The Main Temperature Sensors for Control Systems - Assignment Example

 A Review of the Main Temperature Sensors for Control System and Summary of the Typical Sensors for Measurement of Rainfall Question 1 A review of the main temperature sensors for control systems (Resistance Temperature Detectors, RTD, Thermocouples, Thermistors) outlining the characteristics of each type and providing explanations and examples of the types of systems they are most suited. Introduction Many people virtually ignore the importance of temperature sensors in various thermal systems. Bharathi and Vasantharajan (2008) and Nieuwenhove and Vermeeren (2004) affirm that temperature measurement can be achieved using various forms of sensing mechanisms. Temperature measurement systems consist of a transmitter, a sensor; some have external power supply, and wiring system connecting these components. Ibrahim and Coupland (2009) confirm that resistance temperature detectors (RTD), thermocouples, Infrared Thermometers, and Thermistors are the most commonly used temperature measurement sensors. This research explores three basic types of sensors: RTD, thermocouple, and Thermistors. It will show how the sensors work, and provide their unique features, advantages and disadvantages. Temperature sensors are the “nervous systems” of any controller[Bha08]. Just as human beings rely on their sense of touch, temperature controllers rely wholly on the various sensors. The controller use signals from the sensor to decide whether it should turn the heater on or off in order to maintain a set or required temperature level. Thermocouples Thermocouples are widely used because they are reliable, simple to used, and have a relatively lower price compared to other sensors[Sea05]. Thermocouples are self-powered, thus eliminating the use of a separate or an external power supply to the sensors. They are durable when they are chosen appropriately for a designed application. Ibrahim and Coupland confirm that the thermocouple sensors are used in applications that handle very high temperatures such as incinerators. A thermocouple is a temperature transducer, which operates on a principle that unlike conductive materials is capable of generating current when they are joined (Setback effect)[Jia09]. Such devices are made by joining two wires that are made of alloys (different metals) joined at one end, and then generating a voltage of eAB when heated. Jikwang, Jonsung, and Younghwa (2009) emphasize that the produced voltage is proportional to the difference between the measured joint temperatures and the reference point, which is determined experimentally and it depends on the type of materials that are used. A temperature monitoring system when using a thermocouple includes connectors, thermocouple, isothermal block, extension wires, and a transmitter also known as voltmeter. This schematic (figure 6) is for type J iron (Fe) constantin Cu-Ni thermocouple. Nieuwenhove and Vermeeren (2004) describe that when the thermocouple junction is cooled or heated, a digital voltmeter or potentiometer can be used to measure the resulting voltage. The American National Standards Institute, ANSI, Instrument Society of America have classified thermocouples and that thermocouples have temperatures that range from 2000C to 17000C[Imr07]. They have a tolerance capacity that ranges from ±5 to ±2%. Application of thermocouple sensors There are various types of thermocouple sensors types B, E, J, K, N, R, S, T, C, D, and G[Jia09]. The thermocouple sensors are applied in different industries: Steel and Iron industries Thermocouples types B, K, S, and R are extensively used in the steel and iron industries. They monitor the varying temperatures throughout the steel and iron making process[Nie04]. Type S thermocouples are used in the electric arc furnance to provide accurate temperature measurement before tapping steel. Thermopile radiation sensors Imran and Bhattachryya (2007) and Nieuwenhove and Vermeeren (2004) confirm that thermopiles measures the intensity of radiation infrared light that heats up the hot junction. Commercially available thermopile sensors measure the intensity of radiative of only few μW/cm2. Laser power is one of the best examples that the radiation sensors are applied. Manufacturing Thermocouples are used to test various electrical and mechanical prototype apparatus[İbr09]. Switgear that is an undertest for its carrying capacity have thermocouples installed and they are monitored to prove that the level of temperature rises but do not exceed the designed limits. . Process plants Petroleum and chemical production employ computers to log and limit testing various temperatures that are linked to the process[Imr07]. For these cases, thermocouples leads are brought to a reference block that contains the second thermocouple of every circuit. A thermistor measures the temperature of the block. Thermoelectric cooling Seaton and Leach (2005) say that a Peltier effect can be employed in cooling reversing the role of thermoelectric generator. The thermocouple will work as a heat pump by consuming power, instead of generating it. Resistance Temperature Detectors (RTDs) Bharathi and Vasantharajan (2008) and Seaton and Leach (2005) define RTDs as temperature sensors, which contain a resistor that operates in a way that it changes the value of resistance, therefore, altering the level of temperature. RTDs have been used for decades to measure temperatures in industrial and laboratory processes, and it has developed an accuracy in its stability, accuracy, and repeatability[Jik09]. The RTDs work on a principle stating that the metal resistivity depends on the levels of temperature such that resistance increases with an increase in temperature. If temperature reduces, so it is the resistivity of the metal. Platinum is majorly used in various industries becauseit becomes more stable at higher temperatures and proves the RTDs principle that relates temperature and temperature changes[Imr07]. Platinum wares are wound around ceramic or glass for protection. Applications of RTDs a. RTDs sensors are used in air conditioning and refrigeration services[Bha08]. This type of service requires accurate measurement of temperature that the RTDs can provide. b. Food processing industry where the industries employ the use of RTDs sensors. Food processing industries has to maintain the right accurate temperature so that their produce cannot go bad. RTDs havethe ability to detect any slight of temperature. c. Petrochemical processing d. Textile production e. Stoves and grills f. Exhaust gas measuring of the desired temperature. g. Air, liquid, and gas industries. Thermistors Jikwang, Jonsung, and Youghwa (2009) affirm that thermistors are sensitive resistors. Thermistors are sensitive to any slight change in temperature. Thermistors are majorly composed of semiconductor materials, and they normally have a negative temperature coefficient (TC). The resistance of the thermistor reduces with increasing temperature. Imran and Bhattacharya (2007) confirm thatthe negative T.C can increase in several degrees Celsius that can detect the slightest temperature changes that could not be viewed through RTDs and thermocouples. Application a. PTC thermistors are used to limit currently for protection of circuit, and it replaces fuses[Imr07]. When current increases and generates heat than the device can lose to its environment, therefore, the device the device will heat up allowing increased resistance. The thermistor creates a self-reinforcing environment that make resistance to increase, and this will hinder current flow. b. Most CRT displays use transmitters. Seaton and Leach (2005) explains that when the CRT is switched on current will flow through the degaussing and thermistors. Current will flow through the degaussing coil to a level that the degaussing coil will shut off in a second. A degaussing coil is reliable, inexpensive, and simple to use. c. NTC thermistors are resistance thermometers in extremely low temperatures in the 10K order[Nie04]. d. NTC thermistors are used to limit inrush into the circuit. When current is increasing, the thermistors will increase their resistivity and will hinder currently from flowing. e. NTC thermistors are usually used in automotive sectors[Sea05]. These transmitters monitor various appliances such as the monitor coolant and oil temperature. f. The NTC thermistors are used to monitor and control the level of temperature in incubators[Jia09]. g. Thermistors monitor the packs of battery while charging it in a modern thermostat. h. Thermistors are used in the hot ends of 3D printers[Bha08]. They monitor and control the amount of heat produced and allow the printer to cool down. i. Thermistors are vital in Consumer Appliance industry to measure freezers, toaster, eggs, freezers, fridges, and coffee maker. j. Thermistors are used in Food handling and Processing industry in food storage and preparations[Jia09]. Maintaining the right level of temperature will prevent people from contracting food borne illnesses. Question 2 A summary of the typical sensors for measuring rainfall, summary should compare these sensors with the latest development in rainfall measurement sensor technology (Vaisala RAINCAP, optical sensor etc). Discuss the key drivers supporting development and uptake of the newer sensors. Introduction The attention professionals and researchers are paying attention to reliability and accuracy in rainfall measurement is increasing (Barret and Beaumont, 2007). The rising popularity of practical and scientific related issues has seen a successful assessment of climatic trends such as natural disaster mitigation (floods and storms) and hindering the effect of desertification. Bruin (2009), Morgan and Lourence (2007), and Bruce (2008) confirm that a more reliable knowledge of the atmospheric liquid at a said site or over an extended region such as water catchment basins is vital to various investigative issues, especially within hydrological and atmospheric applications. New technological advancements have seen to development of new instruments that can measure the rate of precipitation[Mor07]. The rain gauge is the widely used meteorological instruments; however, it can only measure the duration and intensity of precipitation. The development of electronic and optical techniques have seen the development of different instruments that can measure. Disdrometres facilities that measures drop size distribution (DSDs) are widely used in climate studies and modelling estimation of rainfall. Although the observations with rain gauge and disdrometers can verify the accuracy of rain, but there is no instrument between the two in obtaining the accurate and true values. The need to develop different ways of studying precipitation has led to the development to new technology such as Vaisala RAINCAP® and optical sensors[Koh07]. Sensor technology is a modern way that professions in the field of climate use to measure the rate of precipitation. Stewart and Urbonas (2004) define RAINCAP® as an acoustic sensor, which aims at measuring the effect ofa single raindrop falling on the smooth stainless surface using piezoelectric detector. Using the machine you find real information on the amount or intensity of rainfall, accumulation of rainfall and duration[Sev08]. The sensor helps professionals distinguish between hail and rain. The sensor is maintenance free because it does not have any moveable part that will require cleaning. The sensor provides real time information on rain intensity, duration, and accumulated rainfall. It also has the ability to distinguish between rain and hail. The RAINCAP® has no moving parts or components that need emptying or cleaning. It is essentially maintenance-free making it easy to maintain. This method eliminatesclogging, flooding, evaporation and wetting losses in measuring of the rainfall[Bru09]. Compared to various precipitation gauges, such as the rain gauge, the Vaisala RAINCAP® provides more detailed information concerning rain. The sensor measures the accumulated rain, duration or the rain in real time. Key drivers supporting development and uptake of the newer sensors 1. For Sophisticated Road The Vaisala Present Weather Sensor provides accurate and efficient visibility information and provides the relevant authority with the right road measurement[Mor07]. A road with a low visibility is prone to have accidents and increase traffic jam. The sensor is ideal for road application. The new developed sensor willprovidevisibility that gives full picture of various weather conditions[Koh07]. The sensor can detect and identify precipitating types giving the road authority for maintenance and operations. 2. The RAINCAP® requires no maintenance. The RAINCAP® has no moving parts or components that need emptying or cleaning. It is essentially maintenance-free making it easy to maintain[Jia09]. Tthis will make it suitable for remote places where it will not be given much attention in terms of maintenance. 3. The RAINCAP® provided data in real time[Bha08]. The data from the sensor is accurate and it reflects the true nature of precipitation. The new technology has enabled various facilities to develop and provide people with accurateinformation. The rain gauge has been there for years, but Bruce (2008) insists that it does not reflect the true nature of precipitation. Therefore, the availability and development of this facility has enabled the development and growth in the provision of proven information. 4. Need for accurate data: The RAINCAP® can provide the difference between rain and hail and it can also provide accurate information on the types of precipitation[Koh07] 5. There is the need to replace older equipment. Some sensors do not provide correct information thus professionals will not provide the right data. References Bha08: , (Bharathi & Vasantharajan, 2008), Sea05: , (Seaton & Leach, 2005), Jia09: , (Jianwei Shen & Shen, 2009), Imr07: , (Imran & Bhattacharyya, 2007), Nie04: , (Nieuwenhove & Vermeeren, 2004), İbr09: , (İbrahim & Coupland, 2009), Imr07: , (Imran & Bhattacharyya, 2007), Jik09: , (Jikwang , Jongsung , & Younghwa , 2009), Bha08: , (Bharathi & Vasantharajan, 2008), Mor07: , (Morgan & Lourence, 2007), Koh07: , (Kohler & Paulhus, 2007), Sev08: , (Sevruk & Zahlavova, 2008), Bru09: , (Bruin, 2009), Read More