What are the differences between Type E and Type J thermocouples

The longevity of Type E and Type T thermocouples depends on a number of things, such as the temperature at which they work, the air around them, the safety measures taken, and how they are installed. In regular industrial settings, Type E thermocouples should last 1.5 to 2 years, and Type T thermocouples should last 3 to 5 years in low-temperature settings. But the exact lifespan needs to be figured out by looking at all the operational conditions.

I. Analysis of the Lifespan of Type E Thermocouples (NiCr-Constantan)


The average lifespan is between 1.5 and 2 years.

Type E thermocouples can work for extended periods of time in medium to low temperatures (-200 to 900 degrees Celsius) and in oxidizing or inert atmospheres because they are resistant to oxidation.

Important things that affect lifespan:

Not allowed to be used in environments with sulfur or that reduce sulfur: In H₂, CO, or SO₂ atmospheres, the constantan electrode is likely to corrode electrochemically, which can cause thermoelectric potential drift or even wire breakage. This can cut the lifespan to just a few months.

Frequent start-stop cycles or rapid temperature changes: If the equipment goes through a lot of heating and cooling cycles, the material will wear out faster. It is best to have the service life less than a year.

Quality of protective tubes: Using high-purity alumina or 310S stainless steel protection tubes will greatly increase the life of the tubes. If the tubes are of poor quality, they could contaminate the thermocouple wire or cause mechanical damage.

Type E thermocouples are the most sensitive (around 68μV/℃), but their thermoelectric potential uniformity is not very good, and they may make nonlinear errors after a long time of usage. It is best to calibrate regularly.

II. Analysis of the lifespan of Type T thermocouples (copper-constantan)

Average lifespan: 3 to 5 years (in a home or lab setting)

Type T thermocouples are very stable and repeatable between -200°C and 350°C. This is especially true in the low-temperature band, where the annual stability can be less than ±3μV, making them good for long-term monitoring.

Important Things That Affect Lifespan:

Do not let the temperature get too high: Copper cathodes oxidize quickly over 350°C, becoming black and becoming brittle, which shortens their life.

Corrosive and Humid situations: Constantan is resistant to moisture, although it can still corrode in acidic or salty situations. It is best to put in a junction box that is sealed.

Type T thermocouples are very sensitive to the temperature of the cold junction. If the compensating circuit gets old or the temperature outside changes a lot, the measurement mistakes can build up and shorten their useful life.

Tip: Type T thermocouples are typically employed as supplementary standard instruments for transferring low-temperature measurements. They are also more stable over time than other base metal thermocouples.



III. General Advice for Making Things Last Longer

Choosing the right type and matching it to the operating conditions is important. Type E is good for high-humidity, quick-response situations like food, drug, and environmental monitoring. Type T is better for low-temperature precision temperature measurement tasks like refrigeration systems, biological incubators, and laboratory thermostats.

Make Protective Measures Stronger

Use airtight tubing to keep bad environments separate;

Put ceramic sleeves in the parts that get hot and stop condensation in the parts that stay cool.

Regular Checks and Changes

JJG 351-1996 says that the inspection cycle for industrial base metal thermocouples usually doesn't last more than a year.

Even if there are no obvious problems, they should be replaced on time to avoid slow performance loss that could lead to temperature runaway.