Sensors & Transducers: Unit 1 Part 1

Que1.1. Define detector and transducer with a common  illustration. 

Answer  Detector  1. It’s defined as an element which produces signal relating to the  volume  being measured.  2. It can also be defined as “ A device which provides a usable affair in  response to a specified measurand. ”  Transducer  1. It’s defined as an element when  subordinated to some physical change   gests  a affiliated change or an element which converts a specified  measurand into a usable affair by using a transduction principle.  2. It can also be defined as a device that converts a signal from one form of  energy to another form.  1. A  line of constantan  amalgamation( bobby

            – nickel 55- 45  amalgamation) can be called as  a detector because variation in mechanical  relegation( pressure or   contraction) can be  tasted as change in electric resistance.  2. This  line becomes a transducer with applicable electrodes and  input- affair medium attached to it. therefore we can say that ‘ detectors  are transducers ’. 

Que1.2. Explain the characteristics of detectors. 

Answer  stationary characteristics  delicacy specified by  trip or  generally error It’s given by, b. Precision It describes how far a measured  volume is reproducible as  also how close it’s to the true value.  Resolution 

1. It’s defined as the  lowest incremental change in the input that would  produce a  sensible change in the affair. This is  frequently expressed as  chance of the measured range( MR). 

2. The measured range is defined as the difference of the maximum input  and the  minimal input, that is, MR =  xmax – xmin. 

3. For a  sensible affair y, if the  minimal change in x is( x) min,  also  the maximum resolution is  minimal  sensible signal( MDS) 

1. Noise in a detector occurs because of  numerous reasons — internal sources or   oscillations due to externally generated mechanical and electromagnetic  influences. 

2. Noise is considered in detail, on individual  graces and  frequently an original  noise source is considered for test purposes. 

3. still, the  minimal signal  position that  If the input doesn’t contain anynoise.produces a  sensible affair from the detector is determined by its noise  performance or noise characteristics. 

4. For this, the original noise source is connected to the input side of the  ideal  quiet detector to yield an affair which is the  factual affair  position  of the detector. 

5. The MDS is  also taken as the RMS original input noise. When signal  exceeds this value, it’s called a  sensible signal.  Threshold At the zero value condition of the measurand, the  lowest  input change that produces a  sensible affair is called the threshold.  perceptivity 

1. It’s the  rate of the incremental affair to incremental input, i.e., g. Selectivity and  particularity 

1. The affair of a detector may change when  tormented by environmental  parameters or other variables and this may appear as an unwanted  signal. The detector is  also said to benon-selective.  2. It’s customary to define selectivity or  particularity by considering a system  of n detectors each with affair yk( k =  1, 2,., n).  3. The partial  perceptivity Sjk is defined as the measure of  perceptivity of the  kth detector to these other  snooping amounts or variables xj as  4. A selectivity matrix would  therefore be  attained with Sjk as the jkth entry. An   immaculately  picky system will have only  slant entries Sjj in the selectivity  matrix.  5. An  immaculately specific system is characterized by having a matrix with a  single entry in the  slant. Following relationship describes selectivity, h. Nonlinearity Nonlinearity can, be specified in two different ways, . divagation from stylish fit straight line  attained by retrogression analysis. 

2. divagation from a straight line joining the end points of the scale.  Hysteresis It’s the difference in the affair y of the detector for a given  input x, when x reaches this value in  upmarket and downscale directions.  The causes are different for different types of detectors. In  glamorous   types, for  illustration, it’s the pause in alignment of the dipoles, in  semiconductor types; it’s the injection type slow traps producing the  effect, and so on.  Affair impedance It’s a characteristic to be considered on individual  merit. It causes great restriction in interfacing, specifically in the choice  of the succeeding stage.  insulation and grounding 

1. insulation is necessary to  exclude or at least reduce undesirable electrical,   glamorous , electromagnetic, and mechanical coupling among  colorful  corridor  of the system and between the system and the  terrain. 

2. also, grounding is necessary to establish a common  knot among  different  corridor of the system with respect to which  eventuality of any point  in the system remains constant.  Dynamic characteristics 

1. These involve determination of transfer function,  frequence response,  impulse response and step response and  also evaluation of the timedependent   labors.  2. The two important parameters in this connection are  Fidelity determined by dynamic error.  Speed of response determined by pause. 

3. For determining the dynamic characteristics, different specified inputs  are given to the detector and the response characteristics are studied. 

4. With step input, the specifications in terms of the time constant of the  detector are made. 

5. Generally, the detector is a single time constant device and if this time  constant is t,  also one has the specifications as given

. Response time of the detectors  Response time Value in terms of  6. This gives t0.9/ t0.5 = 3.32 which is taken as a quick check relation.  Impulse response as well as its fourier  transfigure are also considered for  time  sphere as well as  frequence  sphere studies. 

Que1.3. Give the bracket of detectors. 

Answer  Detectors can be classified grounded on the  volume being measured  1. relegation, position and  propinquity detectors i. Potentiometer  ii. Strain- gauged element  iii. Capacitive element  iv. Differential transformers  Eddy current  propinquity detectors  vi. Inductive  propinquity switch  vii. optic encoders  viii. Curvaceous detectors  ix. propinquity switches(  glamorous )  Hall effect detectors.  2. haste and  stir  Incremental encoder  ii. Tachogenerator  iii. Pyroelectric detectors.  Detectors and Transducers I 1 – 6 E( EN- Sem- 5)  3. Force  Strain hand  cargo cell.  4. Fluid pressure  Diaphragm pressure hand  ii. Capsules, bellows, pressure tubes  iii. Piezoelectric detectors  iv. Tactile detector.  5. Liquid inflow  perforation plate  ii. Turbine  cadence.  6. Liquid  position  Floats  ii. Differential pressure.  7. Temperature  Bimetallic strips  ii. Resistance temperature sensors  iii. Thermistors  iv. Thermo- diodes and transistors  Thermocouples  vi. Light detectors  vii. print diodes  viii. print resistors  ix. Photo transistor.  

Que1.4. Classify transducers. 

Answer  Bracket grounded on the principle of transduction  i. The transducer is classified by the transduction medium.  ii. The transduction medium may be resistive, inductive or capacitive  depends on the conversion process that how input transducer converts  the input signal into resistance, inductance and capacitance independently.  Primary and secondary transducer  Primary transducer  i. The transducer consists of mechanical as well as the electrical  bias.  ii. The mechanical  bias of the transducer change the physical input  amounts into a mechanical signal. This mechanical device is known as  the primary transducers.  Secondary transducer 

i. The secondary transducer converts the mechanical signal into an  electrical signal. 

ii. The magnitude of the affair signal depends on the input mechanical  signal.  Passive and active transducer  Passive transducer 

i. The transducer which requires the power from an external  force source  is known as the  unresistant transducer.  ii. They’re also known as the external power transducer. 

iii. The capacitive, resistive and inductive transducers are the  illustration of  the  unresistant transducer.  Active transducer 

i. The transducer which doesn’t bear the external power source is  known as the active transducer. 

ii. similar type of transducer develops theirs owns voltage or current, hence  known as a  tone- generating transducer. 

iii. The affair signal is  attained from the physical input  volume.  Analog and digital transducer  Analog transducer 

i. The analog transducer changes the input  volume into a  nonstop  function. 

ii. The strain hand, LVDT, thermocouple and thermistor are the  exemplifications  of the analog transducer.  Digital transducer These transducers convert an input  volume into  a digital signal or in the form of the  palpitation. The digital signals work on  high or low power.  Transducer and inverse transducer  Transducer The device which converts thenon-electrical  volume  into an electric  volume is known as the transducer.  Inverse transducer The transducer which converts the electric   volume into a physical  volume,  similar type of transducers is known as  the inverse transducer. The transducer has high electrical input and  lownon-electrical affair.

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