MEMILIH THERMOCOUPLE YANG AWET

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Sebagai seorang purchasing/Bagian pembelian, selain Quality, Cost, dan  Delivery , ada baiknya  juga mengetahui detail pemakaian thermocouple dan aplikasinya sebagai berikut :

1. Tentukan suhu aplikasi
2. Tentukan aplikasi digunakan dimana?
3. Ketahanan abrasi / getaran/Panas
4. Ketahanan kimia, kalibrasi
5. Instalasi dan kompatibilitas.

Tentukan suhu aplikasi

Ada banyak jenis termokopel tersedia dalam beberapa kalibrasi yang berbeda. Termokopel yang paling umum digunakan saat ini adalah K, T, J, E, tetapi juga tersedia dalam kalibrasi lainnya. Setiap kalibrasi menawarkan berbagai suhu tertentu dan hati-hati dipilih untuk lingkungan di mana ia akan digunakan.

Memilih berdasarkan Jenis Material
Compacted MgO Thermocouples

MgO adalah bahan yang selalu digunakan dalam pebuatan thermocouple unutk mencapai ketahanan suhu hingga 2300°F (1260°C). Pastikan bahwa bubuk MgO yang terbaik yang digunakan untuk thermocouple jenis MI (mineral insulated).Jika tidak , Thermocouple anda umurnya akan seumur jagung, dan akurasinya dipertanyakan.

Thermocouples Sheath (pipa pelindung)

Semua Element yang terlibat di dalamnya diatur oleh ANSI. Termasuk sheath material (pelindung element) yang digunakan oleh thermocouple. Beberapa jenis Sheath (Pipa pelindung thermcouple yang umum digunakan antara lain :

• 304 SS Maximum temperature of 1650°F (900°C) and is the most widely used low temperature sheath material. It offers good corrosion resistance but is subject to carbide precipitation in the 900°F to 1600°F (480 to 870°C) range.
• 310 SS Maximum temperature of 2100°F (1150°C) and offers good mechanical and corrosion resistance similar to 304 SS. Very good heat resistance. Not as ductile as 304 SS.
• 316 SS Maximum temperature of 1650°F (900°C) and has the best corrosion resistance of the austenitic stainless steels. Subject to carbide precipitation in the 900°F to 1600°F (480 to 870°C)
• Inconel® Maximum temperature 2150°F (1175°C) and is the most widely used thermocouple sheath material. Good high temperature strength, corrosion resistance and is resistant to chloride-ion stress corrosion, cracking and oxidation. Do not use in sulfur bearing environments.
• Hastelloy X Maximum temperature 2200°F (1205°C) widely used in aerospace applications. Resistant to oxidizing, reducing and neutral atmospheric conditions. Excellent high temperature strength.

Tentukan Diameter Thermocouple

Standard Sheath Diameter berdasarkan atas suhu aplikasi :
020 "+.001 -.0005" 1290 ° F (700 ° C)
0,032 "+.001 -.0005" 1290 ° F (700 ° C)
0,040 "+.001 -.0005" 1290 ° F (700 ° C)
0,063 "± 0,001" 1690 ° F (920 ° C)
0,090 "± 0,001" 1830 ° F (1000 ° C)
0,125 "+.002 -.001" 1960 ° F (1070 ° C)
0,188 "+.002 -.001" 2100 ° F (1150 ° C)
0,250 "+.003 -.001" 2100 ° F (1150 ° C)

Seleksi Thermocouple berdasarkan Measuring Junction

Sheathed thermocouples are available in 3 junction types: grounded, ungrounded, and exposed. Each design offers specific advantages as well as disadvantages and must considered carefully when placing an order.

Grounded
The thermo-elements are welded into the end cap using the same weld rod as the sheath material. Fast time response. Recommended for high-pressure applications, liquids, moisture, contaminating atmospheres, and most general uses. -Least expensive.

Ungrounded
The thermo-elements are welded together and are electrically isolated from the sheath. Recommended for applications where stray EMF’s from electrical apparatus would affect the reading. -More expensive.

Exposed
The thermo-elements are welded together outside of the sheath. This provides the fastest time response, but exposes the elements to contamination. Electrically isolated from the sheath.
Inconel® is the registered trademark of INCO Alloys International.
Hastelloy X is the registered trademark of Haynes International.

Setelah semua spesifikasi terpenuhi dan Permintaan Pembelian dari Engineering sudah dibuat, maka step selanjutnya adalah menyampaikan PP tersebut kepada pihak purchasing.


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