Understanding Thermocouple Accuracy Drift

One constant in industrial processing is that accuracy drift in a measurement device is something to be avoided. For critical applications, where temperature measurements directly influence performance, even a slight drift in the accuracy of a device like a thermocouple can lead to significant issues.

Yet, consumers continuously find that many of the thermocouples out there on the market end up needing to be recalibrated or replaced all together (sometimes after an annoyingly short period of time) due to, you guessed it, accuracy drift.

Avoiding accuracy drift in a thermocouple requires an understanding of – and, subsequently, careful attention to – the variables and factors that cause it. Knowledge is key, and thermocouples manufactured with these variables in mind perform better in the long run.

Accuracy Drift

Two major contributors to thermocouple accuracy drift are:

• Improper insulation
• Contamination

Insulation plays a critical role in maintaining the stability of the thermocouple by protecting the internal wires from external environmental factors, such as moisture and physical wear. When the insulation degrades over time, typically due to moisture infiltration or poor-quality materials, the thermocouple’s performance can become unstable, leading to inaccurate readings.

Contamination, on the other hand, occurs when metal from the thermocouple sheath leaches into the internal alloys of the thermocouple, altering their composition and further compromising accuracy. Together, these factors can cause gradual shifts in temperature readings, ultimately diminishing the reliability of the thermocouple in critical applications.

Insulation

Thermocouples are insulated primarily to protect the wires from external factors. Insulation provides electrical isolation, preventing the thermocouple from picking up interference or creating short circuits if the wires come into contact with other conductors. Insulation also shields the thermocouples from harsh environments, such as high temperatures, chemicals, and moisture, which could otherwise cause corrosion or physical damage to the wires and affect their performance.

Besides protection, insulation helps maintain accuracy by ensuring the thermocouple measures temperature at the sensing point, rather than being influenced by heat along the wire’s length. This thermal protection ensures the integrity of the measurement, making the thermocouple more reliable and durable over time.

Yet, when it comes to insulation, thermocouple manufacturers will often cut corners by using rigid, pre-formed magnesium oxide tubes that are crushed during the manufacturing process. This puts a lot of stress on the alloy wires that, ultimately, will have an effect on accuracy of that thermocouple. Accuracy drift in thermocouples manufactured this way is all but inevitable.

Omega’s Super OMEGACLAD XL™ thermocouples are resistant to this issue because they are manufactured with fine grain, high-purity magnesium oxide insulation, resulting in less stress on the thermocouple alloy wires during assembly and, in the end, a longer lifespan of highly accurate temperature measurement.

In addition, pre-existing moisture inside the sheath is eliminated during the proprietary manufacturing process of the Super OMEGACLAD XL™ thermocouple. Even the slightest big of moisture inside a probe can expand and condense during heating and cooling (either during the manufacturing process or when utilized for an application), resulting, ultimately, in failure.

Contamination

Contamination can significantly affect thermocouple performance by altering its electrical properties which will often result in accuracy drift. When a thermocouple comes in contact with a foreign substance – like metal from its protective sheath – this contaminant can alter the behavior of the materials at the junction or along the wire of the thermocouple, affecting the thermocouple’s response to temperature changes.

Omega’s Super OMEGACLAD XL™ thermocouples are specifically engineered to prevent contamination that could impact performance over time. These advanced thermocouples feature a unique dual-wall sheath design that effectively shields the thermocouple alloys from harmful substances. This design extends the lifespan of the thermocouple by minimizing the risk of failure.

Combating Accuracy Drift with our Super OMEGACLAD XL™ Industrial Thermocouple Probes!

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