06-09-2012, 12:54 PM
POWER PLANT INSTRUMENTATION
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Introduction:
Instrumentation is the art of measuring the value of some plant parameters like pressure, flow, level or temperature to name a few and supplying a signal that is proportional to the measured parameter. The output signals are standard signal & can then be processed by other equipment to provide indication, alarm or automatic control. There are a number of standard signals; however, those most common in a plant are the 4-20 m A.
Electronic signals and 20-100 kPa pneumatic signals . This section of the course is going to deal with the instrumentation equipment normally used to measure and provide signals. We will look at the measurement of four parameters: pressure, flow, level and temperature.
pressure transmitter
As a means of monitoring activity in a number of manufacturing facilities, marine research, and general production control, a pressure transmitter will not only help to ensure positive results; it also can be a great way of maintaining acceptable levels of safety. Here are some examples of what a pressure transmitter is designed to do and how it can be used in several different settings.
When it comes to the monitoring of pressure within a factory setting, a pressure transmitter helps to accomplish two specific goals. First, pressure instruments monitor the amount of pressure applied to a part of the process that is required in order to achieve the desired result. Since the application of too much or too little pressure may result in product that cannot be sold, constant real-time measurements of the pressurised environment is absolutely necessary.
Thermocouple measuring circuit
A thermocouple is a device consisting of two different conductors (usually metal alloys) that produce a voltage, proportional to a temperature difference, between either ends of the two conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a temperature gradient into electricity. They are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. In contrast to most other methods of temperature measurement, thermocouples are self powered and require no external form of excitation. The main limitation with thermocouples is accuracy and system errors of less than one degree Celsius © can be difficult to achieve.
Any junction of dissimilar metals will produce an electric potential related to temperature. Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are used for different temperature ranges. Properties such as resistance to corrosion may also be important when choosing a type of thermocouple. Where the measurement point is far from the measuring instrument, the intermediate connection can be made by extension wires which are less costly than the materials used to make the sensor. Thermocouples are usually standardized against a reference temperature of 0 degrees Celsius; practical instruments use electronic methods of cold-junction compensation to adjust for varying temperature at the instrument terminals. Electronic instruments can also compensate for the varying characteristics of the thermocouple, and so improve the precision and accuracy of measurements.
HOW DO RTDs WORK?
RTDs work on a basic correlation between metals and temperature. As the temperature of a metal increases, the metal's resistance to the flow of electricity increases. Similarly, as the temperature of the RTD resistance element increases, the electrical resistance, measured in ohms (Ω), increases. RTD elements are commonly specified according to their resistance in ohms at zero degrees Celsius (0° C). The most common RTD specification is 100 Ω, which means that at 0° C the RTD element should demonstrate 100 Ω of resistance.
Platinum is the most commonly used metal for RTD elements due to a number of factors, including its (1) chemical inertness, (2) nearly linear temperature versus resistance relationship, (3) temperature coefficient of resistance that is large enough to give readily measurable resistance changes with temperature and (4) stability (in that its temperature
[attachment=33514]
Introduction:
Instrumentation is the art of measuring the value of some plant parameters like pressure, flow, level or temperature to name a few and supplying a signal that is proportional to the measured parameter. The output signals are standard signal & can then be processed by other equipment to provide indication, alarm or automatic control. There are a number of standard signals; however, those most common in a plant are the 4-20 m A.
Electronic signals and 20-100 kPa pneumatic signals . This section of the course is going to deal with the instrumentation equipment normally used to measure and provide signals. We will look at the measurement of four parameters: pressure, flow, level and temperature.
pressure transmitter
As a means of monitoring activity in a number of manufacturing facilities, marine research, and general production control, a pressure transmitter will not only help to ensure positive results; it also can be a great way of maintaining acceptable levels of safety. Here are some examples of what a pressure transmitter is designed to do and how it can be used in several different settings.
When it comes to the monitoring of pressure within a factory setting, a pressure transmitter helps to accomplish two specific goals. First, pressure instruments monitor the amount of pressure applied to a part of the process that is required in order to achieve the desired result. Since the application of too much or too little pressure may result in product that cannot be sold, constant real-time measurements of the pressurised environment is absolutely necessary.
Thermocouple measuring circuit
A thermocouple is a device consisting of two different conductors (usually metal alloys) that produce a voltage, proportional to a temperature difference, between either ends of the two conductors. Thermocouples are a widely used type of temperature sensor for measurement and control and can also be used to convert a temperature gradient into electricity. They are inexpensive, interchangeable, are supplied with standard connectors, and can measure a wide range of temperatures. In contrast to most other methods of temperature measurement, thermocouples are self powered and require no external form of excitation. The main limitation with thermocouples is accuracy and system errors of less than one degree Celsius © can be difficult to achieve.
Any junction of dissimilar metals will produce an electric potential related to temperature. Thermocouples for practical measurement of temperature are junctions of specific alloys which have a predictable and repeatable relationship between temperature and voltage. Different alloys are used for different temperature ranges. Properties such as resistance to corrosion may also be important when choosing a type of thermocouple. Where the measurement point is far from the measuring instrument, the intermediate connection can be made by extension wires which are less costly than the materials used to make the sensor. Thermocouples are usually standardized against a reference temperature of 0 degrees Celsius; practical instruments use electronic methods of cold-junction compensation to adjust for varying temperature at the instrument terminals. Electronic instruments can also compensate for the varying characteristics of the thermocouple, and so improve the precision and accuracy of measurements.
HOW DO RTDs WORK?
RTDs work on a basic correlation between metals and temperature. As the temperature of a metal increases, the metal's resistance to the flow of electricity increases. Similarly, as the temperature of the RTD resistance element increases, the electrical resistance, measured in ohms (Ω), increases. RTD elements are commonly specified according to their resistance in ohms at zero degrees Celsius (0° C). The most common RTD specification is 100 Ω, which means that at 0° C the RTD element should demonstrate 100 Ω of resistance.
Platinum is the most commonly used metal for RTD elements due to a number of factors, including its (1) chemical inertness, (2) nearly linear temperature versus resistance relationship, (3) temperature coefficient of resistance that is large enough to give readily measurable resistance changes with temperature and (4) stability (in that its temperature