Staying Connected - September 2008

Cable Flexibility


Two four-conductor cables with
.187” diameter that exhibit
different degrees of flexibility
due to materials and design
.

The first impression of the quality of a medical cable is how it looks and feels to the user.  Regardless of what’s inside, it is the outside of the cable that is an obvious indication of the product.  The look and feel of a cable is largely influenced by the jacket material and by the flexibility of the cable.

Initial specifications for cable material often only include the minimum requirements:

  • Number of conductors
  • Type of shielding
  • Cable jacket material

An additional requirement that is not as easily defined is cable flexibility.  We often hear requests that cable be “soft and flexible,” a characteristic that is more difficult to measure and quantify than electrical or other physical parameters.  For some applications cable flexibility can be critically important. 

Smaller is More Flexible

Given the same construction, cable or wire flexibility is inversely proportional to the fourth power of the radius of the cable. For example, a 50 percent smaller cable will be about 90 percent more flexible.  With this in mind, cable flexibility is typically improved by using the fewest and lightest gauge conductors suitable for the application.


Cable flexibility is influenced by the choice of components

Cable Components

  • Jacket material – The type of material, thickness and durometer all effect cable flexibility.  Materials used in medical cables that may come in contact with the body need to meet FDA biocompatibility and cytotoxicity requirements.  A medical-grade thermoplastic elastomer (TPE) such as Santoprene® is probably the most common jacket material, but polyurethane can be used for extra ruggedness and silicone for optimal sterilization performance.

  • Insulation material – The type and amount of material can have a large impact on cable flexibility.  The most common conductor insulation material is rubberized PVC, but other insulating material such is also used.

  • Conductor – The size of the conductor plays a significant role in cable flexibility.  To a lesser extent, the conductor material can affect cable flexibility.  For most cables tinned copper is the material of choice.  If high flex life is needed, other alloys are available with much higher flex life characteristics.

  • Solid vs. Stranded Conductors – Stranded conductors are considerably more flexible than solid conductors.  Virtually all medical cables use stranded conductors to increase flexibility.  However, the same gauge conductor can be built up with different strand configurations which greatly affect flexibility.  Standard 28 AWG wire may be made up of the following combinations of conductors:

Number of Strands

Gauge of each Strand

1

28

7

36

16

40

19

40

40

44

65

46

The higher the number of strands, the greater the flexibility of the electrical conductor.  The trade off is that a higher number of strands increases the cost of the conductor.


28 gauge conductor with 16 strands
of 40 gauge tinned copper


28 gauge conductor with 40 strands
of 44 gauge bare copper
  • Fillers – Fillers are often added to “round-out” cable.  Commonly used filler materials are: cotton, vinyl, jute, polyethylene.  Fillers typically have little effect on cable flexibility.


2-conductor cable showing large amount of filler used to both
increase diameter and round-out the cable
.

  • Serves and tapes – These are materials spirally wound around cable components to hold them in position for subsequent processing.  The tightness or looseness of the wind can affect flexibility with a tight wind tending to restrict movement of components and reducing flexibility.


Teflon tape wrapped around a spiral shield before jacketing.

  • Shielding - Shielding can have a significant effect on cable flexibility.  Given the same percentage of coverage, a spiral shield is typically more flexible than a braided shield.  However a spiral shield may separate with continued flexing reducing the effectiveness of the shield.


A spiral shield typically offers greater flexibility
than either a braided or foil-wrapped shield
.

Braided shields typically offer the greatest amount of shielding, but when coverage is high, flexibility is compromised.  In high-flex applications, the braid can break down becoming abrasive and actually reduce cable life.  A foil shield, which is typically aluminum laminated to a film offers reduced flexibility and a shorter flex life.

  • Strength member – When additional tensile strength is needed in a cable, one method is to add a strength member within the cable assembly.  One common method is to add a core of synthetic fiber such as Kevlar which has very high tensile strength for its size and weight.


Example of a strength member as the core of a shielded cable..

Cable torque

While not directly related to cable flexibility, cable torque is becoming an important consideration for some medical applications.  If either the patient or instrument needs to twist during use, low cable torque may be desirable.  Low cable torque is a characteristic that can compliment high cable flexibility.

Summary

The desired flexibility of a cable assembly should be considered early in the design process.  When a high degree of cable flexibility is desired or required, the specification of materials, components and cable construction becomes more important. Involving Affinity engineers early in the design stage can help achieve your design goals, including cable flexibility.

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Meet Candy Golding – Customer Care Supervisor


Candy Golding -
Affinity Medical Technologies
Customer Care Supervisor
.

Everyone at Affinity Medical Technologies and many of our customers know Candy Golding.  During nine years at Affinity, Candy has shared her knowledge, time and skills with all members of the Affinity Medical team.  Her extensive experience in manufacturing, administration, supervision and customer service helps her do an exceptional job Affinity Medical.

Candy is always the first to volunteer assistance wherever needed.  In addition to providing excellent customer service she works on special projects, supervises the Customer Care department and Affinity’s front office with professionalism, business savvy and a humor.  Candy is currently on Affinity’s Lean Manufacturing team and is working with our IT Administrator to implement improvements to our order entry system.

As Customer Care Supervisor, Candy is involved with every department at Affinity Medical. She is always willing to answer questions or help other team members, assist vendors or help customers.  Her philosophy is: “If I accept it, I own it.”  Candy also has the uncanny ability to be able to identify just about every cable manufactured by Affinity.  If the part exists, you can bet she knows all about it!  

You might say Candy Golding wears many “hats” at Affinity Medical.  However, her main focus is our customers. She has been known to go more than the extra mile to provide great service to our customers.  Candy answered the phone late on Friday afternoon after closing.  A customer was facing an emergency situation and could not wait for shipment on Monday. Since everyone else had already left, Candy packed the cables, loaded them into her car and drove 45 miles in rush hour traffic to Los Angeles International Airport so that the cables would be delivered before Monday.


Candy Golding at Affinity’s
10th Anniversary Picnic
.

Candy’s customers truly appreciate her dedication and hard work on their behalf.  “I always ask about our service when I visit customers,” said Affinity Business Developer Hank Mancini.  “Without exception, Candy’s customers say she is the best customer service person they have ever worked with.”

When asked what she enjoys most about her job, Candy said: “I consider myself part of the customer’s team and do whatever it takes to help them achieve success. When the customer wins, Affinity wins.” 

Away from Affinity, Candy is the proud “Mom” to her pets; an active little dog named Pujo, a growing aquatic turtle, Spike and her desert turtle Herman. She has toured several countries in Europe and traveled to Africa on a photo safari. 

With a Bachelor’s degree in physical education, Candy enjoys tennis and other team sports in addition to reading mystery novels and weekly visits with her Aunt Doll.  On “girls day out”, Candy, her Aunt Doll and Cousin Jordan might enjoy dining out, attending the theater or shopping for treasures at specialty shops and boutiques.

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Ambulatory Monitoring Cable


Re-designed hybrid connector with
more robust overmolded strain relief
.

Some of the projects that Affinity has the privilege to work on are re-designs of existing cables.  The two most common reasons Affinity is asked to re-design existing products are to improve the quality and/or offer improved availability.

A little over a year ago we had the opportunity to work with an East Coast OEM to improve the cables used with their ambulatory ECG recorders.  After receiving samples of the existing cable and discussing quality and performance issues with the customer Affinity engineers designed a family of cables for two, three, five, and seven lead monitoring.

The customer had a large base of recorders in the field which used a common seven pin connector.  This meant that the re-design had to incorporate the same connector system, but with improvements.


Five lead version of re-designed
ambulatory monitoring cable
.

Re-design of the cable family included two configurations; with and without a yoke.  The two and three lead cables do not have a yoke, while the five and sevel lead cables do.  A yoke was necessary for the five and seven lead versions in order to use round cable which allowed the height of the connector to be as low as possible.

Another improvement was to change the orientation of the strain relief to direct the cable along the length of the recorder, rather than away from the device.  This allowed the recorder to more easily fit into a pouch or case.

If you would like to see examples of ambulatory monitoring cables that we have designed, contact Affinity Medical Customer Care at 949-477-9495 or email to customercare2@affinitymed.com.

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Announcements, Information and Trivia


Christopher Columbus.

Columbus Day

Since 1971, Columbus Day is celebrated on the second Monday in October.  Columbus Day will be celebrated this year on Monday, October 13, 2008.  The first Columbus Day celebration was held in 1792, when New York City celebrated the 300th anniversary of his historic landing in the New World in 1492.

The date of Columbus' arrival in the Americas is celebrated in most of Latin America as Día de la Raza ("day of the race"), commemorating the first encounters of Europe and Native Americans.

Affinity Medical will be open normal business hours on Monday October 13th.

Chocolate Trivia

Hawaii is the only US state that grows cacao beans to produce chocolate.

The melting point of cocoa butter is just below the human body temperature -- which is why it literally melts in your mouth.

The botanical name of the chocolate plant is Theobramba cacao, which means "Food of the Gods."


Suzann Sitka and Candy Golding
the Affinity Customer Care team


Affinity Customer Care - Hours of Operation

Affinity Medical Technologies customer care specialists are available from 7:00 A.M. until 4:00 P.M. Pacific Time.  You may reach all Affinity team members by phone or by email.  Email addresses are first initial followed by last name @affinitymed.com.

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Affinity Medical Technologies

1732 Reynolds Ave
Irvine, CA 92614  USA
Phone: 949-477-9495
Fax: 949-477-9499
Email: CustomerCare2@affinitymed.com