Thermocouples response time by type

A thermocouple is a temperature measurement tool that connects to a data interpretation device to form a high precision probe. It owes its success at its high reaction speed compared to other sensor models. However, all Thermocouple temperature probes do not offer an identical response time. Thermocouples are in a classification according to types (K, J, T, E, R, S, B) according to the materials used to design them. Does the response time of thermocouples varies according to the types? Should we also seek on the side of the other characteristics of thermocouples? If you want to equip yourself with the most reactive temperature probe as possible, here are the keys to understanding what determines the response time for a thermocouple.

What are the different characteristics of thermocouples?

If the Thermocouples ranges Offered are wide, it is because their design includes many parameters. These influential characteristics on temperature measurement accuracy as well as response time thermocouple.

The materials of the conductive wires

The two wires that constitute the heart of the thermocouple system contain different metals or metal alloys. It is the nature of these metal wires that defines the type thermocouple according to a European standard that classifies them.

The types K, J, T and E are the most common. The R, S and B contain precious metals, which makes their price higher. The big difference between these two categories is the temperature range in Celsius degrees which is covered. Types K, J, T and E, can measure the temperature from absolute zero up to high temperatures (up to 1,200 ° C). In R, S and B, the thermal measure can go up to very high temperatures (up to 1,800 ° C). Precious metals are also less prone to corrosion, which can occur in certain environments. Each of these types offers an optimal measurement range. By ensuring that the thermocouple temperature range is built with the temperatures to be measured, the best conditions are established for precise temperature control.

The protection of thermocouple

The most economical is The thermocouple with naked threads which presents itself without protective sheath. It contains two metallic wires welded together at one end. This type of temperature sensor is durable over time. On the other hand, the lack of protection makes it sensitive to certain external factors such as oxidizing or reducing environments. Thermocouples can also be with Mineral insulation in a metal sheath, this is a lined probe. The most used materials to design mineral insulation are alumina, magnesium, thorium dioxide and zirconium dioxide. The main criterion for choosing these materials is temperature resistance. For the metal sheath, the choice of materials is large. You must again take into account the temperature in its choice, as well as the environment where the sensor will be. The shirt makes the probe robust and electrically insulated.

The junction method

Another characteristic of the thermocouple probe is its junction method, that is to say the way the two wires are connected at the level of the temperature detection to be measured. In the welded junction, the conductive wires are welded to the sheath. When the junction is isolated, the wires and their junction are located inside the sheath. They are then isolated from the sheath. The exposed junction is located outside the sheath. The sheath is sealed around the output point of the metal wires in order to guarantee the best possible seal.

The connection cable

The other end of the conductive wires is connected to a device that transcribes the difference in potential (or electro-motor strength) generated in the volt or readable temperature sensor on the display. When necessary to add distance between the probe and the measuring device, connection cables are used. Two solutions are then available, the thermocouple cable or the compensation cable. The thermocouple cable is made up the same materials as thermocouple, which can be too expensive when the latter consists of precious metals. The compensation cable is made up of conductive wires with thermoelectric properties corresponding to those of the conductive wires of the thermocouple.

What characteristics influence the response time of a thermocouple?

The type of thermocouple determines the precision of the temperature measurement and its durability. On the other hand, he will not play a significant role in the speed of response. Other constituent elements of the measurement probe that we have seen previously influence, on the other hand, on the reaction time.

The more contact with the environment whose temperature is wished to measure (room temperature, gas, liquid), the higher the emissivity. That is to say that Heat transmission is quickly. The thermocouples with bare wires, with an external junction, thus offer a quick response. This is also the case with welded junction probes. The wires being directly in contact with the sheath, the heat circulates quickly.

The response time is also a function of The size of the sheath. A sheath with a small diameter (0.25 mm, 0.5 mm or 1 mm for example) offers a better reaction time. Beware of the choice of this sheath, its resistance to certain environments and high temperatures can be less than that of thermocouple. In the event of the sheath alteration, The calibration of thermocouple (also called calibration) carried out upstream of the use of the probe can be altered.