How to Derate Electronic Components
- 1). Place a resistor on your work bench and a thermometer next to it.
- 2). Place the ohmmeter at the bottom of an insulated box, such as an ice cooler. Place a thermometer in the cooler, next to the ohmmeter. Set the ohmmeter's resistance range to 10,000 ohms. Attach the positive and negative leads to the ohmmeter. Arrange the leads such that the positive and negative leads hang over the top of the box, and then attach them to left and right ends of the 20,000 ohm resistor.
- 3). Write down the resistance on the ohmmeter display and call this temperature the "initial temperature." Write down the temperature in the box and call this temperature the "box temperature." Write down the temperature on the thermometer that is next to the resistor. Call this temperature the "initial resistor temperature."
- 4). Place a heat source in the vicinity of the resistor and resistor thermometer. Slowly increase the temperature of the heat source and monitor the resistance thermometer and the ohmmeter thermometer.
- 5). Wait until the resistor thermometer reaches a value that is 10 degrees higher than the initial resistor temperature. Write down this temperature and call it the "final temperature." Write down the resistance value that is displayed on the ohmmeter. Call this the "final resistor temperature." Check that the temperature in the ohmmeter box has not changed more than 1 degree.
- 6). Subtract the final temperature value from the initial temperature value. Call this value the change in temperature. Subtract the final resistance value from the initial resistance value. Call this value the change in resistance. Divide the change in resistance by the change in temperature. Call this value the "resistor temperature derating factor. "
- 7). Choose a temperature at which you want to calculate the value of your resistor. Call this the derated temperature. Subtract the initial temperature from the derated temperature. Multiply the result by the resistance temperature derating factor. Add this value to the initial resistor value and call this the value of the 20,000 resistor at the derated temperature.
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