Techshore Inspection Services-Kochi-official blog of Techshore Kerala: TECHSHORE INSPECTION SERVICES : ELECTRICAL THERMOMETER

THERMOCOUPLE
Thermocouple is a type of electrical temperature sensor. They are simple, inexpensive and relatively accurate sensor that can be used for variety of environmental conditions. A thermocouple or a temparature transducer is a device which converts thermal energy (measuring temparature) into electrical energy. This is simple device consisting of two dissimilar wires joined at their ends. When the end of each wire connected to a measuring instrument, the thermocouple becomes an accurate and sensitive temperature measuring device.

SEE BECK EFFECT
The joined ends of a thermocouple form a junction called the hot junction or measuring junction. The other ends of the wires which are connected to a measuring instrument from a cold junction, or reference junction. Simply stated, the voltage difference produced by the measuring junction varies with the difference in temperature between the measuring junction and the reference junction.

The see beck effect describes the result of heating one junction of a circuit formed by joining two dissimilar metal conductors. In such a circuit, electric current flows as long as the two junctions are at different temperatures.

PELTIER EFFECT
When a current flows across a junction of two dissimilar metal conductors, it has been noticed that heat is either liberated or absorbed depending up on the direction of current flow. If the current flow is in the same direction as the current produced by the see beck effect, heat is liberated at the hot junction and absorbed at the cold junction.

THOMPSON EFFECT
The Thompson effect is also called as a reversible heat effect. This effect concerns the reversible heat effects resulting from the passage of an electric current through a conductor in which there is a temperature gradient. Heat ids liberated at any point where the current at the point flows in the direction of the heat. This happens with copper. The opposite happens with iron.
In many thermocouple installations, the measuring junction is several hundred feet far from the voltage measuring instrument at which the reference junction is located. Since the pure metal and metal alloy used for the thermocouple wires are relatively more expensive, extension or lead wires are typically connected to the thermocouple and run to terminals at the measurement instruments.

TYPES OF THERMOCOUPLES
Many types of thermocouples are commonly used for industrial applications. Seven of these has been assigned letter designations by the ISA (Instrument Society Of America).
Thermocouples can be divided into three functional classes: base metal, noble metal and refractory metal. Base metal thermocouple are used for measuring temperature under 10000C. This class includes thermocouple made of iron/constantan (Type J), copper/constantan (Type T), Chromel/Alumel (Type K), Chromel/constantan (Type E) and alloys of Copper, Nickel, Iron, Chromium, Manganese, Aluminum and other elements.

TYPE	MATERIALS	OPERATING RANGE	LEAD COLOR
B	Nickel	0 to 1500⁰C	Grey (positive)
	Chromium
	Platinum		Red (negative)
	Rhodium
E	Nickel	-200 to 850⁰C	Purple (positive)
	Chromium
	Copper		Red (negative)
	Nickel
J	Iron	-200 to 850⁰ C	White (positive)

	constantan		Red (negative)
K	Nickel	-200 to 1100⁰C	Yellow (positive)
	Chromium
	Nickel		Red (negative)
	Manganese
	Aluminum
R	Platinum	0 to 1500⁰ C	Black (positive)
	Rhodium
	Platinum		Red (negative)
S	Platinum	0 to 1500⁰ C	Black(positive)
	Rhodium
	Platinum		Red (negative)
T	Copper	-250to 400⁰ C	Blue (positive)
	Constantan		Red (negative)

Friday, December 23, 2016

TECHSHORE INSPECTION SERVICES : ELECTRICAL THERMOMETER

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