4.-Power-Plant-Instrumentation-and-Control-Part-1.pdf

BRIEF OVERVIEW THEORY BEHIND INSTRUMENTS Thomas Seebeck discovered the thermocouple, a tool for measuring temperature, in 1821. It is made up of two separate metals (copper and iron) connected at one end. Seebeck discovered that a voltage is produced when two different metals joined at o...

BRIEF OVERVIEW THEORY BEHIND INSTRUMENTS Thomas Seebeck discovered the thermocouple, a tool for measuring temperature, in 1821. It is made up of two separate metals (copper and iron) connected at one end. Seebeck discovered that a voltage is produced when two different metals joined at one end are exposed to a temperature gradient. According to this event, a temperature difference between two distinct conductors causes a voltage to be generated. A thermocouple circuit consists of a minimum of two junctions: the hot junction used for measurement and the cold junction used for reference. The cold junction or reference junction is kept at a known temperature; in other words, it doesn't change, while the hot junction or measurement junction is the one whose temperature is being measured. For example: Oven The thermocouple is placed inside the oven, where it can measure the oven`s temperature. To determine the current temperature, the oven's control systems measure the voltage across the thermocouple and then modify the heating to keep or maintain the desired temperature. Overall, a thermocouple allows temperature monitoring by converting changes in Basically a thermometer is a device that is used to determine the object's temperature. A thermometer's construction material can be used to classify it. We have two types of thermometers: the fluid filled and bi-metallic. The first one is the liquid-filled thermometer, which utilises a liquid or gas as the temperature sensing component. To understand easily the fluid-filled thermometers operate by having the liquid gas in the tube expand with increasing temperature. When choosing a thermometer filled with either liquid or gas, it is important to consider the "liquid in glass" and "liquid in metal" options. Usually Alcohol and mercury are the most common liquids found in glass thermometers, which consist of thin or small glass tubes with a bulb filled with liquid at the bottom. Basically the fluid expands when its temperature increases and moves up the capillary tube. So the level of liquid in the glass corresponds with the temperature outside of the glass. The results of the temperature can be read using either Fahrenheit or Celsius. A liquid in metal uses liquid as a thermometric substance to measure the temperature. The liquid seeks to enlarge as its temperature increases, causing pressure to rise in the metal tube with constant volume. By using a calibrated scale, the pressure can be converted into temperature. The same thing used in glass thermometers with liquid also applies to liquid in metal thermometers, also known as liquid filled thermometers. But, if the liquid fills a space completely, the measurement will not be of the liquid's temperature expansion but instead of the increase in pressure caused by the rise in temperature. When the temperature increases, a liquid's pressure also increases and the volume stays the same. This is the functioning process of metal thermometers filled with liquid. BIMETAL OR BIMETALLIC THERMOMETERS The second is the Bimetallic thermometers that are part of temperature measuring devices. A bimetallic strip is utilised to convert the fluid's temperature into a mechanical movement, mechanical displacement is the distance moved by a particle or body in a specific direction. The bimetallic strip is composed of two different metals that have different coefficients of thermal expansion. Bimetallic thermometers are utilised in industrial settings such as heaters, hot wires, air conditioners and more. Their temperature measurement technique is simple to grasp, durable, and cost-effective. In certain cases, bimetal thermometers may also be called bimetallic thermometers. The way in which the metal expands with temperature governs how the bimetallic strip functions. There is a unique temperature coefficient for each metal. The relationship between the temperature and physical dimension change of a metal is illustrated by the temperature coefficient. The amount of expansion or contraction of metal is determined by the temperature coefficient. Typically, the strip has a coil-like form. Due to the two metals' varying rates of thermal expansion, the length of the strip increases as it becomes heated. Because the two metals transfer heat at different rates, the strip will bend in the direction of the metal with the lower heat conductivity. The user's temperature is displayed by moving a pointer along a graduated scale using the strip A thermistor is a type of semiconductor that reacts like a resistor, sensitive to temperature. It means that they are sensitive and react even to very small changes in temperature and have a shorter response time compared to RTD. Also, the term thermistor comes from THERM-ALLY sensitive RES-ISTOR, and it is a very accurate and cost-effective sensor used for measuring temperature. There are two types of thermistorsThe PTC or positive temperature coefficient and the NTC or negative temperature coefficient. What's the difference between these two? The NTC resistance decreases as its temperature increases, and the PTC resistance increases as its temperature increases. NTC are usually used for temperature measurement, temperature compensation, and temperature control, while PTC are primarily used for circuit protection, telecom protection, motor starting, and more.In an NTC thermometer, the amount by which the resistance decreases as the temperature increases is not constant. It varies in a nonlinear way. Thermistors are composed of materials with known resistance. As the temperature increases, an NTC thermistor's resistance will increase in a nonlinear way, following a particular "curve.” The shape of this resistance vs. temperature curve is determined by the properties of the materials that make up the thermistors. Thermistors don’t have standards associated with their resistance vs. temperature characteristics or curves; each thermistors provides a different resistance vs. temperature “curve. Thermistors come in various resistance ranges and are suitable for different temperature applications. Lower temperature applications use thermistors with resistance ranging from 2252 to 10,000 ohms, while higher temperature applications use thermistors with resistance above 10,000 ohms. The accuracy of thermistors is approximately 0.2 °C within their specified temperature range. Additionally, thermistors cannot be used to measure high temperatures; they have a maximum temperature of operation of 100 or 200 °C; however, there are devices available that go as high as 750 °C. In summary, a thermistor is a temperature-sensitive resistor that changes its resistance based on temperature. By measuring the resistance or the voltage in a circuit, after that you can determine the temperature..  Early Force-balanced differential pressure transmitter. 1950 transmitters using large displacement principles. s 1970s Advances in technology led to the development of compact 1990 s Transmitters became more accurate and intelligent This innovation marked a major milestone in pressure measurement technology, leading to further advancements in the field. 1938 195 1954 196 1973 197 2 0 9 Roy Arthur Carl thin film William Robert Carlso Peter Ruge Spaulding transcuder Polye Bell n George and Scott Edward Jackson Simmon s  ANY QUESTION? For this topic, the individual who first raises their hand will be the one who answers the question that flashes on the screen. Who discover the thermocouple? Thomas Seebeck What type of instruments this? Pressure transmitter Who develope the first unbonded wire strain gauge for measuring strain in concrete? Roy Carlson What type of instruments this? thermistors