MIL-DTL-55668D
The maximum percent variation in the resistance of any conductor shall be as specified in table IV. At the
completion of the cycling test, the maximum percent increase in resistance of any conductor over the
resistance before cycling shall be as specified in table IV. All resistance measurements shall be at or
corrected to 20 C. The helical portion of the test specimen shall be measured for percent retraction
within 1 hour after completion of the cycling. Measurements shall be made on a horizontal surface as
18V
REFERENCE CORD
120 VAC
SAMPLE
METER
5V
RELAY *
(TYP)
45
K1
K1
12 VDC
K1
MV
A
B
40
50
25
S1
TO MOTOR
FIG. A
FIG. B
FIG. C
NOTES:
1. * Zero center, approximate full scale sensitivity 45 mv, or equal (see 6.).
2. Figure A shows the sample cord connected as one arm in a Wheatstone Bridge.
The opposite leg (reference cord) is an identical cord used to balance out temperature
fluctuations in the sample. The meter relay is set to trip at a fluctuation of 25
milliohms.
3. Upon tripping, the control relay K1 is pulled in, normally open contacts K1A are
closed, and K1 latches in the energized position until release switch S1 is depressed
as shown on figure B.
4. Figure C shows the second pole of relay K1 as it is used to control the flex tester
motor.
5. The power supply is shown as a battery for simplicity.
FIGURE 1. Basic circuit used for 180 degree bending flex control.
18
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