A. Differentiate between the terms “Sensor”, “Transducer” & “Actuator

  • Transducer:
    • A transducer is a device which converts energy from one form to another.
  • Sensor:
    • A sensor is a device which converts a physical parameter to an electrical output
  • Actuator :
    • An actuator is a device which converts an electrical energy to a mechanical or physical output.

B. Difference between Active and Passive Sensors

Active Sensors (AS)
Passive Sensors (PS)
AS generates electrical output directly in response to an applied stimulus or measurements. PS produce a change in electrical output in response to applied electric stimulus measurements. (Passive components used for measurements capacitance, resister or inductor)
AS doesn’t require external AC or DC voltage source to produce electrical signal PS requires external AC or DC voltages to measure output electric quantity signal
e.g. solar cell, Thermocouple, Piezoelectric material etc. e.g. Accelerometers , Gyro sensors, Photo-diode, Thermister, Strain guage

C.Sensors used in Biomedical Instrumentation

Image of PPT Link

D. Types of Sensors errors categories in measurement

Sensors are also sustain certain errors and the errors is defined difference between the measured values and true values

  1.  

    Characteristic ErrorsThe characteristic errors are inherent in the device itself. i.e., the difference between the ideal characteristic transfer function of the device and the actual characteristic. This form of error may include a dc off-set value

  2. Dynamic Errors

    Many sensors are characterized and calibrated in a static condition. i.e., with an input parameter that is either static or quasi-static. Dynamic errors include response time, amplitude distortion, and phase distortion.

  3. Environmental Errors

    They most often include temperature but may also include vibration. shock, altitude, chemical exposure, or other factors.

 

F. Sensors parameter and Specification Terminology

Sensor range

(1) Full scale- range :

  • Minimum and maximum values of i/p or o/p variables

(2) Dynamic Range:

  • The total range of the sensor from minimum to maximum variable measurements

(3) Sensitivity:

  • The input parameter change in require to produce a standardized output change. In other words it says there is a change in output voltage for a give change in input voyage parameters.
  • Amount of change in o/p signal – given i/p =(ΔY / ΔX)

(4) Resolution:

  • The minimal changes of i/p parameter that can be produce to detectable change in the o/p signal

(5) Precision:

  • It refers to measure the degree of reproducibility of same quantity measurements under same prescribed conditions.
  • In other words it says repetability – set of measurement taken over period of time, and degree of reproducibility of measurements.

(6) Accuracy:

  • The maximum difference between the measured value (MV) of given results, and the true value (TV) of measured quantity at output of the sensors.
  • In other word,. it says the measured values of given results how close to true value of measured quantity.

(7) Offset:

  • The offset error: It defined as the output that will exist when it should be zero.
  • The offset sets before reading measurements -> adjust the offset to zero to get desired o/p.
  • The measurements must be made w.r.t. know or defined base line.

(8) Zero offset (Acclo sensor – g value)

  • voltage output at 0 g

(9) Bias drift with temperature

  • effect of temperature on voltage output at 0 g

(10) Linearity:

  • The linearity of the sensor o/p is an expression extent to which the actual measured curve of a sensor departs from the idea curve.

lin nonli

(11) Non-linearity:

  • To measure of how close to linear idea curve to the outputted voltage is proportional to the measured curve.
  • Nonlinearity is measured as a Maximum error (% M error) from a linear fit over the full-scale range.

(12) Hysteresis:

  • Following change in i/p parameters regardless in which direction of the change is made in o/p measured values
  • [OW] Log in measurements in the direction of variation entity – o/p values -> corresponds to same input regardless change in direction.

(13) Bandwidth:

  • Typically measures how many measurements can be made per second by sensors. Thus the bandwidth is usually quoted in Hz.
  • It indicates the limit of the near-unity frequency response of the sensor, or how often a reliable reading can be taken.

 

Ref. Study Links
  1. https://store.invensense.com/datasheets/invensense/MPU9250REV1.0.pdf