Introduction to Measurements

Introduction to Measurements

• Measurements are crucial for monitoring, controlling, and analyzing experiments.
• Applications include process control and experimental analysis.
• Measurement systems use sensors, transducers, and actuators.

Components of a Measurement System

• Active transducers generate their own signals (e.g., piezoelectric).
• Passive transducers need external power (e.g., changing resistor values).
• Analog and digital measurements differ in their output characteristics.

Key Characteristics of Measurement Instruments

• Readability – how easily readings are taken.
• Sensitivity – smallest detectable change.
• Accuracy – closeness to the true value.
• Precision – consistency of repeated measurements.
• Resolution – smallest measurable increment.
• Response time – time taken to detect a change.

Types of Sensors

• Limit switches use physical contact for presence/absence detection.
• Proximity sensors detect objects without touch.
  • Inductive – detect metal via electromagnetic fields.
  • Capacitive – detect metal and non-metal objects.
  • Optical – use light beams (through-beam, retroreflective, diffused).
  • Ultrasonic – use sound waves to detect distance/presence.

Temperature Sensors

• Thermocouples generate voltage at junctions of dissimilar metals.
• RTDs (Resistance Temperature Detectors) change resistance with temperature.
• Thermistors are temperature-dependent resistors (NTC and PTC types).
• IC temperature sensors use semiconductor technology.
• Bimetal sensors use different metal expansion rates, often used in thermostats.

Level and Flow Sensors

• Level sensors measure liquid or solid levels (capacitance, ultrasonic, radar).
• Flow sensors measure liquid or gas flow (turbine, magnetic flow meters).

Specialized Sensors

• Chemical sensors detect gas concentrations (e.g., MQ2 for smoke, LPG).
• Biomedical sensors combine physical and chemical sensing (e.g., glucose detection).
• Position sensors measure location or movement (e.g., potentiometers, LVDTs, encoders).

Actuators in Measurement Systems

• Actuators convert electrical signals to mechanical output.
• Types include electrical (DC motors, stepper motors, servo motors), hydraulic, and pneumatic.

Autonomous Systems & Sensor Fusion

• Autonomous systems make decisions based on real-time data.
• Automatic systems execute predefined commands.
• Systems have a perception system, a planning system, and a control system.
• Sensor fusion combines data from multiple sensors for improved accuracy.

Error Handling in Sensors

• Sensor uncertainty arises from errors in calibration, noise, or environmental conditions.
• Reduction techniques include calibration, sensor fusion, noise reduction, and environmental compensation.

Signal Processing

• Template matching detects signals based on patterns.
• Frequency domain analysis analyzes signals based on frequency content.
• Noise filtering removes unwanted signal components.