industrial users such as gas companies and municipal water districts.

Turbine meters are less accurate than some other types of flow meters but since the measuring element does not severely restrict the path of flow, they are able to measure high flow rates with low pressure loss. Though versatile, turbine meters do best in applications with constant conditions in liquids such as water or lower viscosity fluids. Strainers are generally required to be installed in front of the meter to protect the measuring element from gravel or other debris that could enter the flow system.

Ultrasonic Flow Meters

Ultrasonic flow meters utilize sound waves to measure the velocity of a fluid from which the volumetric flow rate can be calculated. Unlike most flow meters, ultrasonic meters do not include any moving parts and thus are more reliable, accurate and provide maintenance free operation. Since ultrasonic signals can also penetrate solid materials, the transducers can be mounted onto the outside of the pipe offering completely non-invasive measurement eliminating chemical compatibility issues, pressure restrictions, and pressure loss.

Ultrasonic flow meters are affected by the acoustic properties of the fluid and can be impacted by temperature, density, viscosity and suspended particulates depending on the exact flow meter. Homogenous fluids, as well as, advanced digital signaling can eliminate many of the problems associated with noise and variations in liquid chemistry.

There are two types of ultrasonic flow meters:

Transit time flow meters measure the travel time of two sound waves. One wave travels the same direction as the flow while the other travels against the flow. At zero flow, sensors receive both waves at the same time, i.e., without transit time delay. As the fluid moves, it takes an increasingly longer time for the downstream wave to reach the upstream sensor. This measured "transit time difference" is directly proportional to the flow velocity and therefore to flow volume. Transit time flow meters require the fluid to be free from suspended solids or gas bubbles and in a closed and full piping system.

Doppler-shift flow meters operate on the principle that the wavelength of an approaching sound source is shorter than the wavelength of that same source as it is moving away. A transducer emits a sound wave which reflects off entrained particles or bubbles back to the transducer. The measured difference in the wavelengths of the transmitted signal versus the reflected signal is proportional to the process' velocity. Doppler flow meters are used for slurries, liquids with bubbles, or gases with sound-reflecting particles. They can also be adapted for use in open channels by integrating with level transmitters.

Vortex Flow Meters

Vortex flow meters use an obstruction, known as a bluff body, in the flow stream to create downstream vortices which are alternately formed on either side of the bluff body. As these vortices are shed from the bluff body, they create alternating low and high pressure zones that oscillate at particular frequencies directly proportional to the velocity of the fluid. The flow rate can be calculated from the fluid velocity.

Vortex flow meters are universally suitable for measuring liquids, gases and steam while remaining largely unaffected by changes in pressure, temperature and viscosity. Without moving parts, vortex meters are easy to install and require little maintenance. The measuring signal is not subject to drift. Consequently, vortex meters can operate an entire life long without recalibration. Due to the nature of a minimum required velocity for each bluff body, vortex meters will tend to need higher velocities and may have some difficulty reading low flow rates.

Additional Flow Accessories

Flow Indicators

Flow Meter Indicators are simple devices that provide visual indication, often through the use of a float or paddle, that there is movement of fluid in the process line.

Flow Meter Monitors

Flow meter monitors are accessories that, generally speaking, convert the signal sent by a flow meter into a viewable flow rate. Though sometimes flow monitors are simple indicators, they often include sophisticated programming that allow control functions as well as other high-level operations.

Flow Switches

Flow switches are devices designed to trigger an action – such as on/off—based upon a preset flow setpoint. Flow switches may or may not read the flow rate.

Flow Transmitters

Flow transmitters are versatile instruments that may serve a number of functions. Basic transmitters may serve simply to relay the signal from the flow meter to a display. More sophisticated models may include control functions and/or advanced communications as part of an integrated flow system.

Flow Regulators

Flow regulators are simple valves that keep flow constant by decreasing the cross section of an orifice proportionally as the pressure increases. They are particularly suitable for networks supplying several users, as they can maintain the flow rate over a wide range of pressures.


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