Chapter 11: Calibration and Control of Inspection Equipment
🔧 Overview:
In QA/QC, calibration ensures that instruments used in inspection (like vernier calipers, micrometers, pressure gauges, ultrasonic machines, etc.) give accurate results. Miscalibrated tools lead to incorrect judgments and potentially catastrophic quality failures.
📘 Key Concepts:
📏 1. What is Calibration?
Calibration is the process of comparing an instrument’s readings with a known standard and adjusting if needed.
Example: A micrometer is compared against a certified gauge block.
If deviation is found, it is either adjusted or tagged “Out of Calibration”.🏭 2. Why Calibration Matters in Mechanical QA/QC
Prevents false acceptance or rejection of parts.
Maintains traceability (ISO 9001/ISO 17025 compliance).Reduces product liability risk.
Enhances trust in inspection reports.
⚙️ 3. Common Instruments Requiring Calibration
| Equipment | Calibration Standard |
|---|---|
| Vernier Caliper | Gauge Blocks |
| Ultrasonic Testing Machine | Calibrated Reference Blocks |
| Pressure Gauge | Master Gauge/Dead Weight Tester |
| Welding Machine (Amps/Volts) | Digital Multimeter |
| Infrared Thermometer | Certified Temperature Source |
📑 4. Calibration Certificate Must Contain:
Equipment name and ID
Date of calibrationCalibration result (Pass/Fail)
Uncertainty of measurement
Next calibration due date
Authorized signature
🧰 5. Calibration Interval
Most instruments: Every 6 or 12 months
If dropped/damaged: Immediate re-calibrationCritical instruments (e.g., UT machine): Monthly or quarterly
🏗️ Industrial Example:
Scenario:
A pressure gauge at a petrochemical plant showed 20 bar. The operator believed the system was safe. In reality, it was 30 bar due to a faulty gauge, leading to pipe rupture and plant shutdown.
Lesson:
Calibration error cost millions. Every critical instrument must have valid calibration certificates.
📁 Field Application Checklist:
✅ Tag calibrated equipment with "CALIBRATED" sticker
✅ Maintain a Calibration Logbook
✅ Use only certified calibration agencies
✅ Quarantine expired/unreliable instruments
✅ Verify calibration before major inspections (like hydrotests, NDT)
Quiz: Calibration & Control of Inspection Tools
Q1. What is the primary purpose of calibrating inspection equipment?
A) To save time during inspection
B) To ensure accurate and reliable measurements
C) To identify the manufacturer
D) To comply with tax audits
🟩 Correct Answer: B
Q2. Which of the following instruments requires calibration in mechanical QA/QC?
A) Screwdriver
B) Welding rod
C) Vernier caliper
D) Paint brush
🟩 Correct Answer: C
Q3. A calibration certificate should include all the following except:
A) Equipment name
B) Measurement uncertainty
C) Employee ID of user
D) Calibration date
🟩 Correct Answer: C
Q4. Which ISO standard is most relevant to calibration laboratories?
A) ISO 9001
B) ISO 14001
C) ISO 45001
D) ISO 17025
🟩 Correct Answer: D
Q5. How often is a pressure gauge typically calibrated in industrial settings?
A) Once in 5 years
B) Every 10 years
C) Every 6 to 12 months
D) Only if broken
🟩 Correct Answer: C
Q6. Which instrument is used to calibrate a micrometer or caliper?
A) Infrared scanner
B) Measuring tape
C) Gauge block
D) Spirit level
🟩 Correct Answer: C
Q7. What action should be taken if an instrument fails calibration?
A) Continue using it
B) Replace it with uncertified equipment
C) Tag it as “Out of Calibration” and quarantine it
D) Adjust readings manually
🟩 Correct Answer: C
Q8. Which of the following could be a consequence of using uncalibrated equipment?
A) Enhanced product performance
B) Improved visual inspection
C) False results leading to product failure
D) Reduced inspection time
🟩 Correct Answer: C
Q9. Calibration traceability must be to which standard?
A) Local brand guidelines
B) National/International Standards (e.g., NIST, NABL)
C) Plant manager's approval
D) Client preferences
🟩 Correct Answer: B
Q10. What does a “calibration sticker” usually include?
A) User’s name
B) Test temperature
C) Calibration date and due date
D) Paint color code
🟩 Correct Answer: C