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Computing the Tolerance Value of a Resistor
Electronics & Mechatronics
Overview
This video explains how to calculate the tolerance range for a resistor, which determines if it's still functional or needs replacement. It outlines a three-step process: first, calculate the tolerance value by multiplying the resistor's nominal value by its percentage tolerance (converted to a decimal). Second, determine the higher limit by adding the tolerance value to the nominal value. Third, find the lower limit by subtracting the tolerance value from the nominal value. The video provides several examples using different resistor values and tolerances, emphasizing the importance of these calculations for electronics work.
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Chapters
- Resistor tolerance indicates the acceptable range of deviation from the nominal value.
- Tolerance is crucial for determining if a resistor is within acceptable operating parameters.
- If a resistor's measured value falls outside its tolerance range, it needs to be replaced.
Knowing a resistor's tolerance range is essential for troubleshooting electronic circuits and ensuring components are performing as expected.
A resistor with a value of 820 ohms and a +/- 5% tolerance must measure between 779 ohms and 861 ohms to be considered good.
- To calculate the tolerance value, first convert the percentage tolerance to its decimal equivalent (e.g., 5% becomes 0.05).
- Multiply the resistor's nominal value by its decimal tolerance.
- The result is the absolute tolerance value in ohms (or the relevant unit).
The tolerance value quantifies the maximum allowable difference between the resistor's actual measured resistance and its stated value.
For an 820 ohm resistor with 5% tolerance, the tolerance value is 820 ohms * 0.05 = 41 ohms.
- The higher limit is found by adding the calculated tolerance value to the resistor's nominal value.
- The lower limit is found by subtracting the calculated tolerance value from the resistor's nominal value.
- These two values define the acceptable operating range for the resistor.
These limits establish the acceptable range within which a resistor's measured resistance must fall to be considered functional.
For an 820 ohm resistor with a 41 ohm tolerance value, the higher limit is 820 + 41 = 861 ohms, and the lower limit is 820 - 41 = 779 ohms.
- The same calculation method applies regardless of the resistor's nominal value (ohms, kilohms, gigohms).
- Prefixes like 'k' (kilo) or 'g' (giga) should be maintained during calculations or converted consistently.
- Different tolerance percentages (e.g., 10%, 20%) require using their corresponding decimal values in the calculation.
This demonstrates the universality of the tolerance calculation method across various scales and precision levels.
A 2.5 kOhm resistor with 10% tolerance has a tolerance value of 0.25 kOhm, resulting in a range of 2.25 kOhm to 2.75 kOhm.
- After measuring a resistor, compare its value to the calculated lower and higher limits.
- If the measured value is within the calculated range, the resistor is good and can be used.
- If the measured value is outside this range, the resistor is out of tolerance and must be replaced.
This step directly applies the calculated tolerance range to make a practical decision about component usability in a circuit.
If a resistor with a calculated range of 1.44 ohms to 2.16 ohms measures 2.5 ohms, it is outside the acceptable range and needs replacement.
Key takeaways
- Resistor tolerance defines the acceptable deviation from its rated value, crucial for circuit functionality.
- The tolerance value is calculated by multiplying the resistor's nominal value by its tolerance percentage (as a decimal).
- The higher and lower limits define the acceptable range for a resistor's measured resistance.
- Higher limit = Nominal Value + Tolerance Value
- Lower limit = Nominal Value - Tolerance Value
- If a measured resistance falls outside the calculated tolerance range, the resistor is considered faulty and needs replacement.
- The calculation method remains consistent across different resistance values and tolerance percentages.
Key terms
Resistor ToleranceNominal ValueTolerance ValueHigher LimitLower LimitDecimal ConversionOhmKilohmGigaohm
Test your understanding
- What is the purpose of calculating the tolerance value for a resistor?
- How do you convert a percentage tolerance to a decimal for calculations?
- What is the formula for calculating the higher limit of a resistor's acceptable range?
- Why is it important to compare a measured resistance value against its calculated tolerance range?
- How would you determine if a resistor is out of tolerance based on its measured value and calculated limits?