Using Thermocouple Probes in Incinerators

Turning up the Heat: 12 MI Thermocouple Probes get Tested in Extreme Conditions

Challenge

• Finding a thermocouple probe that can withstand extreme heat such as in solid waste incinerators, sintering powdered metals, or gas
• Selecting MI cable sensors that are capable of maintaining their accuracy and durability over time is an important consideration

In an intense heat environment, such as in solid waste incinerators, sintering powdered metals, gas or oil fired-furnaces, the need of a thermocouple probe that can withstand extreme heat is evident.

The optimal choice is the mineral insulated cable (MI cable), because it remains hard to inflame even when exposed to high temperatures. It also achieves precise measurement due to its ability to resist the oxidation.

MI cable’s application in critical processes in high-temperature environments is only possible when selecting MI cable that can sustain accuracy levels and durability over time.

It is extremely important to sustain these because, for instance, it would be extremely dangerous if the temperature controllers used in nuclear plants to monitor core temperatures were not receiving accurate readings, and it would be difficult to repair or replace cables in that environment.

Solution

• Cycle test with 12 probes helped to determine performance
• All probes had a diameter of 3.0 mm
• The test parameters included the ramping of each probe to 1100 °C within 15 seconds and immediately cooling

Testing MI Cables for Performance

A cycle test was conducted in order to evaluate the performance of the several probes manufactured with MI cable. Their accuracy and durability were tested against competing brands.

The test measured the performance on twelve probes, including four sample probes from two competing manufacturers and four probes from each of the three Omega sheath combinations. All probes had a diameter of 3.0 mm.

The test parameters included the elevating of each probe to 1100 °C within 15 seconds and immediately cooling the probe down to ambient temperature within 45 seconds. These parameters were decided on the basis of real customer application of a thermocouple probe placed inside the exhaust system of a diesel engine with a turbocharger.

Cycle Test Results

Based on the average of each combination, the Omega sheath combinations surpassed the probes of the competitor significantly. The review of the data from the test also showed that the Omega™ 310/XL sheath lasted 8 time longer, on average, than any of the competitor’s probes, and nearly twice as long as the other Omega combinations. That makes it the highest performing of all probes.

Nevertheless, often, the cycle of 15 seconds had to be prolonged to 18 seconds as the probes aged, in order to reach the 1100 °C temperature limit. This may have been due to the oxidation of the sheathing and conductor materials.

Figure 1

When evaluating the five poorest performing probes (see Figure 2), it is evident that all of them had broken the negative thermos-element at approximately 2½” from the hot end tip. This concurs with the depth each probe saw when cycled into the induction coil.

Figure 2

There were a number of temperature points at which the probes were tested over time. An electro motive force test (EMF) of all probes showed that most had minimal changes in their EMF output at the different temperatures, after each 1000 cycles.

The one exception was one Omega™ 310 XL probe that lasted 15,900 cycles and experienced very little EMF shift over the entire test.

At the end, term static testing of the probes was also performed at temperatures of 2200 °F. The test was performed because drift was a high concern. Figure 3 shows that three of the Omega probes exhibit drift until 60-100 days. Competitor probes begin to drift almost immediately.

Figure 3

Result

• The test data indicated that the Omega sheath combinations outperformed the competitor
• The Omega 310/XL sheath was the highest performing sheath
• 15 second heat cycle had to be extended up to 18 seconds in order to reach the 1100 °C

Conclusion

Data from the Omega^TM controlled testing reveals that the Omega 310/XL probes have superior performance over other MI cable probes that were tested. There is no guarantee of the lifespan of an individual probe, but the Omega 310/XL probes showed to be superior to the probes of the competitors.

This information has been sourced, reviewed and adapted from materials provided by OMEGA Engineering Ltd.

For more information on this source, please visit OMEGA Engineering Ltd.