Basic Calibrations

Calibration

Meaning: Comparing an instrument with a known accurate standard to determine its error.

Interview Question: What is calibration?

Simple Answer: Calibration is the process of comparing an instrument with a known standard to determine how accurate it is.

Metrology

Interview Question: What is metrology?

Meaning: The science of measurement.Simple

Answer: Metrology is the science of measurement. It helps ensure that measurements are accurate and reliable.

Measurement

Meaning: Finding the value or size of something.

Example: Measuring temperature, pressure, weight, voltage, or time.

Measurand

Meaning: The specific thing being measured.

Example: If you measure room temperature, the measurand is temperature.

Instrument

Meaning: A device used to measure something.

Examples: Thermometer, multimeter, pressure gauge, weighing scale.

UUT or DUT

Meaning: The instrument being tested or calibrated.

● UUT = Unit Under Test

● DUT = Device Under Test

Simple Answer: The UUT or DUT is the instrument that we are calibrating

Reference Standard

Meaning: A more accurate instrument used as the basis for comparison.

Simple Answer: The reference standard is the accurate instrument used to calibrate another instrument.

Standard

Meaning: A known reference used for measurement.

Example: Certified calibration weights are standards for calibrating weighing scales.

ACCURACY AND ERROR

Accuracy

Meaning: How close the measurement is to the true or correct value.

Example: True value is 100 °C and the instrument reads 99.9 °C. It is relatively accurate.

Precision

Meaning: How consistent repeated measurements are.

Simple Explanation:

● Accuracy = Close to the correct value.

● Precision = Gives similar results repeatedly.

Error

Meaning: The difference between the instrument reading and the reference value.

Simple Formula:

Error = Instrument Reading − Reference Value

Correction

Meaning: The value needed to correct the instrument's error.

Simple Formula:

Correction = Reference Value − Instrument Reading

Example:

Reference = 100 °C Instrument = 98 °C

Error = −2 °C Correction = +2 °C

Bias

Meaning: A consistent difference or systematic error.

Example: An instrument always reads 1 °C higher.

Drift

Meaning: A gradual change in an instrument's performance over time.

Simple Answer: Drift means the measurement of an instrument slowly changes over time.

UNCERTAINTY WORDS

Measurement Uncertainty

Meaning: The doubt or estimated range around a measurement result.

Simple Answer: Measurement uncertainty tells us how much doubt there is in a measurement result.

Uncertainty Budget

Meaning: A list of all possible sources of uncertainty.

Examples:

● Reference standard

● Resolution

● Repeatability

● Environment

● Operator

Expanded Uncertainty

Meaning: The final uncertainty after applying a coverage factor.

Usually expressed as:

U = k × u

Coverage Factor

Meaning: A number used to expand the uncertainty.

Usually:

k = 2

This commonly represents approximately 95% confidence, depending on the uncertainty model and assumptions.

Standard Uncertaintu

Meaning: Individual uncertainty expressed in a standard form.

Repeatability

Meaning: The ability to get similar results when measuring the same thing repeatedly under the same conditions.

Reproducibility

Meaning: The ability to get similar results when conditions change.

Example: Different operator, different laboratory, or different equipment.

TOLERANCE AND ACCEPTANCE

Tolerance

Meaning: The maximum acceptable error allowed.

Example: ±1 °C means the acceptable error is between −1 °C and +1 °C.

Specification

Meaning: The required performance or limit provided by the manufacturer or customer.

Acceptance Limit

Meaning: The limit used to decide whether an instrument passes or fails.

Pass

Meaning: The instrument meets the required specification .

Fail

Meaning: The instrument does not meet the required specification.

In Tolerance

Meaning: The instrument's error is within the allowed limit.

Out of Tolerance

Meaning: The instrument's error exceeds the allowed limit.

Decision Rule

Meaning: The method used to decide whether an instrument passes or fails.

Interview Answer: A decision rule defines how measurement results and measurement uncertainty are considered when making a pass or fail decision.

Guard Band

Meaning: An additional safety margin used when making acceptance decisions.

Simple Explanation: We make the acceptance limit smaller to reduce the risk of making a wrong pass or fail decision.

Metrological Traceability

Meaning: The measurement can be connected through documented calibrations to recognized standards.

Simple Answer: Traceability means we can follow the measurement back through a documented chain of calibrations to recognized standards.

Calibration Certificate

Meaning: An official document showing the calibration results.

Usually includes:

● Instrument identification

● Results

● Error

● Uncertainty

● Traceability

● Calibration date

Certificate Number

Meaning: The unique identification number of a calibration certificate.

Calibration Interval

Meaning: The time between one calibration and the next.

Example: Every 6 months or every year.

Calibration History

Meaning: Previous calibration records of an instrument.

ISO/IEC 17025 WORDS

Meaning: An international standard for the competence of testing and calibration laboratories.

Simple Answer: ISO/IEC 17025 provides requirements to ensure that testing and calibration laboratories produce valid and reliable results.

Impartiality

Meaning: Being fair and free from bias.

Confidentiality

Meaning: Protecting customer information.

Competence

Meaning: Having the necessary knowledge, skills, and experience to perform a task correctly.

Validity

Meaning: The measurement result is reliable and technically acceptable.

Nonconformity

Meaning: Something that does not meet a requirement.

Example: Using an expired calibration standard.

Corrective Action

Meaning: Action taken to fix the cause of a problem and prevent it from happening again.

Preventive Thinking

Meaning: Identifying possible problems before they happen.

Risk

Meaning: Something that could negatively affect the laboratory or its results.

Audit

Meaning: A systematic check to determine whether procedures and requirements are being followed.

Internal Audit

Meaning: An audit conducted within the organization.

External Audit

Meaning: An audit performed by an outside organization.

Accreditation

Meaning: Formal recognition that a laboratory is competent to perform specific activities.

Quality

Meaning: Meeting the required standard or customer requirements.

Quality Assurance

Meaning: Activities designed to make sure the laboratory produces reliable results.

Quality Control

Meaning: Checking processes and results to detect problems.

SOP

Meaning: Standard Operating Procedure.

Simple Explanation: A written instruction explaining how to perform a task consistently.

Work Instruction

Meaning: Detailed instructions for performing a specific activity.

Procedure

Meaning: An approved method for doing a process.

Record

Meaning: Evidence showing that an activity was performed.

Example: Calibration data sheet.

Document

Meaning: Information that provides instructions or requirements.

Example: Procedure or manual.

CALIBRATION RESULTS

57. As Found

Meaning: The condition of the instrument before adjustment or repair.

As Left

Meaning: The condition of the instrument after adjustment or repair.

Before Adjustment

Meaning: The measurement results before correcting the instrument.

After Adjustment

Meaning: The measurement results after correcting the instrument.

Adjustment

Meaning: Changing an instrument to improve its measurement performance.

Important: Adjustment is different from calibration.

● Calibration = Determine the error.

● Adjustment = Change the instrument.

Verification

Meaning: Checking whether an instrument meets specified requirements.

Validation

Meaning: Confirming that a method is suitable for its intended purpose.

TUR AND TAR

TUR – Test Uncertainty Ratio

Meaning: Comparing the tolerance of the UUT with the measurement uncertainty.

Simple Formula:

TUR = Tolerance ÷ Expanded Measurement Uncertainty

Simple Explanation: A higher TUR generally means the measurement system has better capability to evaluate the instrument's tolerance.

TAR – Test Accuracy Ratio

Meaning: Comparing the accuracy or tolerance of the UUT with the accuracy of the reference standard.

Simple Explanation: TAR focuses more on the accuracy relationship between the UUT and the reference standard.

4:1 Ratio

Meaning: A commonly used traditional guideline where the reference system is significantly more capable than the instrument being tested.

Important: It is not a universal ISO/IEC 17025 requirement.

INSTRUMENT PERFORMANCE

Resolution

Meaning: The smallest change an instrument can display.

Example: A thermometer displays 25.1 °C. Its resolution is 0.1 °C.

Sensitivity

Meaning: How much an instrument responds to a small change.

Range

Meaning: The minimum and maximum values an instrument can measure.

Example: 0 to 100 °C.

Span

Meaning: The difference between the maximum and minimum range.

Formula:

Span = Maximum − Minimum

Zero

Meaning: The starting reference point of an instrument.

Zero Error

Meaning: The instrument does not read zero when it should.

Linearity

Meaning: How closely an instrument's response follows a straight or expected relationship across its range.

Hysteresis

Meaning: The instrument gives different readings depending on whether the value is increasing or decreasing.

Stability

Meaning: The ability of an instrument to maintain its performance over time.

Response Time

Meaning: How long an instrument takes to respond to a change.

ENVIRONMENTAL CONDITIONS

Temperature

Meaning: How hot or cold the environment is.

Humidity

Meaning: The amount of water vapor in the air.

Environmental Condition

Meaning: The surrounding conditions that can affect measurements.

Thermal Equilibrium

Meaning: When instruments have reached a stable temperature.

Stabilization Time

Meaning: The time required for an instrument to become stable.

ELECTRICAL CALIBRATION WORDS

Voltage

Meaning: Electrical pressure.

Current

Meaning: The flow of electricity.

Resistance

Meaning: Opposition to the flow of electricity

Frequency

Meaning: How many electrical cycles happen per second.

Unit: Hertz (Hz)

AC

Meaning: Alternating Current.

The electrical direction changes repeatedly.

DC

Meaning: Direct Current.

The electrical direction flows mainly in one direction.

TEMPERATURE CALIBRATION WORDS

Temperature Sensor

Meaning: A device that measures temperature.

Thermocouple

Meaning: A temperature sensor made from two different metals.

RTD

Meaning: Resistance Temperature Detector.

It measures temperature through changes in electrical resistance.

PRT

Meaning: Platinum Resistance Thermometer.

A highly stable and accurate resistance thermometer often used as a reference.

Dry Block

Meaning: A temperature source with heated or cooled wells used for calibration.

Temperature Bath

Meaning: A controlled liquid or medium used to create a stable temperature.

Immersion Depth

Meaning: How deep a temperature sensor is inserted.

PRESSURE CALIBRATION WORDS

Pressure

Meaning: Force applied over an area.

Pressure Gauge

Meaning: An instrument that measures pressure.

Pressure Calibrator

Meaning: A reference instrument used to measure or generate pressure during calibration.

Pneumatic

Meaning: Related to air or gas pressure

Hydraulic

Meaning: Related to liquid pressure.

Vacuum

Meaning: Pressure lower than atmospheric pressure.