Staying Connected - April 2009

Locking and Non-Locking Medical Connectors

Medical connectors can be divided into two broad categories: locking also referred to as latching and non-locking.  Each offers advantages and disadvantages depending upon the application.  The Affinity engineering team is often asked by our OEM partners to recommend which type of connector to incorporate into a new device.

Example of non-locking friction-fit
connector used for telemetry monitoring

Example of threaded
locking connector

Example “MS – mil-spec type connector
often used in early medical devices

Early Medical Connectors

Early medical cable assemblies used connectors borrowed from industrial and military cable assemblies.  These “MS” (mil-spec) metal connectors had knurled threaded couplers.  Once “screwed down” to the receptacle, this connector would not come loose inadvertently.  While this type of connection met the requirement that the cable not be disconnected unintentionally, they were typically difficult to connect and remove and provided no safety disconnect feature.

Example of locking connector
used for defibrillation

Locking Connectors

Locking or latching connectors are commonly used where a cable must remain connected to the device.  This is common in many devices including VADS (Ventricular Assist Devices) and defibrillators.  In these applications, inadvertent disconnection could jeopardize a life.  Another common application for locking connectors is when a cable assembly is used to connect two devices that are seldom if ever disconnected.

Ambulatory and telemetry monitoring also commonly use locking connectors.  In both of these applications, the device remains with the patient and cables are only disconnected from the device infrequently.

RJ connector – If “jerked”, locking
mechanism can be easily broken
requiring cable replacement

Locking RJ Type Connectors

We are occasionally asked our opinion regarding RJ type connectors.  We tend to steer OEM customers away from this choice because of inherent design issues.  While RJ connectors include a locking mechanism, if even minimal force is applied to the cable, the locking mechanism typically breaks.  Once the locking mechanism breaks, the plug is so poorly retained by the receptacle that a reliable connection is not possible and the cable is discarded.

Non-Locking Connectors

Medical cables require a positive connection between the plug and receptacle.  Any looseness in the connection will usually cause intermittent contact and poor signal quality.  This may make diagnosis or therapy difficult, if not impossible.  How firmly the connector is held by the receptacle is known as retention force and is almost completely controllable in the design process.  Pin and socket selection as well as the physical design of the plug and receptacle allow wide control over insertion, withdrawal and retention force.

Components of Retention Force

Retention force of a non-locking connector pair, plug and receptacle, is nominally made up of the sum of the retention force of each pin and socket as well as any friction between the plug insulator and the receptacle walls.  For connector pairs with few contacts, friction between the insulator and receptacle wall may be the largest factor in determining the total retention force.  For units with a larger number of contacts, little or no friction may be needed between insulator and receptacle wall.

An additional factor to be considered is that in a connector with more than a few contacts, the total retention force is greater than just the sum of each pin to socket retention force.  This phenomenon is detailed in a paper by Robert S. Mroczkowski, Sc.D “The Mating Game” in Connector Specifier magazine, December, 2001.  Mroczkowski states that “mating force will always be greater than that value (if all contacts mate at the same time) because of tolerance and housing interaction effects.”

Retention Force Specification

Retention force of non-locking pair
established early in the design process

Custom 17 pin non-locking connector achieved
specified retention force using tool-safe design

At Affinity, one of the specifications we attempt to establish early in a project with our OEM partners is the retention force required between the plug and receptacle.  Once established and documented, we design mold tooling in a “steel safe” manner.  This means that the tooling is designed to produce parts that initially have retention force lower than specified.  By removing metal from the mold tool, the part becomes larger and retention force is increased.  Removing steel in small increments allows retention force to be “dialed in.”  Sharing parts produced during mold trials allow our OEM partners to evaluate insertion and retention force and make adjustments, if necessary, before production parts are manufactured.

Safety Disconnect

Many applications, particularly those that connect between a patient and a stationary device, need a safety mechanism that will allow disconnection without harm to the patient or damage to the device or cable assembly.  If a cable is entangled in a hospital bed that is being raised or lowered, it can injure a patient or damage a device if it does not disconnect safely.  A cable lying on the floor can be caught by a foot and injury or damage can occur if it does not release.  The need to insure a reliable connection to the device, yet allow for safe, inadvertent disconnection is a design problem that the Affinity engineering team has devised a solution for a number of times.

Locking Connector with Safety Disconnect Feature

Affinity engineers were offered the opportunity to design a new custom medical connector that would both latch securely, but also would disconnect without damage if pulled or “jerked.”

Unique locking connector system
with safety disconnect feature

Latching mechanism designed to release before
damage to cable monitor or cable assembly

Based on a 9-pin D-sub connector, Affinity designed the locking mechanism and the panel bezel to work together.  When inserted, the connector “snaps” into place giving both tactile and audible feedback.  Held securely, most of the retention force is derived from the latching mechanism.  When pulled with force greater than four to six pounds, the latch releases before damaging either the cable or the monitor.  More importantly, the opportunity to injure a patient is greatly reduced.


Whether our OEM partners specify a locking or non-locking connector, the Affinity engineering team has the experience and expertise to assist.  Let us become part of your design and development team.  We can reduce your workload and speed your project to completion.  Contact Affinity Customer Care at 949-477-9495 or email to

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Meet Linda Snyder – Senior Sales Engineer

Linda Snyder –
Affinity Senior Sales Engineer

Linda brings over 20 years experience in the medical interconnect field.  She began her career in sales at Tronomed, working with Mary Phillipp and Bob Frank.  When Tronomed was sold, Mary and Bob left and founded Affinity and Linda continued her career with Tyco.  “I’ve wanted to hire Linda ever since we founded Affinity,” said Affinity President Mary Phillipp.

Affinity President, Mary Phillipp
and Linda Snyder

As a sales engineer, Linda will be responsible for working closely with medical device manufacturers in understanding their interconnect requirements and providing the optimum Affinity solution – be it a pre-engineered, modified or customized solution. She will report to Hank Mancini, Affinity’s Business Development Manager.

“Affinity’s business is growing and Linda will help make sure that our OEM partners receive the level of sales engineering support they need and expect” said Mancini.  “Linda is smart, very well respected in the industry, and works hard.  It is great to have her as part of the Affinity team.”

When asked why she decided to accept a position at Affinity Linda said “I was attracted to the culture and the people and Affinity’s commitment to total customer and employee satisfaction.  Affinity has a solid reputation for conducting business honestly, ethically and with respect for each other.”

Asked about what she saw as Affinity strengths, Linda said “Many device manufacturers want to work with a company that offers U.S. based engineering, customer support and manufacturing.  I am also looking forward to being an integral part of developing the surgical market for Affinity.”

Asked what she thought she would contribute to Affinity, Linda said “I have a passion for customer satisfaction, love this industry and offer a great deal of market and product knowledge.  I feel that I will fit in and be able to contribute to both our customer-partners and the company immediately”

Linda was welcomed to Affinity by long-time friends Cindy Oldynski (Affinity Quality Manager) and Candy Golding (Affinity Customer Care Supervisor), having worked with both at Tronomed.  When she learned that Linda had accepted a position with Affinity Candy commented “I really look forward to working with Linda again.  She knows the industry, products and customers very well.”

Linda lives in the Salt Lake City area.  Her husband, Ed, is also in sales and is an Account Manager for IBM Internet Security Systems.  She has six children with the last two still in college.  For fun and relaxation, Linda and her family enjoy jeeping, boating, and RV’ing.

Linda has served in the U.S. Marines Reserves for over twenty years.  Her tours of duty have been predominantly on the west coast.

Linda can be reached in her office at 801-572-1366 or on her mobile phone at 949-533-2894.  Her email address is  She can also be reached through Affinity’s office at 949-477-9495.

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PCB Lead Interface

Sometimes eliminating a connector is the best option!  Recently an OEM partner asked the Affinity engineering team to design a new interface.  The connection was intended to be semi-permanent, being captured in a case and only being changed if the lead assembly needed to be replaced.

Custom interface designed to be captured
by top and bottom of device case

Flex circuit and low-cost pin
header plugs directly into PCB

An overmolded assembly was designed to be captured and held securely by the top and bottom of a plastic case.  Instead of using a pair of connectors the interface was simplified and cost was reduced by using a small flexible circuit and a pin header.  The four pin connection on the end of the flex circuit is easily plugged directly into the device PCB. 

The Affinity engineering team has experience in designing unique medical interconnect systems.  If you would like to discuss your needs, contact us at 949-477-9495 or email to

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Announcements and Information

HRS 2009 – Heart Rhythm 30th Annual Scientific Sessions

Affinity will exhibit for the second year in a row at the Heart Rhythm Society’s annual Scientific Sessions.  Visit Affinity Medical in Boston May 14th to 16th at HRS 2009 at the Boston Convention Center.  Affinity will be showing examples of our unique custom cable assemblies and connectors in booth #260.


Electric Eel
Image source Wikipedia

Cinderella’s Slippers

Cinderella’s slippers were originally made of fur.  The story was inadvertently changed by a translator in the 1600’s, who confused the very similar old French words for “glass” and “fur” – verre and vair, respectively!

Electric Eel

With just one shock, an electric eel (Electrophorus Electricus) produces enough energy to light up the average three-bedroom house!

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 Monday through Fridays, except holidays.

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Affinity Medical Technologies

1732 Reynolds Ave
Irvine, CA 92614  USA
Phone: +1 949 477 9495
Fax: +1 949 477 9499