Measurement as an Important Part of the Modern Aspects of Science - Report Example

Measurement Methods By: Professor: Class: University: City: State: Date of submission: Measurement Methods Introduction Measurement is an important part in the modern aspects of science including engineering and commerce. In most cases, measurement is considered a hallmark of the scientific enterprise and source of knowledge considered to be relative to the qualitative modes of inquiry. In spite of the ubiquity and significance of measuring, the philosophers have little consensus on ways of defining measurement, measurable things, and the conditions making measurement possible. However, most scientists view measurement as an activity involving the interaction with the systems aiming to represent aspects of such system in terms of abstract (Alexandrou, 2001). Such characterization seems to fit different perpetual and linguistic activities, which are not in most cases considered measurement. Philosophers wrote on various conceptual, semantic, metaphysical, and epistemological issues associated with the measurement. It is from such background that the paper aims to explore the central philosophical standpoints on the nature of measurement with inclination on various aspects of on temperature, volumetric flow rate, and fluid pressure. Temperature Temperature is the measure of hotness or coldness of something especially measuring the average kinetic energy of the particles within an object, which is the energy type, associated with the motions. Considering that the molecules are small, it is important to use indirect method of measuring the kinetic energy of the molecules of the substance. With increased heat on the substance, the molecules seem to move rapidly. Such increase in motion leads to small increment in volume or the amount of space that the materials take-up. There are various devices using the expansion of substances in giving an indirect measure of the temperature identified as thermometers. Most of the thermometers are made of thin glass tubes that have liquids (Childs, 2001). In addition, most of the thermometers are made of alcohol and mercury since they remain over the large temperature. From the physics backgrounds, it is important o note that a change in temperature leads to small changes in the volume of the liquid. Nonetheless, such effect is magnified when there is expansion of the liquid in the very thin tube used by the thermometer. Infrared radiation thermometers (IRTs) The radiation thermometers are sometimes referred to as the infrared thermometers or the radiation pyrometers, which work like the cameras developed using the optimal systems that have lenses or mirrors and filter responsible for the selection of wavelength range. These ranges are fall within the waveband in which the thermometer is sensitive. In addition, the radiation is focused on the detector which has the output that indicate the intensity of the radiation and therefore the temperatures which could be the photo detector endowed with the incident photons giving rise to the electric current or thermal. As a result, the infrared seem to sense the rising temperature produced through the absorbed energy (Ochkin & Wiley InterScience, 2009). The device is temperature-controlled in making the responses more repeatable. In the application of the low temperature, there is need for the device to cool with an aim of improving the signal-to-noise ratio and reducing the intensity of the radiation. Radiation exchange between parameters If the surface temperature (Ts) that is unenclosed though seems to radiate freely into the surrounding temperature (Tb), then the radiation received through the infrared thermometer focused towards the ground. This could be summed as Ltotal= εL(Ts) + (1 - ε)L(Tb) . The first part is due to radiation emitted by the surface and emissivity product (0 < ε < 1) and radiance of the blackbody L(Ts) and temperature Ts measured in Kelvin. This needs to follow Planck law. On the second part, there is reflection from the background, which is the product of spectral radiance given the temperature Tb and surface reflectivity (1 - ε). Figure 1: Diagrammatic Representation of Radiation Thermometer The thermal radiation is majorly within the infrared; however, with the temperatures increasing above 7000C, the dull red heat might be visible which tend to brighten to yellow, finally, and brilliant white heat. It is essential to note that the consequence is highly sensitive. Therefore, radiation thermometry offers the powerful method of measuring temperature to some extent even lower than -500C. Additionally, radiation thermometry apply the concept of the perfect radiator or the blackbody considering that it is the perfect heat absorber of every radiation incident on it; as a result, it seems perfect when black. While in use, the blackbody seems to be used in calibrating the radiation thermometers. Nonetheless, the real surface of the device emits little radiation compared to the blackbody at similar temperature, which makes it important to correct the temperature measures for the emissivity of the surface. In any particular temperature, the thermometer is advantageous especially while operating as the shortest wavelength due to greater sensitivity and emissivity and little errors involved. The commonly used wavelength ranges from 0.65-1.0 μm through the Si photodiode detector. At low to moderate temperate, the intensity is also low making it significant to operate in similar way into the infrared and above the wavelength bands for acquisition of the signal. However, it is important to apply the parts of spectrum in which the water vapour and CO2 do not absorb the radiations. In most cases, the ranges of wavelengths are 3-5 μm through the InSb photodiodes while the wavelengths for cooled HgCdTe photodiodes is 8-14 μm. Radiation thermometry is a remote-sensing method with the amity of measuring very hot objects within the production line. The thermometer has modern detector arrays that seem to allow the production of thermal images of the objects. Advantages and Disadvantages The radiation that an object emits depends on the temperature and surface features including emissivity. Such features reflects the radiation ability on the scale of 0-1 with 0 for the perfectly reflecting surfaces that do not emit radiation and 1 where possible, applies to the perfect blackbody radiator. With radiation thermometer, it is important to note the emissivity and estimate the accuracy of the acquired temperature. Thermal radiations emitted by the heaters are reflected partially by the target and add some of the radiations detected. If there are no precautions, reflections from the furnace heaters could result in reflections, hence high temperatures. Thermocouple The thermocouple uses the feedback effect, which demonstrates the electrical potential within the juncture points of two metals that are dissimilar with magnitudes of change varying in temperatures. If the junction completes the circuit, the temperature of the measuring junction is measurable. When there is connection of the two dissimilar metals, there is production of small voltage identified as thermo-junction voltage: Peltier effect. When there is a change in the temperature of the junction, the voltage changes as well which the input circuits measure. There is proportionality relationship between voltage and temperature difference between the free ends and junction: the Thompson effect. Combination of the two effects can be combined for measuring the temperatures. By holding the junction at known temperature and simultaneously measure the voltage, the temperature within the sensing junction is deductable. Figure 2: Simple Diagram of Thermocouple Circuit Thermocouples could use different combination of the materials with performance determined through application of the materials with platinum. However, it is important to consider pair of materials with thermoelectric difference resulting into better performance. For the temperatures, chromel-constantan is excellent as it measures up to 20000F while the combination of Tungsten-Rhenium used for temperatures up to 50000F. Each calibration used in the devices has different temperature ranges and environment; however, the maximum temperatures seem to vary with the diameter of the wire used in the thermocouple. For the thermocouple, the standard error of the wires seems to vary from 0.80C to 4.40C depending on the thermocouple applied. In most general applications, the recommended thermocouple is type K since it offers a wider temperature range, low standard of error, and effective corrosion, and better corrosion resistance. In addition, most of the digital multimeters (DMMs) have the ability of measuring temperature through plugging in the type K thermocouple with a standard connection. Thermocouple Laws Consider a case of bath 1 and 2 whose temperatures are T1 and T2; V1-R referred to as the voltage generated through T1 when there is application of proper junction reference at temperature TR. in such case, the V1-R is the voltage listed within the thermocouple at T1. If V1-2 is the difference between V1-R and V2-R, then V1-2= V1-R – V2-R In the equation, it is important to understand the sign convention. Negative sign could be problematic while working with the equations especially if there is no consistency. By convention, the thermocouples are constructed in a manner that higher temperatures seem to yield higher thermo-junctive voltage. In most cases, it is assumed that the two wires in the thermocouple are connected to the voltmeter in a manner that voltage is positive while measuring temperatures higher than that of the reference temperature. Advantages and disadvantages of thermocouple thermometer The thermometer is small, accurate, offers rapid response, and relative cheap compared to the other methods of measuring temperature. However, the method requires amplification and processing of the signal, which increases the amount of materials required for effective processing. Thermistors Changes in temperatures often cause electric resistance of the material to change. Therefore, resistance change is measurable to infer the changes in temperature. Thermistors are one of the thermo-resistive measuring devices. Thermistors are temperature sensitive semiconductors exhibiting huge changes in the resistance over temperature, of relatively small range (Tavoularis, 2005). Although thermistors are similar to the resistance temperature detectors (RTDs), it uses the semi conductor material rather than the metal. In addition, a thermistor is a solid state device with high level of sensitivity compared to the RTD. The temperature resistance feature of the device is non-linear which cannot be categorized through single coefficient. Additionally, the resistance of a thermostor seems to decrease with the increasing temperature Thermistors cannot be used in measuring high temperatures, which forms the base of its disadvantage. The maximum temperature of the operation for the device is between 1000C and 2000C. In most cases, the manufacturers of the thermistors often provide resistance-temperature data in form of curves, tables, and polynomial expressions. While linearizing the resistance-temperature correlation might be accomplished using the analog circuitry, application in mathematics require digital computation. Figure 3: A Typical Thermistor Circuit From the diagram, it is evident that it is a simple voltage divider. The R2 represents the fixed supply resistor. Resistors and voltages are adjustable in obtaining the desired range of output for any given range of temperature. Advantages and Disadvantages of Thermistor The major benefits associated with the thermistors include large resistance change with the temperature, rapid and effective response, good stability, high level of resistance, which seem to eliminate the difficulties associated with the lead resistance. In addition, the thermistor is low cost and interchangeable (Tiab & Donaldson, 2012). However, the disadvantages associated with the device include its non-linearity, limited operating ranges of temperatures, and could be subject to the high level of inaccuracy due to overheating. It also requires the current to process various activities. Fluid Pressure Piezometer Piezometer is the simplest method used in measuring fluid in the pipe. In some cases, it is referred to pressure measuring tube. Such tubes often contain fluids under pressure with the fluid allowed to increase to the high corresponding to the excess of the pressure of the fluid over the one that surrounds. However, in most cases, the surroundings contain ambient air. The pressure with the fluid is measured through allowing the fluid to rise in the vertical tube to the level that meets the equilibrium within the surrounding pressure of the air, the height to which it increases the pressure head existing within the pipe (Patience, 2013). The tube used in the piezometer method is the manometer. The height, which is also the head, relates to the pressure within the pipe through an equation. Generally, P = Z1r1g in which Z stands for pressure, Z1 is the height in which the fluid rises, r1 is the density of the fluid, and g is the acceleration due to gravity. Figure 4: Pressure Measurement in the Pipes The development of the piezometer is in form of the U-tube with another fluid introduced into the pipes being immiscible with the fluid whose pressure is under measurement. There is connection of the fluid with unknown pressure at the arm of the manometer tube to allow the displacement of the measuring fluid. To determine the unknown pressure, there is need to determine the difference between the levels of the measuring fluid within the two arms of the U-tube which is represented by Z3. Moreover, the differential pressure is given directly as the method used in measuring the fluid, which is convertible to the head of the fluid within the system or the pressure difference from the equation. Advantages and disadvantages Piezometer Is one of the simplest manometers used to measure moderate pressure of the liquids. Therefore, it is easy to use and has few requirements. However, the method has limitations. For example, Piezometer can only measure gauge pressure making it unsuitable for measuring the negative pressure. Additionally, it cannot be employed in cases involving large pressures within the lighter liquids because it needs long tubes, which are difficult to handle in convenient manner. Since the gas forms no free surface, it is impossible to use piezometers in measuring the gas pressures. DeadWeight Testers The deadweight tester forms the basis of the most fundamental technique used in measuring pressure since it has primary calibration of the pressure sensors. In some cases, it is referred to as the piston gauge. The deadweight tester applies calibrated weights that normally exert pressure on the liquid fluid through the piston. It is possible to employ the method as the primary standard of measuring pressure considering that it is easy to trace the factors influencing accuracy with focus on standardization elements such as time, mass, and length. The method has a piston considered easy to operate with pressure generated through turning the jackscrew, which play important role in reducing the volume of the fluid inside the tester; as a result, it results in increased level of pressure. When the pressure generated through the reduced volume is higher compared to that generated by the weight of the piston, then the piston is expected to rise until it reaches the point in which the levels of equal or point equilibrium in which the pressures, both at the bottom and gauge of the piston are exactly equal. Based on the above explanation, the pressure within the system would be: P = W/A in which W refers to the weight of the piston and A is the effect area of the piston. Typically, the deadweight testers are used within the calibration laboratories to calibrate pressure transfer standards including the electronic pressure measuring devices. Different pressure ranges are achievable through variation in the area of the piston and size of the weights (Taghvaeian, 2015). However, for the extremely and precise calibration of pressure, most of the errors are adjustable with exact areas or corrections and weight known, and great care is need throughout the procedure. It is important to note that deadweight testers are not a practicable method for the day-to-day measurement of pressure. Figure 5: Deadweight Tester PA = Mg + F Therefore: P = Mg + F / A  where, P = pressure F = Friction drag; N A = Equivalent area of piston – cylinder combination; m² M = Mass; Kg g = Acceleration due to gravity; m/s² Hence, the pressure P is caused by the weight placed on the platform. Advantages and Disadvantages of deadweight tester application The method is used in all the pressure gauges including the industrial pressure gauges, piezoelectric transducers, and engine indicators. The method has different benefits and limitations. The advantages include simplicity in construction and usability. Deadweight tester is usable in a wide range of devices used in measuring pressure and fluid pressure easily varied through addition of weight or changing the piston cylinder combination. The limitation of using the method is associated with accuracy, which is affected by the friction that occurs between the piston and the cylinder. Force-Summing Devices The mechanical pressure gauges and electromechanical sensors within the elastic elements identified as force-summing device play critical role in measuring pressures since they change shape with application of pressure. The change in the shape is converted to a displacement. There are several force-summing devices for measuring pressure; however, the most common ones are diaphragms and Bourdon tubes. The Bourdon tubes provide larger displacement motion compared to the diaphragms, which makes it applicable in the mechanical pressure gauges. The diaphragms have lesser motions, which make it better within the electrochemical sensors. The motion of the force-summing device is linkable to the linear variable differential transformer, which play important role as an electromechanical transduction element. On the other hand, force-summing force is also linkable to the wiper of the potentiomenter usually through the motion that seem to amplify the mechanism. For the reduction of the acceleration error, there is provision of the balancing mass. Any thin metal that has fixed ends between the two parallel plates is the diaphragm. The operating principle of the device is that the applied pressure is converted into proportion displacement. The diaphragm uses different materials including beryllium copper, phosphor bronze, stainless steel, and nickel, which are available in corrugated shapes and flat. Whenever two corrugated diaphragms are joined together, there is formation of capsule at their end. With comparison to the flat diaphragm, the corrugated diaphragms seem to produce greater displacement (State Water Resources Control Board, 2011). The combination of two diaphragms leads to more displacement, which is twice higher than the single corrugated diaphragm. As a result, there is generation of displacement that is proportional to the pressure. The major shape applied employed to the force-summing devices is the C-type. Increased sensitivity is achievable through the spiral and helical shaped tubes. The conversions of the displacement into the pointer rotation occur through the gear and lever systems. Figure 6: Bourdon Tube Pressure Gauge Volumetric Flow Rate Bucket method The bucket method offers the simplest way of measuring the flow rate using the household items. The method mainly requires a large bucket, stopwatch, and preferably two to three people. While using the bucket method to measure the flow rate, it is important to have the measurement of the volume of bucket or the container, and identify the location along the stream with a waterfall. Using the stopwatch, it is critical to measure the duration it takes the waterfall to fill the bucket in use with water. However, the stopwatch should start simultaneously with the start of water and stop it when the bucket fills (Recktenwald, 2006). Record the time taken to fill the bucket and repeat the process severally and identify the average. In the bucket method, it is important to have few trials before taking the records. To determine the flow rate, take the volume of the bucket then divide with the average time taken to fill the bucket. Using the data acquired, the volumetric flow rate (Q) is equivalent to the volume of the bucket (V) divided by the average time (t) Q = V/t There are suggestions to the method for diversion of the water into the flow measuring container: the natural waterfall or building the weir from the available materials and using the wooden channel, the piece of pipe, or corrugated sheet to the channel of the water. Advantages and disadvantages of bucket method The main benefit associated with the method is its easy to use and few requirements for determining the volume flow rate. However, the method seems to provide the flow at a point in time, which limits the scope of experiment. In addition, it might be quite challenging to determine the volume flow rates in areas with no waterfall. The Float Method The float method works properly within the canals or channels. It is also usable within the rivers and streams although with little accuracy. However, to use the method, it is important to first determine the cross-sectional area of the water that flows into the stream or channel and secondly is the speed that the water seems to flow. This is measured through the float and timing the travel between the two points identified as the distance apart. The difficulty in measuring the cross-sectional area depends on the type of flow under consideration. It is easier to estimate the cross-sectional area on the smooth sided channel compared to the shallow and rocky stream (Gardner, 2000). For estimation of area of a given point, it is critical to measure the width and depth measurement at regular intervals across the flow. Based on the measurements, there is need to plot the depth measurement on the squared paper. The plots are joined to form straight lines to the width, which is marked along the axis for creation of an enclosed. The numbers of squares are multiplied to represent m3. The second step is to measure the speed of the flow, which involves setting a length of 10 metres between marking points, which needs to be sufficient. Then put the float within the water some meters upstream as the marking point, float it as passes through the first marker. The third step involves calculating the flows in litres per second through multiplying the average stream area and velocity of the flow. Considering that the water moves faster on the surface compared to the other parts of the stream, there is need for introduction of additional factor, which takes the difference into account. Equation of the Float Method The equation to calculate the flow is: Q = Aaverage x Vsurface x Correction Factor Where Q= Flow rate (m3 /s) Aave= Average cross-sectional area (m2 ) Vsurface= Surface velocity (m/s) Disadvantages and advantages of Float Method The method is easy to use and has few requirements to determine the volumetric flow rate. However, the float method seems to provide the flow or the volume discharged at a point in time contributing to inconvenience of the method. The pipe or trajectory method If the water is flowing fast enough, then it has sufficient drop at the pipe making it easy to measure of how far the water shoot out of the pipe providing an estimate of how the much the discharge is flowing through the pipe. However, the trajectory method needs the pipe diameter and water level within the pipe noted. The method in water measurement is a type of velocity area computation that is usable in acquiring rapid and rough estimate of the flow rate that seem to discharge from the horizontal pipe that is flowing full (Hydromatch, 2012). There are two measurements, which are important in the method for calculation of the rate of water flow: measurement of the horizontal distance (d) which is parallel to the centerline of the pipe needed for the jet to drop the vertical distance (a) that forms the second measurement. The flow Q can be calculated through the following formula: Q = 8.69 (1- a/d)1.88 d2.48 Where: a = the measured distance between the inside upper edge of the pipe and the top of the water surface (ft) Q = the volumetric flow in cubic feet per second d = the diameter of the pipe (ft) For the trajectory method of measurement, the ratio of a/d must be greater than 0.45. Advantages and disadvantages of trajectory method In appropriate cases, the rate of flow can be approximated without purchasing expensive materials and measuring devices as used in the other methods. However, the method seems to require steady state discharge and high level of record keeping. Besides, the method is less effective especially if the discharge velocities are either high or very low. References Alexandrou, A. N. Principles of fluid mechanics; Prentice Hall: Upper Saddle River, NJ, 2001. Childs, P. R. N. Practical temperature measurement; Butterworth-Heinemann: Oxford, 2001. Gardner, R. Science projects about methods of measuring; Enslow Publishers: Berkeley Heights, NJ, 2000. Hydromatch. Flow estimation for streams and small rivers http://www.hydromatch.com/sites/default/files/downloads/DIY-flow-measurement-guide.pdf (accessed Feb 21, 2017). Ochkin, V. N. Spectroscopy of low temperature plasma; Wiley-VCH: Weinheim, 2009. Patience, G. S. Experimental Methods and Instrumentation for Chemical Engineers; Elsevier: Waltham, MA, 2013. Recktenwald, g. Volumetric Flow Rate Measurement http://web.cecs.pdx.edu/~gerry/class/ME449/lectures/pdf/flowRateSlides_2up.pdf (accessed Feb 21, 2017). State Water Resources Control Board. Water Measurement: Examples Of Alternative Measurement Methods http://www.waterboards.ca.gov/waterrights/water_issues/programs/diversion_use/wm_alt_mthds.shtml (accessed Feb 21, 2017). Taghvaeian, S. Irrigation Water Flow Measurement http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2225/BAE-1502web.pdf (accessed Feb 21, 2017). Tavoularis, S. Measurement in fluid mechanics; Cambridge Univ. Press: Cambridge, 2005. Tiab, D.; Donaldson, E. C. Petrophysics: theory and practice of measuring reservoir rock and fluid transport properties; Gulf Professional Publishing: Amsterdam, 2012. Read More

Radiation exchange between parameters If the surface temperature (Ts) that is unenclosed though seems to radiate freely into the surrounding temperature (Tb), then the radiation received through the infrared thermometer focused towards the ground. This could be summed as Ltotal= εL(Ts) + (1 - ε)L(Tb) . The first part is due to radiation emitted by the surface and emissivity product (0 < ε < 1) and radiance of the blackbody L(Ts) and temperature Ts measured in Kelvin. This needs to follow Planck law.

On the second part, there is reflection from the background, which is the product of spectral radiance given the temperature Tb and surface reflectivity (1 - ε). Figure 1: Diagrammatic Representation of Radiation Thermometer The thermal radiation is majorly within the infrared; however, with the temperatures increasing above 7000C, the dull red heat might be visible which tend to brighten to yellow, finally, and brilliant white heat. It is essential to note that the consequence is highly sensitive.

Therefore, radiation thermometry offers the powerful method of measuring temperature to some extent even lower than -500C. Additionally, radiation thermometry apply the concept of the perfect radiator or the blackbody considering that it is the perfect heat absorber of every radiation incident on it; as a result, it seems perfect when black. While in use, the blackbody seems to be used in calibrating the radiation thermometers. Nonetheless, the real surface of the device emits little radiation compared to the blackbody at similar temperature, which makes it important to correct the temperature measures for the emissivity of the surface.

In any particular temperature, the thermometer is advantageous especially while operating as the shortest wavelength due to greater sensitivity and emissivity and little errors involved. The commonly used wavelength ranges from 0.65-1.0 μm through the Si photodiode detector. At low to moderate temperate, the intensity is also low making it significant to operate in similar way into the infrared and above the wavelength bands for acquisition of the signal. However, it is important to apply the parts of spectrum in which the water vapour and CO2 do not absorb the radiations.

In most cases, the ranges of wavelengths are 3-5 μm through the InSb photodiodes while the wavelengths for cooled HgCdTe photodiodes is 8-14 μm. Radiation thermometry is a remote-sensing method with the amity of measuring very hot objects within the production line. The thermometer has modern detector arrays that seem to allow the production of thermal images of the objects. Advantages and Disadvantages The radiation that an object emits depends on the temperature and surface features including emissivity.

Such features reflects the radiation ability on the scale of 0-1 with 0 for the perfectly reflecting surfaces that do not emit radiation and 1 where possible, applies to the perfect blackbody radiator. With radiation thermometer, it is important to note the emissivity and estimate the accuracy of the acquired temperature. Thermal radiations emitted by the heaters are reflected partially by the target and add some of the radiations detected. If there are no precautions, reflections from the furnace heaters could result in reflections, hence high temperatures.

Thermocouple The thermocouple uses the feedback effect, which demonstrates the electrical potential within the juncture points of two metals that are dissimilar with magnitudes of change varying in temperatures. If the junction completes the circuit, the temperature of the measuring junction is measurable. When there is connection of the two dissimilar metals, there is production of small voltage identified as thermo-junction voltage: Peltier effect. When there is a change in the temperature of the junction, the voltage changes as well which the input circuits measure.

There is proportionality relationship between voltage and temperature difference between the free ends and junction: the Thompson effect.

Read More