Sensors and Transducers

Question 1

what is a sensor ?

Answer 1

It is device that provides an electrical signal related to physical quantity being measured

Question 2

What is a transducer ?

Answer 2

often used instead of ‘sensor’, elements used to convert signals from one form to another

Question 3

What are sensors/tranducers ANALOGUE

Answer 3

IF and only if the output is ANALOGUE. An Analogue output changes in a continuous way and its size is proportional to the size of the variable being measured.

Question 4

What are sensors/transducers DIGITAL

Answer 4

IF and only if the output is of a DIGITAL nature.

Question 5

What are smart sensors?

Answer 5

Sensors combined with signal conditioning and microprocessor.

Question 6

What is the Microprocessor ?

Answer 6

It is the brain of mechatronic system. It processes the data and performs all the arithmetic. It is the ARITHMETIC LOGIC UNIT of the mechatronic system. The microprocessor is often called the CPU.

Question 7

What is a microcontroller ?

Answer 7

Single chip with including a Microprocessor, memory and peripherals.

Question 8

Range of span of transducers

Answer 8

RANGE: Defines the limit between which, input can VARY
SPAN: MAX INPUT-MIN INPUT

Question 9

Accuracy of transducers

Answer 9

extent t which the value measured might be wrong (summation of errors, incl calibration error).

Question 10

Hysteris error of transducers

Answer 10

Transducers can give different output from same value of quantity being measured. MAX difference in output for increasing and decreasing value of input.

Question 11

Error of transducers

Answer 11

Measured value - true value

Question 12

Sensitivity of transducers

Answer 12

How much output there is per unit input (O/I) output variation/input variation

Question 13

Non linearity error of transducers

Answer 13

Error defined as max difference from straight line

Question 14

Repeatability/reproducibility of transducers

Answer 14

Ability to repeat/reproduce same output of the same input value. Percentage of full range output.
error resulting from same output not being given with repeated application
Repeatability = (Max-Min values/ full range)x100

Question 15

Stability of transducers

Answer 15

ability to give same output for measuring a constant input over time. Drift is used to express change in output (zero drift: change when there is zero input)

Question 16

Resolution of transducers

Answer 16

Input varies over the range, output signals for some sensors may change in small change (smallest value of I variation observable from output)

Question 17

ex: Resistance temperature detectors (RTDs)

Answer 17

resistance of most metals increases over a limited Tr, in a reasonably linear way with temperature.

Question 18

ex: Thermistors

Answer 18

Resistance of semiconductors (oxides that thermistors are made from) decreases in a very nonlinear manner with an increase in temperature.
Such thermistors have negative temperature coefficient (NTCs)

Question 19

ex: Thermocouple

Answer 19

Two strips of metal joined together, p.d occurs across the junction. The p.d depends on metal used and temperature of the junction. By measuring voltage across junction, can measure temperature

Question 20

ex: (light) different types of photodiodes

Answer 20

Highly non linear, integrated light-to-voltage sensors. Requires A/D conversion to be integrated. Light->sensor->voltage

Question 21

Actuators

Answer 21

devices providing physical quantity related to electrical output of control system.

Question 22

Actuators-main specs and types

Answer 22

No standard specs, depends on type of automation

TYPES of automation:
Pneumatic actuators
Mechanical actuators
Electrical actuators (electrical DC motor)