CCT Calibration Techniques & Procedures 2 — Questions and Answers
Question 1: When calibrating a pressure gauge using a deadweight tester, the weights must be rotated slowly during the test primarily to:
- Increase the applied pressure incrementally
- Reduce friction effects in the piston-cylinder assembly (Correct answer)
- Heat the weights for thermal expansion compensation
- Verify the gauge's response time
Correct answer: Reduce friction effects in the piston-cylinder assembly
Rotating the weights minimizes piston friction, ensuring that the true hydraulic pressure equals the calculated weight force per unit area.
Question 2: A thermocouple calibration procedure requires measuring the reference junction temperature because:
- It determines the thermocouple wire resistance
- The EMF output depends on the temperature difference between measuring and reference junctions (Correct answer)
- It compensates for lead wire inductance
- It establishes the thermocouple's time constant
Correct answer: The EMF output depends on the temperature difference between measuring and reference junctions
Thermocouple EMF is a function of the temperature differential; without knowing the reference (cold) junction temperature, the measured junction temperature cannot be accurately determined.
Question 3: During an as-found/as-left calibration record, the 'as-found' data is most critical for:
- Documenting the adjustment made during calibration
- Determining whether the instrument drifted out of tolerance since the last calibration (Correct answer)
- Setting the new calibration interval
- Verifying the calibration standard accuracy
Correct answer: Determining whether the instrument drifted out of tolerance since the last calibration
As-found data captures the instrument's condition before adjustment, revealing drift and informing whether the calibration interval needs to be shortened.
Question 4: Which calibration technique applies multiple increasing then decreasing input values to characterize both hysteresis and repeatability?
- Single-point calibration
- Up-down (bi-directional) calibration (Correct answer)
- Substitution calibration
- Direct comparison calibration
Correct answer: Up-down (bi-directional) calibration
Bi-directional calibration applies inputs in ascending and then descending order, exposing hysteresis as the difference between up-scale and down-scale readings at the same nominal input.
Question 5: When calibrating a flow meter in situ, the preferred reference standard is often a master meter placed in series because:
- It eliminates the need for temperature correction
- Both meters experience identical flow conditions simultaneously (Correct answer)
- It provides a higher pressure rating than a portable calibrator
- It removes the need for density corrections
Correct answer: Both meters experience identical flow conditions simultaneously
A master meter in series measures the same fluid at the same temperature, pressure, and flow rate, making direct comparison highly accurate without needing to replicate lab conditions.
Question 6: A calibration tolerance of ±0.5% of full scale (FS) on a 0–100 psi gauge means the maximum allowable error at 25 psi is:
- ±0.125 psi
- ±0.5 psi (Correct answer)
- ±0.25 psi
- ±1.0 psi
Correct answer: ±0.5 psi
Full-scale tolerance means the error band is fixed at ±0.5% × 100 psi = ±0.5 psi regardless of where in the range the reading is taken.
Question 7: When performing a zero and span adjustment on a 4–20 mA transmitter, which adjustment should always be made first?
- Span, because it affects the linearity
- Zero, because span adjustments interact with the zero offset (Correct answer)
- Either order is acceptable for electronic transmitters
- Span, to avoid overdriving the output circuit
Correct answer: Zero, because span adjustments interact with the zero offset
Zero is adjusted first because span adjustments pivot around the zero point; correcting zero first minimizes the number of iterative adjustments needed.
CCT Calibration Techniques & Procedures 2
When calibrating a pressure gauge using a deadweight tester, the weights must be rotated slowly during the test primarily to: