---
title: "Factors driving circuit reliability"
subject: "Instrumentation II"
chapter: 7
key: "semester_5/instrumentation_ii:reliability-factors"
source: https://www.bctengineer.com/q/semester_5/instrumentation_ii/reliability-factors
site: BCT Engineering
---

# Factors driving circuit reliability

Instrumentation II · Chapter 7: Circuit Design

- Asked in: 2074 Chaitra, 2 marks; 2071 Chaitra, 2 marks; 2076 Asoj, 1+2 marks (asked 3 times)
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/instrumentation_ii/reliability-factors
- Whole chapter: https://www.bctengineer.com/md/semester_5/instrumentation_ii/chapter-7

## Question

What are the factors that drive the reliability of an electronic system?

## Short answer

Reliability drivers include component quality and derating, operating environment (temperature, vibration), electrical stress, design simplicity, manufacturing quality, software robustness, and maintenance. Failure rate doubles per 10°C rise.

## Answer

Reliability depends on these factors:

1. **Components:** quality, tolerances, failure rate (λ), the number of parts (system failure rate is the sum of part rates for a series system; fewer parts means higher reliability) and derating.
2. **Operating environment:** temperature (failure rate roughly doubles for every 10 degrees C rise), humidity, vibration, shock, dust, corrosion, radiation.
3. **Electrical stress:** voltage, current and power overload, transients, ESD, EMI, power supply quality.
4. **Design quality:** simple design, worst-case tolerance analysis, protection circuits, redundancy, thermal management and good layout.
5. **Manufacturing:** soldering quality, assembly process, testing, burn-in and quality control.
6. **Software and firmware:** bugs, robustness (for microprocessor systems).
7. **Maintenance and use:** preventive maintenance, correct use and operator errors.

Reliability is quantified as R(t) = e^(-λt), with MTBF = 1/λ.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How does failure rate change with temperature rise?
   A. Halves for every 10 degrees C
   B. Roughly doubles for every 10 degrees C
   C. Does not change
   D. Doubles for every 100 degrees C
   Answer: B. Higher temperature accelerates failure mechanisms. (Key point: Temperature)

2. How is the failure rate of a series system found?
   A. Sum of the part failure rates
   B. Product of the part failure rates
   C. Smallest part rate
   D. Average of the rates
   Answer: A. More parts therefore mean higher system failure rate. (Key point: Series system)

3. What is reliability for a constant failure rate lambda?
   A. R(t) = lambda t, MTBF = lambda
   B. R(t) = 1/lambda, MTBF = e^lambda
   C. R(t) = t/lambda
   D. R(t) = e^(-lambda t), MTBF = 1/lambda
   Answer: D. Exponential law with MTBF as the inverse of lambda. (Key point: Reliability formula)

## Related in Instrumentation II

- [Fault tolerance and redundancy for reliability](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Afault-tolerance-schemes) — Instrumentation II, chapter 7, asked 4×
- [Grouping circuits in electronic instrument design](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acircuit-grouping) — Instrumentation II, chapter 7
- [Factors while routing signal traces on PCB](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aroute-factors) — Instrumentation II, chapter 8, asked 4×
- [Routing factors and avoiding crosstalk](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Aroute-factors-crosstalk) — Instrumentation II, chapter 8
- [Case study: critical factors in process control](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-critical-factors) — Instrumentation II, chapter 10, asked 2×
- [Case study: workflow, factors, proposed design, benefits](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Acs-2076chaitra) — Instrumentation II, chapter 10

## Related in other subjects

- [Driving factors for performance design](https://www.bctengineer.com/question.md?key=semester_5%2Fcomputer_organization_and_architecture%3Aperf-design-factors) — Computer Organization and Architecture, chapter 1
- [Electric drive and motor selection factors](https://www.bctengineer.com/question.md?key=semester_6%2Findustrial_power_distribution_and_illumination%3Aelectric-drive-motor-selection) — Industrial Power Distribution and Illumination, chapter 5
- [Exponential reliability and system reliability](https://www.bctengineer.com/question.md?key=semester_7%2Fmachine_design_ii%3Areliability-exponential-series-parallel) — Machine Design II, chapter 4
- [Driving point impedance and voltage ratio, two 0.5 F](https://www.bctengineer.com/question.md?key=semester_3%2Felectrical_circuit_theory%3Adriving-point-impedance-voltage-ratio-two) — Electrical Circuit Theory, chapter 5