Coil Cords – Physical Shape and Performance

Recently Meridian Cable was approached by a medical device company to solve a “spring” problem.  The medical company’s device weighs about 1 pound and will be connected to a patient via a coiled cord.  The medical company wanted the device to stay put when the cable was extended 5 inches, however they didn’t want the 1 pound mass of their device to pull on the patient if the device fell off a standard bedside height surface.  This meant the device had to almost free fall for 22 inches.

The customer also had physical requirements for the coil diameter and overall cable length.  The coil diameter could not exceed 0.60 inches in outside diameter and the overall cable length must be no longer than 42 inches.  The coiled diameter could be smaller and the retracted length, or coiled section, could be adjusted.

To solve this problem the following force parameters were established.  At 5 inches extended the force must be less than 0.25 pounds and at 22 inches extended the force must be between 1.0 and 1.25 pounds.  The 5 inch force was designated “B” and the 22 inch force was designated “C”.

Several cable constructions were made, but all of them had 6, 24 awg conductors.  We settled on two cable designs with the primary difference being the type of shielding used.  Testing was performed over several days using various configurations and the results were achieved.

SAMPLE # CABLE # RETRACTED
LENGTH
(inches)
ROD
OD
(mm)
COIL
OD
(inches)
“B”
FORCE
(pounds)
“C”
FORCE
(pounds)
1 3 6.25 5 0.55 0.55 2.20
2 3 6.25 6 0.57 0.53 1.43
3 3 6.25 8 0.68 0.13 0.66
4 3 5.5 4 0.54 0.59 2.50
5 4 6.38 5 0.55 0.44 1.60
6 4 6.75 6 0.57 0.42 1.30
7 4 6.75 8 0.68 0.08 0.62
8 4 6 4 0.54 0.88 2.70
9 3 6.25 7 0.61 0.26 1.01
10 3 10.25 6 0.57 0.13 0.77
11 3 4.25 8 0.68 0.31 1.10
12 4 6.38 7 0.61 0.29 1.01
13 4 10.5 6 0.57 0.18 0.77
14 4 4.38 8 0.68 0.24 1.03

Based on the above data specific samples were made for the customer to test.  See a video of the coil cord manufacturing process or view some of our coil cord designs.