Staying Connected - August 2014

Triboelectric Noise in Medical Cables and Wires



The constant movement during
stress testing requires low-noise
cable to reduce triboelectric noise


When measuring low-level signals, noise in cable or wire may be problematic.  Noise in an ECG or other medical signal may make accurate diagnosis difficult or even impossible. 

Noise can come from many sources external to the cable but also from the cable or wire itself.  Noise generated within a cable is often called handling noise or cable noise, but this type of unwanted signal is more accurately described as triboelectric noise.

Recognizing that amount of triboelectric noise in medical cables should be minimized, The AAMI/ANSI EC53 requires the maximum peak-to-peak noise shall be less than 50 micro-volts (µV).  Many device manufacturers specify even lower noise limits for their cables and leadwires.

What is Triboelectric Noise?

The triboelectric effect is a phenomenon in which an electrical charge is generated by the friction between dissimilar materials which commonly occurs when they are rubbed together.  The amount of charge generated is largely dependent on the composition of the materials and the amount of friction between the materials.  Within medical cable assemblies and leadwires, random triboelectric noise is generated when the various conductors, insulation, and fillers rub against each other as the cable is flexed during movement.

Keeping triboelectric noise at acceptable levels requires careful material selection, design and processing as cable material is manufactured.

Testing for Triboelectric Noise


Diagram of triboelectric noise test
set-up specified in ANSI/AAMI EC53



Testing for triboelectric noise is done on cable or wire material, not cable assemblies.  EC53 section 5.5.4 specifies to “test a representative sample of cable material….”  A common question is why finished cables are not tested.  Besides the directive to test cable material, 7’ of cable is needed for the test, and most cables assemblies do not have that long of an uninterrupted span of cable material.  More significantly, movement at any termination point within the connector or cable assembly will typically generate a much greater amount of artifact than the noise generated by the triboelectric effect.



Typical equipment, including digital oscilloscope

Test Set-Up and Test Procedure

ANSI/AAMI details the test setup in section 5.5.4 and in Figure 8 of the EC53 standard.  A compliant set-up will include 36” high, heavy gauge steel posts been into a concrete or other sturdy floor set five feet apart, center-to-center.  A one-half inch thick steel plate is centered on the top of each post allowing 5’ of cable or wire to be held firmly between clamps set 48” apart.  Care must be taken in locating the test area away from interference from electrical panels, large electrical motors, vehicle traffic or foot traffic.

A weight equal to 40 times the weight of 1 foot of cable or wire is attached at the center of the wire to be tested.  The weight held level to the cable clamps and is dropped while voltage measurements are taken using a digital oscilloscope


Triboelectric noise drop test

Triboelectric noise displayed
on oscilloscope

Designing to Reduce Triboelectric Noise

A design process that begins with establishing and documenting performance and regulatory requirements is important in the development of medical cable assemblies and the cable material that will be used as part of the assembly.

Within multi-conductor cable the greater the number of conductors and surrounding material, the greater the opportunity to generate triboelectric noise.  Selecting materials that slip on each other easily increases flexibility; however, care must be taken to select materials that when rubbed together do not produce unacceptable levels of noise.

Cable noise can also be reduced by adding conductive materials and elements within the cable or wire that drain or dissipate the triboelectric charge away from the wire insulation.
 
Summary

Most diagnostic devices incorporate noise filtration or compensation; however, reducing noise at the source typically improves diagnostic quality.  Triboelectric noise can be reduced to very low levels by incorporating low-noise cable and wire material and designing connectors and strain reliefs to prevent any movement at the termination of conductors to the contacts.

Let the Affinity engineering team assist with your projects that require low noise cable assemblies or leadwires.  We have the knowledge and experience to help make your interconnect project successful.

For additional information, contact your local Molex Sales Engineer, Account Manager or call Affinity at +1 949.477.9495 or email us at custcare2@molex.com.

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Meet Linda Becker – Production Supervisor



Linda Becker, Second Shift
Production Supervisor


Linda joined Affinity in mid-May as a Production Supervisor for second shift.  The position had been open for several months because the company was trying to find the right person for the job.

Prior to becoming part of the Affinity team, Linda worked in manufacturing for over 30 years.  A large part of her career – 22 years - was with Expedia Media.  Most of Linda’s career has been in video replication starting in the Betamax and VHS days and more recently manufacturing staggering quantities of consumer DVDs and Blue Ray discs.  Linda also brings experience in warehouse operations and production scheduling.

Linda became involved with molding as VHS tapes died out and the media switched to DVSs.  “Pre-recorded DVDs are molded and we molded millions!  We molded DVDs for the major studios and for retailers like Blockbuster.  I was scheduling production in the local plant that I worked in and also for one of our plants in Chicago.”

Asked about her feelings about Affinity and Molex Linda replied, “I feel at home at Affinity.  The people are great – really friendly.  I like the atmosphere of teamwork.  Interviewing with Jennifer and Kevin was great.  They have both been very supportive.”


Linda discussing job being molded
with mold operator Sun Dao



Discussing the challenges of her new job, Linda commented, “Affinity is the first company that I have worked for that has been regulated by the FDA.  Besides learning about the products that we manufacture, I am also learning the regulatory requirements.  It is a big challenge, but one that I am enjoying.”

Linda works alongside Jerry Rivera, also a Production Supervisor for Affinity’s second shift and both report to Kevin Kom, Affinity’s Manager of Manufacturing.  “Kevin is a good boss,” said Linda.  “He is very knowledgeable about everything we manufacture and every manufacturing process.”

Linda grew up in in Orange County California: Garden Grove, Huntington Beach and Newport Beach.  She studied business at California State University Fullerton and now lives in nearby Cypress.

When not working, Linda enjoys sun activities by the pool or beach.  Asked about her hobbies, Linda said I love my dog Coda, a dachshund.  “Coda was a Christmas dog eleven years ago and is my best friend!”

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Hybrid Electronic Enclosures

Requirements for medical cables and interconnect systems are becoming more complex.  This often leads to the requirement that electronics to be incorporated into a connector or cable system.  A cable assembly in which active electronics have been incorporated is often referred to as a “smart cable.”

Encapsulating electronic components as part of a cable assembly is most commonly done using hard plastic shells that are screwed or ultrasonically welded together.  If tactile feel and appearance of the enclosure is important, one option is to overmold the enclosure with a softer rubber-like material.


Hard plastic clamshell case
holds and protects circuitry
from direct overmolding

Finished hybrid assembly after
overmolding inner clamshell with
softer thermoplastic material

Hybrid enclosures are a combination of hard plastic cases overmolded with a softer thermoplastic material.  Typically for this type of construction, the clamshell case is filled with a light weight potting material before being overmolded.  If this is not done, mold pressures could collapse the case.

There are several advantages to this type of enclosure including:

  • Protecting the electronic components from the temperature and pressure of direct overmolding
  • Achieving a lighter weight assembly by using a fill material that is lighter in weight than mold material
  • Producing larger overmolded electronic enclosures than could be achieved by direct overmolding.

With a hybrid design, the outer mold can be designed to follow the contours of the inner case allowing a uniform wall thickness.  A uniform wall thickness will typically produce a more consistent outer surface even when large assemblies are encapsulated by overmolding.

Summary

Incorporating electronic circuits into external enclosures can offer medical device manufacturers additional alternatives.  The Affinity engineering team has experience designing and manufacturing a wide variety of enclosures and incorporating circuits, connectors and cable assemblies.

For additional information, contact your local Molex Sales Engineer, Account Manager or call Affinity at +1 949.477.9495 or email us at custcare2@molex.com.

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Announcements, Information and Trivia



Americans drink
a lot of coffee


Jamaican Blue
Mountain Coffee
– Image by Mario Roberto
Duran Ortiz, courtesy
of Wikimedia Commons

COFFEE TRIVIA

Arabian Wine - Europeans first referred to coffee as, "Arabian wine".  The word "coffee" originally came from the Arabic "qahhwat al-bun" or "wine of the bean."

Americans Drink Coffee - Americans consume about 400 million cups of coffee per day!  That works out to about 146 billion cups of coffee per year which makes the United States the leading coffee consumer of in the world.

Mocha – In the 15th century coffee traders referred to the coffee beans cultivated in Yemen as Mocha.  Mocha – actually Al Mukha – was the name of the port from which coffee from Yemen was exported.

Blue Mountain Coffee – Actually properly referred to as Jamaica Blue Mountain Coffee is a classification of coffee grown in the Blue Mountains of Jamaica. Blue Mountain coffee is noted for its mild flavor and lack of bitterness.  Because of its reputation and limited availability this coffee is one of the most expensive and sought-after coffees in the world.

Mocha-Java:  Mocha-Java is the world's oldest coffee beans blend; combining the acidic Yemen Mocha with the full bodied Java bean.