MIL-PRF-22097 Resistors, Variable, Nonwirewound, Adjustment Type, General Specification ForThis specification covers the general requirements for multi-turn lead screw actuated and single turn nonwirewound, variable resistors with a contact bearing uniformly over the entire surface of the entire resistive element, when positioned by the actuator. These resistors are capable of full load operation \(where maximum resistance is engaged\) at a maximum ambient temperature of 70 Degrees C and 85 Degrees C, and are capable for continuous operation when properly derated, at a maximum temperature of 125 Degrees C and 150 Degrees C \(see figure 1\). These resistors have a resistance of ┬▒10 percent \(see 3.1\).

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MIL-PRF-22097J

4.7.8.1 Setting stability. The contact arm shall be set at approximately 40 percent of the actual effective electrical

travel. An adequate dc test potential shall be applied between end terminals. The voltage between the end

terminals, and the voltage between one end terminal and the contact arm, shall be measured and applied to the

following formula:

E1 x 100

Setting stability =

Where:

E1 = Voltage across one end terminal and the contact arm terminal.

E2 = Voltage across the end terminals.

The difference between the initial measurement made before the environmental test and the measurement made

after the test indicates the setting stability in percent.

4.7.9 Resistance temperature characteristic (not applicable to characteristic A). Resistors shall be tested in

accordance with method 304 of MIL-STD-202 (see 3.14). The following details shall apply:

a. Test temperatures: As specified in table XI.

b. Measurement at the end of each period: Total resistance shall be measured as specified in 4.7.2.1, at the

temperature maintained during the period.

4.7.9.1 Resistance temperature characteristic (applicable to characteristic A only). The resistors shall be

maintained at each of the ambient temperatures listed in table XI (see 3.14). Resistance measurements shall be

made at each temperature, 30 minutes to 45 minutes after resistors have attained that temperature. The temperature

adjustment shall be accurate within 1OC. The percent change in resistance, referred to a reference temperature of

25 C, shall be computed by the following formula:

(R-r) x100

Percent change in resistance =

Where:

R = Resistance at the test temperature.

r = Resistance at reference temperature.

4.7.10 Moisture resistance. Resistors shall be tested in accordance with method 106 of MIL-STD-202 (see 3.15).

The following details and exceptions shall apply:

Mounting: Clamped, or otherwise mounted with the terminals exposed on a stainless steel panel of

sufficient size to extend beyond the resistor extremities, and in such a manner as to allow electrical

connections to made to the terminals.

Initial measurement: Immediately following the initial drying period, total resistance shall be measured as

specified in 4.7.2.1.

Polarization and loading voltage: The resistors shall be divided in two equal groups; one group shall be

subjected to polarization and the other group to load.

(1) Polarization: During steps 1 to 6 inclusive, a 100 volt dc potential shall be applied with the positive lead

connected to the resistor terminals tied together, and the negative lead connected to the mounting

plate.

(2) Loading voltage: During the first 2 hours of steps 1 and 4, a dc potential equivalent to 100 percent rated

wattage, but not exceeding the maximum rated voltage (see 3.1), shall be applied to the resistors.