Temperature is an objective measurement of how hot or cold an object is. It can be measured with a thermometer or a calorimeter. It is a means of determining the internal energy contained within a given system.
When it is 54 degrees outside, 54 degrees is an example of temperature. When your body is at 98.6 degrees, this is an example of a normal body temperature.
Temperature conversion formulas refer to changing the value of temperature from one unit to another. They are many temperature conversion methods. Among them Kelvin, Celsius and Fahrenheit are the most commonly used methods. According to the Kelvin scale, the freezing point of water is 273.15K and the boiling point is 373.15K. According to Fahrenheit scale, the freezing point of water is 32°F and the boiling point is 212°F. According to the Celsius scale, the freezing point of water is 0°C and the boiling point is 100°C.
A temperature transmitter is a device that connects to a temperature sensor to transmit the signal elsewhere for monitoring and control purposes. Typically, the temperature sensor is either an RTD, Thermisor or Thermocouple type sensor and will interface with a PLC, DCS, data logger or display hardware.
The temperature transmitter’s role is to isolate the temperature signal, filter any EMC noise, amplify and convert the temperature sensor’s signal to a 4-20mA or 0-10V DC range for further use.
The term RTD stands for Resistance Temperature Detector. This sensor is also known as Resistance thermometer. This sensor is used to measure the temperature. An RTD is a temperature sensor that operates on the measurement principle that a material’s electrical resistance changes with temperature. The relationship between an RTD’s resistance and the surrounding temperature is highly predictable, allowing for accurate and consistent temperature measurement. By supplying an RTD with a constant current and measuring the resulting voltage drop across the resistor, the RTD’s resistance can be calculated, and the temperature can be determined.
Various types of temperature instruments available for industrial purpose and it can be used its depend upon on your requirements.
Resistive Temperature detector (RTD)
A thermocouple is a sensor for measuring temperature. This sensing device consists of two dissimilar metal wires, joined at the both side end, and A current is created when the temperature applied to one end or junction differs from the other end. This phenomenon is known as the Seebeck effect, which is the basis for thermocouple temperature measurement. One end is referred to as the hot junction whereas the other end is referred to as the cold junction.
Type K Thermocouple provides widest operating temperature range. It consist of positive leg which is non-magnetic and negative leg which is magnetic .In K Type Thermocouple traditional base metal is used due to which it can work at high temperature and can provide widest operating temperature range. One of the constituent metal in K Type Thermocouple is Nickel, which is magnetic in nature.
Thermowells are most often constructed from machined bar stock in a variety of materials and may be coated with other materials for erosive or corrosive protection. They are available with threaded, welded or flanged connections. The stem or shank that extends into the process may be straight with constant diameter, tapered all the way from entry point to the tip, partially tapered, or stepped.
Digital Temperature Sensors is ideal for industrial temperature measure- ment and indication in a wide variety of applications. Digital Temperature Sensors conveniently combines a precision RTD sensing element, measuring electronics, and process fitting all in a single stainless steel temperature transmitter probe. They have a wide measuring range of -58 to 302°F. Choose from four standard probe insertion lengths and two integral male NPT process threads that allow direct mounting to the process or thermowells, eliminating the need for separate probe mounting
Head-mount transmitters are compact disc shaped transmitters most often mounted within a connection head which can be field mounted. Most common styles are DIN A and DIN B which differ slightly in dimensions and mounting method. However, the distance between the mounting screws is identical. These are commonly mounted in single compart- ment housings, such as sensor connection heads or junction boxes.
Diodes are highly sensitive and linear temperature sensors.Silicone and germanium diode temperature elements are available from − 458 to 395 ° F ( − 272 to 202 ° C). They are accurate to 0.2 ° F (0.1 ° C) for temperatures that are above ambient and to 0.2% of their full scale range below that.Figure 4.7c depicts the diode-based thermometer circuits o fa silicone diode with a 1 mA constant current source, and Figure shows the circuits of a germanium diode with a6-V power supply.
When temperature being measured is very high and physical contact with the medium to be measured is impossible or impractical, optical pyrometer based on the principle of thermal radiation are used. These Types of Pyrometer Working Principle are used under condition where corrosive vapours or liquids would destroy thermocouples, resistance thermometer and thermister, if made to come in contact with the measured medium. Radiation Pyrometer Working Principle measures the radiant (energy) heat emitted or reflected by a hot object. Thermal radiation is an electro magnetic radiation emitted as a result of temperature and lies in the wavelength of 0.1 —100 μm.
Thermopile working principle as as Thermocouples , The thermopile is the name given to a temperature-measuring device that consists of several Thermocouples connected together in series, such that all the reference junctions are at the same cold temperature and all the hot junctions are exposed to the temperature being measured. The effect of connecting n Thermocouples together in series is to increase the measurement sensitivity by a factor of n. A typical thermopile manufactured by connecting together 25 chromel–constantan thermocouples gives a measurement resolution of 0.001°C.