Resistor Manufacture and Optimization - Term Paper Example

Resistor Types & Manufacturing Materials Techniques Name: Course: Lecturer: Institution: City & State: Date: Resistor Types & Manufacturing Materials Techniques Introduction Resistor Types & Manufacturing Materials (Checking Noise Characteristics) and Techniques for Each A resistor is a very important component in electrical circuits. It is a component which contains no amplification and power sources, and is thus a passive component. A resistor controls electric current flow in an electric circuit, through resisting the current passing through it and allowing only a prescribed amount of it to pass to the other end of it. Resistors not only control current but also control voltage in electrical systems. This is done by connecting the resistances in series. The power of a resistor to resist is called resistance and is measured in Ohms symbolized as Ω. Experimental research on direct current circuits has proven that current flow in a circuit, is inversely proportional to the resistance of the medium in which it travels. The current is also directly proportional to the voltage running across it in a direct circuit. This behavior follows a law known as the Ohm’s law. In the case of alternating currents (A.C.), the Ohm’s law also applies on condition that the resistor does not exhibit qualities of capacitance or/and impedance in it. In direct circuits, impedance and capacitance do not have any effect on the manner in which devices work. On the contrary, impedance and capacitance have a significant effect on the way in which devices connected in the circuit function. The reason for this effect is that the function of the appliance is made variable depending on the changes in frequency caused by impedance. There is a great variety of many different types of resistors, classified according to the material used, resistor ratings (Resistance of the resistor in ohms), resistor accuracy (measured in percentage error), manufacture, as well as according to the area of application (e.g. the surface mount chip resistor and variable resistors). The accuracy and characteristics of various resistor types are vital for application in many circumstances like high current demands, low or high voltage demands, and highly stable circuit applications. The main characteristics of a resistor worth considering in detail are; noise, power, temperature coefficient, frequency response, voltage coefficient, reliability, physical size, mounting characteristic and temperature rating. The power dissipated by a resistor is the amount of work done by a resistor while it is regulating the current and voltage in a circuit. Depending on the application of the resistor, the power rating varies accordingly. The S.I. unit is Watts (w). The temperature coefficient characteristic of a resistor analyzes the relationship between the changes in temperature in a resistor and the resistance of a resistor. This can be a positive value or a negative characteristic value. When the value is positive, this indicates that the temperature increases directly proportionally to the resistance. A negative coefficient on the other hand, shows that when resistance increases, the temperature of the resistor reduces. Resistor Noise The main characteristic that we are considering is the noise characteristic of the resistor. The resistor noises are classified into three; shot, contact and thermal noise. Shot noise Shot noise in resistors is affected by the average D.C. current and bandwidth. The higher the D.C. current passing through it, the higher the noise. As a result, to reduce the noise, the current should be kept at a minimum. The best stage to reduce this effect in the amplifiers is at the initial amplifier stage. Thermal Resistor Thermal resistor noise can be calculated using the following formula: Vt = √ (4kTBR) Where:          Vt = the rms noise voltage          k = Boltzmann's constant (1.38∙10-23)          T = temperature (Kelvin K)          B = noise bandwidth (Hz)          R = resistance (ohms) As shown above, the formula follows a Gaussian probability function of density. The summation of independent noise powers is equal to total noise power. Output noise in volts will be equivalent to the root of the total sum of individual noises squared. The noise is directly varying with the root of the resistance. Thus, considering only two resistors which are 50% the value, square the root and sum them up. Then find the square root of the sum obtained. The answer is the same as if you had done the root of one resistor which is double the value of each of the two earlier used. Therefore, thermal noise in passive parts is the same as the thermal noise caused by the real part of similar impedance (Raymond and Jewett 2009). When referring to only resistances, the thermal noise is the same as the noise developed by a resistor of similar resistance. Hence, the noise produced by a metal film resistor is the same as the noise produced by a carbon film resistor. The thermal noise is independent on the material used to make the resistor. Thus, in order to reduce thermal noise, reduce the resistance. Contact noise This noise depends on the current and the size or material. This is mostly used in amplifiers used with guitars. The noise varies directly with the resistor size. It is the main source of noise produced by metal film, metallic oxide, and carbon composition resistors. When there is no current passing across the resistor, the noise produced is all thermal noise. The contact noise can be reduced by adding the area and size, effectively doubling the power rating (Raymond & Jewett 2009). Wire wound This is manufactured by the use of metal alloys drawn into thin wires and wrapped around insulating ceramic core, to make a spiral helix like one used in the film resistor. They are mostly found ranging in value from 0.001 ohms to 100ohms. Using the number of turns in the resistor, the value of resistance can be varied by tapping the current at various lengths of coiled wire (Hodder and Stoughton 1990). Wire wound resistors are capable of operating in conditions where the electrical currents are high and the power is 300w. Due to the high ratings of power and current, the resistor is molded onto a heat sink made of aluminum, which contains fins that assist in the cooling of the resistor while it is functioning. This kind of resistor is called a chassis mounted resistor. The use of heat sinks is vital since it increases the current carrying capacity. Metal film and carbon film resistors These resistors are made by putting metals in an insulator, usually a rod made of ceramic material. The metals should be pure like nikel or film of metal oxide like tin oxide. The resistance of the film type resistors is controlled by varying the thickness of the film, which can be thin or thick. After the film is deposited, a laser beam is used to make a groove which is spiral and helixical. The groove causes increase in conductivity or resistance. The final appearance of the resistor is that of a wire coiled onto a ceramic rod. Due to the way in which these resistors are made, they are known to have very low tolerance compared to other types of carbon resistors (Hodder and Stoughton 1990). Metal oxide (metal film resistors) This type of resistor has got a good temperature stability compared to the carbon based resistors. Comparing the metal film with the metal oxide resistors, the oxide resistors were found to have a high temperature rating and high current surge withholding ability. A thick film resistor is made by placing a thick paste of conductive material of ceramic and metal, paraphrased as ceramet, on a ceramic alumina substrate. They have the same characteristics as metal film resistors, and are used to manufacture the chip type of resistors. They have admirable temperature stability, voltage rating, low noise and current surge characteristics. These film types of resistors are precision components for circuits with low power (Kaiser 1998). Carbon (film and carbon composition) These resistors are manufactured by changing the chemical composition of a conductor material that conducts electricity. This is done to create different levels of resistance. The conductive material is carbon and the material used to change the composition (filler material) is ceramics. At both ends of the composite material, caps are put and connection wires soldered onto them. The whole devise is then covered using an epoxy resin. Finally, depending on the resistance rating, the device is color coded (Cengel and Boles 2006). Carbon composite resistors have got very good ability to handle sudden pulses of the load current. This is due to the fact that the entire mass conducts current across it unlike wire wound on a ceramic rod found in wire wound resistors. The performance is also better than carbon film and metal film resistors. For this reason, these resistors are preferred in applications involving medical equipment, spark plugs in automobiles, high power lighting, welding, and surge protection equipments. Analysis of Resistor Manufacture Output DESCRIPTION MACHINE1(UNITS) MACHINE 2 (UNITS) SELING PRICE PER UNIT SALES MACHINE 1 SALES MACHINE 2 PREMIUM 2855 3334 0.016 45.68 53.344 HIGH 1735 1938 0.012 20.82 23.256 STANDARD 3681 3586 0.005 18.405 17.93 LOW 1656 1118 0.001 1.656 1.118 REJECT 73 24 0 0 0 TOTAL SALES 86.561 95.648 TOTAL UNITS 10000 10000   REJECTION RATE 0.73% 0.24%       Graphs and Histograms Discussion The average production of resistors in the case of both machines is the same. This is due to the fact that the production in both cases is the same at 10000 units. The spread values are usually considered to be the variance, standard deviation, quartiles and ranges. Machine 1 The most expensive product in the company is the resistors that have a tolerance range of between 0.00 percent and 1 percent. The product has a sales value of 0.016 pounds. When the production of the product by machine one is compared to machine two, machine two produces more of the premium product compared to machine one. In the case of the standard product, which ranges between greater than one percent to two percent tolerance, machine one produces more than machine two. The same is noted for the range of low quality products, which range from greater than two percent to five percent tolerance. Machine one produces more of these products than machine two. The number of rejected products from machine one is higher than the rejects from machine two. This represents a higher loss in machine one than machine two because the rejects have got no selling price (since they are of poor standard). The average deviation from the mean in machine one is found to be less than the same for machine two, as a result the distribution of products across all the ranges can be said to be more even in machine one than in machine two. However, the standard deviation is higher in machine one than in machine two although not significantly. A study of the variance values shows that the value for variance in machine one is higher than that of machine two. Variance and the standard deviation values are higher in machine one and this is expected since both are measures of how distributed the production data is. Consequently, it is safe to say that the production in the machine one is more spread across the wide range of possible products than in machine two. However, the median being the tolerance of zero percent, it is preferable that the deviation from the mean is minimal for both machines, since the premium product is the most profitable product in the company. Analysis of machine one that the standard deviation is higher than machine two indicate that the products are more spread across the range of possible products, and the average deviation is lower than machine two, indicating that there is little deviation from the premium product (Kybett and Boysen 2008). Machine two The spread indicates that the machine has a lower variance and standard deviation than the machine 2. This means that products are not widely distributed across various ranges in machine two during production as in machine one. A higher average deviation also indicates that most of the products are not concentrated in the premium range of the production process. Information on how the two manufacturing processes are functioning can be obtained from the two sets of data collected from the two machines. The main point that is noted, once the table showing the sales is analyzed is that the machine one has got a bigger quantity of rejected product. Effectively, the machine is using raw material to produce goods which have no sales value leading to a contribution to the losses incurred by the company. This machine must be quickly brought to a halt and relevant calibrations and proper adjustments made to reduce and if possible eliminate the rejects it is producing (Winfield & Horowitz 1989). The second revelation in machine one is that the machine has got a high production of low quality products compared to machine two. The difference is significantly high and cannot be assumed since the low quality goods have a very small sales value of 0.001 pounds per unit. Relevant adjustments in the production process should be made to increase the production of premium and high products. Analysis of the histograms indicates that premium products and standard products in both machines one and two are higher than high products. The data indicates that the manufacturing process favors the production of premium and standard quality resistors. This may be seen to be as a result of the design of the machines and it may also be argued that the machines are from the same manufacturer because the machines are of similar designs. Hence, this also shows that it is easier to optimize the production of premium products and standard products compared to the high products (Göran 2007). The process of machine two is seen to be more efficient than the one for machine one. This can be seen by the evidence of a higher production of premium, high, standard and reject resistor products. A higher income can be achieved from the process optimization and by lowering the rejection rate. In the production processes that involve processing of raw materials such as extraction of minerals, it is possible to have selling prices similar to the indicated selling prices. This is because the cost of raw materials for mass production of small products, which are used as intermediate raw materials for other large client industries is low (Cengel and Boles 2006). In this case, resistors are used in bulk by large electronic product manufacturing industries. Furthermore, the resistors are bought in bulk and at a regular basis; hence the company can afford to place a small profit margin for each of the products that they make (O'Malley 1992). The yield for machine one is: Premium grade- 2855units selling price- 45.68 pounds High grade - 1735units selling price- 20.84pounds Standard grade- 3681units selling price- 18.405pounds Low grade - 1656units selling price- 1.656pounds Reject grade - 73units selling price- 0 pounds The yield from the second machine two: Premium grade- 3334units selling price- 53.344 pounds High grade - 1938units selling price- 23.256pounds Standard grade- 3586units selling price- 17.93pounds Low grade - 1118units selling price- 1.118pounds Reject grade - 24units selling price- 0 pounds Rejection rates are according to the formula below: Machine one- 0.73% Machine two- 0.24% References Cengel, YA and Boles, M A 2006, Resistors: an engineering approach, University of California, Berkely. Göran, G 2007, Brainteaser physics: challenging physics puzzlers, Mc Graw Hill, London. Hodder and Stoughton 1990, Basic electronics B resistors capacitors and inductors by Plant, Malcolm Publication, London. Kaiser, C J 1998, The Resistor Handbook, second edition, CJ Publisher, New York. Kybett, H and Boysen, E 2008, All New Electronics Self-Teaching Guide, Wiley Publishing Inc, Indianapolis. Raymond, A S & Jewett, J W 2009, Physics for Scientists and Engineers, Volume 2: With Modern Physics, M.I.T Press, Massachusetts. O'Malley, J 1992, Schaum's outline of theory and problems of basic circuit analysis, second edition, McGraw-Hill, New York. Winfield, H & Horowitz, P 1989, The art of electronics, Harper Perennial, New York. Read More