The following post has been submitted by Stephen Heale
Some time back – I read that type N thermocouples were used in a brick manufacturing business. They have many positive and stable properties with a good output voltage.
This is an excerpt from the information that I submitted to MFMP back in 2012, comparing type K to type N.
Type K thermocouple:-
Sensitivity 41 µV/ °C, Range -200 °C to +1250 °C.
Causes a deviation in output when the material reaches it’s Curie point (magnetic state change), at 350°C.
Prone to a gradual and cumulative drift in thermal EMF on long exposure at elevated temperatures due to a compositional change caused by oxidation, carburization or neutron irradiation that can produce transmutation in nuclear reactor environments. Manganese and aluminium elements from the negative wire migrate to the positive wire resulting in a down-scale drift due to chemical contamination. This effect is cumulative and irreversible.
Experiences short-term cyclic change (hysteresis) in the temperature range 250 to 650 °C.
Produces random perturbation in thermal EMF between 25 and 225 °C due to magnetic transformations.
Type N thermocouple:-
Sensitivity 39 µV/ °C, Range -270 °C to +1300 °C.
The Curie point is below 0 °C.
Resistant to oxidation with enhanced thermoelectric stability relative to other standard base-metal thermocouple alloys.
Type ‘N’ thermocouples are not merely an improvement but should be considered as the optimum – overcoming all the disadvantages of not only type ‘K’ but any nickel based thermocouple.
A paper presented by Barbara Hudson in relation to the use of type K thermocouples in the clay-brick manufacturing business concluded that they should change to type N.
They were concerned with the problem which occurs between 500 °F to 1020 °F (260 °C to 549 °C) due to short-range ordering, where an erroneous EMF is produced. The paper goes on to discuss the problem caused by hysteresis and cumulative drift when cycled at higher temperatures – which is an area we would expect this research to achieve with further work. (this was in 2012 before LENR was capable of delivering temperatures above 600 °C – hence my comment).
Their ultimate solution was to select a type N thermocouple – (developed by Noel Burley at the Defence Science and Technology Organisation in Australia).