Characteristics of Sensors

Introduction

• Overview of sensor characteristics.
• Two main types: Static Characteristics and Dynamic Characteristics.

Static Characteristics

• Measurement of quantities that change slowly or are mostly constant.
• Based on steady-state response.

Key Static Characteristics

1. Accuracy and Precision

   • Accuracy: Capability to measure close to the true value.
     • Measured by absolute and relative errors.
     • Absolute error = Measured value - True value.
     • Relative error = Absolute error / True value.
   • Precision: Closeness among a set of measured values.
     • Precise when values are near to each other but not necessarily close to the true value.
     • Accurate measurements are always precise.

2. Range and Span

   • Range: Minimum and maximum values a sensor can measure.
     • Example: RTD temperature range = -200°C to 800°C.
   • Span: Difference between maximum and minimum values.
     • Span for RTD = 800 - (-200) = 1000°C.

3. Sensitivity and Resolution

   • Sensitivity: Ratio of change in output to change in input.
     • Higher sensitivity means smaller changes in input lead to changes in output.
     • Example: Sensitivity of thermal sensors.
   • Resolution: Smallest change in input that can be detected.
     • Example: Voltmeter with range 0-10V and 100 divisions = 0.1V resolution.

4. Hysteresis and Linearity

   • Hysteresis: Difference in output for increasing vs. decreasing input.
     • Width of output error known as hysteresis.
   • Linearity: Deviation of measured value from ideal curve.
     • Ideal curve is linear; maximum error is noted as deviation from this curve.

5. Reproducibility and Repeatability

   • Reproducibility: Ability to produce the same output over time, across different operators/instruments.
   • Repeatability: Ability to produce the same output under the same conditions.

Dynamic Characteristics

• Characteristics related to the presence of energy-storing elements.
• Exist when input signals change rapidly.
• Determined by analyzing sensor responses to various input waveforms: impulse, step, ramp, sinusoidal, etc.

Conclusion

• Understanding these characteristics is crucial for effective sensor application and analysis.