A Thermocouple is a sensor used to measure temperature. They are 3 options for how many junctions can be found in a Thermocouple, a simplex Thermocouple (two wire) a duplex Thermocouple (4 wire) & a triplex Thermocouple (6 wire). To create a junction the wires need paired, each pair consists of two dissimilar metals, when welded together this is known as a hot junction. Once the junction of the Thermocouple has been welded and has contact with a heat source, this creates a milivoltage. The milivoltage travels along the Thermocouple wire, which can then be converted in to temperature using Thermocouple reference tables to calculate the temperature.
Northeast Thermocouple Sensors Ltd can manufacture the following:
Type K Thermocouple + Chromel / – Alumel
Type J Thermocouple + Iron / – Constantan
Type N Thermocouple + Nicorsil / – Nisil
Type T Thermocouple + Copper / – Constantan
Type E Thermocouple + Chromel / – Constantan
Type R Thermocouple + Copper / – Alloy 11
Type S Thermocouple + Copper / – Alloy 11
What Is An RTD?
Utilising a high precision sensing resistor, usually of platinum, the resistance value of which increases with temperature. The platinum sensing resistor is highly stable and allows high accuracy temperature sensing. RTD’s offer excellent accuracy over a wide temperature range (from –200 to +850 °C) with various accuracy specifications and numerous packaging options to suit most applications. Unlike Thermocouples, it is not necessary to use special cables to connect to the sensor. The principle of operation is to measure the resistance of a platinum element. The most common type (PT100) has a resistance of 100 ohms at 0 °C and 138.4 ohms at 100 °C.
Northeast Thermocouple Sensors can manufacture your RTD in the following configurations:
Simplex RTD – 2 wire, 3 wire, 4 wire
Duplex RTD – 2 wire, 3 wire, 4 wire
Thermocouple’s are generally:RTD’s are generally:
Relatively inexpensive More expensive
More rugged More accurate
Less accurate Highly stable
More prone to long-term drift Capable of better resolution
More sensitive Restricted in their range of temperature
Tip sensing Stem, not tip sensitive
Available in smaller diameters Rarely available in small diameters
They do need special cabling They do not need special cabling
In both cases the choice of Thermocouple (and type of Thermocouple) or RTD must be made to match the instrumentation and suit the application in question.