Lecture 5: Measurement Standards and Instruments

Introduction

Welcome to the fifth lecture of Electrical Measurements and Instrumentation.
Focus on measurement standards and their classification, as well as measuring instruments.

Definition: A measurement standard is a physical representation of a unit of measurement.
Classification of Measurement Standards:
- International Standards:
  - Units used in contemporary technology and scientific methods.
- Primary Standards:
  - Utilized in national standards laboratories globally.
- Secondary Standards:
  - Used in industrial measurement laboratories.
- Working Standards:
  - Employed in general laboratory instruments for accuracy and performance.

Definition: An instrument is a device for determining the magnitude or value of a quantity to be measured (e.g. voltage, current, power, energy).

Absolute Instruments:
- Determine the magnitude of the quantity directly.
- Example: Tangent galvanometer.
- Reading values vary each time, making them more suitable for laboratory use.
Secondary Instruments:
- Determine the magnitude in terms of instrument parameters.
- Calibration is done by comparing with other secondary instruments (e.g. voltmeter, ammeter, wattmeter).
- More practical for measurements.
Subcategories of Secondary Instruments
- Indicating Instruments:
  - Indicate the magnitude of the quantity measured.
  - Use a dial or pointer for measurement.
  - Examples: Voltmeter, ammeter, wattmeter, power factor meter.
- Recording Instruments:
  - Provide a continuous record of a quantity over a specified period.
  - Use a pen to record values on seed paper (fixed or moving).
  - Example: Graph memory.
- Integrating Instruments:
  - Totalize events over a specified time period.
  - Output is a product of time and any electrical quantity.
  - Examples: Energy meter, ampere-hour meter.