In many sectors of activity, companies need to carry out precise temperature control in their production processes. To carry out 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 requires in particular 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 recall of the basics of Thermocouple operation.
What is a thermocouple?
THE thermocouple is a type of temperature sensor widely used in industry. It is made up of a temperature probe, a sensor in contact with the environment to be measured, and a measurement case that displays the temperature in Celsius degrees. The thermocouple measures the contact temperature, unlike other probes that work remotely, such as infrared probes.
If the thermocouple is so widely used, it is thanks to its low cost, his Simplicity of use, his sustainability and its Large measurement range. It also offers a quick response In case of temperature variations.
How to convert the voltage of a temperature thermocouple?
A Thermocouple probe allows measures to be made thanks to theSeebeck effect. When two different conductive metals are linked and exposed to separate temperatures, An electric current is created. This signal is converted to Celsius degrees.
THE Thermocouple sensor has two junctions: Hot welding (in contact with the environment to be measured) and the cold junction (connected to the voltage measurement device).
Each type of thermocouple has a seebeck coefficient, allowing to convert the temperature between the hot and cold welding. THE Thermocouple curves serve as conversion tools.
The conversion curves by type of thermocouple
How to use a thermocouple conversion curve?
THE tension conversion curves Allow the temperature from an electro-motor force (FEM). The voltage/temperature ratio is not linear, and these data are often grouped in the form of Thermocouple conversion table, displaying the corresponding millivormities and temperatures.
To use these curves, it is first necessary to determine the tension of the sensor when the Cold junction is 0 ° C. If it is not possible, a Compensation for cold welding is performed using another temperature measurement.
For Ensure the accuracy of the measures, it is necessary to perform a Thermocouple calibration. This can be done by comparing it to reference points such as the triple point of the water, the boiling point of the water, or by placing it in a calibration oven.
What differentiates the types of thermocouples?
The differences between The types of thermocouples rest on the Nature of metals Used for conductive wires. Each metal has a specific temperature resistance. By combining two alloys, a sensor is obtained with particular characteristics.
THE The most common thermocouples are classified according to a European standard and appointed by a letter. The guys K, J, T and E are the most widespread and affordable. The guys N, S, R and B are designed for very high temperatures. The guys S, R and B, composed of platinum, are more expensive.
The main difference between thermocouples is their measurement range. Some measure extreme temperatures, such as the type T Ideal for cryogeny. Others are distinguished by their Oxidation resistance and their precision.
Go further on thermocouples:
To deepen the subject of thermocouples, consult our other articles on:
- THE Thermocouples probes and their applications.
- THE Different types of thermocouples and their characteristics.
- L'Thermocouples calibration and its importance.
- There Thermocouples measurement range Depending on their type.
