High speed thermocouple measurements require consideration of temperature, vibration, wire type and protection, length, and type for accurate and reliable readings.
High speed thermocouple measurement is a versatile temperature sensing technique that can be used to make measurements from -269.1°C (-452.6 F) to more than 1700°C (3092 F). Depending on its environment, the thermocouple is limited in its accuracy, primarily in terms of the temperature range it can measure, sensor lifetime and response time. Because of its high speed, thermocouples may be used in applications where traditional RTDs or thermistors cannot be used.
Requirements for high speed thermocouple measurement
For thermocouple measurements, the environment requires certain parameters to meet the accuracy and reliability requirements of the application. These parameters may be temperature, vibration, thermocouple wire type, thermocouple wire protection type, thermocouple wire length and thermocouple wire type.
Temperature
Ambient temperature must be in the range of -50°C to 150°C (58°F to 302°F), and in many applications the temperature range can be much greater, up to 500°C (932°F).
Vibration is a key factor in high speed thermocouple measurements. Thermocouples are especially susceptible to vibration as the lead wires can break and results in inaccurate readings. The magnitude of vibration will depend on the application, but should generally be kept as low as possible. In addition, thermocouples that are intended for use in measurement of rotating machinery, such as turbines, should be designed to withstand the high dynamic loading experienced during operation.
Thermocouple wire type
Thermocouples come in different types, each type having a specific resistance characteristic that affects its speed of response, accuracy and lifetime. The type of thermocouple that is best suited to an application will depend on the operating temperature and the environment in which the thermocouple is to be used.
Thermocouple wire protection type
Depending on the environment, the thermocouple wires may be exposed to high temperatures, moisture and other corrosive elements. Therefore, it is essential to select the appropriate type of thermocouple protection, whether it is a high temperature insulation, stainless steel sheath, Teflon, or other material. Using the wrong type of protection can cause errors and even lead to permanent failure of the thermocouple.
Thermocouple wire length
The length of the thermocouple wire is important, as it affects the resistance of the wire, which in turn affects the accuracy of the measurement. As a general rule, the wires should be short, flexible and free from any sharp kinks or bends.
Thermocouple wire type
Thermocouple wires come in different styles, including stranded, solid and wicking. The type chosen should depend on the environment, as each style will affect the response time and accuracy of the measurement.
Conclusion
High speed thermocouple measurement requires careful consideration of various parameters, such as temperature, vibration, thermocouple wire type and protection, length and type. Understanding these parameters and selecting the right combination will ensure accurate and reliable measurements.