Resistor Manufacture and Optimization Coursework Example | Topics and Well Written Essays

Topic: Resistor Manufacture and Optimization Name: Course: Lecturer: Institution: City & State: Date: Resistor Manufacture and Optimization RESISTORS Resistors are the most commonly used electronic components. The main function of a resistor in an electrical circuit is to “resist” hence the name resistor. It limits or controls the voltage and current in an electronic circuit. It resists by impeding the flow of electrons or current through them by using the material that they are made of. Resistors act as voltage droppers or voltage dividers in a circuit. Electrical resistance is the resistance of the flow of electrical current. To overcome this resistance, there is voltage consumption across the resistor\, and this leads to a voltage drop. Since the resistor causes the electrical resistance then it is a voltage dropper. Resistance has the SI units in ohms Ω. Resistors are passive components in that they hold no power or amplification but reduce the voltage passing through them. When trying to overcome the resistance, voltage used (voltage dropped) turns to heat. A potential difference is needed to evaluate the voltage lost\, and for current to flow between the two terminals of a resistor, a resistor must obey ohm’s law where , and Where: R=Resistance measured in ohms V=voltage I= current Different types of resistors have different values of resistance, so they cause different values of current and voltage. In addition, they are made of two materials in contact, the conductor and insulator. NOISE Resistors make the circuit of an audio amplifier or volume control of a sound reproduction system. The quality of sound reproduced is based on the components of the system so careful selection of these circuit components is required. This minimizes the noise and distortion of the signal at the end. Resistors create audio sound from movement of electrons in the resistor. This creates an ac signal that is superimposed over the original dc signal. From a noise aspect, some things should be taken into consideration. Resistor noise is modeled as voltage in series with the resistor. Contact, thermal, and shot noise are the three principal resistor noise types. Noise calculations Power spectral density: shows how much noise power is generated by a resistor in a 1Hz bandwidth. Where s = the noise power spectral density K= Boltzmann’s constant (1.38 ×10¯²³) T=temperature in Kelvin (room temp 300K) R= resistance Voltage spectral density: is the square root of power spectral density. N is used to calculate the RMS noise voltage of a circuit. THERMAL NOISE Thermal noise of a resistor is equal to B=noise bandwidth in Hz (frequency) The thermal agitation of electrons in a resistance causes thermal noise. At one point, they may be more electrons on one end than the other may. This causes a potential difference so different voltages at instantaneous times. This is the source of the thermal noise. Thermal noise has the following characteristics: Gaussian probability function and the noise from the two sources are uncorrelated white noise. The typical noise results from the sum of thenoise powers. The output voltage noise is the square root of the sum. The thermal noise of passive components is the same as that of thermal noise of equal resistance. This means that the thermal noise of a 1k (k=Boltzmann constant) carbon resistor is equal to thermal noise of a1k metal film. And to reduce this noise one need to reduce the resistance of the component. CONTACT NOISE It comes from the fluctuating conductivity of the faulty contact two materials. The most popular idea in carbon composition, metal oxide, carbon film, metal layer is contact noise. Wire wound resistors do not have contact noise, that is, they have high frequency ratio. This depends on regular dc current and the resistor material and size. Use of a bigger resistor improves the sound signal since the noise is directly proportional to the resistor size. Increase in exposure noise is directly proportional to increase in current. The dc and ac currents should be low for low noise operation, which is equivalent to thermal sound with the codition that no current flows through the resistor. Increasing the power rating, that is, wattage of the resistor, increases the size and scope. This reduces the exposure noise since the sound is dependent on the size. SHOT NOISE Shot noise results from the fluctuations of the current flowing in the resistor caused by the discrete electron charge. A current flowing through a cable is composed of a series of carriers with the charge on each being q. Taking a position on the wire through which the carriers pass can determine the current as the number of carriers n, which cuts the stage at a time t. Each carrier has its own velocity and is separated from its neighbors, so they don not cover the stage at regular intervals. If you count the number of carriers in a sequence of m time intervals of equal duration t, then the average number of carriers passing during each time t, is At any given meantime\, the current is calculated as: Current, differs with current, I. These variations in current are what cause shot noise. Shot noise is directly proportional to the total current flow to the resistor. For low noise operation, the dc current must be at a minimum. Therefore, tradeoff is necessary since higher dc currents are strong in tubes. TYPES OF RESISTORS Resistors are manufactured to provide a fixed value of resistance depending on the application. The electrical resistance may vary from 0.1 ohms to 100000000 ohms. The size of the resistor also varies depending on the amount of energy passing through it. This means that resistors are produced in various forms because their characteristics suit different areas of application. For example, high stability, high voltage, high current etc (Bob, & Jim, 2011). Characteristics associated with resistors are sound, voltage co-efficient, temperature co-efficient, frequency response, power, reliability, physical size and temperature rating. The valued types of resistors are: Carbon Composition Resistor Film or Cermet Resistor Wire-wound Resistor Semiconductor Resistor CARBON COMPOSITION RESISTORS Carbon resistor production process involve mixing of finely ground carbon or graphite with non-conducting ceramic powder that acts as a binder. The ratio of the carbon dust to earth (conductor to insulator) determines the resistive value of the resistor. The blend is made into a cylindrical shape with leads attached to each end and then covered with an insulating material with color-coding. The color coding shows the resistive value of the resistor. In some carbon composition resistors, the binder of the carbon particles is diallyl phthalate resin binder. The conductor path bounces from particle to particle. Each particle touches another along the path. The binder is subject to movement caused by the carbon particles random motion. This causes thermal fatigue, which results to conduction sites at the point of contact to change resistance or start up. Current bounces from one path to another with an audible pop noise. Noise levels in these resistors range from -12 dB to +6 decibels. They are the noisiest resistors around. Figure 1: Carbon resistor FILM RESISTORS These are made of networks of thin film. They consist of metal film, carbon film and metal oxide film resistors. A process that deposits pure metals such as an oxide film e.g. Tin-oxide or nickel on a ceramic rod manufactures them. This becomes the insulator. Therefore, the resistive value of the resistor increase as the film thickincreases. In that case, two types of film resistors namely thick-film and thin –film resistors are available in the market. A laser cuts a high precision helix cut in the deposited layer to increase the conductive path or the resistive path. Closer tolerances of resistors are achievable by this method of manufacture. Tolerance is the difference between the preferred value and the manufactured value. The noise level ranges from -18 decibels to -10 dB. In thick film resistors, the resistive or conduction pathway is a glass frit with ruthenium oxide added onto the ceramic substrate. The touching oxide particles in the fired glass binder form the conduction path (Manfred, 2011). At the point of contact, there is bunching and dissemination of electrons, which causes sound in film resistors. Metal film resistors are produced by evaporation of a nickel chromium coating on a ceramic substrate. The lower the Angstroms value, the thicker the layer of nickel chromium and the less the noise. The noise is due to the non-uniform depositions, surface imperfections and the occlusions. Thus, the noise level are higher if this factor remain. Generation of the resistance grid by grinding leaves a curled and torn edges with eddy-current paths that result in noise. Metal films have a sound range of -32 db to -16 db. WIRE WOUND RESISTORS Thin metal alloy wire (nichrome) is wound on an insulating ceramic former. It forms a helix. Due to the gauge of the used wire and coils on the former, the resistors are only available in small ohmic high precision values (Venkata, 2010). Thus, they have tabs that connect the thin wire to the leads thus creating noise. With a noise rating of - 38 decibels, it makes the least noise of all resistors. The only disadvantage is that the inductance chops the peaks of frequencies resulting in lower frequencies. Figure 2: wire would resistor RESISTOR PRODUCTION INTRODUCTION Production of resistors to a specified value means that inevitably the process will provide a range of values. The resistors have grading depending on their tolerance. Tolerance is the difference between the manufactured resistive value and the required resistive value of a resistor. Those that are closer to the theoretical guidelines have a higher amount as precision items. The outcomes of the manufacturing process need analysis to optimize the same process. Testing has to be complete before the resistor grading according to their respective tolerances (Herman, 2008). Failure to check the resistors may lead to the illegal grading that ultimately leads to the reduction in sales. This is because items with a higher level earn more cash in the market. The information gathered will provide insight to the effectiveness or rather authenticity of the manufacturing machines. This is obtainable from the number of resistors rejected at the end of the process. MEASURED DATA The measurements of both system one and two are in the table below Resistor Value (Ω) Number of Components Machine 1 Machine 2 110 72 12 Total 10000 10000 MEAN Mean of data from machine one is a resistance value of 101.99. The mean of data from machine two is a resistance value of 100. This means that machine two is more precise and efficient than machine one. The reason being, machine two has a nominal average resistance value thus most of the resistors produced by the machine are precise. From the mean of machine one, it is clear that most of the resistors produced a tolerance 2 if rounded off to the nearest whole number. These types of resistors are at a lower price than those with a tolerance of one. MACHINE CALIBRATION Financially, machine 2 has a comparably larger profit margin to machine 1, and this can be changed by calibrating machine one. The increase in sales value will make the recalibration worth it. Calibration of machine one will ensure that the process outcomes mirror those of machine two or at least close to it. The production characteristics to address when recalibrating would be, rejection rate, sales income value, precision, number of premium, high, standard and low quality resistors produced by the process. GRADING OF THE PRODUCTS Of importance, in resistor production is that, there is no high precision. The resistors are not in the market as a single product instead; they are binned into tolerance ranges of four types depending on how close they are to 100Ω. The price depends on the quality of the resistors giving the best prices for the best quality while the rejects have no price at all. This is in the data below Tolerance Description Unit Sales Value 1% Premium 0.016 2% High 0.012 5% Standard 0.005 10% Low 0.001 >10% Reject 0 It is possible to give the unit prices in one-thousandth of a pound HISTOGRAMS Using the data given, that is, the resistor value in ohms and the number of components produced per value, a histogram can be as shown below. From the histograms, comparing both machines the production process of machine two is more efficient and accurate. Comparing with machine one, one it is less less precise\, and it does not produce resistors that are close to the specified nominal value (Venkata, 2010). They further give proof that it is justified to recalibrate machine one. Machine one Machine 2 Predicted behavior of calibrated machine Resistor Value (Ω) Column1 Machine 2 89 12 90 19 91 41 92 83 93 154 94 262 95 410 96 593 97 790 98 969 99 1096 100 1142 101 1096 102 969 103 790 104 593 105 410 106 262 107 154 108 83 109 41 110 19 111 12 The histogram on machine one shows the resistance values as whole numbers although the data are continuous. Anything ranging from 100.499 to 101.499 is recorded as 101. From the histogram it can be concluded that the number of resistors produced that have a resistance value of less than 100Ω are less compared to the number of resistors produced that have a resistance greater than 100 Ω . Thus it is imperative to have calibration for machine 1 for the process optimization to be achievable. PRODUCTS YIELDS Before calibration, machine one yields’ or sales value for the range of products is 86.561 pounds. This is a lower value compared to that of machine two, which is at 95.648 pounds. Since machine two acts like ideal, properly calibrated machine, then machine one should yield the same sales value when recalibrated. As observed from comparison of the two tables, increase in sales is due to; Increase in premium quality resistors Increase in high quality resistors Decrease in standard quality resistors Decrease in low quality resistors Decrease in rejects. The increase in sales income as a percentage This sales income percentage should induce the manufacturer to upgrade his machine by calibration. The rejection rates of the current (machine one) and the predicted recalibrated (machine two) operations are as follows Machine one rejection rate Machine two-rejection rate There is a clear reduction in the rejected number or resistors. All these changes help to optimize the production process. Machine one tolerance unit sale number sales value 1% 0.016 2855 45.68 2% 0.012 1735 20.82 5% 0.005 3681 18.405 10% 0.001 1656 1.656 >10% 0 73 0 total 10000 86.561 Machine 2 tolerance unit sale number sales value 1% 0.016 3334 53.344 2% 0.012 1938 23.256 5% 0.005 3586 17.93 10% 0.001 1118 1.118 >10% 0 24 0 total 10000 95.648 References Bob, D. & Jim. W. (2011). A Tutorial Guide to Applications and Solutions: Analog Circuit Design, New York: Elsevier Herman, L. (2008). The Complete Lab Manual for Electricity, New York: Cengage Learning Manfred, D. (2011). Process Variations and Probabilistic Integrated Circuit Design, New York: Springer Rex, M., & Mark, R. (2007). Industrial Electricity and Motor Controls, New Jersey: McGraw- Hill Venkata, R. (2010). Advanced Modeling and Optimization of Manufacturing Processes, New York: Springer. Read More

Resistor Manufacture and Optimization - Coursework Example

Extract of sample "Resistor Manufacture and Optimization"