Measurement Systems: Instruments and Standards

• Lecture 1 contents covers the basics of measurement systems.
• The lecture will cover:
• Measurement, measurand and measuring Instruments.
• Standards of measure
• Measuring instruments
• The Importance of Measurement in Manufacturing
• Instruments from an idea to be a device
• Classification of measuring instruments
• Sensors, transducer, and actuators
• Transducer principle of operations
• Transducer Static Characteristics /Selection Criteria

Measurement, Measurand and Measuring Instruments

• Measurement refers to gathering information from the physical world and comparing it with agreed standards.
• Measurand is a physical parameter or variable that is being measured, representing the output of the sensor unit.
• Measuring Instruments are man-made devices used to determine the value of a quantity or variable.

Standard of measurement

• Technique for determining object properties by comparing them to a standard.
• It can be an accepted quantity or quality that others are judged.
• It can be a physical representation of a unit of measure
• Used to obtain the values of physical properties through comparison.
• Standard bodies are:
• International Organization for Standardization (ISO)
• International Electromechanical Commission (IEC)
• American National Standards Institute (ANSI)
• Standard Council of Canada (SCC)
• British Standards (BS)

Measuring Instruments

• Instruments are man-made devices for determining the value of a quantity or variable.
• Instruments are designed to maintain relationships between the parameters being measured and the physical variables under investigation.

Measuring System

• It provides information about the physical value of a measured variable.
• In basic cases, the system can consist of a single unit providing an output reading or signal based on the magnitude of the input variable.

SI unit

• The metric system was developed in France in the 1790s
• In 1960, the metric system was revised, simplified, and renamed the System International d'Unites (International System of Units) or Sl system (meters, kilograms, etc.).
• This is the standard form of measurement in almost every country around the world, except for the United States.

Importance of Measurement in Manufacturing

• Ensures correct dimensions, which is key in manufacturing.
• Consistent measurements throughout processes, from material reception to shipping, ensure products match the design and maintain quality.
• Accurate measurement relies on skilled personnel and correctly managed measuring instruments.
• It improves product quality and production efficiency
• It maintains proper operation

Instruments from idea to device

• Consists of 6 steps:
• Instruments are designed on the basis of existing knowledge
• Testing and Use of Instruments
• Response and Drift
• Accuracy and Error
• Error Reduction
• Calibration of Instruments

Design and testing of Instruments

• Instruments are designed from existing knowledge, either from experience with physical processes or structured understanding of the process.
• After design and prototyping, instruments undergo evaluation tests.
• Simulated environment tests include climatic, drop, dust, insulation-resistance, vibration, electromagnetic compatibility, and safety and health hazard tests, regulated by national and international standards.

Response, Drift Accuracy and Errors

• Instrument signal response can be analyzed by assessing static and dynamic performance characteristics.
• Performance is indicated by accuracy, which is the closeness of measured values to the real values, combining dynamic and static responses.
• Ideal instruments have perfect sensitivity, reliability, and repeatability within applicable standards.

Error reduction and calibration of Instruments

• Controlling errors is an essential part of measurements and instrumentation.
• Techniques involve choosing components, filtering, bandwidth selection, reducing noise, and eliminating errors from subunits.
• Instrument calibration is essential for checking performance against known standards.
• It will lead into consistent readings, error reduction, and universal measurement validation.
• After calibration, performance is deemed error-bound for a period under similar conditions.
• Calibration involves comparing the instrument against primary or secondary standards, or against another device with known accuracy.

Methods of Measurement

• Direct methods measure an unknown quantity directly without comparison to a standard.
• Example measurements: current by an ammeter, voltage by voltmeter, resistance by an ohmmeter, power by wattmeter.

Indirect methods

• Indirect methods determine the unknown quantity by measuring functionally related quantities and calculating the desired quantity.
• Example: measuring voltage and current across a resistance to calculate the resistance.

Measuring Instruments

• Absolute instruments calculate physical values based on physical constants, like the angle of deflection, requiring mathematical calculation to determine the physical constant.
• Example: tangent galvanometer.
• Secondary instruments directly indicate the measurable quantities through deflection, which requires calibration with a standard instrument.
• Example: ammeter.

Secondary Instrument Classifications

• Indicating Instruments indicate the magnitude of the measured quantity using a dial.
  • Examples: voltmeter, ammeter, pressure gauge.
• Integrating Instruments measure the total energy supplied over a period of time.
• Examples: energy meter, watt-hour meter.
• Recording Instruments record circuit conditions over time.
  • They record electrical quantity variations over selected periods using a pen on paper.
  • Examples: data loggers like temperature and humidity recorders.