Sound: What Is It … More Importantly, Weighted Scales of Frequencies

We’ve blogged about sound and what exactly it is before, see the link. Understanding that sound is vibration traveling through the air which it is utilizing as an elastic medium.  Well, rather than me continue to write this out, I found a great video to share that is written in song to better recap how sound is created.

Now that we have that recap and understand better what sound is let’s dig a little deeper to better understand why some sounds may appear louder to a person when they may not appear different on a sound scale that is shown by something like a Digital Sound Level Meter.

Loudness is how a person perceives sound and this is correlated to the sound pressure of the frequency of the sound in question.  The loudness is broken into three different weighing scales that are internationally standardized. Each of these scales, A, C, and Z apply a weight to different frequency levels.

  1. The most commonly observed scale here in the USA is the A scale. A is the OSHA selected scale for industrial environments and discriminates against low frequencies greatly.
  2. Z is the zero weighting scale to keep all frequencies equal, this scale was introduced in 2003 as the international standard.
  3. C scale does not attenuate these lower frequencies as they are carrying the ability to cause vibrations within structures or buildings and carry their own set of risks.

To further the explanation on the A-weighted scale, the range of frequencies correlates to the common human hearing spectrum which is 20 Hz to 20kHz. This is the range of frequencies that are most harmful to a person’s hearing and thus were adopted by OSHA. The OSHA standard, 29 CFR 191.95(a), that corresponds to noise level exposure permissible can be read about here on our blog as well.

When using a handy tool such as the Digital Sound Level Meter to measure sound levels you will select whether to use the dBA or dBC scale.  This is the decibel reading according to the scale selected. Again, for here in the USA you would want to focus your measurements on the dBA scale. It is suggested to use this tool at a 3′ distance or at the known distance an operator’s ears would be from the noise generation point.

Many of EXAIR’s engineered compressed air products have the ability to decrease sound levels in your plant. If you would like to discuss how to best reduce sound levels being produced within your facility, please contact us.

Brian Farno
Application Engineer
BrianFarno@EXAIR.com
@EXAIR_BF

 

1 – Fun Science: Sound – @charlieissocoollike – https://youtu.be/xH8mT2IQz7Y

 

Static Elimination Improves Credit Card Printing and Production

PVC Base Sheet for Credit Cards

A company that made credit cards was having issues in their print quality, and static was the culprit.  They used PVC sheets as a base material to print on, and like with any non-conductive materials, static can be generated easily and create problems.  For this company, static was attracting dirt to the surface of the material, causing blemishes in the print.  They contacted EXAIR to find a solution.

When non-conductive materials slide, hit, peel, and rub; electrons from the surface can move from one atom to another; thus, creating static.  The type of material and the amount of movement governs the amount of static forces.  These strong static forces can attack debris and fibers, as well as generate shocks, misalignment, and machine jamming.  Another feature of static is that it can regenerate if the materials continue to slide, hit, peel, and rub.

For the company above, they were printing on 30 cm by 48 cm (12” X 19”) PVC sheets.  They used three different processes to print a complete credit card; silkscreen, digital, and offset.  After each printing process, they would lose sections of the sheet due to poor image quality.  At the end, they were losing between 20 to 30% in visual rejections.

For this application, we had to do two operations; remove the static and clean the surface from debris.  The Gen4 Super Ion Air Knife can do both of these operations at the same time.  With the laminar air stream that comes from the Super Air Knife, it can carry both positive and negative ions from the attached Gen4 Ionizing Bar.  Together, they can remove any type of static charge as well as becoming a very effective tool as a non-contact wiper to remove debris.  With this ability, the print quality would not be affected during cleaning.  Since static is a surface phenomenon, I recommended to also remove the static from the other side of the sheets.  We did not want to have any dirt or debris that could be remaining on the bottom surface to transfer from one surface to the next during stacking.  This could scrape the finish during loading and unloading of the sheets.

I recommended two pieces of a model 112012 Gen4 Super Ion Air Knives that are manufactured to 12” (30 cm) in length.  This customer can easily mount one above the sheet and one below the sheet prior to printing.  To operate the attached Gen4 Ionizing Bar, EXAIR offers two types of power supplies, a two-output unit, model 7960, and a four-output unit, model 7961.  They can save you money when needing multiple Static Eliminators to operate in your system.  With a model 7960 Gen4 Power Supply, they now had a system to remove static and clean the sheets.  Once they installed the Gen4 Super Ion Air Knives onto their system, the rejection rate dropped to near zero.

All EXAIR Gen4 Static Eliminators use one of two Power Supplies – your choice of the 2-port Model 7960, or the 4-port Model 7961.

Rejected parts are costly, wasteful, and reduce production rates.  If you have rejection from static problems in your system, EXAIR has a large line of Static Eliminators to help you.  You can contact an Application Engineer to review your application.  For the customer above, the Gen4 Super Ion Air Knives made it possible to generate more credit cards per sheet.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb