CCT Tools & Equipment Operation 4 — Questions and Answers
Question 1: A calibration technician needs to measure a bore diameter of 25.000 mm ± 0.002 mm. Which instrument is most appropriate?
- Vernier caliper with 0.02 mm resolution
- Outside micrometer with 0.001 mm resolution
- Bore gauge with 0.001 mm resolution set with a ring gauge (Correct answer)
- Steel rule with 0.5 mm graduation
Correct answer: Bore gauge with 0.001 mm resolution set with a ring gauge
A bore gauge set with a calibrated ring gauge provides internal diameter measurement at 0.001 mm resolution, suitable for the ±0.002 mm tolerance.
Question 2: When performing a multi-point calibration of a pressure transmitter, which sequence of applied pressures is required by most calibration procedures?
- Ascending points only from zero to full span
- Descending points only from full span to zero
- Ascending then descending points to detect hysteresis (Correct answer)
- Random points to avoid systematic error patterns
Correct answer: Ascending then descending points to detect hysteresis
Both ascending and descending pressure series are required to detect and quantify hysteresis error in the transmitter's output.
Question 3: Which environmental parameter most significantly affects the accuracy of a laser interferometer used for length measurement in a calibration laboratory?
- Relative humidity
- Ambient light level
- Air temperature and refractive index (Correct answer)
- Vibration from HVAC systems
Correct answer: Air temperature and refractive index
The laser interferometer measures length based on the laser wavelength in air; air temperature, pressure, and humidity affect the refractive index and thus the effective wavelength.
Question 4: A technician is calibrating a tachometer using a stroboscope. If the stroboscope flash rate is set to 1800 flashes per minute and the rotating target appears stationary, the shaft speed is:
- 900 RPM
- 1800 RPM
- 3600 RPM
- Any multiple of 1800 RPM (Correct answer)
Correct answer: Any multiple of 1800 RPM
A stationary image occurs when the shaft speed equals any integer multiple of the strobe rate (1800, 3600, 5400 RPM), so the actual speed must be verified by reducing the strobe rate.
Question 5: What is the correct way to handle gage blocks after use to prevent corrosion and maintain accuracy?
- Rinse with water and air dry
- Clean with solvent, apply a thin film of rust inhibitor, and store in a case (Correct answer)
- Store in open air to allow natural oxidation protection
- Polish with fine abrasive to remove any surface marks
Correct answer: Clean with solvent, apply a thin film of rust inhibitor, and store in a case
Gage blocks must be cleaned with solvent to remove fingerprints and contaminants, coated with rust inhibitor, and stored in a protective case to maintain their surface quality and dimensional accuracy.
Question 6: Which instrument is used to calibrate a thermocouple by comparing its output against a traceable reference at a defined stable temperature?
- Temperature dry-block calibrator or liquid bath with a reference PRT (Correct answer)
- A thermistor bridge calibrator
- A standard mercury-in-glass thermometer
- An infrared pyrometer
Correct answer: Temperature dry-block calibrator or liquid bath with a reference PRT
A dry-block or liquid bath calibrator provides a stable, uniform temperature zone where the thermocouple under test is compared side-by-side with a reference PRT traceable to ITS-90.
Question 7: When calibrating an oscilloscope's vertical gain, the technician applies a precision voltage source and adjusts the oscilloscope to display exactly 1 division per 100 mV on a 100 mV/div setting. This procedure verifies:
- Trigger sensitivity
- Bandwidth
- Vertical scale accuracy (gain accuracy) (Correct answer)
- Input impedance
Correct answer: Vertical scale accuracy (gain accuracy)
Comparing the deflection produced by a known precision voltage against the scope's scale setting verifies vertical gain (scale factor) accuracy.
CCT Tools & Equipment Operation 4
A calibration technician needs to measure a bore diameter of 25.000 mm ± 0.002 mm.
Which instrument is most appropriate?