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Protection Sheaths and Housings
 | The bulk of this guide shows forms of housing and sheaths available to temperature sensors. Consideration needs to be given to: |
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The maximum and normal running temperature of a process
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| Any chemical attack present |
| Physical knocks or vibration in use (including carriage and plant handling) |
| Protect the sensor from contamination |
| Maximum design pressure |
| Abrasion resistant |
| The connection of the sensor to the plant or equipment |
| If the sensor is to be replaceable within the protection sheath |
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At low temperatures PVC, Silicon rubber or PTFE (polytetrafluroethane / teflon) sheaths are common to 250 °C. Above this stainless steel and other metal alloys are used. For high temperatures ceramic is used. Common ceramics include: pythagoras, alsint / recrystalised alumina (RA), alumina and impervious alumina porecelain (IAP). Platinum Rhodium alloys are used for immersion into glass.
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Molten aluminium can utilise special alloy due to its cheapness and adequate chemical resistance. Chemical plants can demand Inconel ( and other Nickel alloys) Monel Hastelloy or a range of fabricated coatings such as tantalum. Mineral insulated designs incorporate the conductor within a metal protection sheath (Usually Stainless Steel or Inconel Alloy 600) held apart with a compacted ceramic powder. This forms the most robust and tough sensors available. Overall sizes down to 0.25mm diameter is possible. The sensor is virtually indestructible except through over temperature exposure. The unit can be formed to almost any shape to suit an application including tip diameter reduction to decrease response time. Compression Glands can easily be used with Mineral insulated thermocouple and RTD sensors to provide sealing.
Process fittings can include fixed or moving threads and flanges.
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