6 071 22 071 Introduction to Electronics Signals and Measurement Class Introduction Goals Describe course philosophy and go over administrative details Define the goals and set the expectations for the course Become familiar with laboratory infrastructure Learn about the lab hardware and software tools Course Description the course is designed to provide a practical introduction to electronics with a focus on measurement and signals The only prerequisites are courses in differential equations as well as electricity and magnetism No prior experience with electronics is necessary The course will integrate demonstrations and laboratory examples with lectures on the foundations Throughout the course we will use modern virtual instruments as test beds for understanding electronics The aim of the course is to provide students with the practical knowledge necessary to work in a modern science or engineering setting We start with the premise that we as scientists and engineers design and built electronic systems in order to accomplish a certain task Electronic devices help us achieve these tasks by detecting processing and controlling various signals For us electronics exist in order to generate and process signals This is an integrated problem and the purpose of this class is to develop the engineering methodology as well as the analytical and technical competency to address it In this light the course may be viewed as having the following four key components 1 2 3 4 to understand signals and how they carry information to design a means of accurately measuring signals to design and analyze systems that operate on signals to design and analyze systems that carryout some physical action based on signals These are very general tasks and are part of any modern laboratory experience The methods learned will be relevant for the measurement processing and control of physical quantities in chemistry biology physics and engineering The same methods are useful for controlling laboratory experiments The course will integrate demonstrations and laboratory examples with lectures on the foundations We will build and test all fundamental electronics circuits that we investigate and we will use modern virtual instruments as test beds for understanding electronics The aim of the course is to provide students with the practical knowledge necessary to work in a modern science or engineering setting 6 071 Spring 2006 Chaniotakis and Cory 1 Transducer is an electronic device that is able to convert one form of energy into another Many devices around us from the light bulb to the cell phone to a computer screen are transducers Broadly speaking a transducer may fall in one of the following categories Electromagnetic Thermoelectric Electrochemical Electroacoustic Electromechanical Photoelectric As our inconspicuous first example let s consider the generic toaster device We can think of a toaster as a digital done not done transducer that uses feedback to determine when toast is done A simple electronic schematic of a transducer is shown on Figure 1 Figure 1 Transducer electronic schematic Why can t you engage the toaster immediately after it pops up For a certain design when a toaster is engaged a magnetic material is placed in contact with an electromagnet The magnetic contact to the solenoid is made of a material whose magnetism is a function of temperature Indeed the temperature at which the material loses its magnetization labeled the Curie temperature TC is in the order to 100 degrees Celsius When the temperature is less than TC the magnet maintains its magnetism however when T TC then the magnetism is lost and the switch opens Pushing down on the toaster engages the switch The control for browning the toast simply moves the magnetic switch closer or further away from the heating elements Notice that the AC plug has two grounds The Earth ground is for user protection and typically is connected to the chassis of the toaster The AC return completes the circuit and allows current to flow The Earth and AC return should never be connected together In two prong AC plugs the Earth ground is missing 6 071 Spring 2006 Chaniotakis and Cory 2 Thermistor A Thermoelectric transducer Thermistors are non linear temperature dependent resistors with a high resistance temperature coefficient They are advanced ceramics where the repeatable electrical characteristics of the molecular structure allow them to be used as solid state resistive temperature sensors This molecular structure is obtained by mixing metal oxides together in varying proportions to create a material with the proper resistivity Two types of Thermistors are available Negative Temperature Coefficient NTC resistance decreases with increasing temperature and Positive Temperature Coefficient PTC resistance increases with increasing temperature In practice only NTC Thermistors are used for temperature measurement PTC Thermistors are primarily used for relative temperature detection In this class we will use an NTC thermistor The temperature versus resistance data of our thermistor is shown on the table and figure below Resistance multiplier 10k NTC Thermistor 40000 35000 Resistance Ohm 30000 25000 20000 15000 10000 5000 0 0 10 20 30 40 50 60 70 Temperature Celcius 6 071 Spring 2006 Chaniotakis and Cory 3 For convenience we would like derive a mathematical expression which describes the behavior of the device The Steinhart and Hart equation is an empirical expression that has been determined to be the best mathematical expression for resistance temperature relationship of NTC thermistors The most common form of this equation is 1 a b ln R c ln R 3 T Eq 1 Where T is in Kelvin and R in The coefficients a b c are constants which in principle are determined by measuring the thermistor resistance at three different temperatures T1 T2 T3 and then solving the resulting three equations for a b c 1 a b ln R1 c ln R1 3 T1 1 a b ln R2 c ln R2 3 T2 1 a b ln R3 c ln R3 3 T3 The parameters a b c for the thermistors provided with the lab kit in the temperature range between 0 50 degrees Celcius are a 1 1869 10 3 b 2 2790 10 4 c 8 7000 10 8 The Steinhart and Hart equation may be used in two ways 1 If resistance is known the temperature may be determined from Eq 1 2 If temperature is known the resistance is determined from the following equation 1 3 1 3 R exp 2 2 6 071 Spring 2006 Chaniotakis and Cory 4 Where 1 2 and b c 3c 4 a The non linear resistance versus temperature