The solution (important points in every answer) as well as the marking scheme for the In-Sem Question Paper of Mechatronics (302050) is mentioned below. Please consider these solutions as well as the marking scheme while marking the InSem Examination of Mechatronics (302050).

Q.1. a) Draw the schematic of LVDT along with its performance curve. Also, discuss in brief the

important specifications of LVDT.

LVDT is a transducer for measuring linear displacement

It must be excited by an AC signal to induce AC response on secondary.

The core position can be determined by measuring secondary response.

Specifications of LVDT (any four): Linearity, Sensitivity, Drift, Phase Shift, Bandwidth

etc.

2 Marks for schematic; 2 Marks for Performance curve; 2 Marks for specifications

(06)

b) A Wheatstone bridge requires a change of 10 ohm in the unknown arm of the bridge to

produce a change in deflection of 4 mm of the galvanometer. Determine the sensitivity of

the instrument.

Sensitivity=Output/Input=4/10=0.4 mm/ohm

2 Marks for formula; 1 Mark for correct answer; 1 Mark for correct unit

(04)

Irrespective of the number of steps taken, give 4 Marks if the answer is correct!

OR

Q.2. a) Strain in a cantilever beam is to be measured using strain gauges. For this, draw the set-

up and explain the principle of working.

With no force applied to the test specimen, both strain gauges have equal resistance and the bridge circuit is balanced.

However, when a downward force is applied to the free end of the specimen, it will bend downward, stretching gauge #1 and compressing gauge #2. This will unbalance the bridge and give voltage proportional to the force applied.

2 Marks for setup kind of similar to above; 3 Marks for explaination

(05)

b) Using a suitable sketch explain the construction and the working of a Servo Motor.

It is an electrical motor, controlled with the help of servomechanism. If the motor as controlled device, associated with servomechanism is DC motor, then it is commonly known DC Servo Motor. If the controlled motor is operated by AC, it is called AC Servo Motor. A servo motor includes: AC/DC motor, Gear Box, Position Sensor, Comparator, PWM to Voltage converter. Servo motor is automatically operated up to certain limit for a given command with help of error-sensing feedback to correct the performance.

1 Mark for block diagram kind of similar to above; 2 Marks for construction; 2 Marks for working.

(05)

Q.3. a) Discuss the benefits and drawbacks of closed loop control system over open loop control (05)

system.

Advantages:

Accurate, since the controller modifies and manipulates the actuating signal such

that the error in the system will be zero.

Self-correcting

Senses the environmental changes and disturbances in the system.

Disadvantages:

Complicated to design

Instable, since due to feedback, system tries to correct the error.

3 Marks for advantages; 2 Marks for dis-advantages.

b) Determine the composite transfer function, C/R, for the system in Figure 3b.

Figure 3b

2 Marks for 1st Reduction 1; 3 Marks for 2nd Reduction;

Irrespective of the number of steps taken, give 5 Marks if the transfer function is

correct!

(05)

NOTE: If the signs at the summing point were not visible in the question paper

because of which the students had to assumed suitable signs at the summing points,

please give full marks if the final answer was correct for the signs assumed by the

students at the summing points.

OR

Q.4. a) Draw a block diagram for any household appliance consisting of various elements which

build the system. Explain the function of each block therein.

Minimum Blocks expected to be shown include: Actuator, Sensor,

Microcontroller/Interface, ADC & DAC.

2 Marks for block diagram; 3 Marks for function of each block

(05)

b) Determine, using block reduction technique, the overall transfer function, Y(s)/X(s) for

the system in Figure 4b.

Figure 4b

(05)

2 Marks for step 1 reduction; 3 Marks for step 2 reduction.

Irrespective of the number of steps taken, give 5 Marks if the transfer function is

correct!

NOTE: If the signs at the summing point were not visible in the question paper

because of which the students had to assumed suitable signs at the summing points,

please give full marks if the final answer was correct for the signs assumed by the

students at the summing points.

Q.5. a) Enumerate the importance of DAQ system in Mechatronics. Explain your answer with

the help of suitable example.

Significance:

Real Time Data acquisition at specified sampling frequency Acquire data in the background while processing in the foreground Seamless Streaming of data between peripherals

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Performs several functions simultaneously Integrates with other hardware (sensor, actuator, amplifiers, signal

conditioning equipment)

1 Marks for suitable diagram, kind of similar to above, that includes most of above

components; 4 Marks for discussing the importance

b) A 4-bit DAC has a Vref of 0-10 V. The binary input is 1110. Find the analog output

voltage.

Binary Input 1110=1x23+1x22+1x21+0x20=14

Analog voltage output=14x10/24=8.75 V

2 Marks for Binary Input; 2 Marks for Voltage Output; 1 Mark for correct unit.

Irrespective of the number of steps taken, give 5 Marks if both the answers and the

unit is correct!

(05)

OR

Q.6. a) Explain the concept of sampling. Also discuss the working of sample and hold circuit.

SHA is used in ADC, to stabilize the voltage while it is being converted to a

digital value

SHA consists of a voltage holding capacitor and a voltage follower

When the switch is closed, the output voltage is equal to the input voltage

When the switch is open, capacitor holds the voltage corresponding to the last

sampled value

(05)

2 Marks for concept of sampling; 1 Mark for SHA circuit diagram kind of similar

to above; 2 Marks for working of SHA

b) Discuss the operation of R-2R type DAC with suitable diagram.

Properly weighted voltages are summed together to yield the analog output. Three weighted voltages are summed. The three-bit binary code is represented by

the switches.

(05)

2 Marks for block diagram/circuit diagram kind of similar to above; 3 Marks for working