Mechatronics Exam 1 Flashcards

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Questions and Answers

What are the elements of a measurement system?

a sensor, 2. a signal conditioner, 3. a display system

What is a sensor?

A sensor produces a signal related to the quantity being measured.

What are the differences between an open and closed loop system, and what are their advantages?

Open loop: input does not depend on an output (advantage is that it is low cost and simple). Closed loop: output compared to input (offer superior accuracy and adaptability by incorporating feedback).

What does a potentiometer sensor measure?

Measures the distance or displacement of an object in a linear or rotary motion and converts it into an electrical signal. Signup and view all the answers

What is a strain-gauged element?

A sensor whose resistance varies with applied force; it converts forces, pressure, tension, weight, etc. into an electrical change in electrical resistance which can then be measured. Signup and view all the answers

What do differential transformers do?

Converts linear motion (displacement) of an object into an electrical signal. Signup and view all the answers

What are pneumatic sensors used for and what is the typical ranges?

Such sensors are used for the measurement of displacements of fractions of mm in ranges which typically are about 3 to 12 mm. Signup and view all the answers

What is a microswitch?

It is a small electrical switch which requires physical contact and a small operating force to close the contacts. Signup and view all the answers

What is a reed switch used for?

Such a switch is very widely used for checking the closure of doors. It is also used with such devices as tachometers (counting turns). Signup and view all the answers

How can photosensitive devices be used?

Can be used to detect the presence of an opaque object by its breaking a beam of light, or infrared radiation, falling on such a device or by detecting the light reflected back by the object. Signup and view all the answers

What is a strain gauge load cell used for?

Used form of force-measuring transducer is based on the use of electrical resistance strain gauges to monitor the strain produced in some member when stretched, compressed or bent by the application of the force. Signup and view all the answers

What are Piezoelectric sensors used for?

Used for the measurement of pressure, force and acceleration Signup and view all the answers

What does a tactile sensor measure?

Measuring device that indicates physical contact between two objects. Signup and view all the answers

What can we measure fluid pressure with?

Mechanical: U-tube manometer, Bourdon tube, Diaphragm and Bellows. Electrical: Strain Gauge, Capacitive sensor, Potentiometric, Resonant Wire, Piezoelectric, Magnetic, Optical Signup and view all the answers

Why do we need signal conditioning?

<ol> <li>Protection (to prevent damage to the next element), fuses, diodes. 2. Getting the signal into the right type of signal, like resistance change to voltage change. 3. Getting the level of the signal right, the signal might be just a few millivolts (Arduino reads 5mV as the smallest value). 4. Eliminating or reducing noise, by adding filters. 5. Signal manipulation, using pulses to get a constant value (to overcome drift</li> </ol> Signup and view all the answers

What is the ideal electrical impedance conditions for measuring and for maximizing power transfer?

Measuring: we do not want any power transfer: Rmeas >> Rsensor. Maximizing power transfer: impedance matching: Rsource = Rload Signup and view all the answers

When would we use a wheatstone bridge?

We would use one when dealing with a strain gauge Signup and view all the answers

How are analog signals sampled for ADC?

Convert a digital representation of potential values to analog (via a DAC) and compare with the analog signal to determine the smallest digital value for which the analog signal is greater (uses binary numbers) Signup and view all the answers

What do Actuation systems do?

Actuation systems are the elements of control systems which are responsible for transforming the output of a microprocessor or control system into a controlling action on a machine or device Signup and view all the answers

What are Valves used for?

Are used with hydraulic and pneumatic systems to direct and regulate the fluid flow. Signup and view all the answers

What are Cylinders: Linear actuators?

Cylindrical tube along which a piston/ram can slide. There are two basic types, single-acting cylinders (an internal spring returns the piston) and double-acting cylinders Signup and view all the answers

What is the purpose/use for basic mechanisms?

<ol> <li>force amplification, e.g. that given by levers; 2. change of speed/torque, e.g. that given by gears; 3. transfer of rotation about one axis to rotation about another, e.g. a timing belt; 4. particular types of motion, e.g. that given by a quick-return mechanism (time for return stroke less than forward stroke)</li> </ol> Signup and view all the answers

Describe the role of an actuation system?

Actuation system takes a control signal and converts it into a physical action or motion which controls the system in some way Signup and view all the answers

Describe the operation of force sensing resistor

They change resistance based on the force being applied to its surface. the input would be a force, the output would be an existence and a typical signal conditioning could be a voltage divider. Signup and view all the answers

What is the operation of an optical encoder?

Measures displacement using concept of angles. So it has a certain number of holes evenly spaced out and based on how many holes it goes through it calculates displacement Signup and view all the answers

Describe a method to protect a microcontroller from both high voltage and wrong polarity

Zener diode Signup and view all the answers

Explain the role of gear trains and the similarities between gear trains and belt drive

Gear trains control the angular velocity of the system through a rotational force produce from gear to gear. belt drives do the same thing as gear trains but instead they use belts and a wheel and a wheel to where since as we can have different gear sizes we could also have different wheel sizes Signup and view all the answers

What is the minimum number of bits required to have resolution 0.5 psi or better given a pressure sensor with range 0-100 psi and sensitivity 30 mV/psi?

Resolution in voltage = (0.5 psi)(30 mV/psi) = 15mV Maximum value in voltage (or range) = (100 psi)(30 mV/psi) = 3000 mV Resolution in voltage = maximum value in voltage / 2n bits, N bits = logbase2( maximum value in voltage / resolution in voltage ) = logbase2( 3000/15 )= 7.6439 bits Since bits must be integer value, n bits = 8 at least: R ≥ range/2n, or 2n ≥ range/R, 2n ≥ 3000/15, 2n ≥ 3000/15, 2n ≥ 200, 2^8 = 256 >200 Signup and view all the answers

What is the resolution of an Arduino ADC that includes 10 bits and range 0 V to 5 V?

n = 10, Vmax = 5 V Res = Vmax / 2^n = 5 V / 2^10 = 0.0049 V Signup and view all the answers

For the same Arduino as question 4, what is the input voltage if analogRead outputs 354?

nsteps = 2^n = 2^10 = 1024 first step is 0 (354 / 1023) * 5 V = 1.73 V Signup and view all the answers

What is the minimum number of bits required to have a resolution of 0.1 N or better given a force sensor with range 0-200 N corresponding to output voltages of 0-10 V?

Res = max value / 2^n 0.1 N = 200 N / 2^n n = log2( 200 N / 0.1 N) n = 10.97 n = 11 bits Signup and view all the answers

What is an actuation system? Give an example

System that takes a controlling action, imparting a change on the rest of the system. Typically involves a significant change in energy: imparting mechanical energy to produce motion, imparting pneumatic energy to produce motion, imparting electrical energy to produce motion, imparting heat to change temperature, etc. A specific example is the conversion of an electrical signal to a linear motion using a solenoid valve and a pneumatic cylinder Signup and view all the answers

What are some parallels/analogous components between the pneumatic and hydraulic actuation systems?

Both systems effectively include a power supply, valve control, and cylinder actuation. Furthermore, both power supplies include a primary component that pressurizes the liquid (compressor and pump) while other components are somewhat analogous to signal conditioning in electrical circuits. Signup and view all the answers

What is the key difference between bipolar transistors and MOSFETs?

Bipolar transistors are controlled by the current at the gate whereas MOSFETs are controlled by the voltage at the gate Signup and view all the answers

Explain the operation of a solenoid and how it may be used to control a pneumatic cylinder

Applying current to a cylindrical coil produces a magnetic field that causes the metal armature inside the coil to move. A solenoid may be used to control a valve, such as a spool valve, to control the pressure of the pneumatic cylinder. Signup and view all the answers

What is the purpose of the 'brushes' in a brush-type DC motor?

The brushes rotate with the rotor and contact the electrical voltage source, allowing current to flow in the armature coil. Since the brushes rotate with the rotor, they eventually switch contacts, causing current to flow in the opposite direction. This change in current direction is necessary to ensure the force generated in the coil continues to produce rotation in the correct direction Signup and view all the answers

What are the relative advantages/disadvantages of DC compared to AC motors?

AC motors are cheaper, more rugged, reliable, and maintenance free, but are more complicated for speed control. Signup and view all the answers

Is the torque of a DC motor proportional to voltage or current?

Current Signup and view all the answers

Describe a circuit that can control the velocity of a DC motor using a constant power supply.

Pulse width modulation can control the effective voltage level on the motor. Switching may be implemented with a MOSFET and an H-bridge circuit can add the ability to rotate in either direction Signup and view all the answers

What is the output of a Wheatstone bridge with one strain gauge if the nominal resistance of the gauge and all other resistors is 120 $\Omega$, gauge factor is 2.1, and strain is 3$\times$10^-5. The bridge source voltage is 5 V. Assume the change in resistance of the gauge is much less than 120 $\Omega$

dR = G * strain * R = 0.00756 $\Omega$ V = Vs * dR / (R1+R2) = Vs *G * strain / 2 = 5 * 2.1 * 3$\times$10^-5 / 2 = 0.1575 m Signup and view all the answers

Given the op-amp circuit diagram and IC diagram above, sketch the output signal if the input signal is one cycle of a 1 Hz sinusoid with amplitude 0.5 V. The resistor values are Rf = 20 k$\Omega$ and Rin = 1 k$\Omega$. Pin 7 of the IC is connected to +5 V and pin 4 is connected to ground

Inverting amplifier: Vout / Vin = -Rf / Rin = -20 Amplitude = -20 * 0.5V = -10V Clipped at 0 and +5 (it cannot amplify higher than the power supply) Signup and view all the answers

Identify one advantage and one disadvantage of active filters compared to passive filters

Advantage: active filters are unaffected by downstream impedance Disadvantage: active filters require a power source Signup and view all the answers

Describe the operation of a variable reluctance tachogenerator

A toothed wheel is attached to the rotating shaft to be measured and adjacent to a stationary pick-up coil wound around a permanent magnet. The flux alternates between the tooth/coil and gap/coil states to create an alternating emf with a frequency corresponding to shaft angular frequency Signup and view all the answers

Flashcards

What is a sensor?

A system that produces a signal related to the quantity being measured.

Open Loop System

Input is independent of output; simple and low cost.