Intuitive Cable and Connector Designs
One aspect of cable and connector design that is commonly overlooked is how intuitive the connection is for the intended user. Ideally, a user will be able to understand which end of the cable is connected to a device and where and how it should be connected.
Less Intuitive Design
USB A connector – is this the top?
USB A connector – or, is this the top?
A USB “A” connector, the end that plugs into computers, is an example of a design that is not intuitive. Without careful inspection, it is difficult to know which way the connector should be inserted into the receptacle. Users have a 50-50 chance of trying to insert the plug the wrong way. In almost any situation, this ambiguity is undesirable.
If an intuitive interface is desired, consideration should be given to this aspect of design at the very start of a project. Answering a few simple questions may help lead to an intuitive and easy-to-use design:
- How will the user know which end of the cable is to be plugged into the device?
- If there is more than one receptacle, how will the user know into which receptacle it should be plugged?
- How can the user determine the proper orientation to mate the connector to the receptacle?
- If there is a latching mechanism, how will the user know what is the proper way to connect or disconnect the cable?
Device End of the Cable
For some medical cable assemblies, it is obvious which end is the device end and which end is the patient end. As an example, EKG cables have multiple electrode connections on one end and it is apparent that is the patient end.
On the other hand, some cables are designed to connect between two devices and it is often not as obvious which end is to be connected to the primary device and which end connects to the secondary device.
Example of color-coded device
receptacle and color-coded
strain relief on cable –
mating is obvious
Besides mechanical and electrical performance requirements, the location and configuration of the device receptacle is often a key element in the user knowing how and where to connect a cable assembly. If multiple cables will be connected to the device extra consideration should be given to differentiate the receptacles, making the connection intuitive. Ideally, any markings should be large enough for those with less than twenty-twenty eyesight to see even in poor lighting conditions.
Connector orientation can be problematic if the user does not know how to plug the cable into the receptacle so that the pins and sockets engage properly. The plug or receptacle can be damaged if the connector is forced, rotated while the pins and sockets are engaged or inserted at an improper angle.
Example of connector with color-coded shell and angled strain relief making orientation obvious to the user
Connection to device is intuitive
due to color coding and
strain relief orientation
Example of a recessed keyway
which prevents a cable without
this specific keyway size and
shape from being plugged in
As medical electronics become smaller, the tendency is to also specify smaller connectors. Design consideration should be given to connector size so that any likely user will not find it difficult to handle the connector. This becomes a more significant design element when the intended user has reduced dexterity.
The unique shape of this receptacle
prevents misconnection and also prevents
all but intended cable from being used
A uniquely shaped connector and receptacle can make it apparent to the user where the plug is inserted and can also prevent misconnection. Besides misconnection, a uniquely shaped connector can prevent all but the intended cable from being used.
The shape of the connector can also make mating intuitive. An ideal situation is that when a user picks up a connector the proper orientation is obvious. One way to achieve this is to use a “D” shaped connector instead of a round connector. Even without markings or labels, it can be obvious that the user’s thumb fits the flat surface of the “D” which orients the connector for proper insertion.
Examples of color coded
overmolded strain reliefs
One way to achieve an intuitive cable design that is easy to use is to use color-coding on both the cable and device. This is especially helpful when the device has more than one receptacle. To achieve color designations on the connector, it is common to overmold the strain relief in a color that will match the color indicators on the receptacle. If a slip-on boot is desired, many off-the-shelf connectors can be ordered with colored strain reliefs. In addition, the pin insulator can be color coded to the device receptacle.
Often markings on the connector are employed to help users understand how the connector is mated to the device. When markings are used, care should be taken to ensure that they are large enough to be effective. If the design calls for a custom connector, raised markings can be molded into the connector which provides both a visual and tactile reference.
Large raised arrow helps user orient connector for proper insertion
Example of pad-printed arrow
to assist in connector insertion
Another option for marking is printing or applying a permanent label directly onto the connector. The materials and shape of most connectors limit printing to simple graphics in a single color. If multiple colors or complex graphics are desired, a permanent and durable label can be affixed to the connector. In either case, printing or graphics should be easily read or recognized to be effective.
When designing a medical interconnect device (a cable assembly or a connector), consideration should be given to making the intended connection as intuitive to use as possible. If the design of a medical connector or cable is intuitive, the intended user should be able to connect or disconnect with little or no thought and without the opportunity to damage the device or connector.
The Affinity engineering team can help you design an interface that is intuitive, robust and cost effective. Take advantage of our experience and expertise and help complete your project on-time by making us part of your team.
Bob Evans leads the
Affinity test lab
Bob Evans is a popular figure at Affinity Medical. His friendly personality and witty sense of humor make daily interaction with Bob a pleasant experience for everyone at Affinity. For over seven years, Bob has run Affinity’s test lab under the direction of Bob Frank, our Director of Engineering.
Like many others at Affinity, Bob worked at Tronomed before it was acquired. When the Tronomed plant in San Juan Capistrano was merged into the Tyco plant in Huntington Beach, Bob continued his career there until that plant was closed. He then joined Affinity working with many of his associates from Tronomed once again.
Bob’s primary function is to perform mechanical and electrical testing of new products. However, Bob’s work is not confined to the test lab. He is also called upon by Kevin Kom, our Manufacturing Manager and Cindy Oldynski, our Quality Manager to troubleshoot problems. His 18 years experience in medical device testing is a valuable asset to Affinity and to our customers.
In the test lab, Bob performs a wide variety of different mechanical and electrical tests to confirm that the product meets the customer’s specifications. The Affinity engineering team works with our customers to design a test protocol for each new product we develop. Once the protocol is approved by the customer, Bob begins testing. Typical tests include: flex testing, hi-pot, tensile strength, defibrillation, triboelectric noise and mate/unmate force testing. Throughout the test cycle, Bob’s attention to detail is valuable as he records and documents test results which are used to compile the test report.
Bob performing Hipot testing
on medical cables
Bob Evans is quoted as saying, “Our products never, I mean never leave Affinity until they fully comply with all customer specifications.” When a cable assembly does not pass Affinity’s rigorous testing, Bob often dissects it to locate the cause of the malfunction as part of our Failure Analysis. After conferring with Engineering, Manufacturing and Quality to determine what caused the failure; these findings, as well as possible solutions to correct problem, are shared with the customer.
When asked what he likes most about his job at Affinity, Bob replied, “The people. I have great relationships with everyone. I really enjoy coming to work every day.”
Bob was born in Washington, grew up in Fairbanks, Alaska and finally made his way to Southern California. He writes poetry and enjoys the beautiful scenery of Dana Point, California by taking long walks by the beach and eating at one of the many restaurants in Dana Point harbor with his wife, Trini.
Most standard medical cable assemblies use common copper as the conductor material. When the appropriate gauge and stranding of the conductor is chosen; this material when coupled with insulation, fillers, jacket and proper manufacturing techniques yield a cable with excellent long-term performance. If additional performance is desired or required and the gauge of the wire cannot be increased, the next option is to use a higher performance copper alloy.
Bare 28 gauge stranded copper conductor used in common lead wire assemblies has a tensile strength of about 5.2 pounds. When we add a shield and jacket to the bare copper conductor and terminate it properly, the tensile strength is increased. Tensile strength at the termination is typically above 12 pounds, well in excess of the ANSI/AAMI EC53 requirement of 7 pounds.
Tensile strength comparison copper vs. copper alloy conductor
In comparison, one of the bare copper alloy conductors we often use has a tensile strength of 8.2 pounds, approximately 60 percent higher than standard copper. With similar construction of a shield and jacket, tensile strength at the termination is above 18 pounds, a significant improvement that results in a more robust wire assembly.
If you would like more information on the option of using a copper alloy to increase cable or lead wire performance, contact the Affinity Engineering team at
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Wood Frog – in warmer months -
image source Wikipedia
The Alaskan Wood Frog, Rana sylvatica, survives long and cold Arctic winters by becoming a “Frogsicle.” It freezes solid and for several months its heart and respiration stop completely. When the weather warms up, the Wood Frog thaws and comes back to life!
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When he died, Swedish chemist and inventor, Alfred Nobel, left the bulk of his estate to endow annual prizes to honor men and women for outstanding achievements in physics, chemistry, medicine, literature, and promoting peace.
Nobel was criticized for becoming wealthy by inventing ways to kill people. He devoted himself to the study of explosives and especially the safe use and manufacture of nitroglycerine. Nobel combined nitroglycerine with diatomaceous earth and patented this mixture in 1867 as dynamite.
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