MIL-PRF-23648F
f. Voltage and current measurements shall be performed with a high impedance measuring circuit of
an accuracy ±1 percent or better.
g. Record Ith and Eth.
h. Compute and record the dissipation constant:
Eth × Ith
P
=
(milliwatts/°C)
50 75°C - 25°C
FIGURE 1. Measuring circuit.
4.8.11.1 Disks, rods, and beads. The test procedure shall be as follows:
a. Measure and record zero power resistance at 43.4°C and 75°C (see 4.8.2).
b. Mounting: See 4.8.2.3.a.
c. Power supply: Use a dc regulated power supply or battery.
d. Place thermistors in a still air controlled chamber with a minimum volume of 1,000 times the
thermistor body and test fixture.
e. With switch AA closed, adjust Eth/Ith ratio equal to the zero power resistance at 75°C. Allow 15
minutes (maximum) for stabilization of thermistors.
f. Set bridge (see figure 2) for null with the zero power resistance value measured at 43.4°C in
4.8.11.1a.
g. Prepare to measure time from the instant the switch is thrown to position BB to the time the bridge
indicator passes through the null point. Throw switch to BB position and record time.
h. Chamber temperature: 25°C ±1°C.
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