The Layman’s Guide to Interconnect

by | Jan 3, 2018 | Medical Connector | 0 comments

Ok, so we’ve discussed a little about what’s inside of a cable/interconnect and we’ve discussed a couple of the protection methods for a connector. In our upcoming posts we’ll dive into IEC 60601, MOPP and MOOP, how to protect your device from being used too many times, being counterfeited, or just being limited, so come back to read those posts.

STOP…  Coaxial, triaxial, stationary, DC Dielectric withstanding voltage, thermocouple—what does it all mean?

Before we go too deep we want to lay some groundwork. Let’s use this week to provide a little clarification on/definition of the terminology associated with connectors, interconnect solutions and cables.

Every industry has their vernacular, their terminology, and their acronyms.  The Connector, Interconnect, and cable market is no different. We have to decide between Coaxial and Triaxial cable and Stationary and Compliant contacts, along with about 20 other items before we can even begin to design the interconnect solution. So what do all of these things mean?

 

Contact Terminology: 

Stationary Contact

  • The non-moving contact, typically a round pin or a flat blade. Often the male contact but female in some systems (i.e. “banana plugs” where the female is a solid wall tube).

Compliant Contact

  • The contact which moves (deflects) to provide the contact force. Often the female contact but male in some systems (i.e. “banana plugs” where the male has deflecting beams).

Gender

  • Male: Connector half that contains the male pins (even if the outer shell appears to be a socket).
  • Female: Connector half that contains the female (socket) style contacts (regardless of the outer shell).

 

Mating Terminology:

Latching

  • A connector that has a positive lock to prevent accidental disconnect.

Detented

  • A connector that “snaps in” and is resistant to accidental disconnect.

Friction Mate

  • A connector that has no detent or latching (your toaster plug).

Insertion Force (aka, Mating Force, Engagement Force or Coupling Force)

  • The peak force required to fully engage two mating connector halves.

Extraction Force (aka, De-mating Force, Disengagement Force or Decoupling Force)

  • The peak force required to fully disengage two mating connector halves.

Live mating (aka, hot swapping)

  • Connectors that will be mated and de-mated with power applied. Okay in low voltage circuits but arcing and contact erosion make this something to avoid in higher voltage applications (> 12V peak voltage).

Non-live mating

  • Connectors that are mated and de-mated in the absence of power.

 

Environmental Terminology:

Operating Temperature

  • The full temperature range over which the connector/cable can operate within specification.

Storage Temperature

  • The full temperature range experienced in shipping and storage (prior to installation) which the system can withstand without damage once the temperature is restored to within the Operating Range.

Vibration

  • When connectors are in a high-vibration environment, the customer will likely have a vibration resistance requirement (and if they do not, then we should discuss and establish one). Types and magnitudes of vibration vary greatly and each requirement must be assessed independently.

Shock

  • Drop or other sources of impact. Same comments as “vibration” apply.

Environmental Sealing

  • There are many levels of sealing to protect both the connector and the surrounding environment (See IP ratings).

Ozone Resistance

  • A common requirement for outdoor applications. Satisfied by selection of appropriate connector plastics and insulation materials of cables.

UV Resistance

  • A common requirement for outdoor applications. Satisfied by selection of appropriate connector plastics and insulation materials of cables.

Chemical Resistance

  • Application specific and can impact plastics, contact materials, plating selection, cable jacket materials.

Sterilization compatibility

  • Sterilization can be one or more of a variety of available methods, the most common of which are: EtO (Ethylene Oxide; also known as gas sterilization), E-Beam (Electron Beam) and Gamma which are radiation based, and Autoclave (high heat, pressurized steam). Compatibility is achieved by understanding the relevant method(s) and the total number of cycles required then selecting materials known to perform adequately under each method’s conditions.

Sanitation compatibility

  • A specific form of chemical resistance (and sometimes a combination of chemical and heat resistance) to dozens of common chemicals and methods. Some of the more common are IPA (isopropyl alcohol), CIDEX® solutions (peracetic acid, phthalaldehyde and glutaraldehyde), Povidone (Iodine), hydrogen peroxide and the Sterrad® and Steris® processes (vaporized hydrogen peroxide).

 

Electrical Terminology:

Cycle Life

  • One cycle is the sum of one mating and one de-mating operation. Cycle life is the number of cycles the connector can withstand without failure.  NOTE!  “Failure” can be defined in many ways such as a) open circuits, b) shorts, c) mechanical failure (broken), d) an increase in contact resistance of a certain percentage or an increase beyond a specified threshold.  The customer’s definition of “failure” MUST be clearly understood before a cycle life can be specified.

Contact Resistance

  • The resistance typically reported in milliohms, measured at the interface between each mated contact pair (each female and male contact).

Current Rating

  • The maximum current the connector is rated to carry without exceeding performance limits. Typically, this is determined by a maximum allowable heat rise in the contacts under continuous current or final temperature of external surfaces.

Voltage Rating

  • The maximum voltage a connector can carry without exceeding performance limits. Typically determined by conductor spacing in consideration of DWV (Hipot) requirements.

DC Dielectric Withstanding Voltage (DC Hipot or DC DWV)

  • A specified voltage potential is applied to a conductor or contact while other conductors and contacts are at ground potential. The test is to quantify the insulation value between adjacent conductors or conductors to connector shell (if metal).  Failure modes include Breakdown (a short), arcing and leakage (low-level current flow through a high impedance short).

AC Dielectric Withstanding Voltage (AC Hipot or AC DWV)

  • A specified AC voltage and frequency (hertz) value applied to a conductor or contact while other conductors and contacts are at ground potential. This test will specify a maximum current leakage value.  In an AC Hipot test, some current flows due to capacitive coupling between adjacent conductors.

Insulation Resistance

  • A measurement of the insulation properties of a connector body or wire insulation and cable jackets. Usually tested with a 500VDC potential with a requirement of a minimum resistance value that is typically in the Megaohm range.

IEC 60601

  • A set of safety specifications for medical devices. Relative to connectors and cables it involves air gaps, creepage distance, touch-proofing, scoop proofing, latching requirements, AC and DC DWV and a host of other requirements.

 

Basic Cable-Specific Terminology (in no particular order):

Conductor

  • A wire, often copper but can be other alloys as well. Conductors can be solid or stranded.  Stranded conductors are made up of small strands of wire twisted together to make a larger conductor

Conductor Size

  • Either specified as AWG (American Wire Gauge) with increasingly larger numbers equating to decreasingly smaller wires or specified as mm2; the actual cross-sectional area of the conductor (common standard outside of the USA). AWG is also known as “Brown & Sharp” wire gauge.

Insulation

  • The dielectric material covering an individual conductor. Common materials include polyvinyl chloride (PVC), TPE (Thermoplastic Elastomer), Polyethylenes (LDPE, LLDPE, HDPE), Polyimide (Kapton®), PU (polyurethane) and both PTFE (Teflon®) and MFA (which are Fluoropolymers).

Jacket

  • The outer covering of a multi-conductor cable. Common materials include PVC, TPE, Silicone rubber and PU.

Standard or “tight” jacket extrusion

  • The jacket material is extruded directly over the insulated conductor bundle filling gaps (little air space remaining) and the jacket wall thickness varies depending upon the cable bundle construction inside.

“Tube Over” or loose jacket extrusion

  • The jacket is extruded as a distinct tube with consistent wall thickness, leaving air space inside around the insulated conductors. The jacket is not bonded to the insulated conductors

Shielding

  • A conductive wrap around one or more conductors within the jacket of a cable. Shields are typically composed of metal braid “tubing” or foil wrap. Foil shielded cables often include a “drain wire” as a method to conveniently terminate the shield.  Shields in cable assemblies can be terminated to ground at both ends (continuous) or one end (floating).  Coverage %, flexibility and cost are deciding factors.

Twisted pair  

  • When two wires twisted together, common construction in data cables to minimize cross-talk and external interference. In multi-conductor cables, each individual pair is often separately shielded (shielded twisted pair)

Tinsel wire

  • A high flex-life conductor; essentially a metal ribbon (like Christmas tree tinsel) is wrapped around a filler to make an expensive and difficult to terminate conductor.

Coaxial cable (coax)

  • A cable with a single insulated conductor surrounded by a second conductor constructed like a shield both thus with a common axis.

Triaxial cable (triax)

  • Similar to coax but with an additional insulation and “shield” layer creating three conductors with a common axis.

Thermocouple

  • Two wires of differing metallurgy joined at each end (the “junctions”). When the distal ends of the wires (each junction) are at different temperatures, the dissimilar metals produce a voltage proportional to the temperature difference.  The voltage is monitored and used as an indirect measurement of temperature.  Thermocouples are constructed from many different metal alloys pairs with Alumel/Chromel (type K), Chromel/Constantan (type E) and copper/Constantan (type T) being some of the more common pairings.

Fillers

  • Cotton yarn or plastic strands used to occupy space in a multi-conductor cable when needed to achieve roundness (used for cosmetic reasons).

Strength member

  • A high tensile strength strand or bundle with low stretch (Kevlar® is commonly used). When properly anchored at each end in a cable assembly, this protects fragile small sized conductors from tensile damage (breakage).

Flex life

  • The number of times a cable can be bent back and forth before conductors fatigue and break.

Well, now that we are all subject terminology experts, let’s continue on this magical mystery tour to becoming well-informed buyers of interconnect. But first, let’s contain our excitement and take a quick recess and gather our thoughts. If you have questions about how your team can work together with the team at ATL to create a fully-customized, high-performance interconnect system for your application—or maybe you just want to connect with one of our interconnect experts for a consultation or quote—either way, let’s talk.

How can ATL Technology help with your next connector or interconnect project?

ATL Technology in an interconnect solutions company, we specialize in design, development, and production of devices that are connector based. We succeed by incorporating our partners engineering teams with our engineering teams, their project management with ours, and so on.  We use our experience and expertise to benefit our partners by commercializing innovative devices that are accessing and treating previously untreated conditions in the human body.

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