The Decibel

The decibel is a unit of measurement that relates the ratio of a physical value to another value and is expressed on a logarithmic scale.  The common symbol for decibel is dB.  The decibel is used as a measure for many parameters in science and engineering such as acoustics (sound), electronics (power levels) and control theory.

The decibel originates from methods used to express performance and loss in telegraph and telephone circuits.  The term ‘bel’ was coined in honor of Alexander Graham Bell, and the decibel, being 1/10th of a bel was established.

For most of us, the decibel is the familiar term relating to how loud a sound is.

With sound, the sound pressure is typically what is measured and is the local pressure deviation from the base or equilibrium atmospheric pressure, caused by a sound wave. In air, the sound pressure can be measured by a standard microphone, and is measured in pascals (Pa.)

To get to the common decibel reading we are familiar with, a little mathematics comes into play.

Capture

  • where Lp is the Sound Level in dB, prms is the measured sound pressure, and pref is the standard sound reference pressure of 20 micropascals.
  • The prms is what is measured by a microphone

Below are some representative sounds and the decibel rating – Note that sounds that are above 85 dB can cause hearing issues, and proper protection should be taken.Decibel Scale Still Photo

Some other interesting blogs about sound for you take a look at-

Measuring and Adding Sounds

Sound Power Level and Sound Pressure

Super Air Knife Math – When 72  + 72 = 75

If you would like to talk about sound or any of the EXAIR Intelligent Compressed Air® Products, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Sound Power Level and Sound Pressure

Energy…all day (and night) long, we humans are surrounded by – and bombarded by – all kinds of energy. Sometimes, the effects are pleasant; even beneficial: the warmth of the sun’s rays (solar energy) on a nice spring day is the sure-fire cure for Seasonal Affective Disorder, and is also the catalyst your body needs to produce vitamin D. Good things, both. And great reasons to get outside a little more often.

Sometimes, the effects aren’t so pleasant, and they can even be harmful. Lengthy, unprotected exposure to that same wonderful sun’s rays will give you a nasty sunburn. Which can lead to skin cancer. Not good things, either. And great reasons to regularly apply sunblock, and/or limit exposure if you can.

Sound is another constant source of energy that we’re exposed to, and one we can’t simply escape by going inside. Especially if “inside” is a factory, machine shop, or a concert arena. This brings me to the first point of today’s blog: sound power.

Strictly speaking, power is energy per unit time, and can be applied to energy generation (like how much HP an engine generates as it runs) or energy consumption (like how much HP a motor uses as it turns its shaft) For discussions of sound, though, sound power level is applied to the generation end. This is what we mean when we talk about how much sound is made by a punch press, a machine tool, or a rock band’s sound system.

Sound pressure, in contrast, is a measure of the sound power’s intensity at the target’s (e.g., your ear’s) distance from the source. The farther away you get from the sound’s generation, the lower the sound pressure will be. But the sound power didn’t change.

Just like the power made by an engine and used by a motor are both defined in the same units – usually horsepower or watts – sound power level (e.g. generation) and sound pressure (e.g. “use” by your ears) use the same unit of measure: the decibel.  The big difference, though, is that while power levels of machinery in motion are linear in scale, sound power level and pressure scales are logarithmic.  And that’s where the math can get kind of challenging.  But if you’re up for it, let’s look at how you calculate sound power level:

Sound Power Level Equation

Where:

Wis reference power (in Watts,) normally considered to be 10-12 W, which is the lowest sound perceptible to the human ear under ideal conditions, and

W is the published sound power of the device (in Watts.)

That’s going to give you the sound power level, in decibels, being generated by the sound source.  To calculate the sound pressure level:

Sound Power Level to Sound Pressure Equation

Where:

Lis the sound power level…see above, and

A is the surface area at a given distance.  If the sound is emitted equally in all directions, we can use the formula for hemispheric area, 2πrwhere r=distance from source to calculate the area.

These formulas ignore any effects from the acoustic qualities of the space in which the sound is occurring.  Many factors will affect this, such as how much sound energy the walls and ceiling will absorb or reflect.  This is determined by the material(s) of construction, the height of the ceiling, etc.

These formulas may help you get a “big picture” idea of the sound levels you might expect in applications where the input data is available.  Aside from that, they certainly put into perspective the importance of hearing protection when an analysis reveals higher levels.  OSHA puts the following limits on personnel exposure to certain noise levels:

Working in areas that exceed these levels will require hearing protection.

EXAIR’s line of Intelligent Compressed Air Products are engineered, designed, and manufactured with efficiency, safety, and noise reduction in mind.  If you’d like to talk about how we can help protect you and your folks’ hearing, call us.

 

Calibration – Keep Your Meters True

EXAIR offers meters to measure the level of physical parameters such as sound and static. Each meter has sensitive electrical circuitry and a periodic calibration is recommended to ensure the meter readings are tried and true.

The model 9104 Digital Sound Level Meter is an easy to use instrument that measures and monitors the sound level pressure in a wide variety of industrial environments. The source of loud noises can be quickly identified so that corrective measures can be taken to keep sound levels at or below OSHA maximum allowable exposure limits.

The sound meter comes from the factory with an NIST (National Institute of Standards and Technology) certificate of accuracy and calibration.  As a good practice, EXAIR recommends a yearly calibration of the instrument, and we offer a service that calibrates the unit to the same NIST standards and provide a written report of the calibration.

The model 7905 Static Meter allows easy one-hand static measurements.  It is useful in both locating sources of high static charge and checking the reduction of static after treatment with an EXAIR Static Elimination product.  The unit is sensitive and responsive, and indicates the the surface polarity of objects up to +/- 20 kV when measured from 1″ away.

It is also recommended that the Static Meter be calibrated on a yearly basis.  EXAIR offers (3) levels of calibration service.  The first two provide calibration in accordance with MIL Standards using accepted procedures and standards traceable to NIST.  The third calibration service conforms to the same Mil Standard, as well as ISO/IEC standards.

Annual calibration service of your EXAIR Digital Sound and Static Meter, along with proper care and storage, will keep your meter performing tried and true for many years, providing accurate and useful measurements.

To initiate a calibration service, give us a call and an Application Engineer will issue an Returned Good number, and provide instructions on how to ship the meter to EXAIR.

If you have questions regarding calibration services for your meters or would like to talk about any EXAIR Intelligent Compressed Air® Product, feel free to contact EXAIR and myself or one of our Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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EXAIR Safety Air Gun Promotion

From August 1st to September 30th, 2017, EXAIR will be giving away a 1” Flat Super Air Nozzle with a purchase of a Precision, Soft Grip, or Heavy Duty Safety Air Gun.  We are promoting the importance of safety in the workplace with the EXAIR Safety Air Guns as well as the versatility of the different types of EXAIR nozzles.  This promotional item, model 1126 nozzle, has a patented shim to blows a 1” wide stream of air to clean surfaces quickly and efficiently; a $43.00 complimentary gift (click on the link below).

Promotional Nozzle with EXAIR Super Air Guns

Compressed air guns are one of the most commonly used pneumatic products in a manufacturing plant.  They are used at workstations to blow off debris and to clean parts and tools.  Because of the large quantities that are used in a plant; they are the most targeted by OSHA (Occupational Safety and Health Administration).  Majority of the common brands of air guns fail to comply with two common violations, rule 29CFR 1910.95(a) for loudness and rule 29CFR 1910.242(b) for dead-end pressure.  The reason is due to the nozzles that comes with the compressed air guns.  Fines can get very expensive, and you can alleviate these penalties by purchasing an EXAIR Safety Air Gun.  We are all responsible for safety; management, HSE department (Health and Safety Engineer), supervisors, and even the operators.  Your compressed air guns should be assessed in your facility to evaluate your safe work environment.

1310 Heavy Duty Safety Air Gun

With EXAIR Safety Air Guns, we supply an efficient, effective, and most important, safe air nozzle with all of our air guns.  They are CE Compliant and exceed the OSHA sound level and dead-end pressure requirements.  With substandard air guns, the operators would have to listen to loud noises all day and have to wear hearing protection.  As for the dead-end pressure; the EXAIR nozzles are engineered to not allow the operator to completely close the end against the hand or skin.  This is very important because if the pressure exceeds 30 PSIG, air can penetrate the skin and cause an air embolism.  Some manufacturers place a restriction inside the air gun to comply with this standard, sacrificing the effectiveness of the blowing force.  With our design, the compressed air is not able to be blocked; allowing the air to escape to atmosphere.  Even with the compressed air system set to 100 PSIG, the pressure against the skin will not exceed 30 PSIG.  Safety is a major concern for all of our customers and a priority for EXAIR in manufacturing our products.

1210-6-CS Soft Grip Safety Air Gun

As I mentioned above, the nozzles are one of the most significant parts in making a compressed air gun safe and OSHA compliant.  In combining our engineered nozzles with a quality air gun, this makes the EXAIR Safety Air Guns one of the best products on the market.  We currently have three different styles; the Precision, Soft Grip, and Heavy Duty.  These Safety Air Guns are ergonomically designed to fit comfortable in your hand; and they come with quality trigger mechanisms and a durable valve assembly.  The Precision Safety Air Gun is great for tight spaces and clearing out small holes.  The Soft Grip Safety Air Gun provides extra comfort for long extended uses, and the Heavy Duty Safety Air Gun is a rugged, heavy duty industrial air gun.  In combination with the EXAIR nozzles, the Safety Air Guns can offer another important attribute; we can save you money!!!  Compressed air is very expensive to make, and with our Safety Air Guns, we use less compressed air but still create a strong blowing force.  We do this by entraining the free ambient air into the air stream.  If you increase the mass of air to the target, it will give you a hard hitting force to remove debris from surfaces or to clean tools and holes.  The amplification ratio can be as much as 25 to 1.  That means that for every 1 part of compressed air, the EXAIR Nozzles will entrain 25 parts of ambient air.  So, the payback period for using an EXAIR Nozzle can be within weeks by the savings in the electrical cost.  With the EXAIR products, we were able to partner with Energy Star and power facilities.  For the amount of energy savings, some power companies offer rebates for using EXAIR products.   We can offer our services to see if your local power company is participating in these rebates.

1408SS-CS Precision Safety Air Gun

A substandard blow-off gun is unsafe, loud, waste compressed air, and increase production times.  EXAIR Safety Air Guns can help improve these situations in all these areas.  They are OSHA compliant, very safe and very quiet.  They use less compressed air which saves you money.  And with a variety of different nozzles, they can better fit your application to decrease down time.  EXAIR offers a 30 day unconditional guarantee on our cataloged items to try.  You can see for yourself on how effective these compressed air guns can be.  If you need help to match the best Safety Air Gun to your application, you can contact an Application Engineer.  And during the next two months, take advantage of the free 1” Flat Super Air Nozzle  offer.

John Ball
Application Engineer

Email: johnball@exair.com
Twitter: @EXAIR_jb

 

Super Air Knife Math – When 72 + 72 = 75

The Super Air Knife is the latest generation of EXAIR engineered air knife that dramatically reduces compressed air usage and noise when compared to other blowoffs.

Super Air Knife Data

From the chart above, the Super Air Knife when supplied with 100 PSIG of compressed air has a sound level of just 72 dBA (A-weighted decibel scale) when measured from 3′ away.  72 dBA is a moderate sound level, and some common comparisons are ‘normal speaking voice’ at 70 dBA and ‘living room music’ at 76 dBA.

For many processes, such as a bottling line drying operation, a pair of the air knives delivers the best performance. When asked, “what is the sound level for (2) of the knives,” a little Acoustic Engineering is in order. Because the decibel scale is logarithmic, the result is not as simple as adding 72 + 72 = 144.  144 dBA is in the range of a jet aircraft take off! Thankfully, both the actual sound level and the numerical value are determined another way.  I’ll spare you a lot of the math but the equation is as below.

Capture

… where SL1, SL2, SL3 are the sound levels in dBA of the each sound makers, for as many that are being combined.

In the case of (2) Super Air Knives operated 100 PSIG, the combined sound works out to be a quiet 75.0 dBA — a powerful, efficient and quiet product ideal for many applications and process within the manufacturing environment.

Super Air Knife
Super Air Knife

As a helpful rule of thumb- combining any (2) items will yield an increase of 3 dBA, combining (3) results in a rise of 4.8 dBA, and combining (4) results in a 6 dBA rise over just (1) of the items.

The Super Air Knives have been successfully used in a wide range of applications, including part drying, sheet and conveyor cleaning, web cooling, scrap removal, pre-paint dust blowoff, and many, many more.

To discuss your application and how an EXAIR Intelligent Compressed Air Product can make your process better and quieter, feel free to contact EXAIR and myself or one of our other Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Excessive Noise Levels Cost You Health and Money

OSHA and the CDC make these statements about noise exposure. Did you know almost 30 million American workers are exposed to dangerous noise levels almost daily, with over 72% of those reported incidents happening in manufacturing environments? Noise induced hearing loss is the second most self-reported occupational injury and since 2004, over 125,00 workers have experienced some level of permanent hearing loss. Excessive noise levels can also reduce productivity, contribute to increased stress levels, communication errors and an irreversible condition called tinnitus or a constant ringing in the ears. In fact, disability claims associated to occupational hearing loss has risen to over $ 242 million per year.

30mill
Noise Induced Hearing Loss Is One Of The Most Common Occupational Diseases.

In effort to reduce worker exposure and increase safety, OSHA introduced Standard 29 CFR 1910.95(a). As the standard reads, employees that are subjected to sounds levels in excess of 90 dBA, some type of engineered controls should be implemented by either using some form of PPE – Personal Protective Equipment, i.e. – earplugs, earmuffs, etc. or replacing the loud device altogether with an engineered solution that is designed to reduce the sound level. When a company is found to be in violation of the Standard, OSHA hands down costly fines, in some cases nearing almost $5,000. While providing PPE may seem like the inexpensive, “quick” fix, it actually could lead to more overall cost in the form of fines or claims, as now it is the responsibility of the operator to utilize the equipment provided. The better choice of the 2 options mentioned above, would be to replace with an engineered solution that is designed to lower the sound level.

OSHA Noise Level
Noise Level Chart per OSHA Standard 29 CFR 1910.95(a)

Take for example, a section of pipe with drilled holes across the length to cover wide area applications or an open end pipe or tube for more focused blowoff, both of which typically produce sound levels in excess of 100 dBA which would limit work exposure to only a couple hours per the above chart.

EXAIR’s Intelligent Compressed Air Products are designed to meet or exceed this standard. Our products entrain large volumes of surrounding air across the profile of the device which helps to reduce wind shear, ultimately lowering the sound level. When considering replacing drilled pipe, take a look at our Super Air Knife. The Super Air Knife produces a much lower sound level at only 69 dBA which is well under the allowable exposure times set forth by OSHA. Depending on the pipe or tube size, these can quickly and easily be replaced with one of our Super Air Nozzles by just adding a fitting to the existing line. For instance, our Model # 1100 Super Air Nozzle, with a sound level of 74 dBA, again falls well within the OSHA Standard.

sound-level-comparison
Sound Level Comparison

In addition, we offer our Digital Sound Level Meter to measure sound levels ranging from 35 to 130 dBA. The unit features a backlit LCD display, fast and slow response times, Max hold and includes NIST (National Institute of Standards and Technology) certification.

SoundMeter_new_nist225
Model 9104 Digital Sound Level Meter

For assistance in gaining OSHA compliance relating to your compressed air needs, please give us a call.

Justin Nicholl
Application Engineer
justinnicholl@exair.com
@EXAIR_JN

 

 

 

 

EXAIR’s High Velocity and Adjustable Air Jets – Now Available in Stainless Steel

Newly released, the EXAIR High Velocity Air Jet and Adjustable Air Jet are now available in Type 303 Stainless Steel, providing greater durability, corrosion resistance and a higher maximum temperature rating of 400 °F.  Type 303 stainless steel has good resistance to mildly corrosive atmospheres along with good oxidation resistance at elevated temperatures, making the stainless steel Air Jet a great choice for blowoff or part drying in your harsh environment. Both types of Air Jets are also available in brass, for applications at 275°F and below, and when corrosion resistance is not as critical.

6013ss
Model 6013SS – High Velocity Air Jet

Air Jets utilize the Coanda Effect – wall attachment of a high velocity fluid – to produce air motion in their surroundings. As illustrated above, a small amount of compressed air to the inlet (large black arrow) is throttled through an internal ring nozzle above sonic velocity.  A vacuum is produced, resulting in large volumes of surrounding, or “free” air, being pulled in through the jet (blue arrows.)

air jet How Air Jets Work

Both the outlet and inlet can be ducted for remote positioning applications.

If the end is blocked, flow simply reverses at well below OSHA dead end pressure requirements, ensuring safe operation.

The High Velocity Air Jet comes standard with an .015″ shim, and a Shim Set is offered that includes .006″ and  .009″ shims to provide additional adjustability and control.  The Adjustable Air Jet has a variable gap design, and can be adjusted and locked to meet the required airflow and thrust parameters.

When you are needing a simple solution to reduce excessive air consumption and noise levels on compressed air blowoff operations, EXAIR has a large line of Air Nozzles and Jets to solve your problems. You can contact an Application Engineer to discuss which Air Jet or Nozzle to best fit your application.

Brian Bergmann
Application Engineer

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