The thermocouples curves by type

In many sectors of activity, companies need to carry out precise temperature control in their production processes. To make the survey of a surface temperature and prevent measurement errors, it is essential to understand the functioning of the thermal probe. In the case of thermocouple, the temperature value is calculated from an electric current. This calculation notably requires the use of thermocouple curves. We explain here what these conversion curves are precisely and how they are exploited.

How is the temperature calculated with a thermocouple?

To understand the role of thermocouple curves, let's start with a reminder of the basics of Thermocouple operation.

What is a thermocouple?

What is called the Thermocouple is a type of temperature sensor widely used in industry. By extension, the probe, that is to say the complete temperature measurement device, is called a thermocouple probe. La temperature probe is made up of several elements including the sensor, which is in contact with the environment to be measured. The measurement case is used to recover the information noted or even transcribe it into temperature in Celsius degrees on the display. For practical reasons, it is often necessary to place extension cables between the sensor and the measurement instrumentation. THE thermocouple Measure the contact temperature, unlike probes that measures the temperature at a distance, such as the infrared radiation probe.

If the thermocouple probe is so widely used, it is thanks to its low cost, coming from the prices of the materials used to make the most common types of thermocouples. She is also easy to use, durable and allows you to take the temperature on large temperature beaches. In addition, it offers a quick response in the event of temperature variations.

How to convert the voltage of a temperature thermocouple?

A thermocouple probe makes it possible to perform temperature measurements of a given environment thanks to a phenomenon called Seebeck effect. When distinct conductive metals are linked together and their ends are exposed to different temperatures, A slight electric current is created. It is then necessary to measure and convert this electrical signal to obtain the temperature into Celsius degrees.

The thermocouple sensor works thanks to the existence of two welds, or junctions, distinct between the two wires of metal alloys that compose it. Hot welding is the one in contact with the environment to be measured. The cold junction is connected to the voltage measurement device.

Each type has its own Seebeck coefficient, which allows you to convert the temperature interval that exists between hot welding and cold welding. This is when the Thermocouples curves come in, which are conversion aid tools.

The conversion curves by type of thermocouple

How to use a thermocouple conversion curve?

Tension conversion curves are essential tools to reach the temperature reading in Celsius degrees from an electro-motor force (FEM). Indeed, the links between voltage and temperature of thermocouples are not linear. The ratio between the tension captured and the temperature is also often represented in the form of Thermocouple conversion table posting Millivorms and corresponding temperatures. The representation in the form of a curve makes it possible to assess the variation in the Millivolt/Temperature ratio. These curves are defined by types, that is to say depending on the type of metals used in making the thermocouple sensor.

To be able to use the curve, you must start by defining the tension that results from the sensor exposure to a given temperature. In the thermocouple curves, this tension corresponds to the one we obtain When the cold junction is at 0 ° C. The simplest, in theory, is therefore to maintain this junction at 0 ° C. When it is impossible, we proceed to Compensation for cold welding. We will then use another measurement system to know the temperature of the cold welding then perform a differential calculation.

Attention, for Ensure the temperature reading accuracy, it is necessary to proceed to The calibration of thermocouple. The calibration is done in several ways, the most reliable being to observe the result of the sensor exposed to the temperature of the triple point of the water. It can also be compared to the boiling point of water or place it in a calibration oven. It's necessary Check the temperature of the sensor over its entire measurement range To ensure its reliability.

What differentiates the types of thermocouples?

What differentiates the thermocouples is The nature of the metals used To make the drivers wires. Each metal presents a specific temperature resistance. By combining two metal alloys to make a thermocouple sensor, a sensor is obtained with specific characteristics.

A European standard lists The most common thermocouples, these are the Types of thermocouples. They are designated by a letter and are 8. Types K, J, T and E are the most used, also the most affordable price level. Types N, S, R and B allow high temperature measurement. The S, R and B being composed of platinum, their price is higher.

The main characteristic differentiate the types of thermocouples is their temperature measurement range. Some may measure absolute zero and others of very high temperatures. Types are suitable for specific applications, such as T, recommended for low temperatures and cryogeny. Beyond the question of temperature quantities, some materials are more resistant than others to oxidation in certain circles. Also note that the Measuring precision level varies depending on the type.

Thermometre.fr advisers are available to answer your questions and help you choose the type of measurement probe that best suits your needs.