Things you need to know about Diaphragm pressure gauges

Things you need to know about Diaphragm pressure gauges

by | Apr 30, 2017

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What is Diaphragm pressure gauges?

Diaphragm pressure gauges, also called seal gauges, are suitable for low pressure and overpressure measuring conditions.

Diaphragm pressure gauges are used to measure gases and liquids. They cover measuring spans from 10 mbar to 40 bars. The measuring element consists of one circular diaphragm clamped between a pair of flanges. The positive or negative pressure acting on these diaphragms causes deformation of the measuring element. The magnitude of the deformation is proportional to the pressure to be measured, and it is coupled to the pointer mechanism.

Diaphragm pressure gauges are considered as specialists in the process industries. They come into play when Bourdon tube pressure gauges reach the limits of their performance. One of the advantages of diaphragm pressure gauges is the measurement of low pressures.

Diaphragm pressure gauges can be recognized from the first look: From the flanges below the case, between which the elastic pressure element – the diaphragm element – is clamped.

These instruments can measure pressures from as low as 16 mbar, with the maximum value at around 25 bar (for comparison: Bourdon tube gauges reach their lowest physically possible measured value at 600 mbar). The larger the diaphragm element, the lower the measurable pressure is, in accordance with the formula – pressure = force / area.

 

Diaphragm pressure gauges working Principle

 

What else do you know about diaphragm pressure gauges

Diaphragm pressure gauges offer a versatile and reliable solution for pressure measurement across a wide range of applications, thanks to their robust design, high accuracy, and compatibility with various process conditions and media.

1. Operating Principle: Diaphragm gauges rely on a flexible diaphragm element that deforms or flexes in response to the applied pressure. This deformation is then translated into a mechanical movement, which drives the pointer or digital display to indicate the pressure reading.

2. Diaphragm Material: The diaphragm is typically made from materials like stainless steel, Inconel, Monel, or other corrosion-resistant alloys, depending on the application and media compatibility requirements. The diaphragm material must be able to withstand the pressures and temperatures encountered while remaining flexible.

3. Pressure Range: Diaphragm gauges are available in a wide range of pressure measurement capabilities, from low vacuum pressures to extremely high pressures, depending on the diaphragm’s thickness and material properties.

4. Accuracy: Diaphragm gauges can provide high accuracy, with typical accuracy ratings ranging from ±0.25% to ±1% of the full-scale value, depending on the quality and design of the gauge.

5. Process Connection: Diaphragm gauges can be fitted with various process connections, such as threaded (NPT or BSPT), flanged, or sanitary connections, to interface with the system or pipeline being monitored.

6. Environmental Resistance: Diaphragm gauges can be designed for different environmental conditions, such as harsh or corrosive atmospheres, high vibration, or extreme temperatures, by incorporating specialized housings, fill fluids, or other protective features.

7. Applications: Diaphragm pressure gauges are widely used in various industries, including chemical processing, oil and gas, water and wastewater treatment, pharmaceuticals, power generation, and many others, where accurate pressure measurement is critical.

8. Maintenance: Diaphragm gauges generally require minimal maintenance, but periodic calibration and inspection are recommended to ensure accurate and reliable performance over time.

How to measuring pressure under 16mbar?

With pressures under 16 mbar, diaphragm pressure gauges hit their limits. For this case, their diaphragms would have to be exceptionally thin in order to achieve the required elasticity.

Then, however, they would no longer remain reliably stable. This problem can be solved, though, with a special variation of the diaphragm pressure gauge: the capsule pressure gauge.

Capsule elements consist of two diaphragms welded together, which are generally loaded with pressure from the inside. This results in a double diaphragm travel.

In this way, even the lowest of pressures can be measured without reducing the wall thickness. However, since the pressure chamber is not self-draining, capsule elements are not suitable for applications with liquid media.

Measuring condition and Media

Diaphragm pressure gauges measure gauge, absolute and differential pressure. In processing industries, they can be installed in applications with highly corrosive, viscous media.

Diaphragm pressure gauges are ideal for these harsh conditions because the media can clog the narrow pressure ports of threaded connections of Bourdon tube instruments as well as the internals of the tube.

To prevent such clogging, diaphragm pressure gauges are connected to the process with an open flange. This configuration provides a large pressure chamber, which prohibits media from settling.

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Basic Knowledge You Need to Know about Pressure Gauge

Basic Knowledge You Need to Know about Pressure Gauge

by | Feb 27, 2017

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In industrial and commercial applications, pressure ranks only second to temperature as the most common process measurement. In fact, knowing the pressure often plays an important role in our daily life. Among the many kinds of pressure measurement devices, including sensors, transmitters and transducers, pressure gauges are meant to be a local display that measure and display pressure in the simplest and most direct way.

What’s pressure?

Pressure is the amount of force acting per unit area. As to the units of pressure measurements, PSI ( pounds per square inch), bar and other units of measure such as kg/cm2, inH2O, mmHg, Pa are common to see.

There are also different types of pressure to consider. The type of pressure refers to the zero reference point of a measurement. For example: pressure falls into several types according to the zero reference point, involving:

  • Gauge pressure:The pressure gauge is referenced against atmospheric pressure.
  • Absolute pressure:The pressure gauge is referenced against a perfect vacuum. It is equal to gauge pressure plus atmospheric pressure.
  • Differential pressure:The pressure gauge contains two process connections to measure the difference between two pressures.

relationship and difference among gauge pressure, absolute pressure, differential pressure

Pressure Gauge Technology

To select the best pressure gauge for a particular application, one must be aware of the differences. Generally speaking, there are two types of pressure gauges, analog gauges and digital ones, which use different technology and excel under different conditions.

Analog Gauges

Analog pressure gauges use a needle that points to a number on a scale corresponding to the pressure sensed by the measuring element. They are widely used for its high accuracy, low cost and little maintenance.

Most analog gauges rely either on the principle of Bourdon Tube or Bellows:

Bourdon Tube

Bourdon tubes pressure gauges, classified as mechanical pressure measuring instruments, are the most widely-used analog gauges. A curved tube is used which tends to straighten out when subjected to pressure, and the tube is connected to a pointing device so that subtle movements due to pressure fluctuations are indicated on pressure calibrated scale on the dial.

bourdon-tube-pressure-gauge

Bourdon tube pressure gauges are available at low price and work well for most applications. In addition, the simple construction makes them easy to use and the high accuracy of up to ±0.1% makes them suitable for precision measurements.

Bourdon tube pressure gauges are not perfect, of course, and they have their limitations, such as sensitivity for shocks and vibration, and slower responding. So they are not ideal option for applications involving rapid pressure fluctuations, thanks to Eastsensor advanced and fine tune design, to a large extent, ESG502 Shock Resistance Pressure Gauge can do a better job, with damp oil filled inside, the buffer has excellent shock resistance ability. It is well suited for measuring those medium which has strong pulsation or pressure concussion or service medium which disappear suddenly in the manufacture, or for the situation which shock fiercely.

Bourdon tubes cannot make absolute pressure measurements nor are they particularly adept at high precision measurements.

Bellows

Bellows gauges are used when measuring pressure ranges below what is ideal for Bourdon tube gauges. Bellows gauges contain an elastic element that radially expands and contracts to respond to pressure changes. The internal bellows is connected to a pointing device so that pressure-fluctuation-caused subtle movements are indicated on pressure calibrated scale on the dial.

ESG503 Stainless Steel Bourdon Tube Pressure Gauge drawing

Bellows gauges do better in low pressure applications with high accuracy and sensitivity for precise measurement. Additionally, bellows gauges are rugged and reliable with low hysteresis and creep.

What’s more, analog gauges often feature temperature compensation for greater accuracy, liquid fill to dampen movement of the pointer, multiple dial sizes to improve visibility and space requirements.

Digital Gauges

Digital pressure gauges use advanced sensors and microprocessors to display highly accurate pressure readings on a digital indicator. Despite of its higher prices, digital gauge is attractive for many applications.

Providing high resolutions, digital gauges make it quick and easy to read results, and are ideal for low pressures or small incremental pressure changes. Besides, digital pressure gauges are more reliable as fewer moving parts are used. Comparing with analog gauges, digital gauges are simpler to operate; they can be programmed for multiple pressure units and can send results to a computer or other instrument for storage or analysis.

Most digital pressure gauges rely on one of two measurement technologies:

Strain gauge

Strain gauge sensors rely on the piezoresistive effect which describes changes in the electrical resistivity of a semiconductor or metal when mechanical strain (pressure) is applied. This technology consists of a diaphragm with patterned metallic strain gauge embedded into it. Increasing pressure causes the diaphragm, and subsequently, the gauge to deform which effects it’s resistivity. That change is measured and converted into an electrical signal proportional to the pressure.

strain-guage-pressure-transducer

Piezoelectric

Piezoelectric sensors rely on the piezoelectric effect in certain materials such as quartz to measure the strain upon the sensing mechanism due to pressure. As pressure is applied a charge develops across the sensor in proportion to the force.

Things to Consider When Selecting a Pressure Gauge

The pressure type and range

Determine if you need to measure gauge pressure (relative to atmospheric), absolute pressure (relative to a full vacuum), or differential pressure (between two points). Identify the minimum and maximum pressure values to be measured.

The output type

Decide if you need a traditional analog gauge with a dial and pointer, or a digital gauge with a numerical display. Digital gauges often offer additional features like data logging, alarms, and communication capabilities.

The required accuracy

Specify the desired accuracy level, typically expressed as a percentage of the full-scale reading. Higher accuracy is required for critical applications, while lower accuracy may be acceptable for general monitoring.

Preferred measurement unit/units

Choose the appropriate unit(s) for displaying pressure, such as psi, bar, kPa, or others, based on your industry standards or personal preference.

Required process connection

Identify the appropriate connection type (threaded, flanged, etc.) and size to interface with your existing piping or system. Ensure compatibility with the pressure gauge’s design.

Material compatibility or chemical resistance

Select a gauge with wetted materials (parts in contact with the measured media) that are compatible with the fluid or gas being measured. Certain media can corrode or degrade specific materials.

Temperature range

Verify that the gauge’s operating temperature range aligns with the expected ambient and process temperatures in your application. Temperature extremes can affect accuracy and performance.

Burst pressure

Consider the gauge’s burst pressure rating, which indicates the maximum pressure it can withstand without rupturing or causing a safety hazard. This rating should exceed the maximum expected pressure in your system.

Dial size

Choose a dial size that is easily readable from the intended viewing distance and environment. Larger dials may be preferred for improved readability in certain applications.

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How to Select Pressure Gauge?

How to Select Pressure Gauge?

by | Jan 26, 2017

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With the ever-increasingly development of modern industry, pressure gauges are indispensable and critical device of most measuring processes. In case of that, a pressure gauge has to be qualified, reliable, accurate and easy to operate to help prevent failure in everyday operations.

Therefore, how a gauge is constructed and configurated is extremely significant for our customers to fully considerate before they make their mind of select one of them. Anyhow, failures can cost time, money and productivity loss.

In today pressure measuring filed, two main categories pressure gauges have been more often than ever involving into our daily life, these are mechanical pressure gauge based on bourdon tube principle and digital pressure gauge also called intelligent gauge. Fortunately, both of them you can find out here at Eastsensor.

Mechanical Bourdon Tube Pressure Gauge

Gauges working with bourdon tubes principles are the most usual pressure measuring devices in our daily life. Mechanical bourdon tube combines a high grade of measuring technology, simple operation, ruggedness and flexibility with the advantages of industrial and cost-effective production. Needing no external power supply, bourdon tube gauges are the best choice for most applications.

Select Pressure Gauge bourdon tube

Applications for gauges with a bourdon tube range from highly automated chemical processes, such as, refineries and petrochemical processing, to hydraulic and pneumatic installations. These types of gauges can also be found at all critical process monitoring and safety points in today’s energy industries, from exploration wells and petrochemical plants, to power stations and wastewater operations.

So what exactly it is? Bourdon tube is radially formed tubes with an oval cross-section. The pressure of the measuring medium acts on the inside of the tube and produces a motion in the non-clamped end of the tube. This motion is the measure of the pressure and is indicated via the movement.

The C-shaped Bourdon tubes, formed into an angle of approx. 250°, can be used for pressures up to 60 bar. For higher pressures, Bourdon tubes with several superimposed windings of the same angular diameter (helical tubes) or with a spiral coil in the one plane (spiral tubes) are used.

For detailed information, please refer to ES most sophisticated model of 

Although mechanical pressure gauges have their advantages, however like all analog gauges, bourdon tubes cannot make absolute pressure measurements nor are they particularly adept at precision measurements, on the other hand, if accuracy is a key factor when measuring pressure, bourdon tube dial type analog pressure gauges simply cannot compare to how precisely digital pressure gauges measure pressure. Digital pressure gauges offer many other advantages as well.

Digital (Intelligent) Pressure Gauge

A digital pressure gauge is ideal for precise and fast pressure readings. Digital pressure gauges, like the ESG101, ESG102, ESG103 digital pressure gauge, are suitable for a wide range of applications and industries, including mechanical engineering, hydraulics/pneumatics, pumps/compressors, and general service/test operations.

Select Pressure Gauge digital

Since they may be transported around in the intervening periods during application, digital pressure gauges feature a stainless steel case, well-designed battery housing, and robust electronics to ensure the longevity of the gauges and subsequent accuracy of readings. Digital pressure gauges can use battery power (ESG103), or loop power (ESG101, ESG102). Both of them have been set forth in details as below.

Battery power

Even the disadvantage to using a battery-powered pressure gauge is that the battery will need to be replaced, and that can be unpredictable however, battery-powered gauges do offer flexibility and convenience while in the field. ESG103 battery based digital pressure gauges that use standard batteries (9V alkaline battery 6LR61) have a long-battery life (2,000 hours or 2 years if serve in power saving model) and consume less power. What is more, the automatic power-off feature will save battery life, and make it last longer.

Loop power

4-20mA loop-powered digital pressure gauges ensure that readings are available at the point of measurement without worrying about battery life. The obvious disadvantage of this method is that wires and a power supply are required. The advantage is that cables that provide power to the unit can also provide an analog output (4~20mA) or digital output (RS485) proportional to the pressure (pls refer to ESG101 digital pressure gauge in our store). If a local display of pressure and an analog output is required, then a pressure transducer that features a local display could be used instead of a loop-powered digital pressure gauge with an analog output and higher accuracy.

Unfortunately and inevitable digital pressure gauges have their disadvantages too as well.

  • They are not easy to see full scale or trending
  • They are not able to read oscillating values
  • They require power (Vdc/Vac)

Which is suitable for you?

A pressure gauge which is a common component in operations from the simplest bike tire gauge to complex gauges for accuracy in industrial and mechanical processing, can measures the pressure level inside a container that holds gas, liquid, vapor, or solid material, helping ensure optimal performance and safety. But not every gauge is created equally or made for every situation.

It is very important that end-users select a pressure gauge that is going to operate the best for them and give them the best results based on what they want to use it for.

At least you should ask yourself 4 questions before you determine whether to employ mechanical or digital pressure gauge for your work.

  • What kind of accuracy is needed?
  • How much are you willing to spend?
  • Do you need any type of outputs?
  • Where is this gauge going to be installed?

If an accuracy of 1.0 percent and greater will suffice, and you have a static application and want the least expensive option, a mechanical gauge would work well. While the digital pressure gauge, on the other hand, will provide a precise, accurate reading – no interpretation is needed – and microprocessor technology will allow for several additional programmable functions which will definitely cost more than mechanical type as usual.

Digital gauges sample at various rates (typically 100 or 250 milliseconds) to average out small pulsations and display a constant value. Further, a digital gauge is desirable when the end-user wants both a local and remote pressure indication, and when an automated process control uses pressure as an input to the control system.

For all the modern advantages of the digital gauge, there are some times when the simplicity of the mechanical gauge would work best and be more cost-effective.

For instance, when only a general reading is required (high, medium, low), a mechanical gauge would be the best choice. Mechanical gauges are offered in many different display sizes as well. And one major advantage is that they require no power or batteries.

Some common problem causers are pressure pulsation, which can introduce premature wear in mechanical gauges; vibration process and ambient temperature, which can affect accuracy, repeatability and functionality; and over-pressure spikes.

Other potential problems arise with media that is slurry or has a high concentration of particulate matter that can clog pressure ports; and corrosion, which can damage both mechanical and digital gauges.  It’s important to carefully select a gauge with wetted parts that are compatible with the media being sensed. Many of these potential problems can be avoided by using diaphragm seals gauges such as ESG504 and ESG505.

A gauge should be examined and recalibrated at least once a year depending on the intensity of its use. Minor problems can be corrected, and the gauge can be recalibrated and recertified. A gauge that is properly taken care of should last years.

Wrapping up

Pressure gauges generally come with either a male or a female mount that can be situated on the back, top, or base of the dial. The dial varies in range and increment depending on the application to which it is suited. The diameter of the dial varies in size, and the case may be made of steel, aluminum, nylon, or plastic.

The gauge may be filled with liquid such as glycerin oil or silicone oil to dampen the effect of vibration and lubricate the gauge movement. A digital pressure gauge has an LCD screen to display measurements and can measure positive, negative, or differential pressure. It may have features such as selectable measurement units, data hold, minimum and maximum measurements, and data storage.

Just as people have continued to wear dial wristwatches long after the invention of the digital kind, so will people continue to use mechanical pressure gauges. Experts say mechanical devices will remain for those looking for non-powered, free-standing, self-actuated, reasonably priced components.

In terms of future technology, experts say mechanical pressure gauges will improve as modern manufacturing techniques are implemented, such as laser welding, automated assembly, and new materials of construction are added. This will result in more reliable, accurate gauges at a lower cost.

On the digital side, there is believed to be much more opportunity for improvements. New sensor technologies are being developed, which are more cost-effective, consume less power, are accurate, repeatable, and offer a wider range of operating temperatures.

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