The advantages of N type thermocouple:


- High temperature oxidation resistance is strong, long term stability. K type thermocouple nickel chromium anode preferential oxidation caused by Cr, Si element in the alloy composition is uneven and thermoelectric drift, Cr, Si content in N type thermocouple, nickel-chromium alloy oxidation patterns by internal oxidation into external oxidation, the oxidation reaction on the surface only;


- Short-term thermal cycling stability at low temperature, and inhibit the magnetic change;


- Radiation resistant ability. Easy disintegration of N type thermocouple is cancelled K type element Mn, Co, further strengthen ability to resist neutron irradiation;


- Within 400 ℃ ~ 1300 ℃, the thermoelectric properties of N type thermocouple linear than K type.


N type thermocouple drawback:


- N type thermocouple material is harder than K type, the more difficult processing;


- The price is relatively expensive. The thermal expansion coefficient of N type thermocouple 15% lower than stainless steel, so the outer casing of n-type armoured thermocouple shall adopt the NiCrSiNiSi alloy;


- In - 200 ℃ ~ 400 ℃ within the scope of nonlinear error is bigger.


how to choose the suitable heat installation casing?


hot casing installation the shape of the main basis of medium temperature, pressure, density, and flow velocity and the required length. ASMEANSI PTC193 for the provision to this, the casing strength analysis software can calculate the casing design meets the technical requirements. Installed on the site of the intensity of the heat need to calculate thermal casing pipe, which affect the strength of the protective casing basically has the following three points:


1 flow caused by vibration; After a protective casing liquid to produce a certain frequency of vortex, called vortex frequency, the frequency is directly proportional to the velocity. If the natural frequency of the frequency and the heat pipe is close to or consistent, can produce resonance, make large amounts of heat energy, resulting in a high stress and potentially damage hot casing and casing sensor. ASME standards requirements: vortex frequency and the ratio of heat tube natural frequency should be less than the euro.


2 flow caused by stress; Fluid flow changes with the velocity and density, and force in the heat pipe, the flow caused by pressure can be concluded by calculation.


3 process pressure; Thermal casing to withstand the maximum static pressure can be calculated. '


general hot to install the casing connections have threaded connection, flange connection and welding type 3 kinds.





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key words: thermal resistance, thermocouple, thermal resistance, platinum resistance, PT100, PT1000, pressure sensor and digital temperature sensor